87 VR, carb problem

[Patch]

Thank you Jeremy, it is obvious to us that once you had the time to you settled into the problem listen to the guys sharing of experience then moved to eliminate the list of potentials. There are times we see here on the forum how many of us at the tail end of are heavy riding days still have a drive to expand out knowledge base and put that new, into practice!

There are some spoilers in here that are likely to frustrate but, that too is part of the sport.

Below and as of this moment I haven't read the entire post, (had commitments yesterday) but I did read enough clues that clearly show some history and likely why we're here at this point.

 

Thanks for all the input Patch.

 

TROUBLESHOOTING UPDATE:

 

IGNITION:

- Verified all connections

- Removed wire caps and snipped a bit off the wires

- Spark check - I don't have a checker for this. Cranked motor with a screwdriver in the cap and held near the engine. All four produced a healthy spark that would jump about 1/4" plus. Also checked a spark plug in a wire, grounded the threads, and cranked engine, producing a consistent spark.

 

- Timing - verified two things. 1) the rotor has not rotated, verified #1 TDC with a rod in the spark plug hole. 2) Ignition timing for #1 at idle is in the specified range, and advances when revved., Ok so we have a wasted spark setup tapping into 1 or 2 ignition shows the same result for a timing check. Its within spec meaning that ignition angle is ruled out.

- Finally, with engine idling and warm, pulled each plug wire, one at a time. Each cylinder cutting out dropped the idle from ~950 down to ~800 rpm. Each cylinder seems to be contributing the idle approximately equally. Below this is contradicted - so says in play as a separate yet issue because of what we know you checked visually last time you had the jet block out.

 

CARBS:

- Double checked pilots. Made small adjustments, but still pretty much need to be out too much - 2 to 4.5 turns. I did notice one other anomaly: #3 pilot didn't affect idle nearly as much as the others, even when totally screwed in. These two reds do not jive.

- Double checked fuel levels. Came out about the same, #1 and 2 on spec, #3 - 1mm low, #4 - 2 to 3mm low. Clearly this needs small adjustment.

 

- Symptom the same - idles fine, but doesn't take throttle quite like it should, slight hesitation So here we are and where we here over the net rely on what you describe yet need to be mindful of our assumptions we jump to to fill in the blanks.. Assuming the slide setup is original, complete, moving without restriction (remember the forgotten spring problem, guys? this year or last) needles are in good shape, needle jest are not leaking and that the box is intact when this problem happens, air filter is clean, pump is above 3 lbs, bowls have enough reserve.

Then we jump to lean, rich, preignition or angle as the most likely causes. Lets not forget the highlighted red lines above.

- Checked for vacuum leaks while idling again, this time with unlit propane torch. Nuthin'. Good

- Plugged Idle Air Jet #2 with pieces of toothpick, see pic. This is the #170 jet under the slide which gets closed off under high engine vacuum by the Coasting Enrichers, which I disabled. This produced marked results. I am not sure what this means, what were the changes? However I can't agree with this patch; you are amusing to much with air pressures and this circuit needs to be put into proper working order, imho.

 

-----Engine clearly idles rich. It actually idles best with pilots screwed all the way in. Had to adjust main idle screw.

-----With the pilots set at 1/2 or 1 turn out, the engine took throttle MOST EXCELLENTLY off idle. This was encouraging.

Lets come around the back and look thru a different window and look up from the bottom of the carbs.

We set idle by plate position, not mixing screws. The starter rotates the crank the pistons traveling down, intake valves open and a low pressure is created then filled by the rule pressure wants to equalize ASAP; which generates velocity, this velocity is used to psiphon a metered amount of fuel, a could engine start is a wet engine start which means low efficiency, equals high soot low temp combustion cycles is also why we want to move off of the choke asap! So we set by plate position, when we install a set of carbs we set them to x turns at the pilot jet screw and align the plates to a jet port in the barrel. How do we find that starting point? Breaks down this way snug up one of the pilot screws two holes above the tip of the screw you see protruding should align with the base of the plate edge! That allows for enough air volume at velocity to work the circuit. (Then tune the circuit by rpm)

As the temperature inside the chambers reach normal and at idle range you should here or feel the cam cycles in a smooth rhythm!

 

This engine can't hit its rhythm because of carbon build up. But and more importantly these carbs were the cause and remain the cause of the issues you are experiencing!

#3 as you said has a clean flowing jet, but it hasn't clean flowing ports! Yet the red marks above suggest that it is still getting fuel, then from which circuit? And for how many thousands of miles? The answer (s) are listed in the potentials I wrote above..

 

DISCUSSION IDLE AIR JET #2 AND COASTING ENRICHERS:

I had thought of the Coasting Enrichers as a binary thing - on or off. Maybe not. Perhaps it engages and blocks off the Idle Air 2 passage gradually, and partially at idle? My bike is too lean on the pilots with them totally disabled, but too rich with Idle Air 2 blocked off. Make sense?

