[SLEEP131MXZX]

I have an 2001 mxzx 440 and the other day I noticed a bog out on the trail. So I brought it to a local pond and when I come out of the whole it only tacks to 8200 but then immediately drops to 7000 rpm and then slowly works back up. After alittle while of tring to find the problem the sled would climb from 7000, hit about 8000 rpms and the the tach would start jumping like it hit a rev limiter. The sled seems to be running fine on low rpms, but it seems to me like it is running out of gas. The plugs are running about a light brown. I went through the clutches and throughly cleaned them. I tried a few different setups including helix changes and springs. It made no difference the sled just seems to be lacking the power. I tried turning the clickers up on the front clutch as well but sled still only tacks to 8200 instead of 8500 rpms. Any suggestions would be very helpful because I have run out of ideas.

 

[Tom White]

Some of the symptoms sound like a worn belt and/or worn springs,,,,but the bouncing tach sounds like bad fuel. What could be happening is that your fuel has water in it and at high RPM the engine detonates slightly (because of the water) and loses power. When I have encountered this, dry gas (isopropyl) would not fix the problem. For me, the solution was to drain the fuel and run it out all the way, then add fresh fuel with isopropyl in it.

Not saying this is surely your problem, but sounds like it could be.

 

[SLEEP131MXZX]

Yea, I have tried a brand new belt and have drained the tank. Using 93 octane with a booster in it. It almost feels like it is running out of gas yet the plugs are burning pretty good. I was wondering if anyone has had a problem with the fuel pump or the fuel filter in the tank becoming slightly plugged? It just seems odd to me, because I have never had a problem with it, I put new reeds, air filters, and plug wires on the sled. It runs great at idle, starts good, and runs fine up to about half throtle. Anything over that and rpms and lack of power become and issue.

 

[Tom White]

Have you tried running isopropyl through it? If you have water trapped in the pump it will enable the system to move it through and burn it up. You have to try this before anything else.

Is there any difference between plugs? Does one look dry the other wet? Does one look lighter than the other, etc?

It wouldn't hurt to make sure the impulse line has no holes in it (sometimes things rub holes) and/or that it isn't plugged. Wouldn't hurt to check your diaphram for pin holes or cracks either.

Is your plug gap .020 or less? Could the engine be missing on the top end do to erroded plug gap?

Could there be something in the carbs or something hanging up the inlet needle of the float?

Some ideas.

 

[SLEEP131MXZX]

Yea thanks, I will try anything right now. This weekend I am gunna tear it down again and check it all over. If the float level isn't set correct, could the carbs be running out of gas and thus the fuel pump can only give it a shot of gas? I was thinking this might cause the bucking at 8000 rpms. It feels like it is getting pulses of gas as you can hear and feel it when the tack is bouncing.