Motorcycle Repair/Carbuerator


\'66 honda 305
'66 honda 305  
I purchased a honda CB77 '66 from a guy in hazelhurst, miss. I also learned that the manuals and cd's that he gave me as a guide referred your name. Crazy! I love the bike but im having trouble with it. The problems is, the throttle has a hestation in it. If you try and give it gas the bike wants to die, but if you ease on the gas it will run (in neutral). After riding the bike for a bit there is fuel coming from the blow off valve or a valve that comes off the top of the cylinder head. I have tried taking it to a car mechanic and a motorcycle mechanic and im still having trouble. The car mechanic thinks it has bad rings but the motorcycle mechanic says carb adjustments. I hope its not rings...BTW the M. mechanic replaced the plugs because he said the right one had fouled up. If you can help with adjustments it would be most appreciated.


Dave, I think I saw that bike on eBay recently, didn't I?

There are a number of potential issues to explore and check for function....

First, adjust valves to .004" on the compression stroke (F and LF marks) when the valves are closed.

Second, check the compression.. It should read out about 170 psi with the throttle held wide open. Ground the spark plugs to the chassis/engine if you are going to use the electric starter to spin the motor over.

Read the spark plugs to see if they were fuel fouled or oil fouled. If black and sooty then the carburetors have issues... ASSUMING that the carburetor slides are both installed correctly! They are left and right side specific and must be installed with the cutaway at the lower edge of the slide facing OUT towards the air filters. The carb tops are also left/right side specific, so that the cables don't interfere with the gas tank.

There should be no "fuel" coming from the breather hose on the top of the cylinder head, only oil solids/vapors. If you smell gasoline fumes in the breather system something is terribly wrong. There is no "valve" on the cover, just a fitting to connect the hose to so that the oil deposits are deposited beneath the engine, if there is wear inside the motor.

The float levels need to be set at 22.5mm where the float tang just nudges the float needle closed, but does not compress the spring-loaded tip. Set idle mixture screws out at 3/4 to 1 turn out from gently seated. Idle mix screws are the ones closer to the intake manifold. Idle speed screws are located in the middle of the throttle slide bore and just raise the slide up and down as the screw is turned in and out.

Most CB77s want the needle clip in the #4 slot from the top. I am putting #140 main jets in these bikes now to compensate for the alcohol in the gasoline now, which causes them to run lean. I had main jets made up specifically for that reason and have them for sale.

Ignition timing is CRITICAL on these engines. Use a dynamic automotive timing light to check the spark timing at idle and at full spark advance. You do NOT want the spark timing to swing out past the II marks on the rotor which are 45 degrees before TDC (F or LF marks). If the spark advancer springs are weak, loose or broken the spark timing kicks in too early, causing issues with idling down and getting the idle spark timing to remain stable. If the spark advancer shaft is easily moved and/or has a lot of side play, the head will have to come off for sprocket repairs/replacement. The riveted unit can loosen up and the sandwiched sprocket can start cycling back and forth causing inaccurate ignition and camshaft timing.

Bill Silver

Motorcycle Repair

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Bill Silver


Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.


I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

VJMC (Vintage Japanese Motorcycle Club) of North America

VJMC newsletter, as editor for two years and as contributing editor currently.

3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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