I am looking for some assistance with a ryobi prob I am having. I have the conversion completed, and the engine running but... the problem I am having is a pulsation at WOT. It wont transition from idle to wide open cleanly unless it is fairly slow and it pulses at the top of the range. I can get it to run cleanly then the next transition, it starts pulsing again. I tore it down and re did the gaskets on the backplate (suspect) and carb base but not the carb itself. My thoughts were an air leak as turning the needles over 3/4 of a turn didnt effect the performance. Today after the rebuild the needles were making a difference, but it would pulsate. On a clean transition, it would turn a 18 x 8 @ 7900rpm. The carb that is on it now is a Walbro (dont have the # in front of me) but is bigger then what originally came on the engine. Any suggestions?

Thanks,
Warren

How far can you reduce the throttle before the rpm starts to drop, if you reduce the throttle opening, say 25% before the rpm starts to drop, the carb could be too big. I used the stock Zama carb off of a Ryobi 31 on my OPS 30 Maxi when running it on gasoline and it was perfect for it.

7900 rpm is very high for a Ryobi with a 18-8 prop. It would take a lot of modification for one to ever achieve that. A stock Ryobi turns a 18-8 about 6900 rpm.

Some Ryobi's had a coil with a rpm limiter in it that wouldn't let the engine run well beyond 7000.

Normally, the biggest effective carb venturi size for this engine would be 7/16" . The Standard carb from the factory is 5/16".

Just thinking

Jim

W8ye,
The actual RPM reading was 7895. I just came from the shop and checked the carb while I was there. The carb on it was a WT 215 (Walbro) with a 5/8 inch opening. It is a twin ring ryobi with a wacker muffler. I tore it down and polished the case as well as smoothed out the transfer ports. But as was mentioned, I am suspect that the problem is to big a carb. I didnt modify the reed at all. I have the original carb that was on it and it is a Zama P171ya with a 7/16 opening on the outer rim and a 9/16 opening at the butterfly. I guess I will go back to that carb for future tests when I get the plane repaired.

Warren

The important size of the carb is the venturi area which is in the middle of the carb. It sounds like your carb may be a 1/2" one? On the Walbro's, you can look in the inlet to the carb and there is a little number. This is the size of the venturi in 64ths. For example, a 32 would mean that you have a 1/2" venturi. A 28 would mean that you have a 7/16" venture. The other dimensions vary from model to model. For example, The size of the throttle butterfly is larger on the original Ryobi carb than on the Homelite 25. However, both carbs have a 5/16" (20) venturi.

A Ryobi with increased good porting and higher compression ratio should be able to handle a (32) carb but a (28) would be big enough.

Added: .... I looked up the number WT215 and it must be a obsolete number? But I did find that WA/WT carbs with a inlet of 3/4" and a throttle bore of 5/8" can have either 7/16" (28) or 1/2" (32) venturi's. Carbs with a 3/4" choke bore and a 9/16" throttle bore can be either a 5/16" (20) or a 3/8" (24) carb. All the WT and WA carbs have a 3/4" choke bore. Take your pick. But the (20) or (24) carbs should not be too big for your engine.

Enjoy,

Jim