I use Enya #3 in many 4 stroke engines, because they work ( for a very long time. Also use the Merlin 2011in some for the same reason. The 2001 and 2002 "work" with OBG ,give good idle and allow leaner top end settings. Lately working with the Enya "4 Stroke" plug on the Saito twins. Will see how they work too.

To pick the best prop, the best thing is to find an engine test report and see where the peak hp line on the graph is. Pick a suitable prop to be just slightly slower than that rpm, as it will unload a bit in the air. It will likely be around 13,000 rpm in something like an FP. Running at full rpm will mot hurt most two strokes, they like it, unless they are too lean. Glad you got it going well. Just so you know, after blowing a few plugs, it is a good idea to check for white pieces of the element that stick to the piston top. This should be removed as it causes plugs to blow even further, much like bearings and plating flakes going through an engine. Your problem is unrelated to this however, and your plugs are likely just fine.

A good location that has many engine test review articles is Sceptre Flight out of Australia. It's website is:

sceptreflight.com Model Engine Tests

Also, a search in RC Groups thread:

RC Groups: Engine Manuals In PDF

may locate the manufacturer's engine manual for your engine.

A. J,, an engine, any engine, will be shown it's peak Torque point on a Dyno, and an engine's peak Torque point is where that engine is most efficient,

and know that different mufflers can alter an engine's powerband a bit,

the "older" OS link below should help with your FP engines, OS suggest the average 46 engine to have it's peak Torque around 12.500 to 13.000, and with that, the old school rule of thumb tells us that the smaller the engine the higher it's peak Torque point is on it's powerband, so this tells us that propping your 35 around 12.700 to 13.00 will get you in the ball park

https://www.osengines.com/faq/faq-q686.html

Jim

even if those engines with those props were in racing planes or speed trials planes with the correct plugs those props still would have been the wrong props

Jim

Hoo Boy! I'll second that! Who in his right mind would put a 9x4 on a .61? It's hard to believe someone did that.

CR

Some time back when I was having trouble with the Swanson Associates NOS Fireball Red Hot standard long plugs, for a song, I bought a grody looking Enya .09-III TV with unmuffled original exhaust baffle. It cleaned up nicely, found to be a very low time engine hardly broken in. The Enya 30 plug that came with it looked aged, but it fired up right away no problems, run fine since.

Reason why I mentioned Sceptre Flight engine tests is that the testers such as Peter Chinn have been intimate with the engine industry. Articles refer to various props tried, RPM's achieved, recommendations what sizes to stay away from as they take the engine outside its power band.

I did a test on my old worn out, beat up 40" wingspan foam Hobby Shack Cessna originally for a Cox .049 reedie. Peter made a recommendation not to use props smaller than 7x4, because it would run it beyond peak power, outside the power band. He was right. I used an APC 7x3 prop, it flew very .049 like. The engine develops its optimal power of 0.16 HP when unloaded to 14,500 RPM.

I put a wood 7x6 prop, now it moved out like it had a .09 on it, really became fun flying it.

Peter recommends selecting a prop that when run static, is around 1,000 RPM less than peak. Once in the air, the prop unloads with the forward motion of the plane, then approaches peak.

Also, the whole plane and engine is a system. Sometimes a lower pitched larger diameter prop is more optimal for thrust because of the airplane's wider cross sectional area than say a narrow profiled speed plane. Those old ignition .60's of the 1930's with the 1/4 horsepower output of a modern .15 glow was able to power those 7 foot (1 meter) wingspan cabin or pylon free flight airplanes spinning say a 14" - 16" prop. A modern .15 glow on such a plane would not work today, because there is not enough prop arc area past the fuselage spinning a 7" or 8" prop.

well he was an elder man, he just was not thinking, but he did swap out plugs, he was a great guy, he knew more about planes than I do, and I was very fond of him

Jim