Crazy High RPM after revving the engine

[Ethan]

So pretty much my bike is running fine until i rev the engine, after that the rpm's seem to go crazy high and wont go back down unless I am to pull on the choke all the way, someone want to enlighten me as to what may be happening? I have a 80' XS400G if it helps
Thanks,

 

[xschris]

Could be a lot of things. Out of sync carbs, bad diaphragm, lean condition, sticking throttle cable, dirty carbs. Post some pics of the bike and any mods or maintenance you have done on the bike.

 

[Ethan]

I just rebuild the carbs so there should be no problem there, haven't had the chance to fine tune them though, it could be that... other than a little fatter tires, the bike is completely stock. I did do an oil chance recently that's just about all the service i've done.

 

[SoulMan]

Spray carb cleaner around the boots when it is idling high. If that brings the isle down then you have leaking boots. When you say you rebuilt that carbs I assume that means you replaced the butterfly shaft seals. Is that right? If not then you should speak carb cleaner around the shaft area as well to see if you have leaks there.

 

[NewHavenMike]

After carb work, especially a full tear down, the carbs will need to be synced. You should also set the valves to equal specs. Bench syncing will get you close but you really need to do it with a manometer.

Id also examine the throttle assembly. Make sure the assembly is not all gummed up. Lube the cable and reset it. Make sure the cable has as little bends as possible. Check to make sure that the throttle doesnt open when you move the bars around and it snaps back. This was an issue for me that drove me crazy with the idle constantly hunting.

The major cause is vacuum leaks, especially at the throttle shaft seals on the carbs. They are often overlooked because they require a 100% complete breakdown to get to, also arent the easiest of parts to source out.

My bike did not run correctly until I replaced these seals. Hopefully, you replaced those too.

Welcome the the forum. Lets see your ride.

 

[Ethan]

ok thank you, the intake boots that connect the carb to the cylinder are kinda old and cracked that must be where the vacuum leak is coming from, I plan on buying a manometer soon so i can thoroughly sync the carbs up. Hopefully this resolves the problem, I wanna get out and ride!