Zorro here...Xplor is almost happy...
We think we found out why he couldn`t get his scram to work...
We mounted everything back as `banshee beater` (aka 12/1 billet head, 39mm carb etc etc), and just to see measured the compression (it had not been done since the rebore/rebuild)...a nice 172psi came out...and when my expert eye looked at his old piston...there were nice combustion remainings...under the piston!
I say detonation...he would like to be sure of this, but comes back with his pessimistic thinkings "why do I hav 170 psi? Hot seat said it should be 140!! (it was actually 138 the first time we measured it...3months ago with the 1 year old piston)


So, what`s your opinion? Do we have our solution?

 

Did you say HotSeat?

 

And he was running it on 92 octane pump gas with pre-mix ??? That thing should have sounded like a Mack Truck !!!!
How bad did the piston crown look ? As far as you were into it, did you pull the pipe and look at the piston ? Are the sides scored or scuffed ? How did the intake side of the piston look while the reeds were off ?? How did the cylinder look while the head was off ??
Put some pre-mixed race gas in it and give it another try.

 

Capt, Everything looked fine because we hardly rode on ther new piston in the midrange...where the problem seems to be centered around. After examining the compression problem more in debth I realized that my dealer must have shaved the top of the cylinder upon re-bore. We are going to calculate the "exact" compression ratio and thicken up the base gasket to compensate. I will then run 98 to 100 octane fuel which is not too expensive but will enable me to keep around 12:1 compression rate and not worry about inferior pump gas and try to avoid detonation. Zorro looked inside the cylinder and thought the bore-job looked rather lousy (rough)but I know nothing about this so I leaft it up to him to speculate.

In the first post Zorro was reffering to the "looks" of the first piston. It had signs of detonation underneith and the top, exaust port side, was melted. The other parts were pretty much fine. At that point I did not have all that compession (about 138)so it was maybe also a jetting/timing problem. The timing will be checked also by the end of next week.

There are a lot more variables than I expected with bolt-on mods! [img]i/expressions/face-icon-small-happy.gif[/img]

 

I am glad you have found something. Once you get the compression back in check, I hope it's the last of it.

Rainman

 

There's always methanol... It keeps the parts clean too, the pistons won't even carbon up !!!

 

Can't wait till you get it roaring again Xplor!

Good Luck to you and Zorro on getting it back in proper working order!