Vmax on 3 out of 4

[nswizard]

Hello everyone,

few months ago I had my valve shims checked, replaced intake rubbers and fuel filter on my 1997 Vmax.
All worked well for like 150km and then I could feel the loss of power. It behaved like there is not enough fuel, stumbling at 3000-4000rpm.
Right-back cylinder now does not want to work in any rpm range.
Checked carbs and they are clean and shiny.
Checked spark and it is good and strong.
If I close the needle jet completely on that cylinder, engine does not stumble.
Checked compression on cold engine and all 4 cylinders are close and within specs.
Fuel tank was coated with epoxy paint so it is clean.

I am out of ideas
Do you have some?

 

[nswizard]

Ah crap, wrong forum

 

[sdt354]

Ah crap, wrong forum

Right forum. Start with a proper sync. Then, if the ignition system is healthy, the carbs should be shotgunned. Most likely the pilot jets are dirty. You can't visually see this condition until stripping the carbs and removing the jet blocks. All you need to know, and how to do it is right here in the archives of the forum. Or box them up and send them out to Danny, and get the carbs back right.

 

[MaxMidnight]

Right-back cylinder now does not want to work in any rpm range.

I agree that a synch. and Shotgun would be in order but if it was just a blocked pilot jet then I'd expect it to fire once the throttle was opened.

You say you have compression and a spark but have you checked that the throttle slide is opening with the throttle?

 

[nswizard]

Stripped carbs completely, cleaned them with carb cleaner and air compressor and nothing seems to be clogged.
Then I synced them and all 4 are bit above 200mm hg. Engine sounds better but still there is no difference if I unplug the coil signal cable (yellow connector) or connect it.
Replaced the coil just to be sure and got no difference.
When I take the spark plug out and let it be on the engine, spark is nice-strong-bluish.

Throttle slide opens normally.

RPMs go up and come down normally when I rev it.

Spark plug is wet (not too much) so fuel seem to be getting into the cylinder.

I did notice one thing. After a few minutes of work on idle, when I turn off the engine and put the ignition switch back to ON, fuel pump is pumping almost entire startup cycle time.
Also, when I tuned needle jets, noticed that when I close them completely on right side carbs, engine does not stumble at all. On the left side carbs, there is a clear sign of stumble.

I would love to do it but sending carbs to Danny from Europe would be a bit too complex

 

[gentsvmax]

Man! my machine had once been plagued with the weirdest issues related to #3 too. Valve's shimmed, carb's rebuilt, one end of the jetting spectrum to the other, boot's, rubber's, new coils, wire's, C.O.P's, no C.O.P's . The real problem was it was mostly intermittent. I would be at a stop light, every one around me checking out my bike, then, but not always you could hear it loose #3...The cammed small block chevy lope would become a putz putz, no nutz idle that was soo embarrassing, maddening and frustrating all at once. I got a chance to meet Gannon a while back, he was riding a big bore bike Sean had just finished for him. The first thing I noticed about the sound was that it was comming only out of the end of the muffler LOL. The contrast is I could hear (and smell) my motor's exhaust from the saddlebecause of many leak's, front to back. The main one coming from the #3 down tube into the header.
The leak's were discovered when in desperation I tried foaming(Sea Foam) each cylinder down thru the carb's. WOW! The smoke came out every where but the end of the pipe.
The bike never ran crappy like a straight up hole in a pipe crappy, but only as good as a an engine could run with series of leaks, but still #3 down tube being the major culprit.
Sooo, very long story short, I got a deal on another unmolested Kerker header sysytem, and an excellent Kerker muffler, I repacked it with Kevlar mat, new copper ring's all around and WOW!!!! what a difference. When I turn an air screw#3,2,1 or 4 the motor responds as it should. LOL, I almost had tear's after all the crap I had been thru. Jetting on the bike is now back to near stock, even at 5280 with a Muscle copied air box, all plug's the same ashy brown. #3 used to fowl with soot.
These bike's can really take you down a rabbit hole, so don't overlook the basic's(like I did) during troubleshooting general performance issue's.

 

[sdt354]

You removed and stripped the jet blocks? it's out of sync,most likely, if the carbs are right.



QUOTE="nswizard, post: 482380, member: 10868"]Stripped carbs completely, cleaned them with carb cleaner and air compressor and nothing seems to be clogged.
Then I synced them and all 4 are bit above 200mm hg. Engine sounds better but still there is no difference if I unplug the coil signal cable (yellow connector) or connect it.
Replaced the coil just to be sure and got no difference.
When I take the spark plug out and let it be on the engine, spark is nice-strong-bluish.

Throttle slide opens normally.

RPMs go up and come down normally when I rev it.

Spark plug is wet (not too much) so fuel seem to be getting into the cylinder.

I did notice one thing. After a few minutes of work on idle, when I turn off the engine and put the ignition switch back to ON, fuel pump is pumping almost entire startup cycle time.
Also, when I tuned needle jets, noticed that when I close them completely on right side carbs, engine does not stumble at all. On the left side carbs, there is a clear sign of stumble.

I would love to do it but sending carbs to Danny from Europe would be a bit too complex [/QUOTE]

 

[nswizard]

So I did another shotgun on all carbs and now 4th cylinder works fine. Engine stumbles when needle jet is closed.
Front right cylinder still does not react on closing needle jet and bangs come from right exhaust. It is also not heating up like other cylinders.
Will try another cleaning round and carb sync.

 

[user 16790]

have you tried swapping your needle jets over to see if one is worn out

 

[nswizard]

New needles will arrive tmrw. Will write what happens.

 

[Fire-medic]

New needles will arrive tmrw. Will write what happens.

It's not just the needles, it's the 'emulsion tube' that the needles ride-in, they should be replaced as a pair. This is usually necessary only in high-mileage bikes. My experience is that if you have 'popping,' you still have a lean condition, an air leak somewhere. Spraying the boots for the airbox and the VBoost, and the area where the VBoost bolts-to the cyl heads, should reveal an air leak, as the RPM's should increase when the leaking area ingests the starting fluid entering the leaking point(s).

 

[nswizard]

Strange, original Yamaha needles arrived and they look exactly the same but I was not able to screw them in. Sounds like thread is different but when I put old and new needle together, threads align perfectly. Anyway, I used new o-ring and spring on the old needle and still engine does not stumble when needle is closed in completely.
Synced carbs to perfection and engine does sound nicely and cylinder warms up. Throttle response is fast and there are no more exhaust bangs.
All intake rubbers are new and I checked for leaks.
Will swap needles tomorrow and see what happens.
In a few days we should have temperature above zero C and I will try how it rides.

I could not find the part number for 'emulsion tube' you mention. I do see some plastic ring in the hole where needle goes but not sure how to remove it and inspect it.

Question is, should I leave it as it is now?

 

[MaxMidnight]

My approach would be if it ain't broke don't fix it...
...but if you want the emulsion tubes, Yameringha call then the Main nozzle, part # 26H1494190 (#34 on the parts fiche)