87 VR, carb problem

[cowpuc]

By the way @Gearhead,, another issue I have ran into with these older bikes is leaky wires, they can cause the same issues you are dealing with too.. A good way to check them IMHO is to pull the bike into a dark area with the side covers off, turn off the lights in the room, drop a rag over the lights, start it up and let it idle and watch the plug wires for leaks. It actually works even better if its really humid out. If you discover your wires are leaking by seeing the light show going on, I STRONGLY advise that you replace with Wire Wires like the wires that come on them OEM. Another similar related issue that I have bumped into dealing with misfire right off the bottom and under a load like you mention is;

[Gearhead]

Thanks again guys. I may not get to this until the 4th. But some good stuff to check.

 

Regarding high tension spark problems, I'm with Patch, they generally happen at high throttle conditions, and when I whack it in the mid or upper range it really scoots. So I don't have a lot of hope there, but I can look. I think I've looked at the wires and caps before, but I've put 80k on the bike, so....

Edited July 29, 2019 by Gearhead

[Patch]

""When it's "good n hot" it almost runs right, but still doesn't quite respond correctly right off idle, you feel this when taking off from a standing stop. Mid range and top end are great.""i

 

is exactly what I have experienced with faulty wires/caps, fouled plugs ect. Patch and that corrusion that Sky mentioned is present and cleaning em up with a 1/4 inch snip is a big part of the solution to correcting the stumble in many cases, especially coming up off idle when the engine is under a load.. It is amazing what doing that and a new set of plugs gapped to 32 thou will do for erradicating a right off idle stumble IMHO. Definitely something that is easy to check.

 

 

I see your point, especially under cold or wet conditions where crushing spark is everything.

 

So and but; in this complaint how would you justify the clue of the enricher improving conditions? Doesn't add;)

 

I beginning to think it the EGR??? Yep!

[cowpuc]

I see your point, especially under cold or wet conditions where crushing spark is everything.

 

So and but; in this complaint how would you justify the clue of the enricher improving conditions? Doesn't add;)

 

I beginning to think it the EGR??? Yep!

 

Cause, like most engines, adding extra fuel when cold makes the other cylinders that may be firing properly run right while warming up. IMHO, these V-4's actually run fairly well on just three pots and supporting those three pots when cold with extra fuel/playing with the fuel/air mixture just a little can make em run a little better allowing them to cover for the misfire.

Funny you mention an EGR valve and it causing similar issues.. I have experienced some of the same issues on vehicles with faulty EGR's due to that valve failing and causing em to suck air and causing lean conditions but truthfully Patch, I did not even know these scoots had an Exhaust Gas Recirculation valve (dont recall ever seeing one on one in all these years of playing with em:doh:). I thought the exhaust systems on em were pretty straight forward with no return connection back to the engine = not even sensors as they are not EFI.. My bad,,, I gotta pay better attention in class:happy34:!! Gearhead,,, as Patch suggests, you might wanna put the EGR check on the list too brother!

[Gearhead]

EGR? You sure about that? Where's the EGR on a Venture?

[luvmy40]

I think Steven's tongue was placed firmly in his cheek as he typed that last statement.

[Gearhead]

Update:

 

Been busy on other stuff, plus had to order jet block gaskets and wintergreen oil. I did the wintergreen oil / alcohol soak trick on the stiff rubber jet block plugs and needle jet o-rings, and it worked as advertised. Truly impressive, the softening and slight swelling effect. Now the plugs fit snug.

 

I have the carbs stripped down, haven't done anything else with them yet. I did re-check the jet block on one, removing the idle jet and emulsion tube, found nuthin'. I should get back to them soon. I'll re-check the pilot passages, then reassemble with new jet block gaskets and good-sealing jet block plugs. Check the compression and plug wires / caps. Man, I hope that does the trick. I'll let you know.

 

Jeremy

[CaseyJ955]

Update:

 

Been busy on other stuff, plus had to order jet block gaskets and wintergreen oil. I did the wintergreen oil / alcohol soak trick on the stiff rubber jet block plugs and needle jet o-rings, and it worked as advertised. Truly impressive, the softening and slight swelling effect. Now the plugs fit snug.

 

I have the carbs stripped down, haven't done anything else with them yet. I did re-check the jet block on one, removing the idle jet and emulsion tube, found nuthin'. I should get back to them soon. I'll re-check the pilot passages, then reassemble with new jet block gaskets and good-sealing jet block plugs. Check the compression and plug wires / caps. Man, I hope that does the trick. I'll let you know.

