I am on my third rebuild in less than 70 hours.

I put it back together after having the heads machined for a o ring, I needed better head gasket seal. I have been getting blow by with factory and cooper gaskets ( heads and block were flat). I put her together and check compression right at 220 per side, I added a ridged carb mount that they use on motor cycles instead of the rubber one.

I also went back to a factory key for the fly wheel ,no advance at all.

It started easier and idled better than it did straight stock,or after stage 1 and stage 3 mods. It had a stronger bottom end with the straight key.

You just can't push these motors that hard, and have them hold up, I am going back to a stock cam, pistons .


It ran great for a 20x60 ( 26.5mph with the hard blind in place and a 175 lb buddy), no blow by, no misfiring, no problem we were turning 4600 rpm with the new prop. I ran from Brenton sound launch ,through hopedale lagoon down dudenheffer's canal to pick up my buddy, ran toward Reggio, she shut down like it had water in the fuel, started back up ran some more then shut down again, I headed in. I did a leak down test this morning found a problem with either rings or head gasket. I pulled the head, the outer ring of the piston was gone, that head is pot-marked badly, and one of the billet rods was damaged. Minimal damage to the other head or piston, no damage to the block.

It had leaned out real bad, I don't know yet if it was a vacuum leak. I have been running a 167 main jet (it was set up and checked with a fuel air ratio gage). The only change was from bps cross over to bps duels. Something must have happened with the carb or intake.It was a little rich,
before the changes.

JD

damn... you sound like me. if it weren't for bad luck, we'd have no luck at all. sorry to hear

Screw internal mods!!!! I dont have the guts for it anymore.

That sucks man.

fuck this mod shit

Not sure if this will help but when racing snowmobiles we found the rigid mounts vibrated so much it would shake the carb causing the fuel to get air bubbles to the point it would cause the motor to go lean. same thing would happen it would pit the edges of the piston and cause the rings to lose the seal and then no compression. With you putting on the rigid mount might have lead to some of the problems. this took forever to figure out while racing but once we went to the soft mounts the motor live the whole season no problems. I know my Prodrive shakes enough to cause the same issues. Just my 2 cents

Sorry to hear of your problems