- Joined
- Jan 31, 2010
- Messages
- 3,087
I fired up my newly rebuilt (rings, valves,) 850 yesterday and was extremely pleased that it started on the first kick. However, after running for a while it got decidedly cranky. It wouldn't idle at normal speeds, seeming to need at least 1500 RPM to keep running. Revving the engine to the 3000+ Rpm range was fine but down low it was a mess. The Amal carburetors were untouched during the rebuild and had been working perfectly prior - idling fine at 700 RPM. I set the timing (Tri spark) correctly and when revved up, strobed it to 31 degrees, which works well here due to the altitude. Again, prior to rebuild it would idle smoothly at 700 RPM.
I pulled the carbs anyway because the bike was acting like it was overfueled. I was thinking that maybe the float needles were stuck or whatever, having been sitting on the bench (drained) for about a month. But everything was fine. I thought about the possibility of a vacuum leak but the equalization tube between the carbs was OK and connected. I have new heat-insulating gaskets between the int manifolds and head. I didn't put any sealant on them - the old ones had sealant on the head side of the gasket. I didn't spray anything on the joint while the engine was running to check for a vac leak because I didn't think about it at the time but visually the joint looked fine - though I realize that's no "test."
The carb mixture adjusting screws work properly, even when "idling" at fairly high RPM, the screws will adjust the mixture appropriately. It is hard for me to imagine it is a carb issue - I recently went through them completely - new needles/jets, rebuild kits, etc and AGAIN, a month ago they idled perfectly at 700 RPM and did so briefly yesterday. There was sufficient fuel in the tank.
Everything directly involved with the rebuild seems to be in good shape - valve clearance is correct, compression is within 1 psi on both cylinders.
Any ideas what I may be missing? As I said, I'm stumped because initially it ran perfectly but went south after running for a few minutes. If I rev it up it sounds strong.
I pulled the carbs anyway because the bike was acting like it was overfueled. I was thinking that maybe the float needles were stuck or whatever, having been sitting on the bench (drained) for about a month. But everything was fine. I thought about the possibility of a vacuum leak but the equalization tube between the carbs was OK and connected. I have new heat-insulating gaskets between the int manifolds and head. I didn't put any sealant on them - the old ones had sealant on the head side of the gasket. I didn't spray anything on the joint while the engine was running to check for a vac leak because I didn't think about it at the time but visually the joint looked fine - though I realize that's no "test."
The carb mixture adjusting screws work properly, even when "idling" at fairly high RPM, the screws will adjust the mixture appropriately. It is hard for me to imagine it is a carb issue - I recently went through them completely - new needles/jets, rebuild kits, etc and AGAIN, a month ago they idled perfectly at 700 RPM and did so briefly yesterday. There was sufficient fuel in the tank.
Everything directly involved with the rebuild seems to be in good shape - valve clearance is correct, compression is within 1 psi on both cylinders.
Any ideas what I may be missing? As I said, I'm stumped because initially it ran perfectly but went south after running for a few minutes. If I rev it up it sounds strong.