carb problems still

[jboughto70]

I have a 79 XS1100 and recently rebuilt the carbs (more than triple cleaned), lapped the valves, installed new gaskets, valve guide seals, and piston rings. I've synched my carbs with mercury gauges. The problem is my idle speed keeps jumping around and when the bike warms up it wants to run away (2, 3, or 4 thousand RPM's) after idling at about 1K RPM. I've sprayed brake parts cleaner all over and can't find any air leaks. I also checked the vacuum advance and did not notice it sticking. While I had the vacuum gauges on I noticed that when it revved out of control, the center 2 cylinders were drawing much more vacuum than the outer two cylinders. I've also checked the resistances of the coils (primary and secondary) and everything checks out when cold. I'm getting really frustrated. I'm also thinking its an electrical problem rather than a carb problem but I really don't know. Any more ideas (as I have posted on this problem before) would be appreciated. Thanks

[strom]

How bout your pilot screws? And float height. Also check the choke... pardon... enrichener circuit.
My bet is pilot screws.
Don't brake any points off em... tighten them LIGHTLY by HAND, just so they BEGIN to sit, then turn em out 1 1/2 to 4 turns. All the same. The idle speed screw... close it. So as the engine won't idle at all. Then set the idle mixture screws, start the bike with a bit of throttle, set idle speed with guess which screw and if that doesn't work, check the enrichener circuit, reset the camchain tensioner, check #1 and #4 ignition coil, check for broken pick-up wires (good bet), try with another TCI unit......

LP

[pgg]

Jboughto, I'd strip and clean the fuel system (taps and hoses - new rubber hoses are good) It sounds a bit like fuel starvation (assuming the pilot circuit is set good) If you've got an octopus set-up I pity you. Also a sticky cable but the carbs should draw the same vaccuum if that's the case. I'd also clean the spark plugs then run the bike on idle, then read them to see what's going on in all 4 cylinders. I'd also go for a ride and read them from high revs as well. Are the high vaccuum cylinders running lean or rich on idle? If the bike runs fine above idle then its probably only uneven pilot circuits with the lean carbs No2 and 3. Even just twisting the pilot idle screws might help. A mix of shady suspect aftermarket jets could be a culprit.

[chevy45412001]

throttle

That was a very good anwser some gave for this problem,Check that the throttle cable is not sticking. I did and that was my problem. Just a thought

[Ken Talbot]

Electrical problems will not cause that kind of runnin gproblem. Your observation that the vacuum on the two centre carbs is higher than the outers is a dead give--away that your carbs are not anywhere close to being synced yet. You need to get the idle speed screw backed down, get the carbs synced, get the pilot screws adjusted, readjust the idle speed, re-check the sync, and you should be just about there.

To work the pilot screws without a Colortune unit, you want to get the snyc as close as possible and the idle speed well below 1000 - down to about 600 or 700 if you can manage it. Then, one screw at a time, turn the screw out a good couple of turns and listed vary carefully for a change in idle speed. You should hear the idle pick up just a bit, then start to fall off again. Carefully, turn the screw back in until you hear that sweet spot again, and turn just a bit past it. Tweak it by turning the screw out and in so you absolutely nail down the sweet spot. Repeat this for the three other carbs. If, as you're doing this, the idle speed climbs up anywhere near 1000, bring it back down again. You want the lowest possible idle speed so you are truly running on the pilot circouit, and not moving onto any of the mid range.

You will probably find that getting the pilots bang on will also throw the sync off a bit. Adjust the sync one more time and you should be good to go.

[nashville_bill]

I had the same problem on my XS650 and fixed it by installing new rubber manifolds. (the things that connect the carbs to the head) I guess it was a vacuum leak that was changing the idle.

Good Luck!

[Badger]

Better late than never??

I'm with Ken, if your mercury for the inner two is higher, it means that they are free-loading, and the outer two are doing more of the work. They dont need to far out before things go sour, conversely its amazing what happens when it is all pulling together, idle mixture is a big part of the [idle] equation.

I found that a small change in one area can show up a discrepancy in another, so just keep playing with it till it is always spot on.