Here's Bob's explanation from the Jett forum to one exasperated customer:

"Look at this first before you adjust anything else..... (this is something we have seen in the past a few times)

Did you get the engine hot along the way? A hot/lean run will cause the head bolts to come loose. Usually will blow a plug too.

Remove the muffler - look into the exhaust port. Make sure the sleeve port lines up proprely in the crankcase. They should center left to right (dont worry about up and down).

If you get a hot run the head bolts can/will come loose. If you change the glow plug with the bolts loose, the liner will rotate when you tighten the new glow plug in place. A mis-aligned sleeve will make the engine either not run, or will make it run VERY poorly.

If the sleeve is not lined up, loosen the head clamp bolts (head bolts) put the piston at the bottom of the stroke. Then use a glow plug wrench on the glow plug to turn the sleeve and head button so it lines up properly in the crankcase.

(if this happened, go over the fuel system again - chance are it went way lean in flight - maybe fuel foam - be sure the tank is padded and not touching the airframe)

..."

MJD