 

See attached diagram from Service Manual p5-2. Idle Air Jet 2 is part number 5, and the air flows through it as shown in red until it meets up with the rest of the pilot circuit. With the Coasting Enricher in its normal, at-rest position, the valve center piston (labeled "A" in the diagram) is down as shown, and the air passes through that gap as shown. Under high vacuum, the valve piston is pulled upward as shown by the red arrow, blocking the gap and thus the airflow from Idle Air Jet 2. That's how it "enriches" - by blocking off that air source to the pilot circuit. The engine vacuum gets above the diaphragm through that passage on the upper right, which I blocked off in one of my genius moments. As I said before, I did this because one or two of the diaphragms are compromised, they are spendy, and my research seems to indicate this feature is ONLY operational under the throttle chop condition, and otherwise that gap is completely open and air flows freely from Idle Air Jet 2. But now that the potential sources for my problem are dwindling, and with what I found in my experiment, I have to wonder if that's not true. Maybe idle vacuum pulls the pistons part way up and meters a lesser amount of air through.

 

So the diaphragms act like a pressure barrier or say a sheet on a clothes line, the coil spring is the braking force, the plunger is the metering, they are brass and the wear as well. Your attempts thus far have been to cut off the actuator low pressure side; how does that guarantee that you have stopped or lock the flow of atmospheric pressure?! See my point.

 

There is also the possibility that the carbon buildup on the pistons is doing this to me. I believe that it could. But it didn't have this problem before I tore it down, and the carbon buildup didn't change with the bike sitting in the garage, did it? Maybe low compression can happen under those conditions from the rings getting stuck, but not more carbon buildup? And I've had a lot of old engines in worse shape than this one, never had this symptom before due to carbon buildup.

Yes it did change, it for one was absent of heat cycles and packing forces, and,, its likely flaking. Instead of being frustrated with its presence deal with it.

 

So I'm thinking the carbs come back off. First thing, I'll visually check the throttle plates for their state of synchronization (bench sync). I will then adjust the two errant floats and re-enable and repair the Coasting Enricher system. I'm reluctant to do the combustion chamber soak because I'm not convinced it needs it, and due to the mess and fine grit tradeoff, but still considering that.

 

Patch? Puc? Anybody? Whaddya think? Are there any more tests that should be done before disassembly?

 

One more thing: You're right about having the parts on hand saving effort. If you've worked on these carbs you know that parts ain't cheap, and everything is x4, and (true confession) MY NAME IS JEREMY, AND I'M CHEAP! So I cheaped out. I've done this many times in the past and it worked out OK, particularly with bike carbs - clean up the old parts, make the adjustments, and everything is fine! But this bike IS 32 years old, the others probably weren't. Actually, the last other one I worked on was an 80's Gold Wing belonging to a friend, and he had to buy quite a few of these parts also...but it was his money, not mine!!! But I will say, those carbs 1) didn't have Coasting Enrichers, and 2) the slide / diaphragms were fine, so either they had been replaced or Honda slides are better built than Yammy slides. Oh well.

 

Look its a sport, we are not always as prepared for.... as we need to be and we should work with budgets, at some point tho you have to pay The Piper!

And the other guy

Patch

[Patch]

I forgot to mention, symptoms like #3 are solved by hot chem baths and a wire run thru the jets and porting's. Generally and like Puc mentioned a strand off an old cable is both stiff and thin enough to do the job without scratching.

Befor you post "I know the jets are clear and you sprayed cleaner and air thru" you missed at least one maybe more.

Include the port from main to pilot.

Patch

[Gearhead]

Patch, thanks again for all the time you are putting into this. I've let it sit while I tend to the rest of life. Just to 'splain briefly, the "toothpicks in the Idle Air Jet #2 " was not intended to be a mod, just a test. I was trying to characterize the contribution of those air jets to the idle mixture, to help possibly understand the Coasting Enricher system behavior.

 

Jeremy

[Patch]

Patch, thanks again for all the time you are putting into this. I've let it sit while I tend to the rest of life. Just to 'splain briefly, the "toothpicks in the Idle Air Jet #2 " was not intended to be a mod, just a test. I was trying to characterize the contribution of those air jets to the idle mixture, to help possibly understand the Coasting Enricher system behavior.

 

Jeremy

 

I see that Jeremy but it soaks time and with pierced diaphragms you have a leaking low pressure right! At the moment I would hazard a guess as to how or what role that is playing? Lets say the vacuum can't leak to atmosphere due to the pick plug (lean), but one thing for sure it will find a path to least resistance should the brass stop not be in proper order (likely) which would be thru the fuel port - I guess and in this case?

It will be interesting to see you pull her thru!

A thank you is nice but, you know we enjoy these problems, especial when they belong to someone else;)

Patch

we'll be here and waiting when you have the time

[Gearhead]

Ok...OK...I'll do it! I have the Deep Creep, extra motor oil, and need to go review the fogging procedure. I may write back with another question or two on that.

