ORIGINAL: diceco
ORIGINAL: madman75
Pretty nice numbers. I only get 7360 rpm with a Top Flight 18X6 Power Point prop. Only mod is a larger bore carb. I'm using a Walbro WT-324 which is 11.1mm. I did open up the inside of the stock muffler some and put a 1/2" outlet on it. I've never had the cylinder off it so I don't know how the ports are in it. I would say it is one of the newer style low emission type engines so I may not get much more from it. What is the best gap for the spark plug when using EI? I've got mine about .020" gap. Any thoughts how to get a little more power out of this thing. I may need to get a new ring(s) from Frank Bowman. I've heard this will help as it has stock ring(s). I don't know if it has one or two rings.
My motor is the newer style with the integral fan shroud, which I've cut off completely. It has the bifurcated (two runners per side) transfer ports and an exhaust port with no bar, and also a 2 ring piston. If you take off the muffler and rotate the engine you can see if the piston has two or one ring and also if the exhaust port has a vertical bar separating the port. The two ring pistons are good. The ring end gaps are very small (I haven't actually measured it) and seals very well. If you then take out the spark plug and shine a light into the cylinder and rotate the crank until the piston is at the bottom of it's stroke you can see the transfer ports and determine if there are one or two on each side. The only complaint I have with the bifurcated transfer ports is the large blunt forward facing edge at the opening to the ports. I made substantial modification to this area in attempt to smooth the flow going into the transfer ports from the crank case. Unfortunately I did not get back to back performance data for that mod. See posts #134 and #145.
My muffler is stock except for a 1/2" piece of EMT electrical metal conduit welded into the original opening.
As for spark plug gap I'm not even sure what it is but .020" sounds about right. I don't think the gap is super critical.
Although I haven't tried a 11.1mm bore carb, mine is 12.7mm, I bet it's fine. av8tor1977 is using a 11.1mm carb to good effect.
If, in fact, you have the same set up as me, I would try the exhaust porting mod next, if you're up to it! The effect on my engine of the exhaust port mod was significant and if you want more power I'd try that first.
If you've got a different version of the Ryobi motor I have no experience and couldn't say what would be the best mod to try first. combatpilot has done a lot of work with the older style motor and might be able to give some input. If you read all the posts in this thread you might be able to glean some info on what mods work best and which ones are not a big pay off.
diceco
I believe mine is the same as yours. I had the integral fan shroud which I cut off also. I looked in the exhaust and it looks like 2 rings. It doesn't have the vertical bar in the exhaust port. This engine has compression out the butt. I noticed that mine will sometimes quit if I go WOT then down to idle quickly. I've had it idling around 1860 to 1950 rpm. The idle is exactly consistent. If I keep the idle around 2000 rpm, all seems fine. I might tear down the carb. and check it out as I got it from Ebay and just bolted it on and ran it.
Did you remove the base gasket or just leave it in? I'm not real keen on messing with the exhaust port. I might screw it up and I don't have another cylinder if I booger it up.