Well the motor on my 400 scrambler blew up for the 3rd time in less than 3 months on saturday. The dealership said the carb was jetted too lean the last time it happened and they put different jets and a different needle in it. I have a 39 pwk carb on it and i'm wondering if maybe it's not getting enough oil either because the oil pump wasn't turned up after i installed it. I probably should have just went to premix but you live and learn i guess. I'm getting tired of all the 2 stroke problems so i'm thinking about just taking it to the dealer and seeing what i can get for it on a trade in for a new 4 stroke 500 scrambler.

 

It seems as though you already have the answer to your own question.

#1 you did'nt bump up the oil inj.
OR
#2 you should have eliminated the oil inj.

Doing one of the two of these should fix you up.
I suggest dumping the oil inj.

EC

 

My friend had the same problems with his an it keeped eating away the exust side of the piston. The problem was he was not running high enough octane gas for it he has had no problem sence running 110 mixed with 92 of 1 to 3 an permixing using amsoil

 

Have the failures been lubrication (or lack there of) related?
Have you been using stock or better quality parts?
Who has been doing the work? If the clearances in the engine aren't set correctly, the engine wont last long at all.
What other mods do you have?
Is the carb jetted too lean?
I have started using pre-mix in addition to what the oil injection system puts into the engine to prevent any problems

 

the first time it scored the exhaust side of the piston and the second time it burned a hole on top of the piston. I've always ran 92 octane fuel so I don't think that is the problem. I'm pretty sure it needs more oil though. What does everyone think i should get out of it if a trade it for a new 500? I'm just gonna trade it in the way it is. The mods i have on it are a hotseat pipe, clutch kit, 39 pwk carb with k&n filter (no airbox)and delta v force reed cage. I think i would be a lot happier with a 4 stroke because i wouldn't be as worried about blowing the motor.

 

My uncle has a Yamaha WaveRunner. He blew the engine everytime he went riding, the first three times. After replacing three "long blocks", come to find out, they were using the same faulty oil injector when they changed each engine. They finally replaced the injector, and it hasn't had a problem since.

Dave

 

the work has been done by the dealership where i bought it at. The carb was jetted lean the first 2 times it blew but they richened it up last time. They put in a wiseco piston both times. They never said anything to me about needing more oil but i really think that is the problem this time. I'm still leaning towards just trading it in for a new 500 though because i'm getting tired of not being able to go riding. We have a lot of snow here and i hate not being able to go out and ride!!

 

Just a question, the dealership where you bought it.. is it a polaris dealer? I had a polaris that was worked on by an artic cat dealer and due to the dealers lack of knowledge or sloppy work had my wheeler that I just bought in the shop 2 days after I bought it, gear busted off in the starter and stuck in the motor, lasted a couple days then back to the shop, overheated, back to the shop, new topend, then the oil inj failed, back to the shop, new topend, and I got rid of it... Im pretty sure it was the dealer or mechanics fault, My guess is they diddnt have much experience with polaris machines... he did all the work for free cuz it was still under warantee... anyways just tellin a story Mabe try taking it to a diffrent dealer/mechanic before you get rid of it...

 

yea it was a polaris dealer

 

Before you get rid of it, give Rick Ritter a call. I guarantee you can fix the engine correctly and keep the quad for less than what the dealer is going to take out of your trade in for the engine.
The first failure sounds like a lack of lubrication at high horsepower output. Same thing happened to mine with less than 20 hours on it.
The second failure definately sounds like lean jetting. Fatten up the jetting above what you think it needs and work your way leaner.
Anything above about 45 - 50 Horsepower NEEDS some pre-mix to keep it alive above what the oil injection provides.
As you move more fuel/air through the engine, the oil injection system doesn't compensate, so the fuel/oil ratio goes out the window. The oil injection only puts out a little oil at the bottom of the manifold and doesn't mix it that well. Pre-mix is the key to keeping a high performance engine healthy. You may have to change plugs a little more often, but they're cheaper than pistons...
Fix it right, start pre-mixing the fuel, jet it rich and work back to proper jetting and the engine will last almost forever.