new here hole in piston please help

[teague adams]

Hello all,

recently bought a 01 banshee yfz 350 that runs on alcohol...HERE IS MY PROBLEM...this particular banshee i was told has tons of mods unfortunately honestly i cant hardly tell what would be stock or not...but you gotta start somewhere...i took the banshee out probably about 3 times for about an hour and all of a sudden the left side started backfiring badly...loaded it up and saw that the spark plug was just trashed at the end...put on new spark plug and still backfires...took it all apart and found that there is a big hole in the piston where it looks like the spark plug punched through it or something? (so i replaced the piston and put it all back together...) took it out a few days later and rode it for almost 45 minutes and it starts backfiring again...havent taken it apart yet but im sure its the same situation...any ideas what i could do to figure out the problem? please help...thanks.

[bansheeseat$$]

I would say you have an air leak or you are just way to lean.Do a leak down test before you tear it down again and then go from there.

[teague adams]

I would say you have an air leak or you are just way to lean.Do a leak down test before you tear it down again and then go from there.

 

haha...new here...........so................leak test?

[Screaming Yellow Zonker]

sounds like an air leak on that cylinder. give your carb boots a good visual and squeeze. If they are dry rotting and cracking replace them. A leak down test would help also. I would also check what your timing is set at. (if it is adjustable).

 

How did the spark plug look? white, gray or black???

[teague adams]

Well I threw away the old plug but it was basically brand new...all I remember about it is that the little pin that the spark has to jump to was completely gone...are all carb boots the same size? ...and as far as timing goes it doesn't reaLly make sense for that to be the problem cause its only messing up on one side, right?

[camatv]

thats called DETONATION> what carbs does it have what kind of alky did you use what kind of oil did you mix wiht it. whats the timing at. what kinda domes do you have. any shops local to you that know anything about the bike that can help you out also..

[BigRed350x]

If your running methanol there are a few basics you need to have... first is a modded gas cap. If you've got a stock gas cap or any kind of cap with a check ball, ditch it and drill it out. Next is a pingel fuel valve. Whaat carbs are you running? Do you have billet bowls? What are your mains and dumps drilled to? What pilots? Needles? What domes? Whats your compression? How much timing do you have?

 

If you don't have much experience with banshees, I'd suggest getting a set of gas carbs and changing your domes out so your down around 140-150lbs of compression and go +4 on the timing. Once you learn to tune the bike on gas and read your plugs and all the basics about maintenance and up-keep for you banshee, THEN step up to methanol. Unless you have experience tuning with meth, and working on banshees you will keep finding yourself breaking down and blowing up.

 

Ask around here on the HQ and see if anyone around you can help you, and has experience with meth.

 

Do you purge your bike? What purge gas are you running and what oil are you running?

 

- Jared