RPMs increase for no reason

westcoastchi · Posted: February 4, 2007, 4:36 pm Post subject: RPMs increase for no reason

I have a set of BS34 carbs on my bike I'm building. For some reason after it warms up and the choke is off it will be idling just fine and then the RPMs start increasing up higher and higher. It's like someone is throttleing it up. I hit a quick throttle rotation and release it thinking that the throttle is stuck but it doesn't bring the RPMs back down to idle. It just keeps increasing in RPM till you hit the kill switch.

After this happens, when I restart it, she runs at the normal idle but then it will start idling up again on me.

Any thoughts on what is happening?

5twins · Full Member Joined: Aug 05, 2006 Posts: 1616

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westcoastchi · Posted: February 5, 2007, 12:38 am Post subject: Re: RPMs increase for no reason

I've got an electronic ignition system and I put some liquid gasket in between the carbs and the intake prior to mounting the carbs on. Running stock air boxes and filters.

grizld1 · Posted: February 5, 2007, 11:11 am Post subject: Re: RPMs increase for no reason

I'd guess the sealant isn't holding. Overtorquing the boot mounting screws is often a source of trouble; the boots themselves can deform under the screws. On one engine, I found that the PO had cranked the screws so tight on one side that the holes in the head had extruded slightly and had to be flattened off before the boot would seal.

westcoastchi

I noticed it was running a little high when at idle so I adjusted the idle down and then let it run on its own at idle to see if the RPMs would take off on their own. Mystery of all mysteries it with the idle adjusted down it ran on it's own for 20 min w/o racing off on its own.

Tried it again the next day, ran it for 10 min on its own idle and again didn't take off.

Not sure if it's magically fixed itself or if it's an intermittent problem that is waiting to pop up again.

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