Motorcycle Repair: carburetion problem 68 cl350 Honda, rubber diaphragm, wooden dowel

Question
Bill, Hello again. Last fall I bought a pair of 68 cl350 Hondas in N.J. One to keep and one to fix up and resell. Bike in question sat on a carport since '81. YOu can imagine. Anyways, after replacing half the bike, it's together and looks better than I ever thought it would. Problem is it idles fine and accelerates well under heavy throttle, but surges like the devil at light throttle accel and cruise. This has Keihin carbs. I disassembled and cleaned them, obviously. Two part question. First maybe you could explain theory of operation. There's the pilot circuit, vv circuit along with a throttle plate and another main circuit. What gives. Second, I think my problem is with the second main circuit as I couln't remove it to clean.Do you know how this jet or emulsion tube just in front of the needle jet comes out? All help would be appreciated along with anything else related you can think of. Thanks for listening, sincerely Ron Willetts

Answer
Ron, there were several series of carburetors on the 350s with all different calibrations, so the series of carb would be useful to know. There is a removable emulsion tube that many people miss up in the body, when you remove the primary main jet. You need a small sharp edged slot screwdriver to get that one out and they are easily damaged, if corroded in place. There are cross drilled holes in the emulsion tube that are usually blocked and plugged up when you get them out.

The slow jet (idle jet) is under the rubber plug. A removeable needle jet can be gently tapped out when you take out the secondary main jet.

Use a plastic or wooden dowel to tap out the needle jet.

The other critical item is, of course, the rubber diaphragm on the slide. Any pinholes are going to affect the performance of that carburetor. The slide is opened by a differential pressure across the carb body venturi, which prevents over-carburetion when you whack the throttle butterfly open.

If you don't have a book, I can scan in a drawing of the carb parts from my Honda carb book. Contact me through my website...

Bill Silver
www.vintagehonda.com