What kind of rpm's are you getting with various props and Jett FIRE 50?
 

I'm pretty sure I've burned up my Jett FIRE 50, probably from running it with too much prop at too little rpm. Don't know for sure but now it just will not unload in the air at all.

I'm sending it in for overhaul and this time I think I'll have them tune it for all out rpm and speed.

What kind of prop is best for maximum speed? What kind of rpm are you guys getting with the various props?

Jett props
 

I have Sport Jett 50 with a Jett Q40 pipe on my DD. I tached it at 19,000 peak on an APC 8.75x9.0W pylon prop. When I richened it up fly (I am not to going to take off at peak rpm), it would not quite get on pipe, so I dropped to an APC 8.75x.8.5NN. It really likes that prop. I haven't tached it but the way it hops in the pipe in the air, I am sure its around 19,000 rich on the ground.

Your engine may be getting tired, but you should try a little less prop before sending it, such as an APC 8.75x9.0, or 8.8x9.0. Performance Specialties stocks the 8.8 sizes for the Nelson Quickies. My local hobby shop orders the 8.75 sizes for me. I just got an 8.8x9.25, but I haven't tried it yet. I will probably cut it down a little.

The APC pylon props have the thick hubs. I would not trust APC sport props at these rpm's.

Paul

Props
 

Thanks Paul. Appreciate the info. I plan to talk to Dennis before I ship it off and see what he thinks. The only reason I haven't gone to the small props is because the engine is set up for bigger ones, but I think that is just a function of pipe length.

Just looking through the glow plug hole the piston is totally black so I'm pretty sure it's ruined. Probably best I get the motor rebuilt first then start playing with props.

Fuel
 

What kind of oil are you using in your fuel? If it castor oil or a castor/synthetic blend you very well may have varnish build up from the castor. This would cause the symptoms you describe.
Cleaning the piston skirt and sleeve bore with Demon Clean or the like (paint stripper works also) will remove the varnish and restore the power you are missing.

Castor
 

Ray,

Talked to Dennis before I shipped off the engine this morning. Asked about the castor issue and he said it shouldn't matter that much. They run their FAI engines on pure castor and it doesn't seem to be a problem. He thought maybe the head bolts had come loose but they were tight.

I just sent the thing back with the MAC's quiet pipe and told him to rebuild and retune as necessary to give me the fastest possible Diamond Dust with a Jett FIRE 50 and quiet pipe. I left the 9X10 flying prop on the engine and threw in a half-dozen others for him to play with. Should be interesting to see what I get back!