2nd Carb issues on 1981 Honda CB750F Bol D'or

[nurmiluka]

Hi!

I own a 1981 Honda CB750F Bol d'Or and I've been having some issues with the engine's performance. The main problem is a lack of power and uneven acceleration. Interestingly, with the choke halfway on, the bike accelerates normally. Based on the appearance of the spark plugs, it seems that the issue might be with the carburetor on cylinder 2. However, I'm not sure whether I should clean the carburetors, synchronize them, replace the gaskets, or take some other action. I don't have access to an ultrasonic cleaner for the carburetors, so I'm looking for an alternative method for cleaning them.

Other symptoms:
- Backfiring when decelerating
- Uneven idle
- Carburetor 2 leaks if the motorcycle sits for more than a week
- Spark plugs get damaged if the bike is left idle for too long

Here are some things I've done over the past year:
- Had the carburetors cleaned and adjusted a year ago
- Replaced the spark plugs and tried different brands
- Noticed slight improvement with Denso plugs
- Adjusted the ignition timing
- Helped with ignition issues
- Replaced the coils, spark plug wires, and plugs
- Improved ignition performance
- Changed air filters
- Changed main jets to 80/120
- The bike runs a bit better without the choke

Any advice or recommendations would be greatly appreciated!

 

[brettp]

2 definitely looks leaner than the others. Your idle, acceleration, and popping can be the result of carbs not synced. Your lean carb is the one all other carbs sync to, so you likely have a pilot or low speed jet clogged.
Believe me when I say you don't want to be chasing carb issues forever, take the carbs off and clean them, jets and all. Then bench sync the carbs, then reinstall. Adjust your mixture screws to 1.5 to 2 turns out, make your idle 1100rpm, then sync your carbs with gauges. It would also be worth mentioning, you should check your carb boots for cracks.
It is a lot of steps, but you don't want to take those off and put them on each time you find a new problem.

 

[nurmiluka]

Okay, thanks for your answer! At the moment it's running well with 1/4 choke on. I would like to drive the retof the summer like that and open the carbs at autumn. Here in Finland we only have about half a month of warm weather and no rain. Do you think It is safe to drive with 1/4 choke on.

 

[nurmiluka]

Rest of*

 

[brettp]

It is definitely not ideal. I want to say that I've read on this forum you can damage the engine. But is have to look it up. You will likely foul your plugs quickly.

 

[nurmiluka]

*Update*

Now I cleaned the carbs and checked the rubber boots. Took every part apart from carbs except the slow jet and threw them all in ultrasonic cleaner. Now it is a bit better but still backfiring in 4000-6000rpms. It is the worst on highway when going 120kph with 5th gear. Engine compression is fine but my valve cover gasket is leaking a bit. Could that be a problem?

 

[brettp]

If the carbs are clean, it is time to adjust all of their idle mixture screws to 1.5 turns out, then resync them. You should also look at your plugs now to watch for spark and make sure they're not fouled.