I recently rebuilt a complete basket case 1994 400L from a greasy dirty rusty old frame and a trailer full of dirty parts. The motor was completely rebuilt with a all new bearings, seals, and gaskets as well as a new wiseco piston and rings in a freshly bored and honed cylinder. Engine had 2 broken case halves which had to be replaced, and was the reason why the machine had been parted in the first place. Nearly all the parts were there, although I did have to buy some from either ebay ( body parts) or from my Polaris dealer for all the other parts. Anyway I have the machine fully assembled and it started right up and seems to run pretty strong!!! Most of the time anyway!!! It will run really strong for the first few minutes after it is started, but after that it seems to start to stumble on accelleration. I thought it must be carburetor so I cleaned and checked the carb for the third time and have completely checked it out. I have pretty much ruled out the carb, but you never know. I also tried removing the black wire from the rev limiter as I have read that they can sometimes cause strange problems with the way the machine runs. Removing black wire changed nothing. Still seems to stumble on accelleration. I even removed the secondary clutch and checked the helix buttons and the buttons were like new. I have also replaced the coil and plug wire and tried another brand new plug. Problem still persists. I even replaced the reed valve with a good replacement one I had and still nothing. I am starting to think maybe it is a bad CDI ignition. Does this seem like a likely candidate?? Dealer wants $225.00 for a new one. I want to rule out all other possibilities before I spend that kind of money.
What else could it possibly be. Could a bad rectifier regulator cause it to run like this?? What would I check at the magneto that could cause this problem?
I think the machine was run with a bad battery or without a battery in the past as all the bulbs on the machine including tailight, headlight, indicator lights, etc. ; were all burned out and had to be replaced.
Thanks to all for any and all ideas on this problem. This forum has been a great source of great information for me!!

 

Pull the choke out a little while its running and warm and see if conditoin gets better or worse, if it runs better, its too lean, may be able to lower the clip on the needl, this will raise the needle and richen it. If it runs worse do the opposit, if yu cant get it with needle may need larger or smaller main jet.