 

I also ordered 4, count 'em, four, new Coasting Enricher diaphragms (I have them out again and they're all shot).

 

Oh, before I split the carb rack, I inspected the sync of the throttle plates. I visually compared them to the pattern of 3 holes that are more or less covered by the edge of the plates at idle, and I also used a feeler gage. The 4 carbs were VERY close to the same as each other by those criteria. I think the carbs were sync'd.

 

More to come

[Patch]

Ok...OK...I'll do it! I have the Deep Creep, extra motor oil, and need to go review the fogging procedure. I may write back with another question or two on that.

 

I also ordered 4, count 'em, four, new Coasting Enricher diaphragms (I have them out again and they're all shot).

 

Oh, before I split the carb rack, I inspected the sync of the throttle plates. I visually compared them to the pattern of 3 holes that are more or less covered by the edge of the plates at idle, and I also used a feeler gage. The 4 carbs were VERY close to the same as each other by those criteria. I think the carbs were sync'd.

 

More to come

 

Right on Jeremy!

 

Here's a cheat I guess I should of mentioned: a guy could set the plates by using a 3 mm x100 mm drill bit (or whatever) as a feeler gauge. Working of the prime carb set it to allow the bit to just pass between the wall and the plate (never slam the plate against one) and repeat carb to carb by each idle screw.

You can use the same shortcut to check which jugs require more or less airflow between the plates and the walls.

Why would you want to or why could we expect to see a difference? The two most likely causes are mixture setting which could be jet related (partial blockage) or how you dialed them in when syncing or, when starting it after re installing the carb rack hunting to quickly for a tune. Next is pressure variance between the jugs.

The only re adjustment you would need to do is the prime rpm set screw, as the other 3 plates will follow off the prime carb.

Patch

[Gearhead]

So Patch, the Service Manual says to fine tune the carb sync with the merc sticks. Do you recommend that as well, after starting with the bench sync?

[Patch]

So Patch, the Service Manual says to fine tune the carb sync with the merc sticks. Do you recommend that as well, after starting with the bench sync?

 

Yes I do Jeremy and you have proven you can as seen in your post!

It's not what I use but it is a proven way. Just as we mentioned start the install with the plates bench sync, this may not be spelled out in the manual however it is assumed!

[Gearhead]

OK, just to clarify on the de-carbonizing. One thread says do Deep Creep first, then carb cleaner. The other says carb cleaner first, then Deep Creep. What do you recommend in this case?

 

So the process is basically:

• Fill chambers and intake ports, let soak for a day
  
• Blow out with air
  
• Fill again, turn motor a little
  
• Repeat the above with carb cleaner AND Deep Creep, 2x each?
  
• After last blow-out, drain and refill oil
  
• Reassemble bike and start, warm up, tune carbs
  
• Shut off
  
• Check compression
  
• Change oil and filter
  
• Done.
  

 

Do I have that right?

 

Thanks, Jeremy

[Patch]

Jeremy I know it s trouble Bud but, look at it this way, when I started it was tear down only! The real problem for a methodical guy is cleanup!

Yes it s a risk and yes it cost, now look at the other side; you alone have to place the bet then its win or loose! I've done it and lived with the results!

It's always tough a penny here a penny there, we only know we won because we played our hunch!

The more oil you rinse with the better your chances, and is the reason I keep pales of the good and other ****! But I never compromise on filters, true story

No\ problem here if you decide to cut it short

[Gearhead]

Ok, it sounds like you are recommending another oil rinse But do I have the steps right otherwise? And which first... the carb cleaner or the Deep Creep?

[Patch]

OK, just to clarify on the de-carbonizing. One thread says do Deep Creep first, then carb cleaner. The other says carb cleaner first, then Deep Creep. What do you recommend in this case?

 

So the process is basically:

• Fill chambers and intake ports, let soak for a day
  
• Blow out with air
  
• Fill again, turn motor a little
  
• Repeat the above Deep Creep, let soak again, after this second soak then use compressed air then carb cleaner, then air.
  
• After last blow-out, drain and refill oil
  
• Reassemble bike and start, warm up, tune carbs
  
• Shut off
  
• Check compression
  
• Change oil and filter Ya unfortunately the chit needs to be flushed from the system
  
• Done.
  

 

Do I have that right?

 

Thanks, Jeremy

 

Sorry Jeremy I missed the question.

As you can imagine she may be hard to start cause its pretty wet. A touch early on when you go to fire her with carb cleaner might just get her to catch.

 

Hope it goes well for you and produces a win;)

[Patch]

These are the 2 long tips I use.

[Gearhead]

OK. So the carb cleaner isn't for decarbonizing, but rather for a starting aid? The Deep Creep does the decarbonizing?

[Patch]

OK. So the carb cleaner isn't for decarbonizing, but rather for a starting aid? The Deep Creep does the decarbonizing?

 

The Deep Creep will soak and loosen the carbon, the carb cleaner will also dissolve the carbon but, only where it has direct contact with it!

