One rich plug reading?

[Unclesol]

I have an 83 GS 750 ES, running a set of 34mm flat-slides from a GSXR 1000. It seems to hesitate at anything below 4 grand. I have pulled the plugs and found that #2,3 and 4 are all running pretty well (nice tan colour on the tip), but #1 is coming up covered in fluffy black soot.
I have not opened the carbs to confirm that the jetting is identical in all 4 carbs, but I did get these from a fellow GSR (OldschoolGS) that had them on a similar bike / set-up as mine. I do know that the clips on the needles are all in the same position.
I have also checked the valve adjustment, and they are all within spec.
I have checked spark, and there seeems to be a good one on that cylinder.
Any suggestions? Thanks for the help!

Ian

[Unclesol]

Any help would be greatly appreciated. Thanks.

[chef1366]

I would check the slide for sticking and make sure the needle is set the same as the others.
If it runs good with WOT and hesitates during the needle circuit that's what I'd look at.

[ianralph]

I spent ages attempting to track down a problem like this - in the end the cylinders that kept fouling plugs were way down on compression - it was burning oil. I'm in the middle of a rebuild now.

Good luck.

Ian

[Unclesol]

I would check the slide for sticking and make sure the needle is set the same as the others.
If it runs good with WOT and hesitates during the needle circuit that's what I'd look at.

Thanks Chef. I re-set the needle clips a while back, so I now they are all the same, but I will check for any sticking.

[Unclesol]

I spent ages attempting to track down a problem like this - in the end the cylinders that kept fouling plugs were way down on compression - it was burning oil. I'm in the middle of a rebuild now.

Good luck.

Ian

Hey Ian,

Always nice to hear from another Ian! Actually, this is something I suspected as well, and I bought a compression tester last night to verify my fears. If this is the case, it will give me the necessary motivation to install the domed (higher compression) pistons and hotter cams from the 700 cc model that are sitting in my garage...
This could be the silver lining after all !

[BlackStar]

Check your float level needle / seat in #1 too.

[Unclesol]

Check your float level needle / seat in #1 too.

Will do. Thanks!

[kingofvenus]

I had to put the floats at 19mm on mine, and drill out the idle air jet to get it leaned out enough to get it to not foul plugs below 3k. (still have 32.5 stock pilots in yet) Went smaller on main jet too. Still not done with it yet (had the carbs off more times than I can remember) it's getting closer, pulls nice and hard with great throttle responce.

[Nicholaschase29]

i have the same problem with my 33mm smooth bores.... anything under 4500 rpm it stutters.. One plug (number 4) is really rich, and if i look at the #1 cylinder it looks like it is running really well... I have the idle air screws in all the way and if I back them out it starts to die really quick.. I think we may need bigger pilots... but I am not sure..

[kingofvenus]

Turning the screws out makes it richer, you might need to go smaller with the pilots.

[Nicholaschase29]

I am pretty sure it is backwards with these carbs... but maybe someone knows better...

[anikmankar]

what was the result ?

I am facing similar issue on the 4th cylinder. using colortune to check the idle screw - the settings are perfect to a bursen blue but the plug seems sooty (dry black)...