Burnt piston on 150 black max

[gr82fish]

What would cause number 5 piston to burn a section off top of piston? I have been having acceleration problems but the motor was cruising at 5500rpm and 52mph when it started knocking. I tore off the heads and found this. Any ideas? I can rebuild the powerhead but I don't want it to happen again. Thanks all

 

[rodbolt]

Re: Burnt piston on 150 black max

normally that is caused by a lean fuel condition creating detonation which eats the piston crown. when you rebuild it go 2 sizes ricer on all the main jets .

 

[gr82fish]

Re: Burnt piston on 150 black max

Sounds logical but the other 5 cylinders look ok- plenty of oil. Could it be a trigger or stator problem because it also seems to have to build up rpm,s before it takes off? I can hear it picking up cylinders as it speeds up.(by that I mean it will suddenly kick in on one or two of the cylinders as though it was not firing on them before)-but it has good spark at idle on all 6 cylinders and did have 120 psi compression on all cyl,s before the piston burned. I have read alot of other posts, both here and on other forums of others having similar problems with these motors. Just trying to cover all the bases and I feel the problems are related.