 

Jeremy

 

I used the wintergreen oil the same way with good results. The PO tried to run screws up into the plugs to snug them up, luckily the holes did not breach the tops of the plugs. I'll give him a B- for ingenuity and a D for execution, he tried to use an adhesive also. The Wintergreen oil works for many rubber things, really decent trick. Good time to check float levels too.

[Patch]

I think Steven's tongue was placed firmly in his cheek as he typed that last statement.

 

 

You betcha; nothing like getting Puc to stand his ground! Lord knows he does it to me lots

[Gearhead]

UPDATE 2019-07-29:

1) Took it all apart again, found nothing noteworthy. Double-ensured everything was clean, especially the pilot jets and full circuits. I took the time with a carb in hand and the flow diagram open on the bench, and ensured that when I sprayed carb cleaner in the correct hole at the jet block surface, it came out in full streams from the pilot feed holes in the throttle bore. This includes the hole that the pilot screw adjusts, as well as three holes in a small pattern under the edge of the throttle plate when it's closed.

2) Rubber jet block plugs were swollen with fuel, probably not leaking. I treated them and the needle jet o-rings with wintergreen oil which made everything supple again - magic.

3) Replaced jet block gaskets

4) Note that the Coasting Enrichers are still disabled, vacuum passages plugged up, as before.

5) Put it all back together. No change to symptoms. Re-synced carbs and re-set pilots, similar to before, 3 to 5 turns out and still too lean.

6) Checked fuel levels and 3 of them are fine, 16-17mm below the line (spec is 15.5 to 16.5). Carb#4 fuel level is erratic and on the low side when idling, varying from 17 to 20mm below the line. This is new to me. Sometimes it creeps up and down slowly, sometimes quickly. Have you guys seen this before? What causes that? The carb vents are clear. Maybe a sticky float? What would it stick on?

 

I haven't yet checked the compression and plug wires / caps, will do that next. The erratic fuel level is definitely something I need to check out, but I don't think that's my full problem because all the carbs need their pilots set very rich for best running.

 

This is quickly passing the frustrating mark. I'm not normally one to give up on this kind of stuff, but I'm getting this bike ready to sell. I may soon be at the point of cutting my losses and selling it as-is. ARGGHH.

 

If you are following my saga, thank you and I value your continued feedback! Thanks!

Jeremy

[Gearhead]

Patch, in response to your questions you posted on the "rubber plug" thread:

 

Are you saying that you went thru the carbs as we mentioned, completely and the bike still won't hold idle without the choke or transition smoothly past a 1/4 throttle?

More or less, yes. It will idle, but with pilots WAY out.

 

Do you know how to check the timing?

Yes. I'll do that when I check out the ignition stuff.

What on my original symptoms has changed?

Nuthin!

[Patch]

UPDATE 2019-07-29:

1) Took it all apart again, found nothing noteworthy. Double-ensured everything was clean, especially the pilot jets and full circuits. I took the time with a carb in hand and the flow diagram open on the bench, and ensured that when I sprayed carb cleaner in the correct hole at the jet block surface, it came out in full streams from the pilot feed holes in the throttle bore. This includes the hole that the pilot screw adjusts, as well as three holes in a small pattern under the edge of the throttle plate when it's closed.

2) Rubber jet block plugs were swollen with fuel, probably not leaking. I treated them and the needle jet o-rings with wintergreen oil which made everything supple again - magic.

3) Replaced jet block gaskets

4) Note that the Coasting Enrichers are still disabled, vacuum passages plugged up, as before.

5) Put it all back together. No change to symptoms. Re-synced carbs and re-set pilots, similar to before, 3 to 5 turns out and still too lean.

6) Checked fuel levels and 3 of them are fine, 16-17mm below the line (spec is 15.5 to 16.5).

Carb#4 fuel level is erratic and on the low side when idling, varying from 17 to 20mm below the line. This is new to me. Sometimes it creeps up and down slowly, sometimes quickly. This is a lean condition.

Have you guys seen this before? What causes that? The carb vents are clear. Maybe a sticky float? What would it stick on? You have to physically check it to find what it is binding on, that is a rich condition.

 

I haven't yet checked the compression This should be the first thing checked before rebuild carbs.

and plug wires / caps, will do that next You need to know what is the voltage at the coils: then the best way is to check the output with a gap tester the procedure is in the manual.

