I know that the general concensus is to break these gas engines in while flying them. I've even suggested it to people.

But, I got a problem with this one. It's a Ryobi 31cc on C&H ignition. It's in a 4*120 and the engine is NOT cowled. It's just hanging out in the breeze, like a Stick type airplane.

It was a new engine when I installed it. As of today, it's got just shy of 3/4 gallon through it. It's not turning the RPM I need to fly this plane very well. The plane is sluggish, and it's not much fun to fly. I've calculated my fuel tank size and figured out it's going to take 120 flights to put 5 gallons through this engine. Thats a LOT of sluggish flying. []

Am I REALLY going to ruin the engine if I strap it down in the driveway and hook it up to a 2 gallon jug? I'm running 40:1 mix in it.

I don't know if it needs to heat cycle to break in right. Run it for a tank and then shut it down for 1/2 hour? Or can I just hook the fuel line up to a 2 gallon jug and let 'er rip till shes dry? Should I do this at all? I know they are cheap engines, but I'd really rather not cook it in the driveway if you guys REALLY don't think it's a good idea. It's just--120 flights with an engine that barely flies the plane is a LOT of tooling around flat and level.

I'm getting 6200RPM with a 17-8 right now. It should be turning 7000RPM + after it's broke in.

Thanks

I am not a Ryobi expert but do you really think it will pick up 800rpm during the break-in? Thats a whole lot of HP. On such a big props I think 100-200rpm gain is more realistic after the break-in. Modern gas engines are very powerfull right out of the box.

I once had a 50cc chainsaw engine and it has a lot less torque than the gas engines made for airplanes. But according to our chainsaw service center it could turn up to 12-13000rpm without getting damaged.
Maybe this industrial type engine you have needs a smaller prop to perform better? have you tried 16x6 or 16x8. The muffler is also very important for high performance. The less restrictive the muffler the more rpm twostrokes will turn.

You may be right. I talked to Ralph, and he doesn't think it will pick up that much power after break in either.

The muffler is more of an exhaust divertor. It's wide open and loud as a drunken trailer-trash momma.

It just seams weird that I'm not getting any power out of this thing. Most guys are running an 18-8 or 18-6 on these things and getting a respectable 700RPM +/- Here I am with a standard Zinger 17-8 and it's turning 6200RPM. []

I guess it might be time to yank the base gasket and start nibbling on it with a dremel.[:@] It's a twin ring engine without the dreaded compression relief slots. So, I'd think it was one of the more powerful Ryobi engines. I guess I should slap the degree wheel back on it and start grinding. I've checked the duration before, but didn't write the numbers down.

I've got another jug and piston on a working weedie. I don't care how powerful that thing is. I may swap this cylinder and piston out with that one and see if I can gain a few RPM.

On Ryobis, I saw quite a lot of different jugs. The new ones might not even be suitable for our planes any more due to internal compression limiting channels in the cylinder wall. Also, newer ignitions are limited electronically to 7000 rpm. No fun at all, and you may just have one of those.

NO.

None of that applies to this engine. It's got C&H ignition. I'm pretty sure those don't cut out at 7000RPM. I already stated that this jug doesn't have the compression relief slots.

It's a twin ring engine with fixed timing C&H ignition system. Not synchrospark. The exhaust is one of Peter Faiths and it wide open. Loud as hell. The jug is good. No compression relief slots. It's all new engine. Not a used up engine from the junk pile at the local small engine shop. It's brand new.

I would try a smaller prop for now. At least you'll be able to fly the plane.

Rcpilot--- I would check the ignition timing first and go from there. If you have 3/4 of a gallon thru that engine you will probably not see any appreciable increase in rpm running more fuel.
I am sure you have adjusted the needles, right?

Needles are tweaked for best running at this altitude. I've got excellent transition, and it's running about 200RPM off peak. I'm going to check ignition timing this weekend. Seam to have misplaced my degree wheel...............AGAIN.[:@]

I'm going to doublecheck the ignition timing first and makes sure thats right. I though I had it, but the hose clamp may have slipped when I tightened it. Then, I'm going to start messing with carbs. I've only got a 20/64ths on it now. Going to try a couple different 24/64th carbs this weekend.

I just want to get it running as good as it will get, then I'm going to start changing things one at a time. Clean up the case/transfer ports mating surfaces to make sure it's as smooth as possible right there. Remove base gasket. I've already tweaked the reed stop as far as I dare. I'm afraid if I go any further, it will hit the crank pin. I'll check the exhaust duration, but I don't really have the right tools or the knowledge to start grinding on it if the numbers are way off.

I might swap a different jug and piston on it. That will be a last resort. I've got 3 or 4 other units lying around. I did make a call to Frank Bowman today, and I'm definetly getting a set of rings from him. That should reduce compression blow-by a lot.

I'll get it figured out. After talking to Ralph today, and also reading what Flyer95 said--I seriously doubt if this thing is going to pick up 800-1000RPM after a couple more gallons of fuel. For some reason this particular Ryobi is just giving me fits. Not ready to call it a turd just yet. It's probably something I did when I put it together. End user screw-up. I'll just keep plugging. I've got too much time invested in building this airplane and engine to just give up and quit flying it.

Thanks for the help.

Sometimes out of a frustrating situation comes enlightenment. I must have heard that somewhere because I know that is not how my brain usually works Have fun experimenting, I always do.

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Swap out the reed valve block for a fresh one. Just a hunch

Welcome to our altitude! Like you've heard (and told others) before, tweak the needles again and try a smaller prop. Sometimes it just take patiences. [sm=wink.gif] Is the carb screen clean? My 41cc gave me fits this spring, too rich , too lean and all I did was breath on the needles. Found a tiny little piece of junk in the intake screen. Good luck!

Isn't that carb kind of small for that engine, 20/64th's ? I would have thought you'd need at least a "24" or a "28".

You might want to take a look at my Ryobi sidesteps at http://home.wanadoo.nl/pereivers/ryobimods.htm

The standard carb is too small, and lots of extra hp can be had by working on the intake side.

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You really did examine this engine in some depth. I am impressed. Thanks for sharing your results.