I have a Ryobi 31cc single ring that I cannot get to tune out. It will idle all day and run at around half with little problem. When I advance above half throttle it dies. I thought it was leaning out, and as I richen the high speed it gets better but does not tune out before the needle loosens. I started with both needles at 1.5 turns out. The low speed is fine around 2 turns. I had it running well for about a ΒΌ of a tank and I stopped to fuel and problem was right back. I have tried 2 plugs, no help. This is with a Walbro carb, I also have a Zama that it seems to do worse with. Operating temps are around 300-325. I am new to tuning and am lost. My fuel tank is a basic nitro setup with the pressure line venting to the atmosphere, could this be the problem, is this right??

Sounds like you are too lean on the high end, even with the NV opened up. This can be caused by constricted fuel flow somewhere in the system. Check the easy things first. Unhook the line at the carburetor and connect a few inches of tubing. hold this tubing below the level of the tank and make sure that the fuel siphons freely from the tank. I have had similar symptoms when the carb filter is plugged up. there is a mesh screen inside the Walbro carb right where the fuel flows in. This can get clogged with a layer of lint-like crud. Also the pump diaphragm or regulator diaphragm can get weak also resulting in less than enough fuel flow. I know you have already tried two carbs, but perhaps each of them has a problem. The temp of 300-325 seems too high, also a symptom of too lean. Finally, air leaks in the case or around the carb block can let air in also causing a lean run. Air leaks are usually visible upon close visual inspection.

Thanks for your quick response and good ideas. The fuel does flow unrestricted when disconnected and even pours threw the carb depending on where the tank is mounted. I did check the filter screen in the walbro and found it clean. At the same time I checked the diaphragm and it looked good. As far as air leaks, I don’t think this is the problem, I have remounted the carb many times and I have a good gasket. I think you are on the right track with fuel delivery, I am not too clear on weather or not my tank is set up properly. I am including some pics, do you see anything wrong.

This is confusing to me: "and even pours threw the carb ...". A properly working Walbro should not let any fuel flow through it unless the engine is running. Even of the tank is elevated 5 feet above the carb. There is a regulator in the carb that stops the flow of fuel completely unless there is a low pressure in the venturi. please clarify this issue...perhaps we are on to something.

Yes, when the fuel tank is above the carb the fuel seem to build up and flood the carb. Engine is hard to start then too.

I have a Ryobi 31cc single ring that I cannot get to tune out.

When I advance above half throttle it dies.
I had this problem on a Zenoah G-23. Turned out I was trying to use a too-large prop. When the engine hits it's mazimum torque to turn the prop, the RPMs won't go any higher.

This is with a Walbro carb
The carb could be messed up. These little things are fairly complex, and great care needs to be taken if you disassemble one. The butterfly orientation is very impoortant, as are the filter screens and jets. They are very sensivite to dirt and dust. Your workplace must be absolutely clean.

My fuel tank is a basic nitro setup with the pressure line venting to the atmosphere, could this be the problem, is this right??
Basic nittro? Are you running gasoline or glow fuel in it? The vent should be open to the atmosphere, and the klunk should be no closer than 3/8" to the back wall of the tank.

Dr.1

I believe all walbro carbs have a built-in regulator. if you raise the tank above the carb with engine off and fuel flows into the carb, then this is wrong. the regulator is stuck open. take the carb apart and look at the regulator assembly. it is a lever (like a teeter-totter) whereby one end of the lever pulls a small needle out of a hole. there is a spring that forces the needle back in the hole. this lever as actuated by a diaphragm that is sucked down by venturi suction in the throat of the carb. With the motor off, the spring should force the needle into the hole, sealing off the fuel flow.

When I took the carb apart, I did see the regulator and it seemed to be fine. Maybe I am misdiagnosing the symptom; I will have to look at it closer. As far as the prop, I am using an 18-8. I thought this was on the big side, maybe this is the problem. What should I use on this being a single ring? Thanks for the help!!

Had a 14-8 sitting around and tried it. It ran pretty good with in, I think this was the problem. The 14-8 is smaller than I hoped to run, what is a good size. Sound like you found the problem Dr1Driver.

You should be able to run an 18-8 on a 31 cc engine. The Zenoah G-26 uses a 16-8 to 18-8 per the manual.

thats what I thought, but this is a single ring. Think i might tyr a 18-4 or a 16-6

I have 2 Ryobi's, an 18x8 is what this engine likes best. It is advised not to exceed 8000 RPM due to the stamped connecting rod. You should swing an 18x8 with no problem.