What's wrong with my Ryobi trimmers???

[Coyote machine]

YES! To whomever has been running last year's fuel it is guaranteed to be useless and very bad for your engine. Ethanol gas at 10% is hygroscopic- which means as it breaks down and phase separates it does NOT recombine and its octane is lost and it absorbs atmospheric water like a thirsty sponge!
It is without a doubt the worst thing to happen to any internal combustion engine, and it adversely effects boat and mower, trimmer, chainsaw motors because they are mostly used seasonally and unlike their car/truck counterparts they use an open to atmosphere fuel system.

If the Ryobi starts easier now you could still have exhaust screen issues, but more likely you need to have someone who knows how to adjust your carb settings do so to let it run properly with clean gas/mix. A 42% mixture, assuming you could even hit it on the money is a waste of time. Virtually every manufacturer today specks out at 50% to get more oil in to keep the pistons from being fried by lean mixture gas. Us it in all you machines that require a mix. you can't go wrong with 50/50.

 

[ol'oilburner]

check the vacuum line, I was having a simliar problem with my chainsaw and it turned out the vacuum hose had a split in it and it wasn't providing enough vacuum for the fuel pump to work properly.

 

[arrabil]

A 42% mixture, assuming you could even hit it on the money is a waste of time. Virtually every manufacturer today specks out at 50% to get more oil in to keep the pistons from being fried by lean mixture gas. Us it in all you machines that require a mix. you can't go wrong with 50/50.

You mean 2% (50:1) and 2.38% (42:1) right? Not 50% (1:1)?

 

[Ryobi310]

Hi everyone,

New member here, thanks for a great forum, I found this older post but wanted to add to it, hopefully the OP will read this.

I have many of these Ryobi's similar to his 790r (31cc half crank with reed valve), and these do have certain quirks that you need to know about for the relationship to work out.

The spark arrestor is located under the muffler between the cylinder flange and the muffler inlet. I always remove it and leave the darn thing out. Never has a string trimmer started a fire in a yard from carbon particles that i know of, plus the clogging of the screen is pretty often and is a headache to service on this design. My 1996 model did not come with one from the factory. Only the west coast states on federal lands require them I beleive.

Air leaks are common between the cylinder and the flange of the crankcase. Use a new gasket but spay both sides with KW copper coat first, let the KW become tacky then reassemble.

Another thing to check is the reed valve under the intake manifold the carb sits on. Some of these 31 cc motors did not have proper clearence between the con rod big end and the tip of the reed stop, causing eventual breakage of the reed stop and internal damage from bits of metal from the reed stop. To correct, install new reed valve and reed stop, then, buy some small aluminum spacers (4) about 3/16" long and instal between the crankcase and the intake manifold. You won't use a normal gasket. Take some permatex ultra grey and fill the gap created by the spacers. I use a tool to smooth it into the gap, like you would if caulking a joint in a bathroom fixture. Be sure to seal perfectly. Let dry overnight. You will need to slighly richen the carb due to the change in crankcase volume.

Use a ester oil to keep piston rings clean - I found Motul 800 or Bel Ray H1R at 25:1 ratio is very clean. Another good option to avoid ethanol is 40FUEL available at Walmart and Sears. This is good stuff for those who only burn a couple of gallons a year. Hope this helps those that like to keep old stuff going.

 

[arrabil]

Wow, thats WAY more work than that stupid trimmer is worth. Welcome to TBN.

 

[doall]

Yeah that's great info. Buy a new one. How in the world did you ever figure that combination of fixes out? I had a Ryobi in 96 too, but not in 98.

 

[Ryobi310]

Hi doall:

I've by circumstance mostly ended up with many of the 31cc Ryobi's and they've become one of my hobbies to fix them up and see how good I can get them to run. No it's not practical, but MTD has all the parts and prices are cheap so it's mostly self-taught. I found the reed valve clearance problem when rebuilding a leaf blower for my girlfriend. I have soup ups I've done using larger carbs and tuned pipes but the crank bearings have their limits. Don't ask how I know that

The 31cc has a very, very long production, and is still used in some MTD brands today. The oldest I've seen is from a lawn-boy model 1460 trimmer from around 1982 or 83. I think these go back to the 1970's but haven't found proof of that yet.

 

[arrabil]

Well, its still a stupid trimmer to me, but I do respect your hobby work on it. :thumbsup:

 

[doall]

I respect all hobbies. keep it up. we all wish we could figure out things like that.

 

[Ryobi310]

Hi everyone-

thanks for your kind words, I thank the members of great forums like this that I've learned so much from over the years, still need to learn the picture attaching procedures to add photos to my posts.