87 VR, carb problem

[cowpuc]

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

 

Nice chattin with ya brother! Definitely a mystery,,, please let us know if you do fatten up those metering rods a slight and what happens if you do!! Always something interesting happening around the club I tell ya!!

All the best!

Puc

[Gearhead]

Been doin other stuff, can't work on the Venture for a couple more weeks. I talked to Puc (thanks again) and have a couple things to try from him and Patch. Puc suggested raising my needles with one washer, just to see what happens, cuz it's pretty easy. Got me thinking. I've been approaching this not as a tuning issue, but rather a "something went wrong" issue. Which still seems like it must be the case, but I can't find it. At this point, what if I try a little smaller pilot air jet #2? They are easy to get to under the diaphragms, and I know that will richen the mix at idle and initial throttle response; remember when I plugged those jets with toothpicks? My pilot mix got WAY rich, makes sense. So I'm thinking about picking up a set of, hmmmm, maybe 160's to replace the stock 170's? Opinions? Does anyone know offhand what type of Mikuni jets those are, and the cheapest place to buy them?

 

Thanks,

Jeremy

[Gearhead]

Just a little bump on my last question. Does 160 seem a good size to try for the pilot air jet 2? Also, I should know this, but are those the same jet type as the main jet?

[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.

So I missed this not that slides were replaced! I asked in another post if you could monitor the rhythm or pulses of the slides so here's the reasons broken down: CV Carbs don't run lean unless air volume exceeds needle position... (assuming no fuel restrictions)

So what does that mean and why are Puc and I talking needles.... Here's the picture, the throttle opens past 1/4 there is then a pressure drop at the plate but because the slide has not yet opened to match the plate angle the slide itself becomes a restriction to air flow which means that velocity is highest at and around the slide piston and slower at the plate... (think about it) While this begins to play out the barrel of the carb is has more wall effect and in this position this helps for the expected transition to the power band delivered by the increasing air volume (in this case is lean) the lean means too much air not enough fuel. How can it be and on how many jugs? And is why I asked the question in my other post!

If you are assuming that all 4 are lean then you would have to prove a fuel flow problem (restricted lines, filter, pump...) so instead we turn our attention to the slides, which one (s) are slow to respond? All the emulsion tubes have been cleaned and check, the needles are not showing bent or worn, the springs are all stock not pulled or fooled with, the slides are clean smooth, the slide bores are clean with no burs or film buildup, and so what is left to chew on; has to be a diaphragm or vacuum issue on one or 2 of the slides or the needles are sticking?

 

Here's something to bare in mind, each piston contributes to the rotation of the crank which also means that one combustion stroke can cause the crank to accelerate more than the next stroke up in the, Q... Think that through, if #1 is running correctly and #2 is not say due to a slide then that carb is running lean and causes a trip or hesitation; the reason for that is, #1 accelerated the crank so more air volume wants to run thru#2 base on plate position and rpm, if only #2 slide would get out of the way, pull the needle out and allow the fuel to flow which would stop the lean condition and cause #2 to contribute more to the crank for the next to combustion strokes waiting in the Q!

 

​Is that it? No thats not it because anything that restricts air in like a slow or stuck slide will also the the rpm climb and that cause a too rich condition on the jugs that want and can work properly! Now that is the answer... You are running lean on the pull but also causing a temporary rich which clears as the rpms gain!

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. More than one thing in play here.. First I suspect it is method and secondly I'd want to know if the o-rings are good, the points are sharp, and how much of a rpm drop is there when you loose 2 truns off of #1, you just may be threading the needle more then is required for a pilot circuit, anything around 1 1/4 to 3ish turns is good enough, its a pilot and you know the circuits are clean so just back it off.

 

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. This is what we expect when the carbs are benched synced and the jug volumes are close.

 

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 as mentioned above

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.eds fuel to the pilot circuit Remember there is also a port that bleads fuel to the pilot circuit after the main and main bleed pipe page 5-2 between 15 & 16 the 15 line travels thru that bleed port, it is small and can be restricted, you wouldn't know it by the procedure you mentioned above, you clean it thru the removed plug with a spray tube till it flows thru to the pilot pipe...

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….

 

Patch

[Gearhead]

Remember there is also a port that bleads fuel to the pilot circuit after the main and main bleed pipe page 5-2 between 15 & 16 the 15 line travels thru that bleed port, it is small and can be restricted, you wouldn't know it by the procedure you mentioned above, you clean it thru the removed plug with a spray tube till it flows thru to the pilot pipe...

