once bike is warm rpms wont come down

I've been riding my 75 xs650 for the last three months with no problems, but in the last week i pulled up to a stop sign and pulled the clutch in and the rpms stayed around four grand. Once i shifted into first and released the clutch until it grabbed then the rpms when down to normal. While shifting into second the rpms stayed high in between shifts. I've greased the throttle cables, and the carb boots are new. Need Help!

Nck156 said:

I've been riding my 75 xs650 for the last three months with no problems, but in the last week i pulled up to a stop sign and pulled the clutch in and the rpms stayed around four grand. Once i shifted into first and released the clutch until it grabbed then the rpms when down to normal. While shifting into second the rpms stayed high in between shifts. I've greased the throttle cables, and the carb boots are new. Need Help!

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sounds like your ATM (spark advancer) is hanging up. It spins on the camshaft inside the cover on the right side (the other side has the points) bob-weights get slung out by centifugal force as the RPM's go up and they twist a rod that goes over to the points side and moves the points backing plate to advance the timing. Springs pull the weights back when the RPM's go down and that retards the timing. When the springs get weak they don't pull the weights all the way back and the partially advanced timing gives you that hovering idle that you are describing.

Many people cut a turn off of each spring to get the tension back. Or you can buy a set of new springs (cheap) at Mikes XS.

You mentioned new carb boots, go back and recheck the bolts and clamps on the metal covers over the boots. Also make sure that you have fresh vacuum caps on the hose barbs if they aren't being used. If they are being used, make sure the vacuum hoses are in good shape and not cracked or leaking. Your symptoms are very familiar to me, my bike was doing the same thing until I changed my old cracked carb boots a few weeks ago. It's hard for carbs to provide the proper a/f ratio if you have an air leak between the carbs and cylinder head.

The advance rod that runs through the cam also needs to be greased. Many haven't been serviced since they left the factory. Obviously, they're due.

maybe you may have some pinholes in your floats allowing to much fuel. i had a similar problem and i replaced mine and it solved the problem.

Nck156 said:

I've been riding my 75 xs650 for the last three months with no problems, but in the last week i pulled up to a stop sign and pulled the clutch in and the rpms stayed around four grand. Once i shifted into first and released the clutch until it grabbed then the rpms when down to normal. While shifting into second the rpms stayed high in between shifts. I've greased the throttle cables, and the carb boots are new. Need Help!

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If you don't find any air inleakage, and the ATU is working normally, and the carbs are sychronized, install new O-rings in the needle jets.

I had the same problem and checked everything mentioned above, then concluded/replaced the advance springs.

It only hovers now (2000-2800) when I've been stuck in traffic too long and figure the excessive heat might be expanding the advance springs a bit. If I'm figuring wrong let me know lol.

Once back on the run it will back down to normal or just (insignificantly) above. All the good advice here was very helpful getting this troubleshot!

Simple but not mentioned- Throttle cable not allowing throttle to return ALL THE WAY TO HOME? My bike will idle at 1600 but when I reach down and push on the throttle/bellcrank the RPMS drop to the set 1100RPM. I am gonna replace my cable as its has cracks in the housing.