Love this site-Found a second hobbie/passion and reasons to use my shop, lathe ect...
Question-My first conversion a Ryobi 31, short shaft, running a #28 carb (11.1) i believe, a Scimitar 18x8 prop and 40:1 mix. I'm getting 6600 even for RPM-Is this about right or is this motor tired. Like to see 7200-7500 with this prop without alot of mods. I'll will try opening the exhaust.

Thats about what I was getting with mine (6700 with a 18x8). It flew a 14lb plane very spirited. I had a cooling problem with mine with the cowl on. Had to increase the oil to 28:1. But mine was a 10 year old already wore out engine.
Edwin

This engine didn't seam to bad, very clean. Is it possible to see 7000+ with an 18x8. I have a Fuji 32 with an 18x10 thats well into the 7's.

I have heard of people doing a small amount of grinding on the exhaust port, mind you - I mean a very small amount. And some put different carbs on with a bigger throat and loose the stock muffler. I seem to recall someone getting around 7700 with these upgrads but that was quite awhile back. Somebody else might know better. Performance isnt this engines strong suite. Its like I've heard a US41 described, its a good airplane truck engine.<g> I was never able to hand start mine. I used a regular sullivan dynatron. The thing to remember is that the crank counter balance is three rivited stamped plates. Just my opinion, not really ment for very high rpm's. But up to 8000 or so should be ok. Mine was more than acceptable in the plane I used. Want to do a ryobi twin someday.
Edwin

I will do what i can on the two i have, but after reading many posts, I'll agree big winged trainers that can carry a load. I have a lead on some echo engines and homelites, I'll play with them.

My brother's Ryobi has an 11mm carb, gutted and larger outlet stock muffler, and electronic ignition. No other mods. It turns an APC 18 x 6 prop at 7700.

The stock carb is very small, so there is room for improvement there, and gutting and opening the outlet on the exhaust (muffler) helps a lot.

The first thing to look at if you are going to get inside the engine is the ring. Every used motor I ever took apart needed a new ring. Optimum ring gap is around .003", which is a very tiny gap. It is not uncommon to find a ring gap of .060" or more on a used engine. Frank Bowman rings are the best and almost always add power, even if the stock ring wasn't too badly worn.

The second thing to look at is the exhaust timing. Some Ryobis have a very short exhaust timing, sometimes around 120 degrees. Raise the top of the exhaust port until you get about 150 degrees. (No more.) Don't forget to lightly bevel the edge of the port after raising it, so as to not damage the ring and/or piston.

AV8TOR

BTW, welcome to the club. You sound like me when I first got into this "conversion engine thing".

Have fun,
AV8TOR

Thats the info i was looking for-thank-you. I gutted the exhaust last night, no easy task with that can!
and put another tube in. I have and 11.1 carb in so if this don't get it out comes the grinder on the port. I have several so don't mind a little experimenting. Do you have a web site for frank or a number i'll pick up a few sets of rings from him.
Thank Guy!

Av8tor-Question, why are most exhausts using two outlets at 7/16, can you use one at 7/8. And i allways thought the exit or stinger should be roughly the same or just slightly larger than the intake hole for back pressure????????

Have you opened your reed valve stop be carefull it does'nt hit your crank pin.
adrian

Yes-I opened and left 1/8" from crank pin. I will test at lunch today with that and opened muffler. Starting point was 6600 with a #28 carb, balance stock.

frenchie79, Franks email is: [email protected]. He should have Riobi rings in stock.

Thanks Old timer, I'll drop him a e-mail and order a couple sets. Thank-you

Heres the results:
18x8 Scimitar Prop, #28 Carb-11mm, 40 to 1 Huski oil, Started at 6600 rpm
Cut extra hole in muffler-6720
Gutted the exhaust with two outlets/ bend reed valve stop-6840
Changed to Amsoil 100 to 1 mixed at 80 to 1-6930

Thats going to be it. The bowman ring should help, but without advancing the timing i don't think she will see 7200 to 7500 with that prop.

That doesn't make any sense that it lost power when you opened the exhaust. Did you re-optimize the high speed mixture after the exhaust mod?

Yours could be one of those with short exhaust timing and it just doesn't want to rev higher. I would throw a degree wheel on it and see what the exhaust timing is, though really the first thing is to check the ring...

AV8TOR

I'm sorry i entered the wrong starting point. The engine has improved with ever tweak, i think I'm tapped out for the easy stuff (great fun). I'll throw the rings in and check again. Maybe this prop is dragging it down compared to other posts i've read indicating higher rpms??? Any other ideas that don't require EI. How about pulling the jug gasket??

Have any of you Ryobi fans tried just one bowman ring and leave the other ring out. May be less drag and more RPM??? Seems like one good Bowman ring should do it. That would be 1/2 the price for rings. Best Regards Capt,n

I have three Ryobis-none with dual rings. I will check the ring gap and hoping the bomans get me into the 7K area. Be a good engine for something. Looking at the Giant big stick (ARF) just for a test plane. Having a hard time with 250 bucks for a simple Arf plane. If i get enough engines done I'll cough-it never fails.

I have a Giant Big Stik. It is a fun plane and a good test bed.

Good idea Captain John:

Frank Bowman says for the most power, use just one of his rings, even if the engine was a two ring engine to begin with. He says for the longest life, use two rings. Lifespan usually isn't a problem with these engines....

AV8TOR

Av8tor-That is a neat engine, do you have a closer shot, looks like you did something to the exhaust-Variable perhaps???

It is a twin I made out of two Echo 23.6 cc engines. There is more info about them in the BME Twin thread.

AV8TOR

That is fantastic-very nice job. Gas/glow-bet the sound is great and AMPLE power.

YEP! All of the above!

The red hose going to the original intake port, and the needle valve on the firewall are for the impulse pump type smoke system. Looks pretty cool with smoke coming out of the four exhaust tubes...

Thanks,
AV8TOR

YES YES THAT TWIN IS EXTREME CONVERSION. BACK TO MORE MUNDANE-I SAW ANOTHER SITE QUOTE POWER GAIN BY PLUGGING ONE OF TWO 7/16 IN. PIPES COMING FROM A GUTTED .31 RYOBI MUFF. TOO LITTLE BACK PRESSURE AT THE WRONG TIME AND ALL THE GAS GOES OUT THE PIPE(S) I RECCON.

I asked that question and no response. I thought the exhaust should be somewhat close to the intake for correct pressure. I know tuned pipes will be very close to this?????????