Without a better techinical explanation my bike intermittently runs..."soft". My exhaust gives a very unique, hard whack when things are running well. Occasionally, usually when it's cold but not always, it runs much quieter. This is accompanied weaker low end throttle response, a bit more vibration etc. It eventually clears up, usually after a run on the freeway for a few miles on my commute. I can't pattern its occurence. I have gone throught the carbueration, air intake, electrical. It stays soft through the rev range. The bike still pulls. It just seems off.

I'm wondering if an exhaust valve could occasionally stick causing a compression problem until it unsticks and falls back on the cam. Is it possible for a valve to just stick and unstick, without causing some other symptoms? Thoughts are appreciated. Thanks.

 

Yes, actually, but only on a really high mileage engine and usually accompanied by a broken valve spring. The loss of power would be more than 50% and the clatter would be very noticable.

It's not your problem. Usually a minor issue or noise that dissappears when an engine warms up is not really a problem.

The thing I'm thinking of that might cause your symptom is leaving the choke on too long.

 

Good to know. I thought of the choke and have tried only using it for a 10-15 seconds thinking the enricher was fouling plugs, but have checked them when symptom is present and they look fine. The symptom doesn't always go away when the engine warms, just seems to be less frequent. Any chance it could be made worse by not properly blocking off the breathers from the PAIR hoses? It's the intermittent nature that has me confused because I can't come up with anything is wrong that wouldn't be wrong 100% of the time. Thanks for the reply.

 

You didn't say if you had checked the valve clearances.
It's more likely a tight valve than a stuck valve.
Could be so tight it's intermittantly seating , intermittantly sealing enough to build enough compression to fire or fires but with reduced power from low compression.

~Jeffers

 

tight valves get tighter as the engine heats up.

 

I haven't checked the valve clearances, they're next in routine maintenance anyway. Thanks.