The erratic fuel level is definitely something I need to check out, but I don't think that's my full problem because all the carbs need their pilots set very rich for best running.

 

This is quickly passing the frustrating mark. I'm not normally one to give up on this kind of stuff, but I'm getting this bike ready to sell. I may soon be at the point of cutting my losses and selling it as-is. ARGGHH.

 

If you are following my saga, thank you and I value your continued feedback! Thanks!

Jeremy

 

Jeremy, there is a reason for the timing port, you did not answer the question? It can save time knowing!

 

The CV carbs need to be balanced from one end to the other, your first attempt was short of predictability and had to be addressed and corrected.

Now you coasting circuits can also create a lean condition.

OK now for some nuts and bolts: CV carbs are all about pressure differentials

you must bench sync the throttles, chasing afterwords is a foolserrand, then you you sync them into synchronization as per pressure results based on jug to jug!

Any port that is subject to pressure change will produce fuel problems, especially venting ports!

Get the carbs in order, check voltage at the coils, check timing mark, check coil output with gap tool.

Patch

 

(pick a post/thread)

[Patch]

I know you responded not sure which thread you're on, I'll just stick to this one.

So over the years I have worked on many such projects either dropped here at my little shop or asked to stop by another. The secret to troubleshooting is logic, regardless of our past experiences we have to zero in to factory bench marks; that is why I ask for compression then and in this case the shortcut of what is the actual time mark at idle - the advance connected then not connected and port stubbed off.

 

In your explanations you claim lean conditions but,, other than turns you aren't backing the claim with pipe temperature reading or any of the other typical signals that point to it? So what might be going on? Well for one you are wasting fuel in the sense that you are getting to little return for the metric you are assigning!

 

I assume the intake seals are not leaking? I assume the carb to intake seals are in good order and not missing bits? I assume you are not attempting to throttle with the box and V-stacks off the carb setup?

 

First quarter is pilot but,,, pulsed via main needle, velocity is critical below and above the venturie. Vacuum is cannot be taken for granted so, the plates in the correct position increases vacuum build and velocity providing the vacuum generator meets spec and is withing differentials.

Carbon on the piston crowns reduces heat tho your compression readings may be higher as a consequence of it being there; this causes a high fuel metric but wastes 1/2 of it and yet requires that metric to run!

You say she runs well when up and off the needle but that too is a double edge cause she could be igniting off the carbon glow, not being under constant load you may not know the preignition is present!

 

Then there is the opposite to the above which is low compression or a mix of the two; and is why we need to know the compression first then rule on the rest!

 

Timing for me would be next because it points to angle and that can save a lot of time putzing about..

Edited July 31, 2019 by Patch

[Gearhead]

Sorry about the “two thread” thing. I just wanted to give some closure on the rubber plug thread in case somebody reads it some future day looking for answers about those little buggers.

 

UPDATE:

 

This morning I pulled the plugs, checked out the plugs, caps and wires and ran compression.

 

- Plugs look fine, they should because I had them out recently. Checked resistance of the plugs from connector to center electrode; all were between 4.0 and 4.6 k ohm. I may replace, but am betting money that won’t fix my problem.

- Caps also look fine. I found my record of when I took them apart, cleaned, put together with silicone grease for corrosion protection. It was many years and 50k miles ago, but the grease worked as there was NO corrosion anywhere. Resistance across the caps measures same as it did in the past:

---- 1 and 3 are factory caps and measure 8.6 and 8.8 k ohms.

---- 2 and 4 are NGK replacements and measure 4.7 and 5.6 k ohms.

---- I don’t know why the fronts were replaced but not the rears. It's always been that way while I've owned it.

- Compression is good and the most consistent of any engine I’ve ever tested. I had all plugs out, carbs drained and fuel pump unplugged, headlight fuse out, battery on a charger to keep fresh, and throttle open, engine cold. Ran each one several times to verify and the results were within 5 psi every run. I recorded the psi registered at 5 strokes / 10 strokes.

----1 – 180/195

----2 – 180/195

----3 – 185/200

----4 – 180/195

 

I didn’t check the timing yet, but I will when I put the plugs and caps back together. So far this is telling me the engine mechanical and spark are fine, which makes sense because they were fine when I tore it down 3 years ago.

 

“check voltage at the coils, check timing mark, check coil output with gap tool.”

