Help diagnose toasted piston

[Snowmark]

burnin

i notice pic 4,looking at the crank...looks bone dry....swappin carbs is a great idea....that much variation in the plugs is definitely an indicator of trouble

 

[Arndtie]

Does your sled have a temp sensor in the expansion chamber? It is for ECT exhaust controlled timing. Check it with an ohmmeter if it reads 0 or infinite that is your problem. The pistons look like a timing problem. My 440 s/p had the same problem, finally figured it out after 2nd melt down!

 

[specialk6r]

Well yesterday I worked on the sled a bit. First I made something of a runout guage with a zip-tie to make sure the clutch was spinning true, and it looked perfect. Then I pulled the carbs apart and synchronized them and swapped almost every component from one side to the other. I also set both the fuel mixture and pilot screws to 1.5 turns out per a members recomendation. Then I swapped the reed assemblies and intake boots and installed them with new homemade gaskets. I also cut up some new gaskets for the powervalves. I wired the oil pump wide open and started it up. The pump is working since it fumigated the neighborhood, but I wasn't worried about that anyway since I premixed 50-1.

Well both of the plugs got real wet after idling for a few minutes, but the PTO side was very noticably warmer when I put my hand on the domes. I putted around the parking lot for about 30 seconds, blipping the throttle just enough to engage the clutch. The plugs looked just the same as before - the MAG side whitish and wet, and the PTO black and dry.

I believe I'm down to timing. Does that seem plausible? Should I buy a timing gun or take it to the stealership?

 

[specialk6r]

ttt

 

[spring snow hero]

have you pressure tested the pto side yet? if it checks good, get a degree wheel on it and measure TDC on both pistons.......need to be 180 out.

 

[76FOMOCO]

after all the conditions you have described my money is on the out of phase crank. When the guy you got the sled blew a belt how long after this did he ride it from when you got it?
just a idea pull the carbs take of the bows and pull the needle and seat out of the carb with the lean side and plug the other side and blow threw the fuel inlet circuit and check for debris.