CB360 Carb Issue - problem with sync screw

[Rusnak_322]

I have been fighting a high idle issue for a while now. I think that I have it tracked down, but I don’t know what the next step is.

Valves adjusted
Timing set and advancing (checked with timing light)
Points not grounding on cover or back plate
No vacuum leaks at carb manifold checked with carb cleaner and WD-40 – no change to RPMs.
Floats set (all new parts)
Diaphragms in good shape, work smoothly.

If I pull the plug wire from the left cylinder (shift lever side of bike) the bike idles fine. If I pull the other plug wire, it sounds like I am at 3500 rpm or more (no tach).

I tried to bench sync the carbs as best as I can with visual and using a stick to measure the butterflys.

If I put my home made manometer on the bike, the left carb sucks so hard I have to shut off the engine in seconds.

If I adjust the carb sync screw to full out, full in or in the middle with the lock nut tight or loose, it make zero difference to the way the bike idles.

Tried with the idle screw all the away out and the throttle cable unhooked – no difference.

But I noticed last night that if I put slight pressure on the carb sync screw, it will idle nicely.

Now I just have to figure out why.

Could I have an air leak at the shaft on the one carb? If so, can it be re-sealed?

Could the linkage be miss adjusted somewhere else that I can’t see?

I have another set of carbs, but they look like they recently spent decades on the bottom of the ocean. I really don’t want to have to clean them up to re-use if possible. The linkage on those looks the same as on my good carbs.

Any help would be appreciated.



Here is my sync screw -

another shot -

Here is the old carbs -

Thanks,
eddie

 

[tweakedlogic]

Be certain your diaphragms have no holes. Yes you can replace the seals for the throttle shaft. I've only seen them available in ful carb rebuild kits. You could maybe try some teflon thread tape for plumbing just to see if it will work. it wouldn't last long I think. You might still have leaks in your carb boots. I did, I was convinced of it but couldn't prove it with sprays like you. I took the carbs off and smeared a thin smooth layer of RTV inside and out and let it cure. re-installed and my troubles went away. I ran it like that for over two years.

 

[OJ]

I had a similar issue and ended up buying new intake boots. The new boots didn't seem to solve the problem at first, but after re-installing the carbs few times, she started running better and I can adjust the idle etc.