What went wrong?

[skinak]

So I put a .035 shaved head on my shee with stock pistions and a dune port. I started out with 330 mains and 30 pilots and it was running super lean. Then worked my way up to 370 mains and 35 started turning a nice brown, then made a few more passes and came to a screaching stop. got home from the dunes and pulled it apart and found that I broke the crap out of the bottom of the pistons. What the went wrong? The plugs were looking great the all the sudden nothing. I had BR8ES plugs. any words of advice?

 

Thanks

Nick

[spurdy]

So I put a .035 shaved head on my shee with stock pistions and a dune port. I started out with 330 mains and 30 pilots and it was running super lean. Then worked my way up to 370 mains and 35 started turning a nice brown, then made a few more passes and came to a screaching stop. got home from the dunes and pulled it apart and found that I broke the crap out of the bottom of the pistons. What the went wrong? The plugs were looking great the all the sudden nothing. I had BR8ES plugs. any words of advice?

 

Thanks

Nick

 

How was the piston broken? Intake side, exhaust side? Bottom under the crown? I'd guess most likely too large of a piston clearance and you broke the skirt.

 

 

SP

[Zwiser]

Your powerband must have bent and hit the piston skirts. its quite common once you go over 100 mph

[erickson483]

Did you ever do a squish test? Compression test? Leakdown test? All of these should be done before you start running a new bike or new rebuild.

[spurdy]

Did you ever do a squish test? Compression test? Leakdown test? All of these should be done before you start running a new bike or new rebuild.

 

 

He never said it was a new bike or fresh rebuild. Only the he changed the head. At which point he should have checked the squish.

 

SP

[erickson483]

A bad air leak would help explain the huge main jet and still being lean.

[BigRed350x]

If the skirts broke off it was probably excessive piston to cylinder-wall clearance or you had some detonation issues and the pistons couldn't handle it and broke.

[vulvafan537240]

35 pilot sounds huge. Are these stock carbs?

[locogato11283]

Must have been an air leak somewhere. Those are huge jets.

[skinak]

these are stock carbs, I don't think I have an air leak cause I had 310 mains before head change and I was running rich. I haven't touched the internals minus getting the cylinders ported, since I was a moron and bought it new in 05. I went from 30 to 35 pilots because that is all the local shops had.

[skinak]

only the left piston is damaged.. intake side is broke from the middle of the windows down and about the same height on the exhaust skirt.. exhaust side has got a v pattern where it broke at

[erickson483]

Can you post pics?

[skinak]

here are the pics

[vulvafan537240]

I do a leakdown test anytime I mess with the head. 27.5 is all you should need on the pilots. 30 was probably too big and 35 is way too big.

[Jereme6655]

correct me if im wrong here guys.....but i was pretty sure you didn't have to rejet when you change out for more compression. I get that its always good to ceck your jetting whenever you cange something.....even if its just to make sure..... however to go up 6 sizes on mains and to go up 2 on the pilot.....makes me think there was an air leak.