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1980 GS450 No high end power, what gives?..

  • Thread starter Thread starter ahmet
  • Start date Start date
A

ahmet

Guest
I spent so much time on this little bike it's scary. But I think it will be worth it at the end.
Here is a description of my problem: I have no high end power, period. After cleaning the carbs four times and rebuilding the petcock I now know that the fuel delivery is fine. I can now get burning in both of my cylinders though the left one not as good as the right one. The right exhaust pipe heats up much faster than the right one. The bike runs quite well on a single right cylinder. I got it to run only on the single left cylinder also but not as smooth as the right one and it is prone to die a lot easier.
When I have both the cylinders running and if I turn the throttle grip fast nothing happens for a little bit and the bike acts like dying the RPM goes down. Once in a while though it catches up and the RPM shoots up to 6000 or so.
I know that the air box side of the carb rubber oring is leaking a bit. When I spray that interface with carb cleaner the RPM goes up. That does not seem to happen on the other carb-airbox interface or the engine-carb interfaces.
The carbs are stock, nothing modified, the airbox is stock and the air cleaner element is clean. I appreciate any of your ideas to pinpoint the problem.
Regards;
 
Ahmet,

You will find a billion posts on this forum about how CV carbs wil NOT tolerate any air leaks on either side and how important the airbox is for CV carbs. CV carbs rely solely on pressure differential to lift the slides. I learned this the hard way.
Also, another many people (including myself) don't realize at first is how large an effect an exhaust leak can have on the pressure situation.
It took me weeks of fiddling to finally realize how critical air-leaks and exhaust leaks are. Once I got those resolved my bike ran great and I realized that all those extra carb cleanings were not the solution to the problem.
Another very important fact that people overlook is that coil performance degenrates at higher RPM. So a coil that works just fine at low RPM may not work well at high RPM. I found this out the hard way too. I put a pair of "known-good" coils on my CB750 and its high-end performance improved DRASTICALLY.

You're almost there - seal the leaks WELL (including aibox lid) and get a decent pair of coils (I'm assuming yours are the originals).
 
How did you get it to run well on the left cylinder? Was it by switching the coils? If so, there's your answer.
 
I just unplugged the plug wires one at a time to get the bike to run on a single cylinder.
The coils are the original ones. Their resistance check seems okay but you never know.
 
So, the bike would run on both cylinders normally, but weak on the left one. Unplugging the right wire would cause the bike to run strong on the left one?
 
If the right cylinder is unplugged the left one runs weay
If the left cylinder is unplugged the right one runs okay
If both cylinders are plugged the bike idles but does not rev up and the left cylinder ends up with a weak plug.
Thanks
 
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