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Hi everyone-

I have a '71 cb350 that I've been working on/struggling with. Right now, I can get it started up but it will only run for 3-5 minutes at between 2-4K RPM idle. It will wander around between 2 and 4K seemingly at random, wind up to about 4-5K and then die (see video below). Here is some recent work that I have done:

1: cleaned fuel tank (metal rescue + mystery oil, looks pretty good and petcock is clean after running a bit of gas through)
2: cleaned petcock (after fuel tank clean)
3: cleaned/rebuilt carburetors, set float heights to 25mm (replaced jets/needles/gaskets with these kits from CM Honda CL350 Scrambler / CB350 Carburetor Rebuild Kit |Common Motor Collective)
4: inspected carb diaphragms (replaced 1 b/c of tear)
5: new battery (kept on tender when not on bike)
6: new fuel lines
7: bench sync'd carbs
8: new throttle cable, sync'd with carbs
9: new spark plugs + boots
10: replaced regulator/rectifier (Rectifier / Regulator Honda CB350 / CB360 / CB450 / CB500T | Common Motor Collective)

I have yet to check the timing; PO installed PAMCO ignition and I do not own a test light. Both cylinders are firing, however, the left side has stronger exhaust flow.

Any ideas as to why the idle is so high/why it will only run for 3-5 minutes, then die?

 

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Go get yourself a proper timing light(30-40$) so you can properly set the timing. It will be cheaper,in the long run, than just throwing new parts at it.
 

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Float spec is 26 mm with carb held at angle with float just touching needle valve. I set floats to at least 26.5 mm and even up to 27.
Check your throttle cables for slack and the clamps at the manifolds for alignment and tightness. I put the clamps close to the edge of the manifold, towards the carb. Turn your idle mixture screw 1 and 1/8 turn out. Adjust your throttle screws a small amount at a time, CV carbs respond a little slower.
 
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