Had my bike running well, still breaking it in on the second tank of gas. Was going down level road pushing it to WOT for ~5 seconds every other minute. After one such WOT, the bike suddenly lost a lot of power, but it did not die. I could let off the throttle entirely and then pull it back up and the motor would respond, but after about 60% or so the motor wouldn't rev any higher. Also sounded like it was idling higher, and after I let it sit I tried to restart it and the motor revved for a couple seconds then died. I have not been able to start it since. Any ideas?
Engine bogged at WOT now won't start
- Thread starter will wei
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crassius
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- Jul 23, 2012
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yes, that is the gasket, but it sounds now like a carb problem
if you have a steel intake, the chrome may have dripped a bit at the tip which causes the carb to fit poorly and loosen with vibration - I like to use a file at 45degrees to the end of the intake and just take a bit of chrome off right there - when carb feels like it is sliding on smoothly all the way to the stop, it should be OK - if you wiggle carb left/right while putting it on and see scratch marks inside when you take it off again, it needs more filing
if you have a steel intake, the chrome may have dripped a bit at the tip which causes the carb to fit poorly and loosen with vibration - I like to use a file at 45degrees to the end of the intake and just take a bit of chrome off right there - when carb feels like it is sliding on smoothly all the way to the stop, it should be OK - if you wiggle carb left/right while putting it on and see scratch marks inside when you take it off again, it needs more filing
I'll have to check that out tomorrow, no matter how much i tighten the collar around the carb it won't stay firmly on the intake and I can usually slide it left to right a bit, and after riding a while it will slip backwards. It's a carb from an old build also, so the collar might not have the same elastic strength anymore...
Steve Best
Well-Known Member
The higher idle points to an air leak, luckily.
One of the things that can go wrong with WOT testing is overheating the piston due to an air leak or lean jet.
There will be a sudden bog at full throttle and if you don't let off right away, the engine will die.
Typically as the piston overheats it scuffs the bore. If it pinches the rings or tears the bore the engine dies.
It will not idle or restart. Your high idle was a good sign.
Steve
gary55
Well-Known Member
If you drill the clamp out just large enough to fit a 6mm allen bolt, and use a self locking nut you should be able to get it tight enough to stop vibrating off.
Steve Best
Well-Known Member
I just replaced the 5mm Philips screw with an Allen head 5mm bolt.
Reason being is to limit force applied on the clamp, and with whitemetal parts to avoid weakening by drilling thin.
The finer thread of the 5mm tends to lock better with the amount of clamping force needed.
More clamping force will damage parts. The locknut is a good idea.
I found if my mounts are not rigid enough vibration will make the carb move no matter how tight the clamp.
Reason being is to limit force applied on the clamp, and with whitemetal parts to avoid weakening by drilling thin.
The finer thread of the 5mm tends to lock better with the amount of clamping force needed.
More clamping force will damage parts. The locknut is a good idea.
I found if my mounts are not rigid enough vibration will make the carb move no matter how tight the clamp.
gary55
Well-Known Member
It all starts with a good foundation. 5mm allen is a better idea.
Update: so i got a chance to look around for air leaks and also replace the bolt that holds the clamp. There are definitely no leaks at the carb-motor junction, and also the exhaust is well sealed. My plug was black, but i assume that was from running a high ratio mix for break in (around 18:1). Currently I cannot get a spark, so i wonder if the electrical may not be functioning properly. I have tried with the fouled plug (a b6hs) and again with a clean b7hs, both no visible spark. It may the case that the CDI wiring has come loose, I hope I have not fried anything or that the original idea of the overheating the piston...
