1978 75 HP Chrysler piston replacement

[charakel]

Back to the drawing board. 2nd piston replacement within a year. 1978 75 HP Chrysler piston replacement. See pic. What is causing this??

 

[Nordin]

That looks like predetonation.

Are the carbs cleaned?
How are the air/fuel mixture screws set?
What is the timing advance at WOT?

Air/fuel screw should be 1 1/4-1 1/2 out from seated. NOT less then 1 turn out!

Timing advance 30 dgr BTDC.

 

[jerryjerry05]

When rebuilding did you just do the one piston or did you disassemble the whole thing?
​The fuel recirc system was it cleaned?

Timing.
Wrong carb setting.
Overheating, poor water circulation.
Sucking air.
Fuel pump not sealing on block.
Bad reeds.
A few things that can make it go bad.

 

[charakel]

Yes that is correct, I just replaced the middle piston last summer. I did not clean the carbs. I am thinking I should change the fuel lines and primer bulb, it may be sucking air. Is there a good spot for piston purchases.

 

[jerryjerry05]

I buy Wiseco pistons.
​They need no special tools to reassemble.

You do need their wrist pin and other recommended parts.