440 Indy reving troubles. - Snowmobile Forum: Your #1 Snowmobile Forum

vaughn · 06-27-2009, 05:12 PM

My 1992 indy 440 wont rev higher than 3000 rpm. My sled had new plugs, cleaned out carbs, and a new aftermarket CDI. When I do floor it my carbs seem to "backfire" for fuel comes out of the front of the carb where air is supposed to be sucking. Is this a reed problem? The sled bogs down and wont rev any higher. I dont know a whole lot about my sled but I am handy and can solve problems if someone helps me out. Please Help

**RJ Gleason** · 06-27-2009, 07:56 PM

No reeds in it.
Did you put in new plugs?

**BC_Dan** · 06-28-2009, 01:51 AM

It's probably running really rich if you are trying to run it this time of year. You can try to lean it out by replacing the main jet with one size smaller, or drop the needle one notch by raising the e-clip... just remember to put it back before it gets cold in the winter...

vaughn · 06-28-2009, 06:31 PM

I did change the level on the carb slide. But I didnt think that running in summer time did that much of a difference. I thought it might run a little rich but not so rich that it wont rev high. I remember a few summers ago I started my sled up and rode it around for a bit. Is my problem common for guys who want to work on their sled during summer?

**BC_Dan** · 06-28-2009, 07:55 PM

When I bought my 1998 440, I got it in August. It was running so rich it would not make enough power to load on the trailer. Mine was jetted rich even for winter, in the summer it couldn't even move. Dropping the e-clip at least gave me a lean enough mix that I could load it.

And you may want to try RJ's advice, if you have a plug that is fouled, it will do the same thing... new plugs, jet it a bit leaner, it should at least be able to move

ridgerunner · 06-28-2009, 09:27 PM

when i did my pipes i change the position on my e-clip and didn't reattach the carb cable tight enough and it poped out. so when i started it it wouldn't rev up because at wot only 2 of 3 carbs were opening. my error and obvious, but maybe something like that for you? start basic... make sure the carbs are opening and closing correctly. check that the needles and seats are closing right. check all passages... just recheck anything you have done recently to the carbs. doens't sound like it would be just the temp. difference to me. i've fouled plugs and such because of summer/winter temp diff. but never had a sled that would't build rpm... just my .02

vaughn · 06-29-2009, 04:24 PM

I put new plugs in and they dont have 15 minutes run time on them. they could not be possibly fouled already. I have rebuilt the carbs twice within the past year and the sled idles just fine so I must be doing something right. Did you guys hear me when I said the carb was blowing fuel OUT of the carb. It was blowing so much fuel that my hand got wet when I put my hand in front of the carb while I was flooring it. Im really getting confused. Could my choke be adjusted the wrong way. My choke on my sled does not choke the incoming air it just has a passageway in which it justs allows more fuel to enter the carb. It sounds like a fuel air mixture problem but idk

**BC_Dan** · 06-29-2009, 05:09 PM

A certain amount of spitback is to be expected in a piston-ported 2-stroke engine. Running with the airbox off makes this a bit more pronounced, but even with an airbox, the inside of the airbox will be wet from air/fuel being shoved back through the carbs.

You are also right, the "choke" system on Mikuni VM carbs is an "enrichment circuit" not a choke. You could have a plunger hanging open, but if it is idling fine, I would not expect that to be your problem.

The air/fuel mix at idle to 1/4 throttle on a Mikuni VM is controlled by the pilot jet.

Air/fuel from 1/4 to 3/4 throttle is controlled by the needle jet/jet needle as it meters fuel from the main jet.

Air/fuel over 3/4 throttle is controlled by the main jet (with a little fuel coming from the pilot jet circuit).

When you drop the main jet size to decrease fuel delivery, it affects the midrange and wide open. Dropping the jet needle further into the needle jet will give less fuel from 1/4 to 3/4 without reducing top end fuel delivery.

To figure which circuit of the carb to work on, identify where your problem is; idle, 1/4 to 3/4, or above 3/4. That will point to the correct circuit in the carb.

Where are your e-clips set now? Try going one notch higher (thus lowering the needle into the jet) and see what happens. Can't hurt, and its free

**RJ Gleason** · 06-29-2009, 06:04 PM

It may also be an ignition problem instead too.
Bad plugs (even new) or loss of spark energy will also cause the same symptoms.