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1979 GS750EN with exhaust from a 1980 GS750LT

  • Thread starter Thread starter rustynissan
  • Start date Start date
R

rustynissan

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As far as I can tell, a previous owner of my bike replaced the stock exhaust system with one from a 1980 GS750LT. :clap:

I broke down and bought the Motion Pro carb balancer and cleaned and balanced the carbs. The low end response (1/4 throttle and lower) is quite snappy and feels correct. When I get above that it has problems accelerating. My friend says it smells like gas when it runs and I am getting something like 17MPG!!! The bike will not go faster than 65MPH on flat ground currently.

I have come to the conclusion that I might need different main jets (#102.5) since the exhaust system has changed. Is this a correct diagnosis? If so, how do I know what size jets to purchase?
 
rustynissan said:
As far as I can tell, a previous owner of my bike replaced the stock exhaust system with one from a 1980 GS750LT. :clap:
Click to expand...
Are you telling this from numbers stamped on exhaust system?
Well, to my untrained eyes, they don't look alot different ( all criticisms taken happily). Anyway, why would you contemplate- let alone do- a carb sync, if the bike can't accelerate and won't go above 65 mph?
Are you sure that nothing is blocking up these exhaust pipes? Is air cleaner able to pass air?
 
Yes, both the numbers on the exhaust and the look of them indicate that they are from a 1980 GS750LT. They match the pictures in the parts fiche. They have a crossover between the pipes coming from cylinders 2 and 3, whereas the stock version does not. They are also shorter than the stock ones.

When I received the bike, I was told it was "not running". It had about 8,800 original miles on it. I tore apart the carbs to clean them and they seemed pretty clean already. Everything seemed to move properly, so after cleaning them I put them back on the bike and decided to balance them. There appears to be a bit of an exhaust leak at one of the connections on one of the pipes and one of the mufflers has a bit of a dent in it (about 1/2").

I have also tried spraying copious amounts of WD-40 all around the carb holders and the intake rubbers with no change in performance to rule out an air leak. No change in operation was observed.

As to your questions, what is the best way to check exhaust blockage and air cleaner flow-through?
 
Spraying junk around the carb boots is not a reliable method to determine if the engine is drawing false air. The best thing to do is completely disassemble the carbs, soak the carb bodies in carb dip, and replace all the various O-rings, including those on the intake boots. And replace the boots too if they don't look crack free and soft. You can not build a solid base toward a reliable 31 year old bike by doing less than a complete job.
 
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