Cm400 help
 

I have a 2006 Honda shadow. And acquired a 1981 Honda cm400e. It runs drives fine. But has a low rpm stumble.
I have tried to clean the carbs couldn't get the the mixture needle out.
Replaced plugs with denso oem.
Replaced plug boots
Changed oil could not be the bolt looses for filter striped it.
Drained tank and it was coated with something no rust. Put 1/2 can sea foam and 4 gallons of gas.
Runs great and revs freely just has off idle stumble maybe 1/8 to 1/4 throttle.

Has 6 k miles on it also.
Any ideas?

Most likely the idle mixture needs richening.

There should be 2 screw on the side of the carb - 1 for idle speed (inline with the slide, and just below it. All it does is lift the slide as you turn it in) and one for idle mixture. On most Honda carbs (Keihins) the mixture screw is an air-bleed - not a fuel-bleed. An air-bleed screw is usually a lot farther back on the carb than a fuel-bleed screw.

To richen the mixture on a carb with an air-bleed, you turn the screw IN - closing off the air passage and richening the mixture. 1 to 1 1/2 turns out should be in the ballpark. Most come about 2 1/2 turns out from the factory (lean).

If that doesn't cure the problem, next thing to do would be pull the slides and move the clip on the needle (assuming it has an adjustable needle). You would move the clip DOWN to raise the needle and let more fuel flow at the same slide opening.

Just grab the filter bolt with a vicegrips and spin it out, then buy a new one.

Also - gas with Ethanol (E10) will make a perfectly-adjusted carb run lean, and will make a lean-adjusted (factory) carb worse.


Jay

Concur with the problem being the idle mixture needle. The SeaFoam mixture is pretty strong also, which could exacerbate the problem. Check to see that there are no vacuum leaks, ensure the seals between the carbs and head is clean and tight.

the adjuster a brass piece heat the motor? on the bottom of the carb? is so i tried to adjust and snapped the head of it off....

I had on old SL 350 Honda and it had similar symptoms and it was the coil. Would stutter at low rpm's but then run ok once it was wound up a bit.