Outside carbs too lean.

[stevec5000]

On my 1100 with dual K&N pod filters I put on a fresh set of flat slide carbs that I got on ebay to replace the old worn out stock ones. They are in very good shape and look just like new. However it's hard to start, misses and runs poorly at idle and the #1 and #4 plugs show the mixture to be too lean. I cleaned the carbs throughly, blew out all the jets and passages until everything is squeaky clean, even though nothing looked dirty to start with. I was trying to adjust the idle mixture and it's better but still too lean on #1 and #4 with the idle mixture screws almost all the way out. With Colortunes in the cylinders it show that #1 and #4 are not firing some of the time at idle but work ok at faster speeds. It does drive pretty well just hard to start and idles poorly.
I took them apart again and cleaned and blew out all the passages, even took out the choke assy and the float and cleaned the starting jet , everything else looks OK and float levels are all the same but #1 and #4 are still too lean.
My question is how can #1 and #4 be too lean while #2 and #3 are fine when all the jets and other parts are identical? I exchanged jets between #1 and #3 with no difference. The compression is the same in all four cylinders.
The ignition could be a suspect but there is a constant spark even when the cylinder does not fire and timing is good on all cylinders. Putting the old carbs back on makes cyl #1 and #2 too rich (because the float valves are leaking again) so I'm pretty sure the problem is the carbs since #1 and #4 were never too lean before. I just don't see how it could be possible since all 4 carbs are identical. Does anyone have any ideas?

[randy]

Steve,

The only common denominator of the #1 and #4 is the ignition. Check every connection on that coil from the TCI to the plugs and you'll probably clear the trouble. Good luck and keep us posted.

Randy

[stevec5000]

I've ruled out the ign after checking both coils with an ign scope and the spark is identical on both. Besides the problem follows the carbs.

[TopCatGr58]

Hey there Steve,

My understanding of flatslide carbs were that they were high performance carbs mostly for racing, mostly for W.O.T. kind of action, not so much for finesse or idling!? Since these carbs aren't OEM, are they truly the same spacing apart as the OEM's? Perhaps the boots are not quite sealing and you are getting some vacuum leaking, which would account for lean and rough idle!? Tried spraying around the boots to check for leaks!? The way our cylinders are set up, with even carbs, the inner 2 cylinders should be the ones to run hotter since they get less air flow than the outer 2!? Good Luck!
T.C.

[pgg]

Yeah steve those older flatslides were all performance and a b*tch to keep tuned. I remember spending weeks and weeks dicking around with keihin flatslides on a gsxr 1100 a few years back. Just when you thought they were setup sweet, a couple days later they'd lose the plot again. They were on/off switches when riding. W.O.T was their thing. CV carbs are far better on streetbikes. Mind you the more modern flatslides are probably more civilised. Maybe your compression's a bit uneven? Maybe swap carb1 with carb2 and carb3 with carb4 and see what happens.

[stevec5000]

I did put some sealant under the flange on the rubber manifolds to make sure they were sealed good. Didn't seem to help any though. What I ended up doing was making the pilot air jets slightly smaller on the two outside carbs so the mixture would be rich enough at idle. Not sure why I had to do that but it works.
I hate carbs, can't wait to get my Megasquirt built so I can get rid of those suckers.