Also the carbon/carb cleaner will help dry the areas that the Deep Creep has effected. Deep Creep foams quickly expanding its coverage, so it takes a bit of doing to dry the chambers this is where the carb cleaner will help that process as well as its dissolving efforts!

 

When the chambers are damp in this case wet, it can be a mother to start and so, spraying a combustible fluid early in your first start attempts will lessen the chance of flooding! Be prepare to help it continue to idle with the odd bust of cleaner.

 

Its really not hard just be patient with the soaking time. That fine high pressure tip will help allot.

[Gearhead]

OK, cylinder fogging / soaking in progress. Carbs in work...again. Coasting Enrichers, new diaphragms installed, restored to normal functionality. Carb#3 - verified once more that all pilot passages are PERFECTLY clean.

 

Addressing float levels on #3 and 4. Reminder, checked per the book with the engine idling, spec is -16 +-.5 mm, #3 was at -17mm (1 mm low), and #4 moved around from -17 to -20mm, mostly between -18 to -19. There's a couple things weird about these.

 

First, the moving around of #4 is obviously weird. FP is producing plenty of flow, evidenced by key on open flow, and also the fact that the bike runs great while hard on the gas in an acceleration run. Other 3 carbs are rock steady. Seems like float must be sticking, but I seen no evidence of that, or any reason why it would stick that I can tell by looking in there. That said, it's difficult to tell for sure because it might be hanging up on the fuel bowl which is removed for inspection. Another thing, looking back in my records, I checked the fuel levels a couple times before. #4 has always run a little low, and not super consistent, so this is an old and persistent condition. Ideas?

 

Second, the levels I'm measuring 1) on the bike idling, 2) wet on the bench while tapping carbs, and 3) dry on the bench aren't consistent. I'm assuming method 1 should be the trump method, the one method to rule them all The others are in-process indicators. When I bench checked them (method 2) over a month ago I found #3 and #4 to be spot on, but then on the bike they ran low as indicated above. And using method 3, these two floats have to be set quite high compared to how others set their carbs, as if my floats are super buoyant. Refer to the following thread about bench testing, post #4 , my floats #3 and 4 are now set to 25.5mm by the measurement shown in those photos:

 

https://www.venturerider.org/forum/showthread.php?138114-When-Bench-Testing-Carb-Float-Levels-Should-Fuel-Be-Added-Under-Pressure&highlight=float+adjustment

 

One thing that just occurred to me is to be very careful about making sure the carbs are very level when checking this wet. I'll put a level across my intake boots to verify that the bike is level on the center stand, and I'll do the same on these carbs when I bench test them wet again.

 

Jeremy

[Patch]

OK, cylinder fogging / soaking in progress So the engine is not part of any of the testing listed below. The deep creep will sook thru and hopefully release the bond between carbon and components.

Carbs in work...again. Coasting Enrichers, new diaphragms installed, restored to normal functionality. Carb#3 - verified once more that all pilot passages are PERFECTLY clean. Checked

 

Addressing float levels on #3 and 4. Reminder, checked per the book with the engine idling, spec is -16 +-.5 mm, #3 was at -17mm (1 mm low), and #4 moved around from -17 to -20mm, mostly between -18 to -19. There's a couple things weird about these. OK so why is the process set forth and described this way? The short answer is for the same reason we sync the carbs both on the bench then while running jug to jug! Things you could include are, condition of fuel tubing, filter, pump pressure, bowl venting... Remember the rule for pressure and flows, path of least resistance.

 

First, the moving around of #4 is obviously weird. FP is producing plenty of flow, evidenced by key on open flow, Lets add some dynamics to this which may shed some light as you obviously have a need to understand why, which is a good thing. Pressure has to do with lift/head and flow restrictions. To get the set volume to the bowl a greater than the rate of consumption @ WOT is targeted. Setting it at idle is a benchmark or an agreed to "should meet requirements".

​The bike is not equipped with a header at the bump therefore, the distance and volume are not equal from a filling prospective (patch of least..). The bowls nearest to the the main tubing will be fed first; as each float moves to close the float needle the next inline will receive more volume, but, the pressure is a remains a constant. So that is what effects the speed at which each bowl fills; which means, that if the difference is too great then you must check flow rate using a measuring container and a stop watch.This only rules the pump in or out, so if it proves good then we address the routing of the tubing. (I assume the float valves are matching #1.5) Fuel needs to flow thru a bend not kink, so if we can't trust the tube to stay cylindrical then it should be changed. i can't stress this enough, the wall needs to be cylindrical start to finish. Venting can also cause a filling issue tho likely not a problem here (volume in, volume out, displacement).

and also the fact that the bike runs great while hard on the gas in an acceleration run. Other 3 carbs are rock steady. Seems like float must be sticking, but I seen no evidence of that, or any reason why it would stick that I can tell by looking in there. That said, it's difficult to tell for sure because it might be hanging up on the fuel bowl which is removed for inspection. Another thing, looking back in my records, I checked the fuel levels a couple times before. #4 has always run a little low, and not super consistent, so this is an old and persistent condition. Ideas?

