Another #1 cylinder cold thread!

[sparkfly88]

Been chasing this backfire at 3k for a bit, and I think I got it narrowed down when I was colortuning in this thread;

http://www.xs11.com/forum/showthread.php?t=40410


It kicks in when I pull the choke out, as seen by a bright yellow flame in the colortune, AND when I'm somewhere above 3k RPM

I just took the carb out and blew all the passages out with cleaner, and airgun.

The mix screw is NOT broken, and there is NOT broken piece in there, I have confirmed it with a flashlight, and while it was running you can hear air rushing into it when its removed.

I just hope its nothing too bad, like REPEATEDLY missing something inside the carb.....I've cleaned em too many times....ugh.

Click the video!!!

[skids]

The three pinholes in the top of the ventouri throat are cleared out? Pilot jet clear? Float level good? Vacuum synched? Mixture screw (pilot screw) adjusted? What you can do is warm-up the engine, screw in a new plug and color it for about 5 minutes to check it. See if it is rich and sooty or bone white lean. You may want to adjust the pilot screw with quarter turns (keep track) until the pipe starts warming up quickly. Use a spray bottle for the head pipe.

[skids]

P.S. I saw the manometers for the synch. Be aware that the synch can change the mixtures at idle.

[sparkfly88]

Doing anything with the mix/pilot screw does nothing.

All the floats are at 23mm.

I just went through the number one carb this afternoon, I must have missed something, So I'm removing it tomorrow afternoon, and going crazy on it.

[skids]

All the floats are set at 23mm?
You have 79 carbs?
79 carbs are to be more like 1 inch, (25.4mm).
Recheck requirements for floats.
23mm would be very rich for that year of carbs.
Plugs look black or wet?

[sparkfly88]

I have plastic floats in the carbs, and set to whatever the measurement was for them. Sorry if it wasn't 23mm....

Plugs not wet. Slightly brown.

[sparkfly88]

Okay. Well I just went through the carb, again. With 120psi of air.

I'm getting air through every single passageway. Including the triplet holes by the butterfly.

I have plenty of spark

Nothing I just did changed a single thing.

Hmmmmmm

[tcoop]

Did you check the diaphragm for holes? Possibly need to polish the slide area (where the diaphragm piston slides) so that it moves freely?

Just some thoughts here.

[sparkfly88]

Did you check the diaphragm for holes? Possibly need to polish the slide area (where the diaphragm piston slides) so that it moves freely?

Just some thoughts here.

Yup, everything there is a okay.

[newc4]

Did you check the pilot jet? The bowl passage? Gotta be something in the pilot circuit.

[sparkfly88]

Yup yup. And I realized it only fires sometimes when it's on higher idle. Not all the time.

I'm gonna Bring it to a friends house to compression check it.

[bikerphil]

You may have a vacuum leak at the carb boot to the engine. I'd take it off and RTV it in place of the gasket, then wipe the excess off from the inside of the boot. I had a similar problem where I could not get the colortune to turn from blue to orange, I resealed all the carb boots and that solved the issue. YMMV

[skids]

Of course the measurement with the caliper is to determine what the approximate pool level would be without directly measuring it. If you have plastic floats in an earlier model carb, you should ask someone what the pool level should be and do the direct measurement with the manometer hose. The size and bouyance will be different than the metal float bulbs. I suspect that your pool level is too low for that carb if it only its on higher rpms, but that is just a guess.

[sparkfly88]

You may have a vacuum leak at the carb boot to the engine. I'd take it off and RTV it in place of the gasket, then wipe the excess off from the inside of the boot. I had a similar problem where I could not get the colortune to turn from blue to orange, I resealed all the carb boots and that solved the issue. YMMV

I will give this a try, right now I have the paper gaskets on all the intake tubes, they came with them when I bought them a couple months ago.

I'll RTV them tomorrow

[bikerphil]

I can't recall, did you try switching the 1 and 4 spark plug wires to see if the problem moves or stays the same?