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  1. #1
    Hircflyer's Avatar
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    Ryobi 31 cc Conversion

    Can some one please tell me what the correct spark plug to use and the gap setting?

    Thanks

    Finally! Everyday is a weekend

  2. #2
    Moderator w8ye's Avatar
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    RE: Ryobi 31 cc Conversion

    There's several plugs that work satisfactory.

    What plug was in the engine?

    You will need a resister plug. On the Champions the resistor number starts with "R". Other brands have a "R" in the number somewhere.

    Mine has a RCJ7Y It's has a gasket base. I've also used the RDJ8J tapered seat plugs. The engine ran the same or at least I couldn't tell any difference... They tached the same and neither seemed to foul. The RDJ8J is smaller.

    I got mine at the NAPA Auto Parts store but I had to order them. They came the next day.

    Enjoy,

    Jim
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
    Recipient, Mangledhand award August 2008
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  3. #3

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    RE: Ryobi 31 cc Conversion

    You want a 14mm thread and a tapered seat, resistor type. Champion = RDJ7Y, NGK = BPMR6F, . Set the gap at .020 inch.

    edit: Autolite 2554 is not a resistor plug.




  4. #4

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    RE: Ryobi 31 cc Conversion

    If you have a tapered seat cylinder head you should use a tapered plug, why, because the tapered plug is part of the cooling process just as the cylinder fins are; you can probably get away with a gasket type plug,unless you are reaching critical head temps. The taper is meant to be a close fit , not just for sealing , but for the ability to absorb heat from the head to the plug body(the metal part)

  5. #5
    Moderator w8ye's Avatar
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    RE: Ryobi 31 cc Conversion

    The Ryobi type engine has been around for over 25 years under a number of different names. Over the years, there's been a lot of different plugs used in them. Mine, as a weed whacker, origonally had a CJ7Y plug which I changed to a RCJ7Y when I converted it for model use. I have used the other plugs mentioned by others in my engine to get a comparison, and it ran good with all of them. Surprisingly, I've swapped between the "C" type gasket plugs and the "D" type tapered seat plugs. You can swap back and forth between the gasket and the tapered seat plugs.

    I have a 1999 model that is still a weed whacker and it has a DJ7Y plug.

    I was over at a guy's house the other day and he must have had 20 used plugs in his flight box. He's only had his US 41 about 4 years. He says that they don't last very long and his engine will not start. Other than being oily and a little black, they all looked fine to me.

    My converted Ryobi was made in the early 80's and had the original plug in it until 1999 when I converted it and installed the resistor plug in it. The original plug showed little errosion wear. The old whacker had worn me out many times over the years.

    What ever makes you happy,

    Enjoy,

    Jim
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
    Recipient, Mangledhand award August 2008
    Club Saito Member #7
    Original AMA #31261

  6. #6

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    RE: Ryobi 31 cc Conversion

    Just saok those extra sparplugs in acetone, carb cleaner or lacquer thinner in a jar with a spin on lid. Let them soak for a few days and the oil and crud will just wipe off. Use compresed air for a better job. Check gap and re-install in engine. I have cut the electrode on a angle with a dremmel cut-off disc. The spark will jump off it more easy in a certain spot and stay cleaner longer. Some engines gain RPM with this mod. Smooth landings Capt,n
    I never met a engine I did not like !

  7. #7
    Hircflyer's Avatar
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    RE: Ryobi 31 cc Conversion

    Thanks for all the info...........I installed a Champion RDJ7Y....found it at the auto parts store. Engine would not start ...even after choking and many flips. I also installed a CH ignition system.
    I was at the field trying to start the engine and one of the guys came over and we tried another method. He removed the plug and filled the cavity around the plug electrode with gas .....reinstalled the plug flipped twice and the engine popped....open the throttle a little more, next flip and it roared off.
    Engine ran very well.....we adjusted the needles a little and the engine ran really well and idled.
    We ran the tank dry and after a bit we tried starting it again........well you guessed it we could not get any fuel into the engine by choking or any other method.
    Again removing the plug and putting fuel directly on the plug...reinstalling and flipping twice engine started and ran as before.

    Anyone have any ideas?

    Thanks
    Finally! Everyday is a weekend

  8. #8

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    RE: Ryobi 31 cc Conversion

    I've a theory.... (Like everyone with elbows ;>)
    Suspect a LEAK....... Either in the fuel line or most likely at the carb gasket. The suction created by the intake once started over-rides the leak rate and once started, the engine continues to run. I'de also check location and distance of fuel tank from the carb, check the fuel lines for kinks, multiple bends and diameter size.
    I hope this helps... Please let us know how it turns out..



  9. #9

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    RE: Ryobi 31 cc Conversion

    Engines can and should start with normal priming and choking. Before the needles are set the engine can be a real pain to start. When I run across a balky engine a squirt of WD 40 in the throat of the carburetor will usually get the engine running.

    WD 40 is not a solution but a means to get the engine running so the problem can be found.

    Bill

  10. #10

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    RE: Ryobi 31 cc Conversion

    Starting fluid works good too
    I never met a engine I did not like !