Yes this float may be slow to react for many reasons but if it is inconstantly defeating your efforts then you need accept that the mounting post or bracket is the issue. Another possible is that it is heavier, or that it is leaking. I assume they have been check for flotation in a bowl and that, when you shake it next to your ear you hear nothing bouncing inside, so weigh it after soaking it in fuel, compare it to the others.

Second, the levels I'm measuring 1) on the bike idling, 2) wet on the bench while tapping carbs, and 3) dry on the bench aren't consistent. I'm assuming method 1 should be the trump method, the one method to rule them all The others are in-process indicators. When I bench checked them (method 2) over a month ago I found #3 and #4 to be spot on, these are not paired does that tell you something?

but then on the bike they ran low as indicated above. And using method 3, these two floats have to be set quite high compared to how others set their carbs, as if my floats are super buoyant. It is a volume issue, first come first served, so check the above points then make a suitable compromise remember this isn't a track bike.

Refer to the following thread about bench testing, post #4 , my floats #3 and 4 are now set to 25.5mm by the measurement shown in those photos:

 

https://www.venturerider.org/forum/showthread.php?138114-When-Bench-Testing-Carb-Float-Levels-Should-Fuel-Be-Added-Under-Pressure&highlight=float+adjustment

 

One thing that just occurred to me is to be very careful about making sure the carbs are very level when checking this wet. I'll put a level across my intake boots to verify that the bike is level on the center stand, and I'll do the same on these carbs when I bench test them wet again.

 

Jeremy

& Patch

Edited August 12, 2019 by Patch

[Patch]

Very sorry guys my French was allover my last post. I corrected it, it should read better or make more sense.

[Gearhead]

Hello helpful fellow Venturers. I’m sad to report that I have done ALL the stuff and the bike runs the SAME. Seriously. After putting it together the first time 2 or 3 months ago, it ran great at anything mid range or top end. It was lean on the pilots, had pilot screws way out to help compensate, but it wasn’t right and wasn’t quite enough so it had a bit of a stumble off idle. And now it still does the exact same thing.

 

Since that first time, as a recap, I’ve replaced stiff / sketchy slides, replaced and re-enabled the Coasting Enrichers, replaced the jet block gaskets and a few other things, fine-tuned the float levels, de-carboned the engine per the enclosed instructions, thoroughly checked out the spark and timing, and probably a few other things. And it runs EXACTLY THE SAME! I can’t remember a time I’ve been so frustratingly unsuccessful with an engine.

 

That tells me the carbs aren’t really ALL THAT sensitive to minor stuff, but they’re sure sensitive to something I did. Before I took these apart way back I had the pilots set between 1.5 and 2.5 turns and off-idle response and power were fine.

 

PATCH – COWPUC – MARCARL – ANYONE ELSE WITH CARB EXPERIENCE - I’m issuing one more call (beg?) for a great idea before I sell the bike as-is. In retrospect, I shoulda sold it 2.5 months ago. Actually, in better retro-retro-spect I shoulda sold it 3.5 years ago before taking it apart in the first place.

 

Here’s my current stats / adjustments:

 

PILOTS (turns):

1 – 4.5

2 – 2.25

3 – 2.5

4 – 3.25

So overall, they are a bit less “far out” than some of the previous iterations. But not normal.

 

COMPRESSION (PSI, checked cold as before, 5 revs / 10 revs):

1 – 180 / 190

2 – 175 / 185

3 – 180 / 190

4 – 180 / 190

Just slightly less than before de-carboning. Very consistent, did each one 4+ times. I checked my gage with my shop air, and it’s quite accurate at 95 psi.

 

FLOATS / FUEL LEVELS (idling, spec is -15.5 to -16.5mm):

1 - -16

2 - -16

3 - -15.5

4 - -16

I mentioned that sometimes #4 would change levels, dropping and sometimes rising rapidly. I think I figured out why. The engine was HOT at that point, burns on the backs of my fingers to prove it. I did #4 last. I think fuel boils in the tube right where it comes out of the bowl when I take too long and it has time to heat up. If I drained some fuel from the check tube and quickly checked again, it would be steady. There’s no way that a sticking float would cause the level to drop quickly…rise, yes, but not drop, because an idling engine doesn’t use fuel fast enough to do that. Anyway, all good now.

 

SYNC:

I did the bench sync, then small adjustments with mercury sticks while idling, maybe ¾ turn max.

 

The work done this last time was de-carboning the engine according to Patch’s procedure (and yes, black stuff came out), new Coasting Enricher diaphragms, another thorough check of #3 pilot circuit, and adjust #3 and 4 floats. Lots of oil changes afterward, one more to come.

 

A couple other observations:

-- As before, the hotter it gets the better it is, consistent with lean. It’s ALMOST normal when good and hot, but a quick rev off idle, or taking off from a start with low revs reveals the hesitation. When only “warm” but not “hot” it is more pronounced.