 

Thanks Patch. Looking for clarification on this. Are these tiny ports you are referring to in the jet block? If so, I cleaned them as well. If not, help me find them!

 

Thanks! Jeremy

[Patch]

Thanks Patch. Looking for clarification on this. Are these tiny ports you are referring to in the jet block? If so, I cleaned them as well. If not, help me find them!

 

Thanks! Jeremy

 

 

The port that feeds the pilot circuit.

 

The fuel enters thru the main jet shown as 16, it then fills #17 main bleed pipe; then because of demand its drawn thru the pilot circuit #15 !

In between 17 & 15 there exists a port which can only be accessed thru #17 via cleaner with the spray extension! When you spray up thru the bottom of the pilot you only clear/clean the jet and what ports lie after it - not before it!

 

Anyways Jeremy don't over estimate the pilot circuit.

The transition problem you describe must lie in the

needles

diaphragms

springs

slides

or needle jet

Meaning they are not acting equally/not in sync or, they are not exact matches to each other.

Patch

[Gearhead]

“The fuel enters thru the main jet shown as 16, it then fills #17 main bleed pipe; then because of demand its drawn thru the pilot circuit #15 !”

 

Gotcha, they are clean.

 

“If you are assuming that all 4 are lean then you would have to prove a fuel flow problem (restricted lines, filter, pump...) so instead we turn our attention to the slides, which one (s) are slow to respond? All the emulsion tubes have been cleaned and check, the needles are not showing bent or worn, the springs are all stock not pulled or fooled with, the slides are clean smooth, the slide bores are clean with no burs or film buildup, and so what is left to chew on; has to be a diaphragm or vacuum issue on one or 2 of the slides or the needles are sticking?”

 

Slides are new and move freely. Springs are stock, same as I pulled out. I need to run it and observe with the airbox lid removed. Needles look good. Emulsion tubes are NEW – so that’s a change from before I took it apart. They were worn oval, so were rich, now are not. I ordered factory parts from Yammy, so they should be good.

 

Fuel level is good and consistent, and the bike pulls great under WOT. These two things make it unlikely that fuel supply to the carbs is insufficient.

 

I tried replacing the Pilot Air Jets#2 this morning, out with the stock 170’s, in with 155’s. It did fatten the pilot mix just a bit. Throttle response is slightly better, but not quite perfect. Pilot screws are a little more reasonable, but still don’t behave like I am accustomed to. Remember that before all this nonsense I had them tuned to 2 turns or less.

1 – 3.5

2 – 2

3 – 2

4 – 3

 

If I screw them in more the idle degenerates and the throttle response gets worse. I haven’t tried yet to set them all to 2 and then to 4 turns, need to do that. BUT, lean pilot usually causes a hanging idle, and I don’t have that symptom!

 

“First I suspect it is method and secondly I'd want to know if the o-rings are good, the points are sharp, and how much of a rpm drop is there when you loose 2 truns off of #1”

 

O-rings seemed fine. I will replace them. The screws look normal, same as when I first pulled them out. The tips look good to me. I didn’t connect a tach, was setting by ear for max rpm, so I don’t have a rpm drop figure. I can try to connect my tune-up tach, I think I’ve done it before.

 

Jeremy

Edited September 20, 2019 by Gearhead

[Gearhead]

Today I replaced 8 tiny o-rings - 4 on the pilot screws, 4 under the diaphragm caps. They seemed OK and weren't high on the suspect list, and I don't think replacing them changed anything :-(

 

Per Patch's suggestion, I removed the air filter and lid (airbox bottom in place) and observed the slide movements. It doesn't run right or take throttle well at all like this, but I remember that was always the case; I think it's normal for these bikes. I posted some videos, get 'em now before they go on Netflix None of the slides stick. The light reflects differently off #2 than the others which makes it look different already on the videos, but I think #2 consistently moves more vigorously and responds quicker than the other 3. What's interesting about that is that #2 IS different - it's a OEM part with limited use on it. The other 3 are all new aftermarket replacements that I just bought a couple months ago. I verified that the slide lift hole is the same size on the aftermarket units; I'll double check that it's oriented correctly.

 

Tomorrow I plan to run it with pilot screws all at 2 then 4 turns and observe any difference, then take a look at the slides and needles. Maybe I'll shim the needles up .020 per Puc's suggestion.

 

Jeremy

[Gearhead]

FINAL UPDATE: for anybody who’s still reading.

