xander18
CB750 Member
Hello everyone,
After a few evenings of troubleshooting I turn to you, almighty internet, for a bit of help. I have a 1979 CB750K (the rare and highly sought after 10th anniversary edition, featuring such additions as plastic sidecover badges and... okay that's it). I purchased a Randakk's rebuild set and went through the carbs. JIS screwdrivers and a handful of JIS screw from McMaster make this much more enjoyable.
Put the carbs back in and it fired right up... on 3 cylinders. The #4 header doesn't get hot and pulling the spark plug wire doesn't cause an RPM drop. Troubleshooting thus far:
1. All four cylinders are at just under 150 psi compression.
2. Pulling the spark plugs and cranking over with the plug held against the block yields approximately the same brightness of spark on all cylinders.
3. Swapping spark plugs doesn't seem to work.
4. There is fuel in the #4 carb bowl.
5. To ascertain that the problem is fuel I removed #4 plug and poured a bit of gas directly into the cylinder, started the bike and had all 4 firing until the gas ran out.
6. After I determined all this I pulled the carbs back out and pulled apart #4 again.
7. All passageways seem to be clear, probed with either thin wire or aerosol carb cleaner.
8. Jets are in the right place and clear.
9. Throttle plate and choke plate are synced with the rest of the carbs.
10. Vacuum puck moves smoothly.
There is fuel in the bowl and the jets are clear up to the venturi. Other things could be wrong that would prevent it from running well but given this, wouldn't it at least fire a bit?
Any other tips?
After a few evenings of troubleshooting I turn to you, almighty internet, for a bit of help. I have a 1979 CB750K (the rare and highly sought after 10th anniversary edition, featuring such additions as plastic sidecover badges and... okay that's it). I purchased a Randakk's rebuild set and went through the carbs. JIS screwdrivers and a handful of JIS screw from McMaster make this much more enjoyable.
Put the carbs back in and it fired right up... on 3 cylinders. The #4 header doesn't get hot and pulling the spark plug wire doesn't cause an RPM drop. Troubleshooting thus far:
1. All four cylinders are at just under 150 psi compression.
2. Pulling the spark plugs and cranking over with the plug held against the block yields approximately the same brightness of spark on all cylinders.
3. Swapping spark plugs doesn't seem to work.
4. There is fuel in the #4 carb bowl.
5. To ascertain that the problem is fuel I removed #4 plug and poured a bit of gas directly into the cylinder, started the bike and had all 4 firing until the gas ran out.
6. After I determined all this I pulled the carbs back out and pulled apart #4 again.
7. All passageways seem to be clear, probed with either thin wire or aerosol carb cleaner.
8. Jets are in the right place and clear.
9. Throttle plate and choke plate are synced with the rest of the carbs.
10. Vacuum puck moves smoothly.
There is fuel in the bowl and the jets are clear up to the venturi. Other things could be wrong that would prevent it from running well but given this, wouldn't it at least fire a bit?
Any other tips?