matthewt1023

We had no snow last year at all...anyhow, the year before I was told by the ONLY sled mechanic in town that my snowmobile (86 phazer) needed crank seal and bearings. For the same money he told me I purchased a rebuilt 93 motor and dropped it in. IT FIXED NOTHING.....

The problem was it backfired and died at high rpm under load. It would/will idle all day long and rev up to low rpms. We got some snow and pulled it out today (first time with rebuilt motor) and it does the same thing. With that I know two motors don't have the exact same issues....I know they can, but odds of it being? Plus I bought the rebuild from a reputable dealer, not the local mechanic.

As I think about this from the little knowledge I have, it seems more to me like a fuel issue. A LOT of smoke, then a backfire and kill. I watched the fuel line right above the fuel filter and the fuel is actually pulsating through it; is that common? It definately isn't continuous flow. I took the line off with it running and nothing came out? Is this supposed to happen...or maybe a fuel pump or carb issue? Please help, my son is about to kill me if I can't get this thing on the snow.

joshkidner

The fuel is supposed to pulsate. Did you use the old exaust? That could cause backfire. Mis-spark could too. Also (this has happened to me) a loose ground. On the trails a couple a years ago i was riding with a loose ground. At high rpms only it would spark and backfire.

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yamadad4

consider the constants and the variables. what all did you change?

i am assuming you simply dropped the engine in, kept all else the same like wiring, carbs, exhaust, etc.

your constants would be the same, wiring, carbs, fuel system, etc.

if you had a running issue prior, look at what wasnt changed. typically a backfire is a lean condition. under load and high rpm sounds like its starving for fuel. check your carbs.

from there, plugged or kinked fuel vent lines, a pinhole in any of the fuel supply lines or even the impulse line can trigger these symptoms, down to the fuel pump itself.

electrical can come into play as well. the ground was already mentioned, but you could have an issue with a wire in the mag or anywhere else arcing under load. bad spark plugs, bad connection at the plugs, even bad plug caps.

matthewt1023

I replaced the fuel line coming from the tank...I have a feeling I am lacking fuel from the source! New lines and new filter to start after what I noticed from tearing it down and doing complete test. If this doesn't do it, we are definately into carb and fuel pump! Doesn't it suck to have a sled not running when you're expecting snow!? At least I have the 800 can ride if desperate...btw, anyone want a 96 ski doo mach z rotax; needs a track, fresh motor...$600

aduck

May be interested if your serious. have u checked your pick up line in the tank. Good sign if its the pump its pull the pulse line if it has fuel time to rebuild

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kccats

Replace the Pick up in the tank, clean the carbs! Rebuild or replace the fuel pump! Check your Compression @WOT!