 

I reached a 97% solution. Good enough. Pilot screws are still out too far, but once fairly warm the throttle response off idle is pretty good, and it feels good taking off with the clutch now. The bike is ALL BACK TOGETHER with all the plastic installed for the first time in 3.5 years, and it feels good!

 

Key points:

 

#155 Pilot Air Jet#2:

This is an important aspect, down from stock 170. If I had a little smaller ones like 140, I’d try those, but I don’t. If I wanted to take the carbs apart again I’d try 42.5 pilot fuel jets (stock 37.5), but I DEFINITELY don’t want to do that!

 

Aftermarket Slides:

I realized that the aftermarket slides don’t quite clock the slide correctly with respect to the carburetor. The diaphragms are rotated a bit on the slide bodies. All 3 are the same, so they just seem to make them this way. I compared them to my 4^th slide which is a low-mileage used OEM part. The lift hole is supposed to be straight down toward the throttle plate, and on the aftermarket ones it was off by maybe 15-20 degrees to one side. I trimmed the clocking tabs off the diaphragms and rotated them so the lift holes were straight down. I think this made a small difference in slide and throttle response.

 

Pilot Screws:

Patch, I followed your suggestion and tried riding the bike with all the screws set at 2 turns, 4 turns, and compared to the settings I came up with for best idle. The differences in throttle response were quite small, which is a little surprising to me. I left them at what seemed like the best for idle and throttle response: #1 – 4.5 turns, #2 – 3 turns, #3 – 3 turns, #4 – 3.5 turns.

 

At all-2-turns it wasn’t bad. Idle speed was down maybe 100 rpm, throttle response off slightly. At all-4-turns it was almost the same as my optimal settings.

 

Last Question:

Does ANY fuel come out of the needle / needle jet at idle? If so, maybe replacing my old ovaled-out needle jets (with factory new) was the “big change”.

 

Takeaways:

- Just because I think I can understand everything doesn’t mean I actually will!

- I still don’t understand what makes it different from before the teardown requiring a jetting change. That just feels wrong. So be it.

- These Mikuni carbs are complex, more so than some of the other MC carbs I’ve worked on.

- Aftermarket parts always carry some risk of being not totally right.

- Choosing to forgo complete carb rebuild kits and piecemealing instead is risky, can cause much time and expense in the long haul. That said, this approach has worked fine a number of times in the past.

- Thank God for this community who loves to help, particularly Puc and Patch!

 

Jeremy

[made2care]

I have attempted carb rebuilds in the past ( goldwings) with no luck! This carb setup appeared to be very unique. I leave this job for the pros, shipped off mine and Presto! 6 weeks later i have a new set using only OEM parts. Plug and play from then on out. I took my bike for its first ride in over 10 years and she rides like a dream.

Well done on yours!!

[jfman]

I have attempted carb rebuilds in the past ( goldwings) with no luck! This carb setup appeared to be very unique. I leave this job for the pros, shipped off mine and Presto! 6 weeks later i have a new set using only OEM parts. Plug and play from then on out. I took my bike for its first ride in over 10 years and she rides like a dream.

Well done on yours!!

 

I tought I knew about carbs until I started to work on these venture carbs ;-)

[Gearhead]

After finishing up this project in September as reported, the bike has been for sale on Craigs and FB Marketplace. Turns out it's not that easy to sell an old but nice, high mileage, full-dress touring bike in Autumn and Winter. Dang. Had several trade offers...no thanks, I trade for cash...until someone traded me an old, high-end Fender Stratocaster that tickled my fancy. Takes up much less space than the Venture! I watched my ol' friend ride off a week and a half ago. So, buyer-Charley is happy, I'm happy, and the ol' friend is back on the road daily like it should be...with a new friend.

 

This community has been so soo awesome and helpful over the years. Holy cow, I joined in 2006 and made almost 1000 posts! Tempis fugit, as they say. Thanks to ALL for your kind participation. Special thanks to the tech gurus along the way, most recently Puc and Patch (and many others). And extra special thanks to Freebird for holding it all together and keeping this ship afloat. I am thankful to you all.

 

God bless!

Jeremy in Tucson

[Patch]

Eh J. sounds like you traded one pretty lady for another!

My boy picked up a John Paul replica for lots of $$ we all like to pull her strings, but he insists we wash up first and no grease allowed under our nails:)

 

With or without a bike you can always stick around and harmonize with us!

[Gearhead]

Thanks. And I still have a bike... But it's finally only one bike! The VStrom keeps me entertained these days.