Does anyone know of a replacement/better carb for the Ryobi 26cc 4 stroke? I'd like to get as much out of this little guy as I can to try and overcome the extra weight the 4 strokes carry around. It seems to run ok with the stock carb (Walbro WYL) and an aluminium muffler from Peter Faith. Just hoping to get a little more out of it if possible. I put a large bore carb on the 31cc two stroke conversion I did previously with decent results so I'm hoping there might be something available for the 4 stroke as well.

If anyone has any other suggestions beyond the carb or muffler that might also help I'd sure like to hear them too- Thanks!

DougT and I have be talking about this off and on for a bit now. Seems that the ryobi 4-stroke needs a special carb because of the way the vacum works the carb. Its been said that no other carb other than the one that comes with it will work right. I havent got mine running yet so I cant test that theory but I havent heard anyone else that has tried a different carb on it yet either. Untill I can verify it one way or another for myself I still believe a carb change would do the motor good. There might be a simple work-around to get any carb to work on the motor out there, I just got to get testing as soon as I can get a mount for it. Piper

MrPcub and rcflyer.

I think you could get about any carb to work but would take some modification. I've been thinking about and working at this problem for about a year, off and on, and have come up with three solutions.

1. Leave the stock 9mm alum body WYL and bore out the main jet. I also took the needle sheath out and widened the narrow part of the taper ever so slightly to richen up the transition. I havent found a way to get the needle to move with out ruining the barrel assy.

2. Put on some sort of one-way check valve, like the stock one, but with a higher opening pressure to let some crankcase pressure build up before the valve opens to vent. This way you could drill/tap the crankcase and use + pressure pulses like two strokes. You would either have to build a custom carb spacer/pressure line to case or drill/solder in a pressure tap into the carb pump cover.

3. Use any two stroke carb and put in a diaphram return spring. I've tried this a couple times and can't get it to work as well as the stock pump setup. I tried to swap pumps but they are a different design from the two stroker's carb body. Also, the stock WYL has a flat spot milled into it to locate the spring and keep it perpendicular to the diaphram. I haven't tried to mill a flat spot in any other carb. I couldn't seem to find a spring with the same rate as the stock one. I also wasn't sure if it stayed upright while assembling the carb/pump.

Check out my last post on "ryobi 4-strokes, who's running them and what do you think?" thread. I rotated the carb barrel and gained 100 rpm. Also, turn the carb so the barrel linkage is facing up. Worth another 1000 on mine. Also, I posted jetting sizes and what effect they had.

I've read posts on RCU claiming people were running 22" props and getting over 5000 rpm. I don't believe it. With CH Ignition, dialed in jetting and a low restriction muffler I'm getting 5700 rpm with an APC 18-8W.

Oh, I flew my 14# Nosen Champ for 45+ minutes mostly 80%+ throttle on an OJ juice bottle(12 or 16oz????). Pretty fuel efficient.

Let us all know if you try anything and how it turns out. I'm still pondering an opposed twin. 52cc!!!

Doug

Which version of the motor do you have? I have one of the first Generation 1 motors and it turns a Pro Zinger 18x8 at 6400rpm with the stock ignition, carb and muffler.

Made a simple mount from aluminum and bolted on a ST 3000 carb. Hooked up a Kline pressure regulator. No pump problems and adjustable needles. Perry pumps has gas/smoke oil pumps and big bore ST carbs too.

Flipflop,

I have the gen 2, plastic oil pan model, I think from a 925 trimmer. I ordered a gen 1 carb, WT456, and haven't tried it yet. It is a 7.5mm where mine is a 9mm. But it does have adjustable high/low needles. I'll try it soon.

Doug

tkg, can you post a pic of that? I'd like to get mine going and that may just be the answer!

Seems like if a WT 456 carb would work, so would any other Walbro..The shindaiwa 4 stroke I just converted uses a WYL carb, no adjustable high speed needle.....There were no extra springs in the WYL on the Shindaiwa...It worked OK, but the Shindaiwa is like a YS, with oil in the fuel and another reed in the crankcase..There are no crankcase vents, so there is a good pulse for the carb....I got almost 7000 rpm with a Mejzlik 18-6 and about 6300 with an 18-8...A 20-5 PK turned about 5400..
I made an adapter from 3/8 G10 for a WA167 to get an adjustable high speed needle, it worked out OK...
A WYK90 is 10.5mm, has a high speed needle, costs about $43 from Walbro...Didn't get one to try, the owner will be doing some more tests next week when he gets it back...
the Shindaiwa is PRICEY..[8D]Not at all like the $79.95 Harbor Freight Ryobi..

I tried various 2 cycle Walbro carbs on my Ryobi 4c to no avail. It would idle fine, nut when you would run it up it would starve and die. Just didn't seem to be able to pump the fuel. I even route a groove for the pulse port into the mounting block.

Must be more pulse pressure in the Shindaiwa...Try weakening the small spring under the inlet needle so it takes almost no pressure to open it...They work from atmospheric pressure on the diaphragm, and a really weak spring sometimes works better..It normally takes anyhwhere from 10 to 15 or more pounds to unseat the needle, but if you can make it weaker it might work better.....You need only enough pressure to keep it from leaking when the engine is not running..We set the pressure at about 5 lbs on our methanol fuel race engines....Weaker springs are available from Walbro, or you can carefully clip the spring a little at a time...

Sounds like a way to go. I'll give that a try. I only have about 25 or so new carbs here!