All new 54mm Pistons are not created equal is all I can think of. But I rebuild my top end once again with a Koso 54 Piston/rings vs the Chinese junk previously installed. So im tuning the air/fuel mixture to idle and wondering why its starts but then dies. So pull plug and the gap is closed!!! Im thinkking its running wayyy lean so I dial the air fuel mix 2 turns out instead of 1.5 then fire it up again. Stays on for a whole 5 secs and wont start. Pull Plug and same thing, closed gap. Pull head off and sure enough, there is a clear mark on top of the new piston where its hitting the plug!!!! Maybe the Chinese rings/piston is better than Koso?? Anyone have any input? LT???

 

Something has obviously changed with your deck hieght..Are you running the same thickness of head and base gaskets as you were before?..If so it almost has to be the piston..

 

I'm with yeller.
Do you have a "P" plug ie: bp7hs? If so get the b7hs.
I'd try a nice BR8HIX. [img]i/expressions/face-icon-small-smile.gif[/img]

 

Same gasket and it is new. I'll check the plug but im sure its the piston. Although I did switch head to a highcompression head which I've used in the past with no issues. I wish I could have kept the high comp head cause I was getting 150lb comp vs stock head at 122lb. dont matter cause It running now and gonna be put up for sale!!