Milled head

[Sandking]

I had a head milled for a pump gas bike by a sponsor. The bike has t6s, k&n filter with airbox no lid, +4 timing, and stock reads, 300 main 27.5 pilot. Compression ended up at 150. The bike blew a hole through the left side piston and broke the skirt a few hundred yards from camp on the first ride. Question is 150 too high for this set up.

[sleeper06]

No my guess is airleak because your a tad rich on jetting . You guys need to start getting in th habit of leakdown before tear down , it takes away the what ifs and guessing . If it passed a leak then u move on to mechanical failure

[sleeper06]

Post a pick of piston hole was it a clean blowtorch hole or was there deto around it

[Sandking]

This wasn't my bike I just sent the head out for milling. I did a leak down test before tearing it apart and the intakes on both sides leaked pretty good.

[Sandking]

Is there a way to tell the difference between a lean pop vs another type this guy's bike was put together by a yamaha mechanic and I've been fixing things since.

[sheerider11]

Yeah that's a super lean condition

[Sandking]

Yeah that's a super lean condition

Thanks, I really don't want to send the head back for 10 lbs of compression.

[n2otoofast4u]

I'm just a dummy, but there had to have been some signs that shit was whack! To do that with a few hundred yards of camp, there had to have been some funny business going on.

[Sandking]

I'm just a dummy, but there had to have been some signs that shit was whack! To do that with a few hundred yards of camp, there had to have been some funny business going on.

His bike always had a deep sound to it from the first time it came out which I told him wasn't right, he originally had different mains in each carb, and one of the carb caps was sealed with silicone and a set screw due to stripped threads. He was also fouling plugs. I replaced his carbs and jetted the bike then when I put a timing plate on it I found a post on the stator came loose which was fixed and tested. Sucks but the guy who completely rebuilt the motor recently screwed it all up. And I found the crank seals were in backwards. The bikes in pieces in my garage now waiting on cylinders.

[sheerider11]

That thing must of run away, or he thought he was wfo.

A bike that lean will make zero power and a whole lot of noise

[Sandking]

That thing must of run away, or he thought he was wfo.

A bike that lean will make zero power and a whole lot of noise

He said it ran pretty well then he herd it pop and immediately turned it off.

[sleeper06]

They always run great rite before they pop