CL77 Carb sync question

joel1234567 · Post by **joel1234567** » Tue Aug 21, 2018 2:09 pm

Hi, new to the board. This is my first post here.

I've done a lot of tinkering with older single cylinder Hondas (CT90, CT70, Cub/50, S90, CL90, etc) but I bought my first older twin cylinder last fall- a 1967 CL77- and have been trying to get it running in top shape but having some issues getting things just right.

I'm getting a LOT of popping on decel and also when I hold a constant cruising speed. It doesn't seem to be bad when the bike is cold (choke off) but once it's warmed up (after maybe a mile or two) it gets worse. If I just barely keep on the throttle- just enough to feel that tension point where the throttle slack starts to open the throttle, it lessens the popping quite a bit. And when I let off the throttle to shift I usually get a nice pop or two as well.

I've read a number of posts that this usually indicates a lean condition or the throttle slides not matching up in position and synced so that one side is running a little more open than the other. But I'm not sure how to tell that the slides are operating in sync, at the same amount of "openness"?

I saw "Ed Moore's Special Tuning Recipe" referenced in this forum and read thru that, but had a couple questions... It says "Remove the tool can and put middle finger in left carb and thumb in the right carb." Why am I putting my fingers in there? Is that how I access the carb slides to validate that they're moving in sync? Should I have my finger/thumb in the carb with one hand and then be working the throttle gently with the other hand?

Thanks-

rpr851r · Post by **rpr851r** » Tue Aug 21, 2018 4:52 pm

You got it. Thumb in one carb and pointer finger in the other (from the same hand) and work the throttle with the other hand. you should feel both slides open at the same time. If not adjust the cable fitting on top of the carbs until they do. Before you start on the process, back out the idle adjuster screws so they are not holding the slides up and make sure the cables are well seated into the carbs and into the splitter on the cable. I have chased carb sync when the cables got a bit held up in those areas. I would get the sync right then the next moment it would be way off. Most recently a poor reproduction cable was driving me nuts when the cables would come out of the splitter a bit and then pop back into place.

joel1234567 · Post by **joel1234567** » Wed Aug 22, 2018 8:39 am

Thanks for the info and first hand knowledge.

When I took my first ride, after it got warmed up the idle would hang... When I just blipped the throttle it would rise and not come back down. I unscrewed the slide adjustment screw and opened the air/fuel mixture a bit more and this hasn't happened again. Hoping I can fine tune it as described above.

Just one more Q... Once I get them bottomed out and moving together, and then I readjust the slide adjustment screw do, I assume they should theoretically stay adjusted/synced properly? The amount that the screw goes in doesn't unsync them (for example, if the screws on both sides aren't exactly perfectly screwed in the same distance)? If they do need to be screwed in the exact same amount, is the best method to screw them all the way in and then back them both out the same number of turns on both sides?

joel1234567 · Post by **joel1234567** » Wed Aug 22, 2018 8:42 am

I lied, one more q... When you say " I have chased carb sync when the cables got a bit held up in those areas. I would get the sync right then the next moment it would be way off. "- what are the symptoms when this is occurring? Is it the popping that I described? Or something additional?

rpr851r · Post by **rpr851r** » Wed Aug 22, 2018 9:42 am

Answers to questions:

-Correct, After getting the slides synched then adjust the idle screws.

-I was chasing the sync issues before even starting the bike so I can't tell you if that would cause popping like you are getting.

Good luck,