HI GUYS, I'm having a HUGE problem with my sled. Being a 2 stroke, I think you can hel me.
The machine: it's a '97 440 MXZx (Bombardier-Skidoo), and has some preparation in it (I bought it like that).
The engine is a twin 440 (436cc) wit rotary valve (for the intake) and power valves, and 2 into 1 pipe. The carbs are Mikuni 34mm that seem rebored. They are now 34mm.
I rode it last winter, and my only troubles were some electrical details...never did I have trouble starting it or whatever mechanical related.
At the end of the winter, a "friend" crashed and destroyed th whole left front suspension. Got everything repaired, and running for this winter. Last week, a water hose got ripped off, I didn't see it and the engine seized. I changed pistons, and cleaned of the aluminium off the Nikasil cyl. walls (too much time and $$$ to repair...380$can per cylinder and 1 week).
It has compression (at least as good as before)...but is a pain to start (when it does). I cleaned the valves, gaskets are new (base and both head), and I cleaned the whole fuel lines (fuel filter and carbs). Nothing changed...and seems to be OK.
The only way to start it is take off the plugs, shut the fuel, pull the damn rope 2-3 times, out the plugs back on...hold the throttle wide open when pulling the starting rope, and it starts.
Like if fuel kept coming in the crankcase (but carbs seem to do their job perfectly).
Once it's started, it runs perfectly, idles, no problem at all...I just won't shut it, it won't strat again. Engine cold or hot makes no difference.
Here's my thought. When it seized, the engne got very hot (Powervalve plastic caps melted, the coolant reservoir started to melt...and the paint on the head is now more like pee yellow more than Bomb yellow...the paint is cooked!!). So cold th rotary valve be damaged (bent because of the heat), and let fuel in even when in "closed" position? Can it happen...?
I'm out of clues, or possible solutions!!!
Help me please!!!
If you want any more info, just ask!!
One more detail, last year, when the engine was hot, I just had to pull the rope and it would fire after one crank revolution...no throttle, no primer, just pull a little (even my 11 years old sister could start it) and it would fire, with no throttle or priming or whatever...it would simply idle, and wait for the powder.

Again, please help me, I'm out of ideas...can't see what could be wrong.

 

check the rods and mains!

 

When the engine was opened, I checked the rods, and they were OK. Just a tiny sign of hitting against the low part of the cylinder (when I turned the crak to pull the piston out of the cylinder), but nothing is bent.
Mains? Are you talking about main jets? If so, then they are clean (blowed all jets and carb with compressed air). Otherwise, mains???
Thanks

 

it may have ruined the main bearings, it would be hard to start as you described. Did the rod spin EASILY?

 

Main bearings? (sorry about my english technical knowledge...I probably know it in french...but in english). crank bearings, crank/rod bearings, rod/piston axle bearings?
Anyway, the rods did move very easily, I didn't really pay attention to it (didn't look for the trouble that could have happened there), but they would go "all around" normally, at no time they would grip...
Actually when I said it wouldn't start, there's an update, it almost starts when cold, it runs for 2-3 cycles and then shuts down, and nothing cankeep it running (primer or throttle just kill it faster).
Thanks again

Another idea. could it be the plug that's not powerful enough to start the engine (is it "harder" (for the plug) to start an engine? more than simply keep it running?). The spark didn't seem to be very powerful (but it was the same on Xplor's 670MXZ, so it's not the problem). Anyways, I'll change wires, plug caps and plugs, see if there's any better.
Thanks again(again).