Good advice, need to do these.

 

More thoughts on the carbs, since those are the only things that changed since I tore it down. I have one slightly wonky float, need to address that, but all 4 carbs are acting up so I don’t think that’s the whole problem. I’m wondering about the Coasting Enrichers. Other than cleaning and some new parts installed, disabling those is the only thing I actually changed in the carbs (did so because 1 or 2 of the diaphragms were compromised and they’re spendy). As I’ve said, everything I’ve read says they ONLY come into play under the very high vacuum of throttle chop deceleration, and only briefly, to enrich the pilot circuits under that condition to prevent lean misfire and exhaust popping. But what if that’s not accurate? Maybe they also “enrich” at standard idle vacuum…and if so, disabling them would cause my lean problem. I took a chance by disabling them, maybe it bit me. I think I can test this pretty easily. The diaphragms are the only part of the carb easy to access with them on the bike, and pilot air jet #2 is under the diaphragm. (Pilot air jet #2 gets closed off when the Coasting Enrichers engage.) I could easily plug those with toothpicks or something similar – something temporary – in about 20 minutes. Then I could run the bike and see if the pilot circuits and idle behave normally. Seems a good experiment.

 

Patch, to address more of your questions and excellent suggestions:

 

“Now you coasting circuits can also create a lean condition.”

Please ‘splain what you mean

 

“The CV carbs need to be balanced from one end to the other, your first attempt was short of predictability and had to be addressed and corrected.”

I have not done this precisely in the manner you described. However, I have the following evidence to tell me they are good.

- They were balanced before.

- I didn’t change the adjustment screws when I disassembled the carbs. I did, however, split the rack which affects the physical relationship and adjustment.

- I did take a good look at the throttle butterflys after reassembly and they were all sitting about the same in the bores.

- When I balanced them with the mercury sticks after reassembly, twice now, they only required small adjustments which tells me they weren’t far from where they started.

- I believe this is the factory specified way of balancing carbs, which I’ve done successfully on a number of bikes.

 

When I disassemble them for the third and final time, I can use a feeler gage to ensure they are set the same before reinstalling them. QUESTION FOR YOU: Are you saying you ONLY bench set the butterflys, and do NOT fine tune them by vacuum?

 

“In your explanations you claim lean conditions but, other than turns you aren't backing the claim with pipe temperature reading or any of the other typical signals that point to it?”

Evidence of lean pilot:

- Many turns out required on pilot screws.

- Stumbles when first given throttle, then takes off.

- Choke (enricher) greatly improves the condition.

- Condition gets gradually better as engine warms up, with it almost normal when engine is very hot.

 

That said…I haven’t fixed it yet so all possibilities are on the table!

 

“I assume the intake seals are not leaking? I assume the carb to intake seals are in good order and not missing bits? I assume you are not attempting to throttle with the box and V-stacks off the carb setup?”

Correct, I checked by the spray method with engine running. Correct. And correct.

 

“Carbon on the piston crowns reduces heat tho your compression readings may be higher as a consequence of it being there; this cause a high fuel metric but wastes 1/2 of it yet requires that metric to run!”

Please ‘splain. I understand the potential for high compression readings, but not the rest.

 

“You say she runs well when up and off the needle but that too is a double edge cause she could igniting off the carbon glow, not being under constant load you may not know the preignition is present!”

Well, I don’t hear any pinging which I normally detect by ear, plus now we know my compression is consistent and I would say in the normal range.

 

This just keeps getting more fun…Thanks!

Jeremy

[Patch]

Great let me think on it a bit but the compression I know is too high and is a problem!

Have you checked out "a case for fogging" ?

[Gearhead]

Yes I have read it. Lots of good stuff. Fogging would have been a good idea for me, but of course I did not intend to take a 3 year hiatus on the project! But given my indoor, mild temp storage environment and good compression readings today, I think I'm OK there. Stuck rings would tend to lower compression, yes? And usually not evenly across the cylinders?

 

Compression test by the book is to be done hot; I did mine cold. Not sure if they read higher or lower when done cold, I can see arguments both ways but have not tried it to find out. Anyway, the manual lists the following:

- Min - 142 psi

- Std - 171

- Max - 199

 

I'm right in the range between Std and Max. (I have not had my gage calibrated, so that's a variable.) I guess that probably indicates a little carbon build-up, which is fairly common I'd say, but shouldn't be problematic...do you agree?

