Gave up finding any Nelson 36s

Fred, someone already massaged that engine. The MK VI is ABC engine if you weren't already aware. The crank is larger than the earlier MK engines and should be propped with a 8x6. APC makes the 7.8x6 which uses the D-1 hub. That's incredibly important D-1. DON'T run that engine on a Master Airscrew prop unless you desire a trip to the emergency room. Woodies will work, I would just use caution. Your safest bet is the APC and not the sport versions. The Tiger needle in that engine will take bladder pressure. If it doesn't work, the OS 1A R/C needle will work but you will have to do some bracket fabrication. Remove the needle and take out the restrictor reinsert the needle. That engine will run fine on 10% nitro but can easily handle 40%. Plugs shouldn't blow but if they do, see Jeff for head shims. That head had it's fins milled off so that tells me someone already did their homework on the engine. The head buttom should be the double bubble hemi. Use a high pressure bladder which is the thick wall. No restrictors within the tubing anywhere. You will probably see 112-116 mph flying a 500 sq foamie. Ken

That engine looks like one mean chunk of aluminum Fred! Very nice.

I see Fox .36X engines all the time on Ebay. Grabbed one for myself for $22.

Thanks for the information...now to relearn about prop hubs.....crap this stuff gets complicated for an old guy with CRS! grin

http://www.apcprop.com/v/index.html

Fred, another suggestion that works well is the mist for priming. Suck fuel into your syringe and and squirt it back into the container. Before running, have the bladder filled. Don't purge the bladder, there's no reason to do so with this engine. Point the venturi to the ground with the wing straight up and open the bladder. Adjust your needle so that fuel is dripping to the point of a steady stream.  Just before your ready to start it, lower the piston and prime with the misted fuel. Don't overprime the engine with raw fuel. It will want to run backwards. Rotate the prop clockwise bringing the piston up to TDC. Hook up battery and smack the prop backwards and it should fire right off. Wear a glove. and one other thing, wear a glove. Important tips, don't use a ni charger on this engine. This can be a violent engine. If that pops off not only can it knock your teeth out, it could severely injure the one holding the plane who may release it unwantedly. Get behind the prop as soon as it's running. If this means pinching the bladder line until you can get a needle setting, then do so.

Seeing that your attempting combat, one important factor that I would recommend would be hand placement on the plane itself. Not only for you, but for your launcher. This engine is LOUD and it becomes extremely difficult to communicate to your helper if need be. Wear ear & eye protection.  You should place high vis tape or high vis paint on your leading edge which is placed on a safe area away from the prop area. Seeing that many combat planes have their engines recessed into the leading edge, this is a helluva a lesson to learn if your not aware of it. Certainly an engine to be well respected. Ken

Sounds like one scary mean engine.

These engines (well any engine really) but these buggers can surprise the hell out of you until you help start and launch them a few times

Last year for combat camp they used OS 25s for practice on the big planes and surprisingly they do a good job of hauling them around a 60' circle...They taught me how to hold and launch them

Later at the bladder grabber I got my first experience with the Nelson36...serious loud and mean engine!
Most pilots had them well adjusted and the prime and start with one flip was normal for most...only guys having trouble were almost all from bad plug or low battery.. First day there Jeff brought his predator with a Fora on it and I launched....then he hooked up a Nelson powered plane to the lines and it was the first Nelson I held to launch.... surprising torque as it fires and burns the prime until bladder released......you get real about hand placement and prepare for the sudden pull forward as your pilot is directly in front and will get seriously injured if you don't pay attention!

The hardest thing I had to learn was how to tweek the needle as the pilot heading on a run for the handle and the engine sagged, sputtered or went too lean...My left hand was around the leading edge out side of prop circle and I had to release my right hand to tweek the needle or pinch the fuel line.....right elbow in front of leading edge was needed to hold back the plane
Most pilots don't want you even touching the trailing edge as the soft foam will take a set from your hard grip and screw up the inner or outer wing flight....some planes have a real spar to the tail feathers and you can hold that but many are just a wing and the elevator is ON the trailing edge

At the end of the contest Mel Lyne brought out a balsa plane with a Fox 36 Mark VI and let 80+ year old Bob Carver (of professional audio gear fame and biggest sponsor of the Bladder Grabber) fly a few tank fulls ....I was seriously impressed that Bob could have competed very well with the Fox and the older style airplane. I was also happy to know that the FOX timed and tuned correctly can be relatively competitive with the Nelsons

So thank you gents for the tips and advice

Think I will do my training this spring with full sized Fast combat with 25 on front. First, to preserve the hard to find fast engines, and also because I think I would have to seriously redesign my stooge to hold back that much forward power

Which OS 25's were they using?

FP's or FX's would be my guess.

Any of the ball bearing OS's. The late FSR's, the newer FX's. ASP's and Magnum XLS's which are clones to the OS. The FX is by choice due to it's weight which is essentially the same as the Nelson .36. Propped with a 8x5 and 52' lines, a 500 sq foamie will be at 100 mph.

While the FP does work well for us 75mph max flyers in the northeast, it doesn't have the power that the ball bearing versions have. Although, some of the competition here has made Nelson heads for the FP and done some porting mods which send the rpm's over the top compared to stock. Ken