-- I checked for vacuum leaks with water, carb cleaner, and an unlit propane torch. Sprayed all 3 (separately of course) EVERYWHERE on and around the carbs, no effect on idle at all.

-- It sure does act like it’s getting extra air from somewhere, or kinda like the airbox is not installed. The spray check shows no leaks, see above.

-- If I shot propane into the airbox intake for a few seconds, it would start to die from lack of air. But if I shot it in there just for a second and revved the engine, it revved quickly and took throttle like it is supposed to. It needs that extra fuel.

-- Regarding the pilot passages in the main carb bodies: there are 2 places the pilot mix comes out, at the adjustment screw and at a pattern of 3 tiny holes near the throttle plate. When I had them apart, I could SEE on all the carbs the spray flowing freely and equally from all those holes. This was when I had the jet blocks off and shot fuel in the appropriate port that leads to that area.

-- I'll mention the pilot jets again. I've stuck a wire thru them, soaked them a bit, shot spray through them countless times, blew air, and looked at light thru them carefully with my reading glasses on. All 4 are (and always were) clear. The light visible through them is round and the same size on all 4 of them. I know these are the first suspect, but they are clean!

 

Well, that’s all. Thanks for sticking with me through this trial. Special thanks to Patch who surely knows more about how the IC engine works than most of us have forgotten. Remember, I’m still looking for that one genius idea….

 

Jeremy

[cimmer]

I just thought I would throw out there that I havent read every single post in this thread, so I hope I am not repeating anything.

If you think you are not getting enough gas at idle and off idle, then you can increase the Pilot jet size from 37.5 to 40.0 or even a 42.5 and this will increase the available gas to the engine. This jet is #13 in the carb schematic on page 5-1 of the service manual, and fits into the bottom of the jet block. The jet are available from Yamaha and I have attached a file I made with the different jets and the Yamaha part numbers for them. It is also possible that they could be available on the aftermarket also.

When watching Damon Ferraiuolo carb rebuild video, he even suggest replacing the 37.5 with a 40.0 jet as it makes it easier to get the bike to idle better. It is also my understand that this jet provides the fuel for the carbs till about 3500 rpm when the main jet, needle jet, and jet needle take over fuel delivery.

Just a thought.

 

Rick F.

Mikuni Jet sizes and Yamaha part numbers.docx

[Patch]

Hello helpful fellow Venturers. I’m sad to report that I have done ALL the stuff and the bike runs the SAME. Seriously. After putting it together the first time 2 or 3 months ago, it ran great at anything mid range or top end. It was lean on the pilots, had pilot screws way out to help compensate, but it wasn’t right and wasn’t quite enough so it had a bit of a stumble off idle. And now it still does the exact same thing.

 

Since that first time, as a recap, I’ve replaced stiff / sketchy slides, replaced and re-enabled the Coasting Enrichers, replaced the jet block gaskets and a few other things, fine-tuned the float levels, de-carboned the engine per the enclosed instructions, thoroughly checked out the spark and timing, and probably a few other things. And it runs EXACTLY THE SAME! I can’t remember a time I’ve been so frustratingly unsuccessful with an engine.

 

That tells me the carbs aren’t really ALL THAT sensitive to minor stuff, but they’re sure sensitive to something I did. Before I took these apart way back I had the pilots set between 1.5 and 2.5 turns and off-idle response and power were fine.

 

PATCH – COWPUC – MARCARL – ANYONE ELSE WITH CARB EXPERIENCE - I’m issuing one more call (beg?) for a great idea before I sell the bike as-is. In retrospect, I shoulda sold it 2.5 months ago. Actually, in better retro-retro-spect I shoulda sold it 3.5 years ago before taking it apart in the first place.

 

Here’s my current stats / adjustments:

 

PILOTS (turns):

1 – 4.5

2 – 2.25

3 – 2.5

4 – 3.25

So overall, they are a bit less “far out” than some of the previous iterations. But not normal.

 

COMPRESSION (PSI, checked cold as before, 5 revs / 10 revs):

1 – 180 / 190

2 – 175 / 185

3 – 180 / 190

4 – 180 / 190

Just slightly less than before de-carboning. Very consistent, did each one 4+ times. I checked my gage with my shop air, and it’s quite accurate at 95 psi.

 

FLOATS / FUEL LEVELS (idling, spec is -15.5 to -16.5mm):

1 - -16

2 - -16

3 - -15.5

4 - -16

I mentioned that sometimes #4 would change levels, dropping and sometimes rising rapidly. I think I figured out why. The engine was HOT at that point, burns on the backs of my fingers to prove it. I did #4 last. I think fuel boils in the tube right where it comes out of the bowl when I take too long and it has time to heat up. If I drained some fuel from the check tube and quickly checked again, it would be steady. There’s no way that a sticking float would cause the level to drop quickly…rise, yes, but not drop, because an idling engine doesn’t use fuel fast enough to do that. Anyway, all good now.

