Does anyone know what the stock compression ratio of a ryobi is and what it can or has been increased to?

Chris

See post #294 in this thread for the CR of the later twin runner T port cylinder with the two ring piston

diceco

While it's getting a little OT i'll add my experiences with octane and ethanol:

Ethanol is ok apart from the fact that it tends to harden the fuel pump diaphragm in the carb. However, if you replace it with the teflon (brownish colour) item in a walbro gasket kit, you should not have any problems.

In my part of the world, the higher octane fuels are not JUST higher octane, they also have a higher energy rating meaning higher octane for me IS worth it. I see a significant improvement in power when using premium fuel.

Stick to getting your fuel fresh from a station that has high turnover. Fuel is not meant to last more than a month or so and most of the 'volatiles' evaporate off quickly. For my (rc) boat, i only buy,mix and use on the day. I do not store fuel at all anymore. Once I had some old fuel but unmixed in a sealed container for 2 months. When i used that, the boat would just not run right - fresh fuel and it was back up to pace.

with my combination I am running more compression than the newer motors I believe, but not sure how the fuel will effect it till I try some tests of different fuels. I am running a WALBRO WT 29A carb right now I am not sure of its size. Is there a cahart or a web site with specifics on Walbro carbs by part #? I also have a Walbro 610 I want to try it has a 34 stamped in the venturi.

Chris

Not by PN, but by series, try here:

http://web.archive.org/web/200501161...ro/family2.asp

The number stamped on the venturi is the size of the carb in 64ths of an inch - i.e 32/64ths = 1/2"

Yes I remember reading that a while back about the numbers in the venturi, my WT610 is somewhere around .53125" just over 1/2"

WT-610
13.49mm
0.531102362"
It has a #34 cast into the inlet.

This is a little on the large size for the Ryobi

However it does have a power check valve and a accelerator pump

The WT-610 carb is obsolete and no longer available

The WT-29 has a 28 cast into the venturi and is the proper size for a Ryobi
It is also obsolete but has the high speed check valve and a accelerator pump which is good

That is great info. Thanks so much! I got the carbs from a chain saw shop near by that sells them for 5 bucks a piece. They are used but in good condition and he has a big box of assorted walbro carbs. It is really handy when you want to tinker. I actually bought my first Ryobi from him as well. It was already partially converted, with a mount and a prop hub but still running a magneto.

Thanks again for the carb info
Chris

That's a real treasure trove box of carbs.

You must know how to spot the high speed check valve spud in the venturi and the accelerator pump on the side of the case by the throttle lever?

Even though the carbs above are obsolete - repair parts are still available

The original Walbro and Zama carbs on the Ryobi, Ryan, and Lawnboy 31's was a "20" size

They run a lot better with a "24" and a "28" is about as big as you want to go.

I like the WA-167 carb for it is a "28" and has the high speed check valve but no accelerator pump. It was the Carb for the Zenoah G23 just before they came out with the G26.

Without a lot of porting and running high rpm, a carb bigger than a "28" doesn't run well. On the Ryobi, you start running it at 8000 and the stamped steel rod breaks.

what kind od cdi system is needed? its a 31cc engine but will a 26cc cdi electronic ignition work?

w8ye I got these carbs by chance, how do you tell if a carb has the high speed check valve or accelerator pump circuitry?

chris

The HS check valve is a little brass spud sticking up out of the venturi right where the high speed fuel nozzle should be.

The accelerator pump can be spotted by looking at the throttle arm shaft. There will appear to be a device riding against a flat place on the throttle shaft.


There's another device on some Walbro's called a governor that is a brass spud (3) near the throttle arm(2). This is undesireable and is usually removed and the hole filled with a lead plug.

If you can fit the ignition timing sensor and the plug cap fits a plug that will work in your engine, the ignition will work

Anyone have an idea how long a 12 oz fuel tank would run?

It depends on your flying style and how you have the needles set.

It should be big enough for a normal flight.

I bought a new short block on ebay last week and it came and looks awesome. I also bought a cylinder, it looks great but is smaller bore than a 31cc ryobi. It is about .060 smaller? what is this would that be a 28cc are pistons available for this size motor? also I have heard of a 33cc unit does anyone have any info on that as well?

chris

what is a cheap way to put an electronic ignition on a ryobi 31cc. Mine has oone now but I am considering doing another engine and possibly making some of the parts I need?

there are several places to get the RC Exl ignitions for like $60, if you have your own lathe make your own prop hubs that are tapered, this is the cleanest way to do it. a cheaper way with the mag ignition parts is to cut the center out of the flywheel with a hole saw and put the magnet in what's left.

moparcolt ,
If you're interested, I'm having a machine shop make up timing adapters for short shaft engines (5/16 shaft) only. These will have a 1.375" finished diameter, and will be a direct replacement for a flywheel. They will come with a 1/8" diameter rare earth magnet installed and will have an internal taper to match the crankshaft taper. It will be retained by the prop adapter you already have and rotation will be prevented from any rotation after installation by installing with red Stud and Bearing Mount Loctite or JB Weld applied to the taper when tightening the prop adapter. These timing adapters will sell for $21.90 including shipping and should be available in about three weeks. Complete instructions will accompany each adapter.

I needed about 6, so I took a chance and am having more made.

Let me know if you are interested.

After running my long shaft Ryobi 31 in my Rascal 110 quite a bit in 2009......I decided I was quite happy with the way the ZAMA carb performed. The engine ran smooth as silk all year and produced some respectable power considering the engine is all stock. I earlier thought I might swap out the carb with a Warlbro, but I think I will leave well enough alone on that engine. I have another short shaft Ryobi project I am still working on, and this Ryobi has the Warlbro carb. So be interesting to compare the two. This engine is either going in a large profile plane or a 120 size Super Sportster I am scratch building.

I think I posted a photo months ago of my Rascal with the Ryobi when I was rebuilding the Plane, but here is a photo of the Plane as I flew it all 2009. One sweet thing about using the Ryobi in this particular plane is that the engine is entirely hidden under the cowl. I use the plane to mainly drop parachutist, but would like to rig up video on the plane this year. This plane is a real heavy lifter and don't seem to mind haulin a payload.

Looks like a nice combo. I have a Ryobi on a 76" wingspan Tiger Moth, and also like the fact that the engine is entirely cowled. A Ryobi might work out nice on a 120/140 size Mustang as well....

AV8TOR