f@&*%ing bike runs irratic and idles 4-5k rpm when warmed up

so i cleaned the carbs, valves are all good, still having an irratic running problem, i did the spray the flammable shit at the intake/carbs, cant find a leak, i took off the intake manifolds they were seated, no visible cracks or leaks and the seal area was all clean and black indicating good seal all the way around, diaphrams are good, slides work perfect, float levels are good (did the old clear tube in the drain trick the level was right at the bottom edge of the lip on the lower float bowl (thats correct isnt it?) one plug is a little lighter then the other (lean) but not much needs balancing but definatly not causing the irratic running, timing has been set, point gap is set, plug gaps are on. compression is 125 on the dot both cylinders. on cold start this thing runs good. it will idle fine choked starts up first kick (why use the electric when it takes one kick) warms up fine but i'll take it down the road and back and by the time i get back (approx 1 mile of riding) i pull in the barn and pull the clutch and the damn thing shoots up to 4-5 grand. it runs really well untill it gets good and warmed up, i rode it about 14 miles the other day and by the time i got back into town i was riding the brakes just to keep under the speed limit (25mph) its making power though 1st and 2nd with a quick shift will pull the wheel off the ground, i did all the obvious lubrications adjustments and all that hooplah and the problem persists. any other ideas?? :huh:

Post edited by: ratridekz750, at: 2007/05/14 00:54

If you have CV carbs the slides are probably
staying up.Old stiff diaphrams will cause it.

My bike's doing that too..though mine only idles at 3grand.

I'm going to look at the mixture screws, and change the exhaust gaskets as soon as my package from Z1 gets here.. that might help. I've got my throttle stop screw all the way out too, so I don't know what the deal is at all.

The diaphragms in my carbs are hella loose.. almost like there's too much rubber in there now. Last time I opened them up to adjust the clips on the needles (I had lowered them - making it way too rich), there was gas on them too. I hope they're not stretched/expanded because of that.. which would make the slide not close like mentioned.

It only really affects me when I'm idling, the bike rides fine the rest of the time. Try using one gear higher instead of riding the brakes?

Post edited by: pyxen, at: 2007/05/14 09:39

i did have the top of the carbs off the diaphragm seemed pretty supple how soft should it be>? it wasn't stiff. however i did notice that the tan plunger thing in there with the 4 holes around the base if i played with that a little bit it would stick everyonce in a while but as far as i know those sit at the bottom and the rest of the piston in there moves is that correct? or is that supposed to be smooth, i wonder if once its warm the vibration of riding 55-60 mph makes it stick because it stays at the rpm i was riding at or slightly higher maybe thats it?

ok so when i took the tops of the carbs off the diaphragm had a bunch of uhh i guess waves like a curtain all the way around, is that supposed to be like that for movement or are they warped and wore out im not sure. also one small uhh not really a tear (red arrow) but more an abrasion but the inside edge of the diaphragm is still in tact so i think it is still sealing

Post edited by: ratridekz750, at: 2007/05/14 12:19

The tan plunger thing is your slide.If it sticks
your bike will not idle down.Even a pinhole in
the diaphram will make the bike run crappy.Those
diaphrams are not cheap.I would get some smoothbores
or some older 28s.

I had a similar problem with my throttle not returning to idle.
Have you checked the throttle cables? Mine had been lodged between the backbone and the tank mount. The cable plastic looked worn where it had been pinched, and it turns out that the cable had frayed inside the cable just enough to hang up the throttle return. I didn't think it would be enough to hang up the cable but once I replaced the cable, the throttle would return to proper idle.
Now, whenever I remove and remount the tank, I always check the cable isn't pinched by gently pulling and pushing on it to make sure the cable casing moves back and forth.
Grant.

So you can back your mechanical idle set out all the way and she still idles at 4000+ ?

You may want to check the fuel level again. On my KZ750 4 cylinder the fuel level was 3mm higher than the manual suggested and the bike with the idle set would want to sit at 3000+rpm when warmed up. I don't know the specs on the 750 twin (but I did own a '79 at one time).

yea duck it does, with the screw backed all the way off one kick and it shoots up to the moon,

so what kind of carbs should i look for and what can i expect to have to give for em?? i was already thinking about scrapping these cv's for something a little more reliable seems that when they work they work and when they dont they dont.

You might want to put your bike year/model in your signature... As far as your problem, sounds like you have left a vacuum port uncapped... Some of the keihin carbs have screws that go in the vacuum ports and use screw in adapters to sync. If one is missing your idle will be high.

Check the throttle cable adjusting screw at throttle housing. Should have a hair of movement before the throttle plates open. Also check throttle cable at the other end. Only three things that will create a fast idle; the cable has no slack, an air leak or choke assy.