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Old 02-13-2013, 12:46 AM
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Default Carburator Tuning Advice

I just bought a CM400T last fall, haven't really driven it around yet as I have been working on fixing it up. I've got about everything but the carbs working as it did when it was new.


Before I continue I just want to jet people know that I have had the carbs completely apart, and have cleaned out EVERYTHING in the carbs very thoroughly, and I've checked all the passages and they are ALL clean.

The air filter and box are stock and VERY clean with NO leaks that I could find.

I just installed new manifold gaskets, repaired a crack in the left boot, and installed new plugs, and the valves were also recently adjusted and the carbs have been balanced.

By the way the compression is around 130psi on the left and 145psi on the right.


The only thing that isn't shock is the exhaust system, it's an asymmetric 2 into 1 un-muffled exhaust, sort of like this:
http://www.dimecitycycles.com/media/...system-1_2.jpg
But mine doesn't have ANY restrictions at all, you could drop grapes through the exhaust pipes and they would fall right through.

Anyways, the issue I'm having only seems to be with the right hand carb, and that is that it doesn't like to idle, and then when I accelerate it will usually skip a few "pops" before it gets going, however once the engine gets over 3000RPM everything seems fine. When decelerating I also hear a few backfires in the same low RPM range, and I assume that they are from the same cylinder.

If I pull the choke out ever so slightly the engine runs GREAT.
And if I spray a little carb cleaner into the sputtering carb while the bike's idling it will fire up. This leads me to believe that it's running too lean, I have played around with the mixture screw but it doesn't seem to do much, so I'm thinking a slightly larger Main Jet (75) might be in order, as I have heard that these aftermarket pipes can cause lean conditions.

What do you guys think.

Thanks in advance.

Last edited by ForrestForce; 02-13-2013 at 10:11 AM.
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Old 02-17-2017, 11:56 AM
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Since you posted this a couple years ago I'm assuming you've resolved the issue but I just wanted to recommend if you do a lot of work on your bike yourself it is worth investing in a repair manual. I try to do as much as I can myself and it has truly been a money saver.
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