Need Help Tuning a Carb
 

I am toying around with several Ryobi 31CC motors. Through all the great info here, I was able to convert them and actually flew one on my Great Planes Giant Supersportster. The plane handled very well but the power was lacking. With a 18X8 prop, I was only turning around 6300 RPMs. My goal was to turn at least 7000 RPMs.
After reading all the threads in the Conversion Forum concerning Ryobi's. I ordered several Frank Bowman rings, By the way, Frank is a first class person. He was very patient with me and answered all my questions about the rings and their installation. Next I got several of the 11.1 mm walbros with the high & low needles and primer. The engine on my test stand turned a 16x8 prop at 7800 RPMs with both mods. A gain of almost 800 RPMs. Here is what I am up against. With all new gaskets and the carb tuned for max RPMs and good throttle response. I can't get the idle below 3000 RPMs and the engine slowly dies if left at and idle. I have checked for air leaks and all looks good. The engine transition to full RPMs instantly. Is this a common problem when going to a bigger carb or am I not doing something right. I adj the high speed for max RPMs and the go 1 click rich. Then I hold the idle up a little and adj the low speed for the best idle and transition.
The motor with Frank's ring that is on the plane will idle at 2200 but it has the stock 7.9 mm carb and will only swing a 18x8 prop 6700. I did gain about 400 RPMs with just the ring change only. I am going to try a APC 18x6W and want to use the 11.1 mm carb if I can. The 11.1 carbs I have are WT-600 and WT-610. I also have 2 others that have 34 in the venturi. The 11.1's have 28. I am also running the stock mag ign with a lightened flywheel. I would like to use the motor on the test stand with the larger carb as it seems a lot stronger but the idle issue prevents it. I have not run this motor with an 18 inch prop yet. Will a larger prop allow the motor to idle lower? Any help will be greatly appreciated. Sorry for the long post but I wanted to include as much info as I could as to what I have done so far. Thanks again. Pat

RE: Need Help Tuning a Carb
 

Idle does get better with the 18" props.

Zinger props don't do much for me. Use something else.

The plastic APC's will idle lower than a Xoar. Wood props are lighter and offer quicker gain in rpm on acceleration but they idle higher.

I have a Ryobi with a 5/16" carb and it runs just under 7000 with the old Dynathrust 18 X 8 prop. There is nothing about it that is not stock. The original muffler had a 3/4" outlet.

I wouldn't be running a Ryobi over 7500 or so because of the stamped steel connecting rod

Maybe your reed valve is seeping a little?

RE: Need Help Tuning a Carb
 

I will definately check the reed assembly. I haven't tried the larger carb on the motor in the plane as it is a pain to swap engines, I was able to change the ring without taking the motor out off the plane. I will try the 18 inch prop on the test motor and see what the idle does. Thank for the reply. Pat

RE: Need Help Tuning a Carb
 

Check me on this, but I think the WT-610 is a 13.7mm venturi, which is too large for a Ryobi.

If the engine just won't go below 3000 rpms no matter what you do, it probably has an air leak somewhere. The way you describe it running for a bit at idle and then slowing down and quitting sounds like a too rich idle.

AV8TOR

RE: Need Help Tuning a Carb
 

You are correct on the WT-610. I looked and it has 32 in the venturi which is 32/64th or 1/2 or a little over 13mm. I have not tried this carb yet. Only the WT-600 which has 28 stamped on the venturi. The Ryobi in the plane idles good at 2300 with a stock carb and 18 inch prop. I guess I'll try a WT-600 on it as I know it will idle ok. I have 7 of these motors and will try another reed assembly on the test motor and see if that stops the engine from dying at idle. If I can keep this engine from dying at idle, the 18 inch prop may get the idle RPMs to a useable level. Thanks for you reply. Pat P.S. Bye the way, I talked to Aero Nut last night on the phone and he is building me a Charly Boy. I believe I read somewhere where you had one.

RE: Need Help Tuning a Carb
 

Look over your different reeds.

Some assemblies are made better than others and shroud the reed less.

In addition, some Ryobi's have a magneto coil that doesn't seem to want to run over 7000 rpm. So if you encounter this, swap out the coil.

I doubt if a carb bigger than the "28" will run very well on a ryobi?

I'm thinking of swaping the "20" carb on my Ryobi for a "24" as I have a WT-20 with a high speed nozzle check valve.

RE: Need Help Tuning a Carb
 

The 4 motors that I have taken apart all have the same reed assembly. They are the less shrouded type that the stop is "V' shaped. I set the gap to 1/8 inch.

RE: Need Help Tuning a Carb
 

Good, I see you have already been there and done that.

RE: Need Help Tuning a Carb
 

Tomorrow I will try an APC 18x6W on the test motor and see what RPMs and idle I get. That set-up would be a Frank Bowman ring, APC 18 prop, WT-600 (11.1mm) carb. I am still using the stock flywheel that I have not lightened yet. This set-up should give me the top RPMs I want(around 7000). I'll keep at it untill I get the idle corrected. If not, I have a new DLE30 that I can put on the Giant Super Sportster and use the Ryobi's on lighter planes. I am trying to get away from glow except for a couple of planes. I have a 40 size Super Sportster with a GMS 47 that really rips it up. I will keep it along with a couple of others but from now on all new planes will likely be gas.

RE: Need Help Tuning a Carb
 

If you use an accellator pump carb it might let you lean the idle and still have good transition.

RE: Need Help Tuning a Carb
 

I really appreciated all the responces given. Here is where I am at now. Swapped the 16x8 prop for an 18x8 wooden prop. Carried the engine to the field for testing this AM. I figured that the neighbors have heard it enough. LOL. Idle slowed to below 2300 with the larger prop. Yea!, but engine still died after about 30 seconds at idle. Made very minute adjustments to the low speed needle to richen it and "Walla" she idled like she should. Transition was also good.I got almost 6900 RPMs with the 18X8 prop on the test stand with only about 20 minutes running time on the new ring. I will swap it out with the Ryobi in the plane that srill has the stock carb on it. I'll wind up with a net gain of between 700 and 800 RPMs with the same prop. I will see how this will fly my Giant Super Sportster. Thanks again for helping me with my problem. Pat

RE: Need Help Tuning a Carb
 

Have you done any thing with the exhaust pipe to help with breathing.

Adrian.

RE: Need Help Tuning a Carb
 

I have the Pitts style muffler from Wackerengines. I should get a few more RPMs when the new ring seats.

RE: Need Help Tuning a Carb
 

I found my Ryobis to die suddenly and unexpectantly when idling at speeds below 2000 rpm, even with the heavy props like APC18x8. On magneto AND on CDI ignitions. No big deal, but it seems to be something in that engine that does not want to have sustained low rpm.
Some ignitions have a 7000 rpm limit as well. So if your engine does not want to go higher in rpm than 7000, fit a larger prop to bring it in the 6500 range.