[Patch]

Yes I have read it. Lots of good stuff. Fogging would have been a good idea for me, but of course I did not intend to take a 3 year hiatus on the project! But given my indoor, mild temp storage environment and good compression readings today, I think I'm OK there. Stuck rings would tend to lower compression, yes? And usually not evenly across the cylinders?

 

Compression test by the book is to be done hot; I did mine cold. Not sure if they read higher or lower when done cold, I can see arguments both ways but have not tried it to find out. Anyway, the manual lists the following:

- Min - 142 psi

- Std - 171

- Max - 199

 

I'm right in the range between Std and Max. (I have not had my gage calibrated, so that's a variable.) I guess that probably indicates a little carbon build-up, which is fairly common I'd say, but shouldn't be problematic...do you agree?

NO! But its your bike and your choice!

I wrote a breakdown to your last post and I'll post it shortly.

Best of luck to you

Patch

[Patch]

So you've asked quite a few questions and I am for the moment just going to sum things up. This is as I see it and you'll likely catch on as to why I wanted the timing angle!

 

1st) reading compression at 5 and 10 is a better way then only knowing the maximum numbers.

For those of us that raced or had to decide whether to do a tare down or wait is often followed by a leak down test which more or less suggests roughly how bad or how far and how much we're in for.

Now your 180's at 5 seems nice but not for these chambers, 200 +- at the end tells us what is going on and why the carbs are not wanting to dial in;

in fact and for the moment the carbs should be put aside.

 

Angle of ignition is a teltale and it seemed obvious as I made the leap with you that the carbs were now in reasonable order!

One thing I always appreciate about Puc joining a conversation in troubleshooting is that he causes me to check for cracks where least expected or want to venture his stubbornness really makes me dig! In more cases then not and tho we stay in our respective dimensions and in this case as well we are both viewing multiple ignition problems tho thru different lenses!

 

The carbon question isn't an easy one but it can cause angle issues as it relates to crank angles and ignition and refereed to as preignition which means wrong angle and wrong ignition timing! So lets just except that.

 

The coasting valve question is base on plus or minus atmosphere; meaning one pulls and so the other pushes. The velocity at the throttle plate when chopped or at idle is highest when chopped, so any porting exposed will experience low pressure or a psiphon effect! The psiphoning is stalled when atmosphere is is cutoff and is why these fuel systems are vented and so that is what the coasting circuit does it switches on/off, allows for atmospheric pressure to flow above the charged fuel port just above the 2 pilot ports, at least usually.

 

Summing it up the 3 to 5 turn plus choke suggested that the metric was too high and we know that the throttle plates can not be in the correct or expected position, you just think they are. The carbon in the chamber is at low speed when cool soaking the droplets and producing a low combustion heat for a couple of reasons; it can't transfer heat well and then once hot it glows where it is flaky or thin, which gives you the preignition.

 

199 psi I believe is the max and recomended tare down mark, (that in no way suggests it is OK to run that high, it is the end of the line). Not something I suspect most of us want to do so what are the options?

 

Well Ajay and were working on a Kat some years back, something we have lots of parts for, I pulled an engine off the shelve which read 188 by 4 so hey lets swap! Well it had been sitting round for some years so I did my "fogging" trick and low and behold after sitting for 2 days 166 psi DANG what a bummer eh! Was it a bad move? Nope if I had taken our setup and run it on that engine I would have had it back in chasing my tail trying to figure where I went wrong!

In 17 we had a venture high on 4, right at the limit however when I started working on her, her numbers were allover the place and sure enough it explained all the busted pieces that made up the carbs; see, the fellow kept blaming the carbs for the troubles when in fact is was the air pump its self!

Now getting the low ones up was easy but the high on down, not so much.

 

The problem with chamber carbon is that it is very abrasive so removing it is double edged. It takes a lot of flushing to get it out of the engine, so here is what you can do or try...

Pull the carbs

pull the plugs they stay out

2 cans of Deep Creep

Fill the close intake port with the spray

then move to the jugs and spray each one for about 5 give or take seconds

let soak for a day and repeat like the fogging thread says

But each time and before you refill the jugs take a long neck air gun/duster and drop it about an inch below the plug threads and blast away using a bunched rag around the nozzle to deflect the crap being forced up "don't try to prevent it from leaving the jug, refill then rotate the crank by hand and repeat till you have done all 4 jugs and intake valves!

