Motorcycle Repair: Carburetor repair service

Question
Bill:

I bought some mufflers a number of years back from you for my 1967 CA-77. The bike is a real head turner! Anyway ...... I picked up a 1978 Honda CB550K4 a few years ago (it has less than 8,000 miles on it). Three of the mufflers were rusted out so I installed a 4 to 1 muffler system. The acceleration was sub par and after a number of shops looked at it one mechanic determined that because of the different exhaust system. It was rejetted but only runs slightly better. A friend of mine looked at it and found that the outside carburetor on the shifter side is hardly pulling any vacuum. Can you recommend anyone to overhaul/rebuid all 4 of them?

Thanks,

Jeff Laskowski/Gig Harbor, Washington

Answer
The owner of Hinshaw's has a large vintage Honda collection in the store... I would start with them...

http://www.hinshawsmotorcyclestore.com/

If the carburetor vacuum readings are low, that is generally a sign of engine compression issues, unless the fuel circuits are really blocked off in a major way. Have a compression check done after valve are adjusted to see if it is having any effect on the engine performance.

Changing the exhaust, plus the use of alcohol-based fuels causes engines to run lean. I would re-jet a stock bike these days, just because of the fuel issues. You might have to bump the main jets up 1-2 sizes. The needles might need to be shimmed up a bit, as well. These carbs were all about emission control, not performance.

You might well need new carburetor intake manifolds after all these years...

http://www.ebay.com/itm/Honda-New-CB550K-Carburetor-Intake-Boot-Carb-Insulator-5

Basically, you need to do a full tune-up and check the fuel flow to the carburetors... there is a filter screen inside the tank that might be blocked, too.

Bill Silver