tahitianrider
Been Around the Block
Hi,
I am in the process of restoring a 78 CB750 Super Sport, the last SOHC model of the 750 fours.
The bike sat in a barn for about 20+ years but was in good condition. I completely rebuilt the carbs: tore them apart, did ultrasonic cleaning on every carb body and parts and rebuild everything with rebuild kits (new seals, jets, etc.).
The bike restarted right away! I then synchronized the carb using vacuum gauges. They are perfectly synchronized!
However I am have a issue I can't resolve: when the bike is warm, after a 5min ride. It does not want to go back to idle, as soon as you rev it up, in stays up around 3500 rpm! it doesn't go back to the 1200 rpm idle, unless you put in it first gear and gently let go the clutch while braking to try to stall the engine.
I was almost sure this was a carb sync issue, I had the same problem on a FJ600 and solved by re-sychronizing the carbs. But it is not, I did another carb sync with the bike very warm and the readings are still perfectly the same on each carb!
There is no vacuum leak either, I spray some carb cleaner around every carb and intake boot while the bike was running and it did not rev up.
Is there another thing to check on the carbs? maybe the accelerator pump is sticking?
Could this be an issue with incorrect valve clearances?
Thanks for the help!
I am in the process of restoring a 78 CB750 Super Sport, the last SOHC model of the 750 fours.
The bike sat in a barn for about 20+ years but was in good condition. I completely rebuilt the carbs: tore them apart, did ultrasonic cleaning on every carb body and parts and rebuild everything with rebuild kits (new seals, jets, etc.).
The bike restarted right away! I then synchronized the carb using vacuum gauges. They are perfectly synchronized!
However I am have a issue I can't resolve: when the bike is warm, after a 5min ride. It does not want to go back to idle, as soon as you rev it up, in stays up around 3500 rpm! it doesn't go back to the 1200 rpm idle, unless you put in it first gear and gently let go the clutch while braking to try to stall the engine.
I was almost sure this was a carb sync issue, I had the same problem on a FJ600 and solved by re-sychronizing the carbs. But it is not, I did another carb sync with the bike very warm and the readings are still perfectly the same on each carb!
There is no vacuum leak either, I spray some carb cleaner around every carb and intake boot while the bike was running and it did not rev up.
Is there another thing to check on the carbs? maybe the accelerator pump is sticking?
Could this be an issue with incorrect valve clearances?
Thanks for the help!