85 xr 600 twin carbs- air cut off valve

I have an 85 xr 600 with twin carbs. I bought it not running. I took the carbs off and cleaned them, checked the float levels, put them back on and after kicking and kicking and some more kicking I managed to start it, it runs with the choke on....but when I tweak the accelerator it dies. I pulled the carbs off again and seperated them and found the air cut off valve had a couple of holes in it, would the holes make it difficult to start? I thought the air cut off was to prevent backfiring when deaccelarating.

Any advice support would be appreciated.


I doubt it, you need a bigger slow jet and mains too,make sure you shim your needles .020.

Edited by pwrpapa


I had the same issue with my 88 xr600. The bike WOULD NOT idle without the air cutoff valve INTACT. there is a method to deactivate it but I simply replaced it.

Mine was torn and I had to keep the rpms up by hand, it was annoyng at every stop, the bike would run but simply would not idle.

Everybody said check jetting, leaks etc...but I got tired of searching and bought a K AND L acv valve kit for about 25 bucks and the bike idled beatifully until I got crashed into! jajaja

so do it, dont think twice. If its torn, its screwing with your carb.



The air cutoff valves are 30 bucks through K&l......it's a good idea to replace it.

The bike should still run with a few pin holes in them.

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