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CB360 Carb vs electrical: Runs rough when warmed up

2.9K views 4 replies 4 participants last post by  MagnificentB  
#1 · (Edited by Moderator)
My '74 CB360 runs rough when it's warm. I've cleaned and changed the carb jets, sync'd the carbs, changed the fuel filters and installed a NOS fuel petcock. I've had two different mechanics work on it, with no improvement.

It starts easily and runs great until it's warmed up. Once it's warm, it starts to miss and run rough and lose power. It seems like a fueling problem to me, almost as if it we running out of gas, but clearly, I've addressed these possibilities. It's been suggested the problem might be electrical...Any thoughts or suggestions would be greatly appreciated!

Thanks
 
#2 ·
Warm it up and ohm out the coils, they can have heat failure.
If you have a timing light you can watch the flashes to see if they are steady or intermittent, this will tell you if it is getting steady spark or not.
 
#3 ·
#4 ·
It could definitely be a vacuum leak. Try spraying a bit of starter fluid near the intake manifolds and see if the rpm changes. It could also be that the felt seals in the throttle shaft have dried up, or that the carb tops are warped and air is getting in there. It could also be that the end caps for the throttle shafts are leaking. If you check all of that by spraying starter fluid near them and the rpm's don't change it could very well be electrical. I've had a coil that when the bike was cold it would fire just fine, but would cut out when the bike was hot. It was made more frustrating because it could create spark when the spark plug was outside of the cylinder, but not in the cylinder under compression. This gave me the illusion that the bike had spark. Looking at the timing with a strobe timing light will let you know if the bike is getting consistent spark. Also testing the resistance of the coils once they are really warmed up and the bike is having the problem will also help you to hone in on the issue.

Good Luck!