Super Jet Melted front (mag) piston - still trying to diagnose, help me out

[smoofers]

Make a piston stop around top center, mark both stops on either the flywheel or coupler, split the difference and call it zero degrees. Mark the case/flywheel or coupler 21 degrees early and check it with a timing light. Most aftermarket flywheels have more spark lead than stock. I saw a three cylinder with a new top end do the same thing before it ever got on plane, the cause was 35 degrees spark advance. Always verify timing.

So Kevbo, getting ready to verify timing on my motor. My static timing should be 21 degrees advanced, correct?

 

[JetManiac]

That is a 62t stator in your pics. Is the flywheel a 62t also?

 

[smoofers]

That is a 62t stator in your pics. Is the flywheel a 62t also?

Yes it is. 62t stator and 62t flywheel (RAD)

 

[smoofers]

Just checked the timing with a timing light. Just so happens the RAD flywheel has timing marks at 0-30 in 5 degree increments. I found top dead center with a dail indicator on the mag piston, then marked a line at zero degrees on the case (in line with 0 deg mark on the flywheel). I'll post a picture in a bit of how I set it up.

At 1640rpm (was using a PET tach), the line looked to be exactly in the middle between 20 and 25 degrees. I would say that is pretty close to what it should be at. Opinions?

Edit: Picture of my setup.
I used a black and silver sharpie to highlight the marks on the flywheel as well as writing the numbers on.

 

[Freakrider]

Imo front piston lacks enough piston wash equals lean...that's your problem...on a side note XScream has us running no internal carb filters... just filters after the tank...front crank seal was working fine per pic....insufficient high rpm fuel delivery my guess.

 

[smoofers]

Just realized I never replied to this thread for closure.

I ended up pressure testing the carbs (thanks SQUAREJOEL) and the front carb was leaking all around the fuel pump (rectangular plate). The front carb was never supplying the proper amount of fuel at full throttle. No combination of Oring/gasket (from new kits) would make it seal. I replaced the plate and BAM, held pressure the first try. I assume the plate either warped or corroded.

No problems since then.

Edit: The plate that was leaking was the rectangular "dummy" fuel pump plate for the slave carb. Back when I melted the piston, I rebuilt the motor a couple weeks later and found the leak when rebuilding my carbs. Did a leakdown on the carbs and the front wouldn't hold pressure, you could watch the gauge needle steadily fall. Using soapy water, I found that the plate was leaking all around the edges. I tried 2 different new orings and gaskets and at least 2 or more used ones (hoping a swollen oring might work better) to no avail. Got a used plate from a buddy that had one, slapped it on with a new oring and it sealed first try. The ski has been running great ever since.

 

[88kawi5fiddy]

that sucks.... do we all need to true the plates with some 600 grit and plate glass?

 

[smoofers]

Nah, I would just leak test your carbs after every rebuild. It would probably be easier to buy a replacement plate than to try and true yours. Also, if I remember correctly, the plate has little ridges cast in to pinch the gasket. You might be hurting yourself by flattening those out.

 

[RBM37]

That piston looks gnarly

 

[smoofers]

That piston looks gnarly

Yeah, its been one my "conversation starter" desk pieces at work for the last 2 years.