Remember the open intakes will blow out as well so lay a heavy rag/towel across them.

Finally clean up, spray a touch of crab cleaner down each let sit then blow out again.

 

I would then change the oil with cheap stuff but a good filter, run it till warm and repeat with fresh oil; you don't want that carbon floating around the crankcase!

 

I would make sure that the carbs are in proper working order before reinstalling them no patches and also that the choke cable isn't too tight, I prefer a a minimum deflection on the cable or a mm or 2 depending on what set I'm working on.

Patch

Edited July 31, 2019 by Patch

[Gearhead]

Thanks, will keep you posted.

[Patch]

I'll mention a couple of other notes here for you to consider.

One the compression you posted is high there is no denying this but, not as high at it may actually be. The reason for the high numbers is due to the carbon build but lets not forget that the engine sat for 3 years and as I've shown before here on the site and others, you can not stop gravity from setting the rings deep into the landings!

In other words, remove via magic the carbon, your numbers would most likely be low!

 

A year or so ago we have a member that posted he needed to turn his set screw out 4 plus turns and what appeared to be a sudden and unexpected result! After posting his compression numbers we could see that they too were too high for his model! See what I'm saying about the carbon effects.

 

Ok this isn't adding for me how you are balancing your carbs.

1st the bench sync needs to be equal and approximately where I mentioned.

2nd a quick hunt for highest rpm per pilot screw then back 1/8th

3rd you must reset idle, then not sure where you balance off of 12 or 1500 and if you match front and rear

(I use an uncommon tool and I set the bikes for how they're to be driven)

4th reset idle then reset mixture

Taking for granted that the air box is on and I prefer the filter and lid in place (as it will be when on the road) And that the throttle cable is properly set.

 

Now if you can't maintain idle then how are you balancing? You can't be running the enricher?

 

Some more on the lean: These coasting are bypassed for lack of a better word; the passages are block, you are trying to blip the throttle - first the air box needs to be installed with the velocity stacks and for the heck of this problem place the lid on, these CV count on velocity and an organized stream above the slides at velocity!

Next each time you blip then chop the throttle even off the stand (not moving) you create a lean condition which will appear as a stumble, because the coasting valve is bypassed; so you will need to allow for it to recover before blipping again or you prolong the stumble!

 

Hope this helps clear up some missing explanations

Patch

[Gearhead]

So Patch, on the Coasting Enrichers, do you agree with the majority opinion out there that they only "enrich" momentarily under throttle chop conditions, and NOT at idle?

 

Now if you can't maintain idle then how are you balancing? You can't be running the enricher?

 

I didn't say it won't idle. It idles pretty smooth with the pilots out 3 to 5 turns. But it hesitates taking throttle off idle, pretty much every time.

 

Jeremy

[Patch]

So Patch, on the Coasting Enrichers, do you agree with the majority opinion out there that they only "enrich" momentarily under throttle chop conditions, and NOT at idle?

 

Now if you can't maintain idle then how are you balancing? You can't be running the enricher?

 

I didn't say it won't idle. It idles pretty smooth with the pilots out 3 to 5 turns. But it hesitates taking throttle off idle, pretty much every time.

 

Jeremy

 

 

The calibration is set via the recoil! This is set to above normal idle generated vacuum.

It just takes a sudden closing of the throttle from high rpms to cause the spring to give, open the passage and then to close off again at normal pressures.

 

What I said was, is that the bike does not have to be moving for the coasting cycle to kick in.

[Patch]

Had some time so thought I’d do a short revue and some support for the decisions that needed to be made. I do know how difficult it can be to absorb this stuff when we are not in it every day or how simply accepting that some rules just won’t bend to our liking?

Engines carboning up is just a reality so coping with it becomes just a procedure, one way or another.

Some engines carbon faster than the exact same sister engine, sometimes its pilot style at fault and sometimes its small mods that over time leave their mark; also like many thing s it’s just to be expected.

The only thing for you and others that discover this is perhaps and most reason is that likely this could have been added to a maintenance schedule keeping the issue at bay longer.

Lately I’ve read posts that date back early in the Venture history, well some brain poster came up with a plan for rejetting based on the similarities to the V-Max this was read on a site before this VR site was established. By the time I finished reading his post I hadn’t a clue to what he had accomplished or what gas and air jets he ended up using!?

