Left Cylinder Not Firing

jpweaver

jpweaver

Member
Joined
Sep 13, 2025
Total Posts
11
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Location
Raleigh
Hi guys - I'm trying to get a 1980 CM400T running that has been sitting for roughly 30 years. I was finally able to get the old girl started today, but only the right cylinder was firing - left exhaust was cold while the right was piping hot after a minute or so. Things I've done so far are...

1) Checked for spark - spark is good (new plug, coil, cable and CDI)
2) Checked compression - 150psi cold on left cylinder
3) Checked that there is fuel in the bowl by loosening the drain screw - watched fuel come out of nipple.
4) Did the best I can to clean out fuel/air adjust valve. Replaced o-ring and washer.

My thinking is that there is no fuel going to the cylinder. When rebuilding the carb I did not remove the pressed-in pilot jet - I just sprayed a bunch of carb cleaner down the hole.

Any ideas for next steps? Will I need to tap the pilot jet and pull it out? Trying to avoid this if possible.

*Additional note - I'm doing this testing without the gas tank installed, just pouring small amounts of fuel directly in to the fuel line between test runs. I don't know why this would matter, but wanted to mention it.
 
Last edited:
I know you had the stuck throttle earlier so, sounds like pulling and cleaning the pilot jet is in your future, but a few things you can check to verify your fuel issue.

1. after running the right cylinder shut it down and pull the left spark plug to see if it is wet with fuel.
2. when running the bike does the left start firing if you give it some throttle.
3. fill the carb bowls with fuel, then try to drain and catch all the fuel into a container and measure and compare how much is in each carb, this will give you an idea if they are filling equally.

KM carburetor sells an extractor for the pilot jet if you are interested.
https://www.kmcarburetor.com/products/honda-press-fit-pilot-jet-removal-tool

Or you can do the 4-40 drill and tap method.
 
Another method I’ve used is to work a guitar string (the high E string) through the orifices. It’s fiddly and patience is needed. Once through, chem cleaners will work to finish the job.

Just looked at the video, they use a variation with copper wire.
 
TangoDelta72 said:
Search against "Set of 4 Carburetor Carbon Dirt Jet Remove Cleaner" in Amazon (e.g.), but see if this link works. Money well spent on a plethora or carb cleaning apparati.

Good luck!
Click to expand...
OH GOD NO! Those are oxy-acetylene torch tip cleaners, basically small round files guaranteed to ream out your jets.
 
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