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Bought a 1975 CB360T and I'm having trouble with the left cylinder. Can start the bike with the left spark plug unplugged on just the right cylinder but not the left. Bike idles fine at 1,100 but I'm hearing mild popping/gurgling from the left muffler. Tac seems to oscillate slightly. When I rev the bike it comes back to idle quickly but if I sustain the throttle at 3 to 4K it seems to not like it. Here is what I've done:
1. Reset cam chain
2. Set valve (tappet) clearance to spec.
3. Calibrated the timing with the CMC Shockwave system (any of you had experience with it?) Timing is dead on. But will check again since it could have come out of alignment. I heard if you didn't put "spacers" in the sensors can come loose. I did use lock-tight when I calibrated it.
4. New coils
5. New plugs
6. Stock Carbs. Carburetor cleaned and jetted at stock 110. (Floats are at18.5) But the left float seems to not move as freely as the right. I might switch up the floats and see if the problem is replicated on the right side.
7. CMC Regulator/rectifier installed
8. New manifolds. I don't think there are any air leaks but I didn't check.
9. Did a bench and running carb synch. Checked again the carbs are ever so slightly out of synch.
10. Mufflers I think are "Mac" and the baffles are removed.
11. Battery is fairly new.

Any thoughts why the left cylinder is off while the right is working perfectly
 

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3. I have the CMC Shockwave ignition as well and it works great so long as the sensors remain in position with the correct timing and gap to the camshaft.
8. Check the insulator manifolds for leaks between the carbs and engine. Some folks spray WD40 or carb cleaner, but I think these petroleum fluids damage the rubber and cause cracking and the very leaks you want to avoid.
10. Mufflers without baffles can reduce exhaust backpressure and upset carburetor tuning. These factory jetted carbs need the restrictive air filters and some exhaust restriction to achieve proper calibration.

My guess from the symptoms are that the right cylinder produces all the power at idle. The carbs need a little tweak to their synchronization adjustment, to hold open the left-side carb a little more. Pressure out the exhaust at idle should be about the same from each muffler. The idle mixture on the left might be too lean.
Sustained throttle problems could be caused by a sticking float in one carb, leading to a fuel level too low to maintain power. Test the rate of fuel flow from the tank into each carb. Poor fuel flow into the carb bowls might be the issue, due to debris above the float needle, restrictive fuel filter, dirty fuel shutoff valve below the tank, or a restrictive tank vent in the filler cap.
 

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I had a similar issue with my cb200. I agree with the notes Scramblr addressed, try and use mufflers with baffles, and to check for leaks around the intake manifolds use quick start fluid (ether) and not WD or any other penetrating oil. Also try pulling a spark plug and holding it against the cylinder to head and confirm that you see a consistent and strong spark across the electrode; sometimes even though you have new coils and plugs, you might not have spark because there is the odd time that there isn’t connection between the plug wire and the plug boot, make sure it’s buttoned on tight.

Other than that, it sounds like you have confirmed or eliminated all other things, except for what ended up being the issue that I had: compression. Perform a compression test and make sure that both cylinders are within 10% of each other, and that neither is below about 90-95 PSI. I had my left cylinder only reading about 88psi, and the right one just over 100. Upon further inspection by doing a leak down test on the left cylinder I discovered that my exhaust valve wasn’t fully seating, so while I would get a fair amount of squeeze out of it, it wasn’t enough to maintain proper idle and performance. I did a top end rebuild and lapped that valve in the head, and whether it was pitting or an extremely small bend in the valve, that took care of it.

If you’re unclear on how to do a leak down test I’m sure there’s vids on YouTube, or I can walk you through it, it’s simple and you don’t really need any specialized tools
 
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