wandering idle problem

[trance]

hey guys i have a 82 xs650

just finished redoing the top end - new cam chain, lapped the valves, new valve guide seals, new gaskets, etc.

I've cleaned the carbs and jetted with +2 sizes on the mains, +1 size on the pilots

the idle wanders. If I start and just let it idle, it'll be fine, but then if I rev it, it will go up to 2500, 3000, back down, up again, etc. this is with the throttle closed.

I've sync'd the carbs w/manometer, have the screws 3 turns out, floats are at 22mm.

Getting ready to go work on tuning again, I will readjust the valves, cam chain tension, but I think the problem is in the carbs.

any ideas

 

[trance]

and, can someone explain the dead cylinder method? questions:

1) kill the right cylinder
2) adjust left hand mix screw
3) kill the left cylinder
4) adjust the right hand mix screw
5) sync the carbs

correct?

kill the cylinder by removing the vac barb plug, correct?

 

[TwoManyXS1Bs]

Wandering idle? How tight are those spark advance springs?

 

[wherearewe]

My first instinct was also the advance (if you have one fitted). Maybe an air leak?

 

[TwoManyXS1Bs]

Oops, waitaminute, `82, TCI, no mechanical advance.
TCI?

 

[peanut]

sounds like an air leak . Check plugs are tight and no leaks on the inlets ,check diaphrams etc

 

[trance]

sounds like an air leak . Check plugs are tight and no leaks on the inlets ,check diaphrams etc

which plugs?

I sprayed with wd-40 last night with no obvious change in anything. Should I get a rebuild kit? I would think it'd help regardless.

 

[weekendrider]

Use a sight line to confirm the fuel level in the bowls( a pic in my album for example).
Open the mix screws another quarter turn.
A lean condition may be a lack of fuel as well as too much air.

 

[trance]

So, last night I did the dead cylinder method to adjust the mixture screws. Honestly, I need to do it again. I only got a stumble down at about 1/2 turn open, and opening it up did not change the revs at all. I guess I don't understand how to do it right.

BUT - I did figure out what was going on with the idling. I simply had the idle screw set too high. It was set to give ~1300 RPM when the engine was cold. Once it warmed up, the idle speed rose. So, I cranked it down to ~1300 RPM warm, and what do you know, it idled correctly. I still probably have an issue, because the idle screw is barely contacting the throttle, but now I know at least I'm in the ballpark with carb tuning.

Had some other issues, which I'll start a new post about...

 

[plattey]

Just a heads up, when performing the dead cylinder method, you actually remove the spark plug cap from the cylinder that you want killed. With the TCI ignition though, it has a dual lead coil and wasted spark ignition. Therefore, you MUST place a sparkplug in the empty spark plug boot you just pulled off and ground it to the engine to keep your coil from getting burned up. Once you do that, you can start the engine and adjust the idle mixture screw until you reach the highest and most stable idle speed. If it idles too high, loosen the idle speed screw and adjust the mixture screw to attain the highest idle speed again until you are satisfied. If the idle speed screw is just barely touching the throttle arm, you might still have an intake leak yet or the throttle plates are out of sync. Also, just a heads up, watch your idle speed, really low idle speeds sound wicked cool but it also means your oil pump isn't spinning very fast. Low idle speed=>low oil pump speed=>low oil pressure=>long term harm to internal components=>not good for the pocketbook haha!
Good luck!