I had been chasing a poor running problem for WEEKS that was carb related on my '67 Dream and just couldn't get it sorted. There was a big problem with the mid-range mixture that couldn't be adjusted out.
I had rebuilt the original carb and I am VERY careful about taking things apart, organizing all the parts, and carefully putting it back together in reverse order substituting the new parts from the overhaul kit where provided but there was just something 'off' about the original so I picked up another carb from a salvage yard and installed it without opening it.
The air screw on the replacement had a poorly formed slot so I took it out to fix up the slot (to make it easier to adjust) and noticed there was a small O-ring just under the head of the air screw. There WASN'T one on the original carb and there wasn't a small O-ring in the overhaul kit.
I put an O-ring in the air screw, just like on the replacement carb - I had to sand it down a little to get the profile thin enough to fit in the carb - and put the original carb back on the bike.
It ran like a charm!
The parts manual shows an O-ring on the air screw, below the spring but putting it farther up the screw worked fine.
I had no idea that enough air could leak through the threads on the screw to bugger up the mid-range mixture but apparently it does.
I still need to adjust the clip on the main needle - now running a little rich - but that one little O-ring made a world of difference.
Just thought I would share in case anyone else is chasing an "un-adjustable carb".
CA77 carb - interesting discovery.Some carbs had 0-ring screws and some didn't.
The ones that did had a deep groove just under the head, the others just a shallow "groove". Attached pic shows both types, with the ones shown with no o-rings don't get one.
66 dream, 78 cb750k, 02fz1, 09 wing
Interesting DiscoveryWelp, Diane. I gotta thank you for solving part of my problem (Whatever it is). The o ring on the air screw made considerable difference in how my CL77 runs.
I'm still having difficulty with it running roughly under throttle. Any suggestions? I'm counting on you since you nailed the o ring. This is starting to make me crazier. Thanks. Well ramwing7, you are counting on the wrong person LOL!
"Running rough under throttle" I assume means at high speed/throttle. Once you are past the mid-range, it is almost 100% needle and jet (if low and mid-range are set right). Setting the needle on a CA77 or C77 is a P.I.T.A. 'cause you have to pull the carb for each change. Then you have to put it all back together again to find out what effect the change made. I like to start a bit on the rich side, run for awhile, and check the colour of the plugs. If they are too black, pull the carb again and drop the needle a notch or two. Maybe someone else has a better procedure for setting the main needle - I hope so! P.S. I spent an entire summer chasing that damned O-ring problem - it was more stubbornness than smarts LOL!
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