I am planning on doing a Ryobi 31 engine conversion and have done a reasonable amount of research as far as the major players in supplying conversion kits and parts. What I haven't been able to find is what the difference is between the engine model numbers. So what is the difference, physically and performance wise between a 700R, 720R, 725R and whatever else is available. Also, what models have the dual piston rings and what is the advantage of it.

Thanks, Sedleniek

As far as I know, all ryobi trimmers uses the same engine, basically. in ones you would find the long shaft version and in others the short shaft version, but the power in both seems to be equal. I vote for buying the cheapest one, and long or short shaft, the supplyers have spare parts for either version.

Don´t know if there is any special model with twin rings.

tato Lazo.

FWIW Ryobi with clutch ( you can rotate cutting w/o turning engine over) will yeild a long shaft engine; without clutch will be a short shaft engine. I would imagine that new ones sold in CA will have only a single needle for carb adjustment. You will probably end up putting larger carb on it anyway...
I believe the long shaft when converted is actually shorter in OAL ( firewall to prop) due to the components you have to use.

Hi converts!
There is one big difference that I've noticed on the Ryobi engines sold for california and the ones sold outside, if you pay attention to the cylinder head the exhaust port has a retarded timing( this means that the port is lower thant the regular one) thus giving less power I have several ryobis that I've purchased in Yuma, AZ. that perform just about the same but when I bougth one here in California I couldn't reach the same performance as the others beside it was missfiring all the time, so I changed the carb, no change, the plug, no change, the coil, no change, the coil and flywheel, no change, so I was going to disassemble the engine to check if the reed valve was bad that when I took of the muffler I've noticed that the exhaust port looked funny so I then compared it to my other engines ports and guess what? they where different, I then went on and traded cylinder heads and my performance was even better than the other engines by 100 rpm's. so now I will have to travel to Yuma AZ.
every time I need an engine to convert It is only180 miles from where I live besides I will enjoy a leisure drive!!!

aero nut

Rumor here is TJ has a Home Depot.... If so do they stock weedies and chainsaws and how do the prices compare to say HD San Diego? Cabo is due to have a HD by year end.

Now if a CA resident had a friend in another state that would forward a package to CA Ordering from Harbor Freight would be an option.....

yeha your are right but it never ocurred to me to go on and check for their inventory on weedies or blowers, I will soon go and check on their "gas goodies" and see what they've got, thanks for the pointer.
AERO NUT