I have a twin ring Ryobi 31 without the compression relief slots. Should be pretty tight. It's a brand new engine.

I'm using 40:1 chainsaw oil in it with a 3-blade Master Airscrew 16-8 prop. Getting right at 6000RPM--maybe 6200RPM. The tach fluctuates a bit.

I had a Top FLite 18-10 on it and got about 5200RPM from it.

It has a Zama carb. Stock carb--couldn't tell ya what size it is.

What kind of RPM should I expect out of it?

Does anyone know the biggest carb I can put on it? I used to know a Walbro number--but I'm getting old. Seamed like it was a WT438 or a WT 343--something like that. It has the same opening as the hole in the backplate of the engine.

Do you think it'll get stronger as it gets some time on it?

Thanks

Are you running itr with the stock muffler? you'll get more RPMS with an open muffler, the other thing is you can open the venturi by scraping the aluminum with an exacto or if you arecarefull enough to do it with a dremmel just make sure you don't damage the bronze fitting that's coming out on the venturi, you want to enlarge the venturi to about 3/8" diameter, Also is your carb twin needle or single needle? single needle carbs don't work well for R/C applications, the other thing you'll need to do ist take the back cover plate and lift the reed valve stop plate just to where a 1/8" drill or allen wrench can pass in between the stop plate and the reed valve, with all these changes you should be able to spin a 18X6W APC prop (top choice for the Ryobi) at about 7600- 7800 RPM considering that you are several feet above sea level, I am spining mine at 8300 but I am at sea level

It's a twin needle carb.

Muffler is from Wacker Engines. It's nothing more than an exhaust diverter. Very loud.

I have already bent the reed stop out to allow for more fuel flow.

Oh man, I don't see this thing turning an 18-6 at 7800RPM.[X(] It might break in a bit, but I can't see it coming on that strong, even with a couple gallons through it.

I want a bigger Walbro carb. This is my first Zama carb. My third Ryobi engine. My other Ryobis used Walbro carbs. Thats why I'm thinking it's the carb. Either the carb totally sucks, or the engine just needs some more time on it. I've only got 1 tank of fuel (12oz) through it so far.

Does ANYONE know what the number of the Walbro carb is--that I can bolt on here and it's got the same size venturi as the backplate hole?

I have a Walbro HD series carb that will bolt up. But, it's for a 45--65cc engine. Wouldn't work on this engine.

WT-9 works as our universal weedie carb. It has a choke too. 11.13mm

The other thing you'll need to check is exhaust duration timing, some Ryobis I have encountered have a very low exhaust duration timing as low as 120 degrees where the regular ryobi has it's timing at about 140 degrees, my latest engine a 31CC McCulloch (Ryobi Hybrid) had the timing at 120 degrees and had to cut the exhaust port to bring up to 140 degrees, check and see what you have on yours

aero nut: about how many thousantds to you cut off exhaust port to change from 120 to 140 degrees? Do you cut the top of port or bottom? Thanks Capt,n

I cut the top portion of the port, that's to let the exhaust gas come out sooner, I cut roughly about 1/16" from the top, already used my engine and its working great with the glow fuel/gasoline mix.

RCPilot,
That sounds low. Mine gets 6400rpm on a TF 18x8. And I was told that was a tad low but in the acceptable range. Was a stock carb (not zama). I ran klotz oil at 28:1. Had trouble with over heating in the cowl at 40:1.
Edwin

I think it's low too. This is my third Ryobi. It's a new engine from Harbor Freight. My other engines were old and used, but they ran better.

It's spitting out black gunk right now. Still breaking in the rings. I'm going to put a smaller prop on it (16-10 or 16-8) and let it spin up to 7500RPM. Hopefully, that will fly the plane. I'm hoping that if I let it spin up a bit, the rings will seat sooner and the engine will loosen up a bit. It seams pretty low on compression for a twin ring without any compression relief slots in the cylinder. I'm attributing that to the rings being new and not fully seated yet. So, I guess I want the compression to tighten up and the rest of it to loosen up.

I'm also looking for a new carb. The Zama carb has not got a choke plate. VERY hard to start. I can't get my finger in there to choke it--I got big hands. My friend has skinnier fingers, and he has to stick his little pincky finger in there and choke it for me.

I guess if it doesn't come around after a couple gallons of fuel--I'll get the die grinder and the degree wheel out and start checking and hacking.

Glue half of a small rubber ball to a popsicle stick. Makes a great "little pincky"...

AV8TOR

Yours does sound a little down on power, give it some time, maybe it will come around. The last one I did turned an 18x8 Bambula at 7190rpm the first time it ever ran with the stock muffler. This was with the stock Walbro twin needle carb off my first single ring Ryobi, the latter Ryobis with the Zama carbs seemed to be more difficult to get the proper settings on. I've tried the larger G-23 carb on this motor and there was only about a 50rpm difference (plus, depending on what mount you are using, the G-23 carb can be a pain to mount)

I got 6200 RPM today with a 16-10. Engine sounded MUCH better.

So far--only about 1/2 gallon of fuel through it. I talked to a local flyer who does lots of conversions. He said not to worry about it and just fly it as much as possible. He said it would easily come up 1000RPM after 4 or 5 gallons.

I'm kinda thinking the same thing now. It puking out black goo all over the plane. The rings are still seating. I usually mix my oil 40:1, but I'm running it about 35:1 or 38:1 right now. 3.75oz in a gallon.

I have come up with a way to choke the engine. A popsicle stick with a piece of rubber glued on. Just stick it down in there and turn the prop.

I'm still wanting to put a different carb on it. Something with a choke, and a bigger bore. This one has got to be at least 1/8" or 5/32" smaller bore than the hole in the backplate.

I'll just keep flying it. It'll come around eventually. I think maybe it just needs some more break in time.

I have two Ryobi 31s. One has the decompression slots and turns a MAS Classic 16x8 at 8100 rpm. The other does not have the slots and turns the same prop at 8400. Both engines use the stock carb with Wackerengine mufflers.

Mike

I think you will find that a 16-10 is simply too much prop. A 16-10 is 25% more load than a 16-8. Your engine calculates to turn at least 7700 RPM with a 16-8 prop. Since it would more likely be in the power band it might turn as much as 7900 RPM. Why don’t you try the smaller prop?

Bill