I recently did a rebuild on a conversion Ryobi 31cc. The carb that came on it was an 11mm Borg Warner carb that did not have a choke. The only carb I had available to replace it was a Walbro wt414 which is a 12mm carb. I also put an electronic ignition on it. When I tried to start it all I could get was for it to run for a few seconds then die. It seemed to be flooding out. Gas was dripping out of the back of the carb. This is with the choke off. I tried moving the sensor several times to advance the timing and I tried leaning out the carb untill they were almost closed. Same result. I finally concluded that either the carb was too big or something was wrong with it. I knew the engine ran with the other carb so I put it back on. Haven't had time to try it yet. Also, I know the ignition is good because I had it on another engine that ran fine. Mods I made to the engine was to put a Bowman ring on it and I opened up the back stop for the reed. Changed out the muffler to a gutted Ryobi muffler with a larger exhaust hole. The muffler had also been on another engine. What do yall think? Was the carb the problem? Also, after it would quit I would pull out the plug and it would be drowned in fuel. The engine is mounted inverted on a 4 star 120.

Thanks
Jim

Mine runs great with a CH ignition and Wt644 which is 12.75. Had to play with the timing sensor position awhile and make sure the piston is in the right BTDC. Did it run before you got it and is it broken in? Also make sure the pulse hole is open and working or make an external pulse line.

Yes it ran before I got it. I know the pulse hole was ok because it was drawing fuel.

Thanks
Jim

I am thinking there is something wrong with that carb. It had fuel dripping out of it when cranking. I have not run this carb on another engine. I put the borg warner carb back on it and will try it this evening and see what happens.

Jim

Ok, the carb had a problem. Last night the engine ran fairly well on the other carb. Another question though. I could not get it to idle as low as I would like. The top end ran like a bat out of **ll. Can I bring the idle down by adjusting the timing?

Jim

Jim, How much had that engine been used before you got it? It may not be broken in yet. What does the exhaust look like (black?) That would indicate the ring(s) are still breaking in and you won't get the idle right until that happens. I assume you have run out of adjustments on the needles? I don't mean to sound like an expert here. Just talking from recent experience.

The ring is fairly new. It is a Bowman ring that I had installed on another Ryobi but I chipped the piston on it after about two tanks of fuel. It is still fairly new. The exhaust is still a little wet I think. This was the first time the ring had run on this engine. So I am sure it still needs some breakin. The cylinder and block are not new. This engine as converted with the original piston ring before and flew for while. I dont know how long as I got the engine and airplane second or third or fourth hand. You suggest leave alone for while.


Jim

Yes, I would run it some more until the exhaust clears up some and then try the needles again. Alternate the rpm don't just let it run wide open. What prop are you turning? I used an 18x10 (wood) MA for break in.

OK, I will leave it alone for a while. Right now I have a 17x10 apc prop on it. Also what I will fly with. I did not have time to run it for long last night. I'll probably just break it in flying. Hope to Saturday.


Jim

Well I got the Ryobi in the air yesterday. Had it mounted on a 4 star 120 and an APC 17x10 prop. Way more power than needed for this airplane. Was a lot of fun. However, landings were a little hot because I never could get it to idle as low as needed. Also, It wanted to blubber all the time when not at wide open throttle. Did not do this on the ground. I leaned out the low end until the idle started getting worse. Do you guys think it would be helpful to retard the timing a bit more? I think it may be set a little less than 28 degrees BTC. I guess what I am really asking is how does the timing affect the engines running? It only blubbered while in the air. I could not hear it blubbering on the ground.

Thanks
Jim

Thinking of starting a new thread to discuss how timing affects engine performance and how to adjust to get best performance.

Feel free to experiment, but these little engines aren't very sensitive to timing. 28 degrees is very close to optimum for most.

If your regulator diaphragm on the carb is exposed to the oncoming airflow, it will often make the engine go rich in flight. In cowled installations, I solder a brass tube into the little hole on the diaphragm cover and route a hose from it to an area of non-pressurized/disturbed air, such as into the fuselage. On my non-cowled engines, I usually just solder a 90 degree piece of brass tubing into the cover, pointed anywhere away from the oncoming airstream.

This usually isn't a problem with the rear mounted carb on the Ryobi, but maybe it is somehow getting some pressurized air to it in flight.

AV8TOR

Also, when an engine won't idle down enough, check to see if the carb throttle butterfly has a hole in it. If so, they often won't idle down enough until you solder that hole shut.

My brother's Ryobi recently wouldn't idle down enough, and we discovered the throttle butterfly was worn. It was letting too much air in around the edges when closed. We replaced the butterfly and the engine now idles down just fine.

Your problem of going rich in the air however, is probably as I mentioned; air pressure on the regulator diaphragm. I've seen this happen many times.

AV8TOR

Thanks av8tor1977,

The problem with the idle is that the engine dies when I try to idle it down. As a matter of fact, right now, I use the throttle to kill the engine. By closing the throttle all the way I can kill the engine after a flight.

This engine has a Borg Warner carb on it. Not too familiar with the regulator hole on it but will take a look at it when I get home.

Jim

Got a few minutes to look at it last night. The regulator hole on the carb faces to the side and the motor is open to the slipstream. By that I mean that there is no cowl or side cheeks. Motor just sits out front so the regulator is 90 degrees to the slipstream with no obstructions. I also retarded the timing a little bit more. Found that the engine mount was loose so am going to pull the motor back off. Put a tube on the regulator air hole. Put some fuel line on it and run it into the fusalage. Sound like a good plan?

Jim