 

SYNC:

I did the bench sync, then small adjustments with mercury sticks while idling, maybe ¾ turn max.

 

The work done this last time was de-carboning the engine according to Patch’s procedure (and yes, black stuff came out), new Coasting Enricher diaphragms, another thorough check of #3 pilot circuit, and adjust #3 and 4 floats. Lots of oil changes afterward, one more to come.

 

A couple other observations:

-- As before, the hotter it gets the better it is, consistent with lean. It’s ALMOST normal when good and hot, but a quick rev off idle, or taking off from a start with low revs reveals the hesitation. When only “warm” but not “hot” it is more pronounced.

-- I checked for vacuum leaks with water, carb cleaner, and an unlit propane torch. Sprayed all 3 (separately of course) EVERYWHERE on and around the carbs, no effect on idle at all.

-- It sure does act like it’s getting extra air from somewhere, or kinda like the airbox is not installed. The spray check shows no leaks, see above.

-- If I shot propane into the airbox intake for a few seconds, it would start to die from lack of air. But if I shot it in there just for a second and revved the engine, it revved quickly and took throttle like it is supposed to. It needs that extra fuel.

-- Regarding the pilot passages in the main carb bodies: there are 2 places the pilot mix comes out, at the adjustment screw and at a pattern of 3 tiny holes near the throttle plate. When I had them apart, I could SEE on all the carbs the spray flowing freely and equally from all those holes. This was when I had the jet blocks off and shot fuel in the appropriate port that leads to that area.

-- I'll mention the pilot jets again. I've stuck a wire thru them, soaked them a bit, shot spray through them countless times, blew air, and looked at light thru them carefully with my reading glasses on. All 4 are (and always were) clear. The light visible through them is round and the same size on all 4 of them. I know these are the first suspect, but they are clean!

 

Well, that’s all. Thanks for sticking with me through this trial. Special thanks to Patch who surely knows more about how the IC engine works than most of us have forgotten. Remember, I’m still looking for that one genius idea….

 

Jeremy

 

Thank Jeremy,

Been waiting for you to chime in, I would like to complete the project with you before I log off, and, will forward my email in a PM as well as my number should you find this helpful.

 

So some years back I caught a new to the dock's mutated virus in my eyes; the one thing I heard over and over was "we are going to try this, see what happens".

 

So may I suggest these, (I need a pointer to the next step) Set all pilots to 4 turns, balance rpm to 1k, take it for a spin; sett all pilots to 2 turns which is better?

 

Now while I think I know a couples of potentials I would like to know the above answers.

Also I ask this, when you rev to 4k ish on the stand, is your box and stacks on? (no filter)

Do all 4 slides slide evenly?

Do they pulse at idle exactly the the same? Where they stop and to what distance they back down is important, or they will trip the jugs! (cause drag)

 

Ok now for a quick connection: If these were direct slides I would think you have a pressure issue or a accelerator pump issue! Right guys that would be easy go to! The thing is, compression is equal and therefore vacuum is assumed equal as is volume; therefore we look to response time differences!

So when you pop the the T_plates open you initiate a lean condition at the plates but not on a CV carb! Aw you ask what a a rich condition? 1st deal with the lean because that assumes as in this case stock jetting; because you must have a failure for the carbs to go lean!

That is why the CV carb is the closest a carb gets to C or EFI.

The reason is in the slide which is actuated by pressure drop or vacuum (there is a reason for viewing it as pressure below atmosphere)

When you hit lean or rich the engine stumbles/reacts, both can cause issues low down, the answer lies in air volume and velocity, not jet if funtioning and sized correctly.

 

Jeremy, you have been patient and worked hard to bring the project home! Something went a miss and to find it from here is a bit of a challenge.

As for the remaining high numbers I would worry about it, they will drop, we only did the fresh air side, a long run with several\low gear deceleration's will change the readings.

 

crimmer, nice to see your interest in the carbs! If I may again... suggest that you always consider the complete circuit, in this case the history of.. as well as the intention/targets of the project, whatever that project may be! For example a 3/4 to WOT issue after changing needles or needle jets then yes you would need a fatter main whatever that # may end up being, but not for idle when the remaining feed circuits are inactive! The theory expressed to you was incorrect... and as Puc says IMHO;)

Patch

[cowpuc]

Hello helpful fellow Venturers. I’m sad to report that I have done ALL the stuff and the bike runs the SAME. Seriously. After putting it together the first time 2 or 3 months ago, it ran great at anything mid range or top end. It was lean on the pilots, had pilot screws way out to help compensate, but it wasn’t right and wasn’t quite enough so it had a bit of a stumble off idle. And now it still does the exact same thing.

 

Since that first time, as a recap, I’ve replaced stiff / sketchy slides, replaced and re-enabled the Coasting Enrichers, replaced the jet block gaskets and a few other things, fine-tuned the float levels, de-carboned the engine per the enclosed instructions, thoroughly checked out the spark and timing, and probably a few other things. And it runs EXACTLY THE SAME! I can’t remember a time I’ve been so frustratingly unsuccessful with an engine.

