High-idling slide carb

[xwhatsit]

Hello all,

Looks like all the usual suspects are still here :)

The CB250RS is still going, takes me to work every day. It must be 150,000kms+ now. Yes, Motu, it's still running that dodgy hand-chiseled cylinder head :shit:

Funny thing this morning though. It just started idling really high, sounds like 2500-3000rpm. I pulled over and checked around the carb. There's slack in the throttle cable at the carb end, nothing seems to be snagging the spindle that pulls the slide up.

If I rotate by hand the throttle spindle the other way and push it hard the idle speed will drop.

It almost seems like the throttle slide itself within the carb won't seat fully?

I'll strip it when I get home, but anybody know any reason for a slide carb to suddenly pull these kinds of tricks?

Thanks everybody.

[Moooools]

I had that issue with cb125t carbs and someone suggested that it could be because of air getting in through the inlet manifold.

I have no idea if they were correct because I put new carbs on. Worth a look though.

[Motu]

I was hoping both you and the bike had died a horrible death,but was too scared to mention it in case someone started a grief thread.Greetings.

The first suspect is inlet leaks,they could be anywhere,and on you bike possibly everywhere - so double check your recheck.Is it a twin cable? Disconnect and test.Make sure the slide clicks down with positive pressue,vacuum will stick the slide to the body that spring pressure won't overcome,so make sure it really holds it down to the stop.

[xwhatsit]

No such luck! :scooter:

It's not a twin cable -- well, it should be, but it never had the return cable to begin with and I wasn't going to add it.

It didn't seem like an intake leak (I had one once before), as the carburettion was still perfect; still just as much (or little) power, still pulled cleanly and didn't misfire or pop or anything. The only thing was that it idled high, like somebody had turned the idle screw right in.

However I was riding home this afternoon and all of a sudden it went back to normal! Revs dropped down and back to idling at a normal low speed. Very thankful as changing down gears is 50% of my braking :P :woohoo:

In my head it's like the throttle slide was binding in its cylinder on a piece of dirt or something and then it dislodged itself (into the cylinder...). Who knows.

So unless it happens again I don't think I'll bother to strip the carb.

Now that I've said that it'll happen again tomorrow.

Cheers everybody!