Ok I have a big problem, I bought an 87 banshee about six years ago and it was bone stock besides being bored .020 over, well some1 didnt get a circlip in good and it fell out and i had to buy new jugs (unported) and they were at .050 and rough so I bored them to .060 and rebuilt it oh yea had head shaved .040 too. It ran good for about 4 years and i decided to get aftermarket exhaust. I got toomey t5 exhaust and started the task of rejetting. I thought I had an idea of what it should be at and bought a jet kit and was just going to put in the biggest jets and watch it flood and then jet down until it ran good. I put in .350 mains and ran it through the gears and wow it ran good, i thought it would flood like hell. I took my plugs out and they looked good too. I ran it for a year like that and then one night i was racing and burned a hole in my right piston. I had cylinders bored to .080 bought new pistons and put it back together. I rode it a couple days and took it easy on it , checked my plugs and decided to run it through the gears. It ran fine until 5th gear then it seemed like 1 cylinder cut out so i let off, stopped, and ran it through the gears again same thing only this time it burned a hole in my piston again right side. I got home and noticecd my right carburetor cap had popped off and thought that was what caused it to burn up. It didnt hurt the cylinder much at all just a little piece of melted piston stuck to it so i honed it and put a new piston in it and it still fit nice and tight. I wire tied my caps on my carbs and took it for a ride for 2 days and then ran it throu the gears, same thing started cutting out in 5th gear. I brought it home and it had melted the electrode half way off of the right side plug and started melting the left plug. Looks like it scratched my cylinder a little but it still has good compression. I squirted starting fluid around intake boots, carb caps, boost bottle, crankcase, crank seal, choke tube between carbs and I even checked for air leak around the spark plugs out of despiration, but it never would make it idle down and I have it idling so slow it barely stays running. Checked my floats since it didnt cut out until 5th gear thought it might be running out of gas, and thats what it seems like it wont completely cut out but it wont pull any more its like it gets to a certain rpm in 5th gear and just stays there and wont pull any more. The only thing I can think of is my cylinders start getting hot and my fuel is preigniting but I dont see why It wasnt when it was bored .060 and all I have done is bore it to .080. If any one has any suggestions not only would I appreciate it but you might just save a banshee from getting set on fire. Ive still got a raptor I can ride but its just not as fun. Thanks

 

cylinder walls are too thin, you dont have enough metal left in the cylinder wall to transfer heat away from the combustion chamber into the coolant, get new jugs again, and dont bore it over approx .060 over stock, if you want a higher displacement look into a stroker kit, or get custom fabricated jugs.

if anyone knows that you can bore over .060 and have it still reliable, let me know, just as a rule of thumb ive never recommended it more than that to any of my friends

 

My cousin had a banshee bored .100 over and didnt have any problems I have even heard people say you can go .120 over, but people say a lot of things. Anyways i seen one .100 over without this problem. Thanks for the info. I got some BIGGER jets and some high octane fuel today that im gonna try out.

 

I say it is from the high compression ratio.

 

hey, works for me... sorry for any false info... good luck wit the high octane fuel

 

What fuel were you running in it when it burned up?

 

I was running 89 octane fuel which is what I have been running in it since i bought it.

 

Hey yfz450kid I wasnt saying flat out u are wrong. I wouldnt tell you that without me knowing what is wrong. I hope your wrong but I was just saying I am going to test some other theories before I just throw my fresh cylinders and pistons away and go buy some new ones, I mean if I had to throw them away I should just go ahead and burn them up trying to get it to work at .080. If all else fails I have a buddy with a banshee bored .020 and I will let them both idle the same amount of time or run them down the road side by side and test coolant temperature with infared thermometer and see if my coolant temperature is close to his and that will tell me roughly if I am getting a good heat transfer.

 

sounds good, for your sake, I am hoping that im wrong tho... Im just going on what has been said in a few of my classes, but then again, not many ole 5.7L chevy motors can be re sleeved... hope everything starts working better for you soon

 

That octane sounds low to me. After all you did take 40K off the heads.
I would jack up the octane.
What did 40k do to the static compression ratio?
Oh, BTW when you bored it out, you also jacked in some more compression beyond the 40K head shave.