Black smoke out exhaust when WOT

[Shuriken]

Anyone know what would cause a bike to puff out a big cloud of black smoke when attempting to go wide open throttle? Bike sputters all the way in this range as well. Not sure if the carbs just flood it or if the ignition drops out on me.

[Crazcnuk]

It's getting a shot of too much fuel. This is very common, most vehicles will give a puff of black any time you suddenly hit full throttle.

If it is a BIG puff, or sustained black, you're putting more fuel than the engine can burn properly, ie; very rich.

Sounds like your 'flooding' theory is pretty close. May have to do a carb clean, and check the setup while your in there.

[Shuriken]

Thanks for the help. This is occurring on my VMax, and the Max is useless when running like this.

I saw my friend's fuel injected BMW do this to a small degree, but it was a very disturbing black puff on the Max.

Carb problems and electric problems can be hard to diagnose because if it's a spark problem, the plugs can be black because there is no spark to burn the fuel, and if the carbs are too rich, the plugs can be black.......

Compression on the bike is over 150psi on all 4, so I assume the engine/valvetrain to be good. I think it has to be an electrical or carb problem for sure, but it's been hard to tell. Swapped coils around because I thought 1 cyl was a problem. Not sure the problem followed the coils. If it were a pickup coil problem, I'd for sure lose 2 cyls at a time.

[Crazcnuk]

Try running a stiff load of Seafoam through, and see if it improves. If it does, even if it doesn't cure it, you can be fairly sure the issue is i the carbs.

[Shuriken]

Already doing that with some kind of Chevron product. Will try with Seafoam and see.

[egsols]

Ummm, how's the air cleaner? JAT

[Shuriken]

Thanks for the help. Air filter is very clean. I suppose I could try running the bike without it - briefly - to check.

I'm betting on an electrical fault.

[Shuriken]

Bought an inductive light today - as an upgrade to my existing one - that has an RPM meter built in.

Warmed the bike up to operating temp, then clamped pickup to plug wire #1. Took the bike out. In first gear, with the trigger pulled, I accelerated as safely as I could, having only one hand on the bars. I could not see any drop out in strobe when the engine started to crap out.

The Max, like the XS, has 2 pickup coils. Can I assume that the following are in decent working order?:
#1 and #3 spark plug, lead wire, ignition coil, and pickup coil for #1 and #3

Since #1 and #3 are on the same pickup coil, I assume that repeating this test on lead wire #3 will produce the same result.

That is of course, unless ASSuming is going to turn me into a fool...

I cannot test #2 and/or #4 with the light, tonight, because someone will probably call the cops on me due to the noise.

[egsols]

I thought it was 1 and 4 and 2 and 3?

[Shuriken]

Firing order for the VMax is 1-3-2-4.

[egsols]

Firing order for the VMax is 1-3-2-4.

Sorry, thinking of wrong X

[Crazcnuk]

Firing order for the VMax is 1-3-2-4.

Firing order is immaterial as to which ones are on the same coil.

It has to do with which are mated on the crank. Form that firing order I would not think that 1 +3 are on the same coil/pu?

Not sure, of course, but I don't think they would fire two cylinders back to back off the same coil?

[Shuriken]

Okay.....

The other night I didn't operate the timing light correctly. Tonight I did.

What I found did not surprise me. The timing light indicates that the bike is getting good spark.

The only time the light would shut off was when I disconnected the inductive sensor from the spark plug lead and occasionally, on deceleration on only the front 2 cylinders.

I was not able to observe any loss of spark when the bike started to flub when I opened it up from mid to full throttle. I repeated this test on all 4 cylinders.

Therefore, I am concluding that whatever problem the bike has is a carb problem. I just can't see how it could be electrical.

The only strange thing I noticed is what I already said, which is that the spark seems to drop out for a few cycles on the front cylinders only when decelerating. This does not seem to happen on the rear cylinders. The front cylinders are fed by stock coils, caps, and lead wires. The rear cylinders are fed by stock coils and caps but with yellow aftermarket lead wires.

The bike would not idle or run very well when I bought it, so I removed the carbs. I cleaned them with cleaner and compressed air, checked everything, reassembled, and then synched them. Then the bike ran pretty flawlessly for months. Then while riding straight and level on the interstate, I noticed all the sudden I had no VBoost, and the saga began.

The only thing I can think of is that the bike is getting a crap load of fuel on mid and full - too much to burn, hence the black smoke cloud, sputtering, etc.

[Shuriken]

It was an ignition coil problem on 1 or more coils. For some reason they worked at idle but broke down at high RPM.