BANG!! pop pop sputter 5000rpm idle

[livelifenowff]

so... my bike was being a little turd yesterday. I was driving along and it started to sputter like it sometimes does. usually i just tap on the bottom of carb #2 til gas stops pouring out of the filter, then restart it just fine after it burns off excess gas. well this time it kept sounding like it was only running on three, then popping back into rhythm then after a couple miles back to dying. It's done this #2 thing before with the stuck float but never like this in succession and it hasn't really happened since its been more broken in. so, i decided to take off the carbs and spray them down and take off the bowls just to see if there was anything obviously wrong. put it back together and started it up with a huge backfire, took off the choke and tried again no backfire but it reved up strait to 5000 rpm and didnt back down. so i shut off. throttle position looks perfectly normal. whats up with my bike.. no big hurry. i may just leave it out of commission and wait till i actually get the kits.

thanks
Kyle

[livelifenowff]

BTW... it holds pretty even at that 5 grand rpm range otherwise i would suspect its just excess cleaner fluid in the gas
Kyle

[mro]

I take it your waiting to clean/tune/sync the carbs until you get carb kits?

Cause that's what it sounds like you need.
Good practice to take em off and just clean em.
Might not need any parts, but will need to be careful with the float bowl gaskets so you can re-use em.


mro

[livelifenowff]

yeah mro, I was going to wait until I got kits before i really tore into them, but after taking off the bowls everything seemed good enough that i shouldnt bother.. I do plan on just rebuilding them with no new parts.

What i'm still really curious about is.. why would my engine rev up like that to 5000 at idle? everything was normal besides a sticky bowl on #2 when i took them off.. whats the deal now?

[mro]

Have you tried to sync them yet.
My experience with "bench sync" has been that they get close enough to idle at about 1000/1200 rpm to allow vacuum sync.
(have revved throttle to 3000 and had it stay there, shut down engine and re-start w/o touching throttle so could vac sync.)

If it's going that high right from the start, lower rpm with main idle screw and check "free play" in throttle cable.

Would check for any vacuum leaks too.


mro
btw, pesky little holes in needle jet seem to be one place I found get over looked when cleaning. (they don't effect idle tho) My eye sight's so bad I need to use a magnifying glass and light to see if clear or even to read jet sizes.

[DiverRay]

Kyle,
As mro said, check for vacuum leaks, and also be sure the clamp on #2 carb isn't in the way of the throttle cable. I would suspect the vacuum leak, as I had the same problem at one time. Check all the caps on the manifolds, as they can get hard and leak, even as they look good.

[livelifenowff]

Thanks guys I'll be getting to work on that shortly.

[livelifenowff]

mro, about the main idler...

The throttle is adjusted to be loose enough to sit about a mil above the resting plate of the idle screw, but it does hover and wont go all the way down, this little bit of gap is the same as Pre-fiddle, and doesnt seem enough to cause that much rev, my cable doesnt seem to loosen up any more than it is at the handlebar end either.. any ideas?

[mro]

Watch the cable/carb connection as you twist the throttle. Should have to turn just a little before the cable starts to open the carbs. (free play) No free play could be because throttle cable is not routed properly.

If main idle screw having no effect then you need to pull carbs and do the "bench sync" so there close enough that main idle screw does have an effect. Then can set idle at 1000 to 1200 or so and vac sync em.

I've not found any way to get an XS running RIGHT without vac sync.


mro

[rev79xs11]

you might want to check the nut on the end of the throttle shaft. It is held in place with a washer folded over a flat on the nut. Mine was binding and eventually stuck full throttle. Just put a wrench on it and loosen a hair if it is binding your throttle plates will snap shut. I just re adjusted mine and bent a fresh edge of the washer to hold it. If i remember correctly it was just after having the carbs off the bike also.