I just finished a Ryobi 31cc conversion using JAG Engines parts (excellent kit). I fired it up for the first time yesterday and it ran great; surprisingly smooth, great acceleration and a nice smooth idle. I am wondering though about the top end. Using a Zinger 18x10 I am getting 6100 rpm with the JAG muffler and stock carb. Anyone else tried this setup? What are other people getting with the same engine? I realize this prop is a bit big for this engine so I was actually quite impressed but should I be expecting more?

Brian

you are slightly over propped . reduce the pitch to 6 . mine will turn almost 8000 rpm with a 18x6zinger. for the money they are awsome little engines. most guys run either a 16x8 or 18x 6 props

I built mine using a Walbro WT644 and am using Ignition. So far, it has turned a Master Airscrew 18X10 wood prop at 7900. I will be using a 20x8 MA, wood Schimitar prop, to fly I think. The muffler makes a big difference. I am using one from Wacker engines. Check out my 1/4 scale Loening build at the RCSB web site, forum under "other designers".

johnF: What type of ignition are you using? Also did you use the stock flywheel? Thanks Capt,n

Captin, Don't need the flywheel. I am using a CH Ignition. Cost $128. with prop hub and sensor.

Fireman,
If you use a stock 7mm carb, your rpm will be lower with a oversize prop. Also you can bend the reed stop plate out some to get more intake flow. Be careful that it is clear of the crankpin and rod. If the engine is new, it will get better as you run it in.

Dave

Also you can use an APC 18x6W prop and get better rpm's, the carb's ventury needs to be open if you are using stock carb (to .400" diameter)

fireman
check your exhaust duration, I have one engine that was low at 120 degrees duration it too ran in the 6000 rpm range opened it up to 150 and its the best ryobi I have now .
john f
those are some respectable numbers from a ryobi , Iwould be interested in your20x10 prop numbers when you get them . have you done anything else to the engine other than ignition?

flyjoe, no other mods to the engine that I know of. It started as a Best Engines conversion or referbished. I replaced the carb and removed and replaced the magnito with the CH Ignition. Also replaced the stock muffler with one from Wacker engines. The muffler makes a big difference as I said above. During my break in one of the screw in exhaust pipes fell out of the muffler and the RPM's jump'd up a bunch and so did the noise of course. This tells me that using the right muffler has a big effect on the RPM's. The exhaust tubes are 1/2" diameter. It will be interesting to see how it does with a 20x8 MA, wood, Schimitar prop. and I'll post the results.

I look forward to it , I use wacker parts also , mine will turn a 18x6 at 7800 rpm consistently but I have also ported and polished the exhaust , opened it up to 150 degrees , ch ignition with syncro , I still need a 11 mm carb ,I beleive this is what is holding my power back .

flyjoe, The Walbro Wt644 I am using has a venturi of 12.7 and bore of 15.85. Have no idea what kind of fuel consumption I'll get when it's in the air yet. Hope to be able to fly at 1/2 throttle.

How bad is the viabration on the Ryobi engines without flywheel? The exhaust coming loose may be caused by vibes. It would help to use no gasket on exhaust. Capt,n

mine seems to be no different with or without the flywheel . exhaust tubes tend to come out unless they get either jb welded , welded or low temp brazing roded in , the vibration and heat expansion contribute to this

My first conversion was with Jag parts. I got 6700rpm using a zinger 18x8, stock carb. In a 14lb modified bandito grande it had great performance, very spirited. "sigh" I loved that plane. It died being shreaded through power lines. The next conv will get a wacker carb I bought awhile back.
Edwin

The pipes are now JB Welded in. I expected they would come lose. Engine is actually pretty smooth now that it has had some run time on it.

john where did you get your carb from? was it expensive?

I picked up a brand new Walbro WT499 carb at a swap meet the other day. Paid $15 for it so I couldn't pass it up. I don't know what the venturi size is but it is a good bit bigger than the stock one. I'm gonna try it today and I will post numbers.

About the smoothness, I was very surprised at how smooth this engine is with the flywheel. I expected it to be a shaker but it is smoother than my US 41.

Brian

Got the carb. on Ebay and it was brand new. Paid about $20. for it.

I got some tests on the Ryobi with the new carb the other day. It did spin up a little faster but not the jump I expected. It ran about 6500 rpm with the same prop. I kept the 18x10 on it because I already had a baseline. Although the engine didn't turn up as high as I thought it should, I don't think I have the needles tuned right. Could someone help me out a little? Not sure I understand how this is supposed to be done since I have never had to set up a gas carb from the start.

Thanks,
Brian

Fireman,
You won't realize the full advantage of the larger carb as long as your eng is over proped.

Dave

DaveWallace and flyjoe are correct. Engine changes are not likely to be observed until the engine is geared (proped) to run in the power band or closer to the sweet spot. A Ryobi engine will turn 8100/8200 as a string trimmer.

Bill

Fireman, you went completely in the wrong direction with your carb.

If you want to spin a big prop on a Ryobi, then you need a smaller carb, not bigger. Think--RPM = velocity = fuel draw

If you wanted to run a little bitty prop and spin it at crazy high RPM then you would want the bigger carb.

The guys are right. You are overpropped. You need to accept it and drop down in pitch if you ever want to get any power out of that Ryobi.

Ok, I hear you. I have to ask, though, that if what you are saying is true how could JohnF's rpm numbers be possible? He stated 7800 rpm with an 18x10 prop. It stands to reason that a smaller prop will turn higher rpm but that doesn't necessarily mean more thrust. According to the theories presented to me here, there is no way JohnF's claims could be true. I don't have any way to measure thrust so all I have to go on is rpm. I am not trying to tell anyone they are wrong but the posts I am seeing are contradictory. I have a couple of 16x8's. Would these be about right or are these a little too light? I could get an 18x6 or 18x8.

Thanks,
Brian

Most likely JohnF has a tack that is reading high! John, if you get a chance have the engine checked with another tackometer. Those RPMs (7800) out of a stock 32cc Ryobi do seem high on a 18x10 Master airscrew. Thanks Capt,n

My mildly modified Ryobi turns a 16 x 8 APC prop at 7500 rpms, and an 18 x 6 at about 7300. It has very little time on it, so I'm hoping for more when it breaks in more. I don't believe it will ever turn an 18 x 10 at 7800. (I wish)

I use the TNC tach, and I verified it with an (full size) airplane tachometer. They agreed to within one (1) rpm. I have a couple of other tachs that I consider junk because of unreliable readings...

AV8TOR