 

That tells me the carbs aren’t really ALL THAT sensitive to minor stuff, but they’re sure sensitive to something I did. Before I took these apart way back I had the pilots set between 1.5 and 2.5 turns and off-idle response and power were fine.

 

PATCH – COWPUC – MARCARL – ANYONE ELSE WITH CARB EXPERIENCE - I’m issuing one more call (beg?) for a great idea before I sell the bike as-is. In retrospect, I shoulda sold it 2.5 months ago. Actually, in better retro-retro-spect I shoulda sold it 3.5 years ago before taking it apart in the first place.

 

Here’s my current stats / adjustments:

 

PILOTS (turns):

1 – 4.5

2 – 2.25

3 – 2.5

4 – 3.25

So overall, they are a bit less “far out” than some of the previous iterations. But not normal.

 

COMPRESSION (PSI, checked cold as before, 5 revs / 10 revs):

1 – 180 / 190

2 – 175 / 185

3 – 180 / 190

4 – 180 / 190

Just slightly less than before de-carboning. Very consistent, did each one 4+ times. I checked my gage with my shop air, and it’s quite accurate at 95 psi.

 

FLOATS / FUEL LEVELS (idling, spec is -15.5 to -16.5mm):

1 - -16

2 - -16

3 - -15.5

4 - -16

I mentioned that sometimes #4 would change levels, dropping and sometimes rising rapidly. I think I figured out why. The engine was HOT at that point, burns on the backs of my fingers to prove it. I did #4 last. I think fuel boils in the tube right where it comes out of the bowl when I take too long and it has time to heat up. If I drained some fuel from the check tube and quickly checked again, it would be steady. There’s no way that a sticking float would cause the level to drop quickly…rise, yes, but not drop, because an idling engine doesn’t use fuel fast enough to do that. Anyway, all good now.

 

SYNC:

I did the bench sync, then small adjustments with mercury sticks while idling, maybe ¾ turn max.

 

The work done this last time was de-carboning the engine according to Patch’s procedure (and yes, black stuff came out), new Coasting Enricher diaphragms, another thorough check of #3 pilot circuit, and adjust #3 and 4 floats. Lots of oil changes afterward, one more to come.

 

A couple other observations:

-- As before, the hotter it gets the better it is, consistent with lean. It’s ALMOST normal when good and hot, but a quick rev off idle, or taking off from a start with low revs reveals the hesitation. When only “warm” but not “hot” it is more pronounced.

-- I checked for vacuum leaks with water, carb cleaner, and an unlit propane torch. Sprayed all 3 (separately of course) EVERYWHERE on and around the carbs, no effect on idle at all.

-- It sure does act like it’s getting extra air from somewhere, or kinda like the airbox is not installed. The spray check shows no leaks, see above.

-- If I shot propane into the airbox intake for a few seconds, it would start to die from lack of air. But if I shot it in there just for a second and revved the engine, it revved quickly and took throttle like it is supposed to. It needs that extra fuel.

-- Regarding the pilot passages in the main carb bodies: there are 2 places the pilot mix comes out, at the adjustment screw and at a pattern of 3 tiny holes near the throttle plate. When I had them apart, I could SEE on all the carbs the spray flowing freely and equally from all those holes. This was when I had the jet blocks off and shot fuel in the appropriate port that leads to that area.

-- I'll mention the pilot jets again. I've stuck a wire thru them, soaked them a bit, shot spray through them countless times, blew air, and looked at light thru them carefully with my reading glasses on. All 4 are (and always were) clear. The light visible through them is round and the same size on all 4 of them. I know these are the first suspect, but they are clean!

 

Well, that’s all. Thanks for sticking with me through this trial. Special thanks to Patch who surely knows more about how the IC engine works than most of us have forgotten. Remember, I’m still looking for that one genius idea….

 

Jeremy

 

IMHO, all my 1st Gens (and 99.99999% of the carbed scoots I have had the honor of getting my greasy, untrained, back yard mechanic fingers on) have never ran correctly until warmed up to operating tempt so I will make these statements with total disregard of how your scoot is running pre that status

How does it idle when the temp gauge gets full up to operating temp Gearhead? No choke, air cleaner inside a good, properly sealed airbox,,, shoot the headers with an infra red (or use some spit on the tip of your finger if your an old school fool like me) to make sure she's idling on 4.. Is it?

Now when you touch the throttle does the hesitation happen instantly as soon as you move it or does it bog as the R's are climbing?

By the way,, you been running Seafoam? How old are your plugs and when was the last time you took a peek at your plug caps (where they screw onto the wires and also ohmed em out?

[cowpuc]

Oh,, by the way Gearhead,, do you have any experience with tuning NON CV Carbs?

[cowpuc]

Gearhead,, I just tried to call you at your number listed in your profile and got a wrong number.. Please advise..

THANKS

Puc

[Gearhead]

Must be my old home number. Just pm'd you my cell!