But one thing was certain in my thoughts as I read on, he had overlooked the main ingredient that punches the V-Max intake and exhaust strokes!

The thing that most folks don’t understand about CV carbs is that they are pressure sensitive, all carbs are flow designed with compensations built right in such as and in this case, slides tuning/tweaking, and another is the coasting circuits.

On these carb setups we need velocity and we need it above the slide (or before the slide) so we use the V-stacks and box with a calculated intake port. Now with the direct/mechanical slide carbs we can work around that but not with these CV carbs at least not with performance in mind.

A properly setup CV carb won’t bog but instead it will delay response, that is because of the pressures it needs to do its job, having said that they pull thru both strong and consistantly. They have to build off the air pump, this is where cams change response times, outputs and of course jet needs but with that, power bands also become a compromise best left often for the track style pilot!

These are touring bikes packing a few pounds, what we expect is solid power to pull her up through the gears from the many stops that a touring rider will experience. We also tho have all those unexpected things that pop up in front of us suddenly and are where the throttle chop effects now need a compensating circuit.

The crank rotates because we apply controlled energy to it, how much, for how long and at what angles adds up to a well thought out choreograph, chopping the throttle forks it up so doe’s carbon buildup tho for different reasons.

Another way we drive the crank is when we use the gears to bleed speed, the rpms go up yet the throttle angle is reducing air flow, and yet the intake strokes are speeding up, so vacuum continues to build against the throttle plates, which now act as engine brakes slowing the decent of the pistons

(imagine what the compressions rings are going thru) also the slide is now in the closed position with just short rapid pulses but, air flow is down to bare minimum and what is getting past the slide is both speeding and slowing thru the sequances; anyways, your rpms are up, vacuum is up, plates are at idle, metric is too lean for the rpm. In a sense you have stalled the engine because there’s just not enough fuel at that rpm so; this is when the spring calibration gives way to allow atmospheric pressure to flow the extra fuel above the pilot port! Now here’s the common misunderstanding; the coasting circuit is not a rich mix – it is a richer mix under that perimeter of a chop which produces too lean of a mix! The purpose is to keep the engine combusting even tho it is nowhere near a stoichiometric!

In the above we have driven crank rotation via combustion and engine braking, let’s not overlook mass.

Where mass takes effort to get moving this too is now part of engine braking, it is still in motion when the clutch is pulled or, when the bike is running on the stand there still exists some kinetic energy behind the rotating mass and so chopping the throttle under this scenario still poses the same lean condition all be it for a shorter duration, if you then try to throttle up she will stumble because, the cycles are still in the rpm string which are too lean and, contrary to that CV carb design so, deleting the circuit causes that stumble response!

Helpful?

The jet block, sure in your case you’ve spent a lot of time on it but doesn’t have to be that way, a proper kit at the ready and it would have been done just once. The rubber plus chapter 5, 2^nd page it clearly shows the plugs force flow thru the main jet also shows the porting that feeds the pilot, same for the jet block gasket. Some carbs need cleaning some need parts.

Always consider we’re are working on 30+ year old bikes. They have a proven reliability and often more so than what we spend way too much on for performance today.

Everything has a duty cycle, us included

That’s my take on it

Patch

 

OK finally desperate action is attempted, and I mean desperate action!

If you do this it is at your own personal risk of safety!

Place a large fan in front of the bike

Leave the carbs on pull the slides, leave them out replace the caps only

Ready a can of choke/carb cleaner

Dial your rpms up to 15/1800

Short burst of cleaner down the thought of each one

Allow for recovery

Monitor heat stat

Don’t flood or she’ll backfire and chase your spray can

Can you see the potential for risk doing this?

 

It may be that you are able to blow off enough carbon per jug to reduce the predetonation, which may be causing your stumble.

Then slip it back together and see what what

 

Mikuni tuning guide

“Please note that there is no point in attempting to tune any carburetor unless the engine is sound and in a good state of tune. If you have any doubts about the general condition of your engine, have it checked by your dealer or an experienced mechanic before attempting to fine-tune your Mikuni.”

[Gearhead]

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.

- 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.

 

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.

- 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.

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

- 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.

-----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.

 

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.

 

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.

 

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.

 

Jeremy

Edited August 3, 2019 by Gearhead

[Patch]

Hat is off to you Jeremy for completing the troubleshooting list!

 

I'll need some time to break it down for you, likely tomorrow morning.

I should be able to paint you a pretty clear picture;)