Need Help - Blown Engine!!!

Hi Guys

So since my original post I rebuilt the motor, cleaned the carbs, had the crank seals repalced, ran the sled for maybe 300kms and now this happened;

http://i223.photobucket.com/albums/dd63/filow_bedow/IMG-20121211-01038.jpg

I have torn the motor down, the carb jets had some jelly but I think thats because the sled has been sitting for almost a year. All 3 jets had the same amount of jelly. The carbs were cleaned at the start of last season before this blow happened. The carb boot is solid, no rips or tears. I am about to re-check the crank seals which have almost no run time since they were done 2 seasons ago. I know most are going to tell me that the piston was leaned but I am running out of things to check to learn why it was lean.
I will be rebuilding the oil pump since the motor is half way apart.

My carb jets are 148.8 148.8 and 150. Are these correct? I think I already asked this and was told these are stock. I need to check the size of my pilots.

Fuel tank filter has been replaced before this blow up.

Anything else I can be missing????

Thanks for all your help

Chris
 

first of all..are you running premium fuels??Next ..did you not drain or run carbs dry before sitting for a year?? I have never had any jelly substance in my carbs. My carbs are spotless but I still go thru a cleaning prior to season start.That jetting is higher then with what I run.The fuel most probably is the issue..sorry to say and good luck on the rebuild again.I have 2 seasons on both my sled motors after rebuilds and have no issues.
 
you must not have fuel sitting in the tank either for any length of time,siphon out the fuel and put it in your car instead otherwise you are looking for more problems.Storing a sled motor properly is key,you really can't trust fuels as much as years back,I also have Fitch Fuel Catylst in my tanks,in all my equipment and truck.It will actually raise octane a little and keeps fuel fresher .It works for me.
 
filo_bedo said:
Hi Guys

So since my original post I rebuilt the motor, cleaned the carbs, had the crank seals repalced, ran the sled for maybe 300kms and now this happened;

http://i223.photobucket.com/albums/dd63/filow_bedow/IMG-20121211-01038.jpg

I have torn the motor down, the carb jets had some jelly but I think thats because the sled has been sitting for almost a year. All 3 jets had the same amount of jelly. The carbs were cleaned at the start of last season before this blow happened. The carb boot is solid, no rips or tears. I am about to re-check the crank seals which have almost no run time since they were done 2 seasons ago. I know most are going to tell me that the piston was leaned but I am running out of things to check to learn why it was lean.
I will be rebuilding the oil pump since the motor is half way apart.

My carb jets are 148.8 148.8 and 150. Are these correct? I think I already asked this and was told these are stock. I need to check the size of my pilots.

Fuel tank filter has been replaced before this blow up.

Anything else I can be missing????

Thanks for all your help

Chris
Click to expand...

how about a couple pics of the other 2 piston tops, the pic you posted definitely a lean burn down. lots of causes for that, but a couple questions first:

1.) old gas.., did you put a new fresh tank of premium in sled before riding it? or was it the gas in tank from last winter?

2.) you didnt clean the carbs before riding it this year?

3.) wheres the oilpump gap setting on the cable at?
 
Hi Guys

Thanks for the help. The carbs were cleaned prior to running the sled at the start of the season BUT there was old gas in the tank. I do a stabilizer at the end of every season and run the sled for a bit before it get put away.

Could bad gas really cause a blow up like that in one cylinder?

I dont have pics of the other 2 pistons, but both looked black on top and what my mechanic would consider normal looking....I will take pics of the other 2 pistons and post.

Thanks again
 
I have torn the motor down, the carb jets had some jelly but I think thats because the sled has been sitting for almost a year. All 3 jets had the same amount of jelly. The carbs were cleaned at the start of last season before this blow happened


Did this blow/burn down happen this year or last year? Maybe I am a little anal after my girlfreinds sxr burnt down due to a plugged needle but I clean carbs like its going out of style! If "life" gets in the way and I dont fire up the sleds for a months or so in the winter I pulled the carbs for a walk threw before I fire em up and hit the trails......Havent had a second burn down yet! The days of letting the snow melt out from under our sleds then just putting fresh gas in them when snow returns are over. Maybe I am wrong in this but seems to me the higher the performance of a engine the higher prevenative maintance.
 
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