  11. #11

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    RE: Ryobi 31 cc Conversion

    hircflyer,
    Had a similar problem with mine. Ran fine on the bench, wouldnt start in the plane. After fueling, I raise the tail of my plane so the fuse is level. Choke, ignition off, spin the prop with the starter to prime, lower the tail, ignition on, hit it with the start and it starts right up. Dont understand it, but it works. My tank is right inline with the carb. Its also the stock carb off a ryobi weedeater. Was rebuilt when I modified it.
    Edwin

  12. #12

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    RE: Ryobi 31 cc Conversion

    I second the starting fluid suggestion. That and a starter with 16 nicad cells attached to it.
    Using that it starts every time without incident.

  13. #13
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    RE: Ryobi 31 cc Conversion

    I have the engine mounted on a stand....so it's level. The carb intake is behind on these engines so it is very hard to get to the intake to squirt anything into it.

    I removed the engine last night and I noticed that when I move the choke lever the sliding part does not completely cover the carb intake. I plan on adjusting that to see if that helps also going to remove the carb and see if I left any thing loose. This engine sat for a couple of years in my shed maybe the gaskets have dryed out. Anyone know where I can get a rebuild kit for this carb, it's the stock Ryobi carb........better yet can someone tell me a good upgrade carb to install?

    Thanks for all the help.
    Finally! Everyday is a weekend

  14. #14
    Moderator w8ye's Avatar
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    RE: Ryobi 31 cc Conversion

    There are two different brands of carbs on the Ryobi's that I know of.

    Most had Zama's

    Some had Walbro's

    Enjoy,

    Jim
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
    Recipient, Mangledhand award August 2008
    Club Saito Member #7
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  15. #15
    Hircflyer's Avatar
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    RE: Ryobi 31 cc Conversion

    Yes, sorry should have mentioned the one installed is a Walbro. Can't find the model number.
    Finally! Everyday is a weekend

  16. #16
    Moderator w8ye's Avatar
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    RE: Ryobi 31 cc Conversion

    I think the repair kit is the same for all the small Walbros of like the WT and Wa series.

    Enjoy,

    Jim
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
    Recipient, Mangledhand award August 2008
    Club Saito Member #7
    Original AMA #31261

  17. #17

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    RE: Ryobi 31 cc Conversion

    If your chock plate has a small hole in it, solder it closed. That made mine start much better. But watch you can flood it.

  18. #18
    Hircflyer's Avatar
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    RE: Ryobi 31 cc Conversion

    I removed the engine from the test stand and found that the choke was not going full closed. I checked it after I did the conversion and it was working fine. However when I mounted the engine mount to the engine I didn't check it again..............dumb.............the choke lever was hitting the mount before the choke was going full closed. DUH!

    I made the necessary corrections and now the choke goes fully closed. Tomorrow I am going to the field and give it a try.

    BJH1, your right my plate does have a small hole in it, pending on what happens tomorrow I will solder it closed before I mount the enging on the airplane.
    Finally! Everyday is a weekend

  19. #19
    Moderator w8ye's Avatar
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    RE: Ryobi 31 cc Conversion

    Sometimes the worst problems have the simplest solutions?

    Enjoy,

    Jim
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
    Recipient, Mangledhand award August 2008
    Club Saito Member #7
    Original AMA #31261

  20. #20
    Hircflyer's Avatar
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    RE: Ryobi 31 cc Conversion

    w8ye, when your right, your right! Engine drawing fuel with full choke now........I thought it wasn't when i could not get the engine to fire....so I pulled the plug and it was swiming in gas.............that's why it didn't fire... it was flooded. Blew the plug dry and two flips later it was runing like a champ.

    AS soon as I learn tecnique this engine shoould start right up. Made a couple runs and adjusted the needles a little more, good top and good steady idle at about 2000 rpm. Using 16x 6 Top Flight prop.

    Only problem the muffler came loose so I had to quit playing with it for the day.

    Thanks for all the help.

    Going to install in Ryans Rebel as soon as we finish them up. We are building two.
    Finally! Everyday is a weekend

  21. #21

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    RE: Ryobi 31 cc Conversion

    I thought the Ryobi needed an 18" X 8 prop or bigger? I have been researching this for a couple of weeks now. My wife has a 31 on a 1/4 scale Hanger 9 Super Cub. We haven't started it yet but I was sure that 18 x 8 was the prop we were going to use.
    It\'\'s never too late to have a Happy Childhood!
    AMA# 763492 -IMAA# 40348 www.thistledownflyers.com

  22. #22

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    RE: Ryobi 31 cc Conversion

    I use 18x8 and 18x6. Seems to like it.
    Edwin

  23. #23

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    RE: Ryobi 31 cc Conversion

    I've been running my coverted ryobi 31cc on a test stand spinning a 16-8. I tached it at 8500. Since everybody is recommending this engine to run between 7500 - 8000 I plan on trying an 18-8 when I mount it on my Stinger 120.

    Jim

  24. #24
    Hircflyer's Avatar
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    RE: Ryobi 31 cc Conversion

    I thought mine was spinning a little fast at full throttle, my tach indicated 8800, I thought the tach was not very accurate, thats why I said it was idling at about 2000 rpm.

    Should I consider going to a 18 inch prop or I have a 16x10 I was going to try.
    Finally! Everyday is a weekend

  25. #25

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    RE: Ryobi 31 cc Conversion

    I checked my tach recently against another brand and it matched right up on a .60 we were tuning, so I know mine is fairly accurate. As for what prop to use, that depends on what you are trying to do. For example my Stinger 120. It has a thick fully symetrical airfoil and is designed for slow speed aerobatics. That means I want to spin the largest diameter, lowest pitch prop that loads the engine to the point where it is in the correct RPM range. A 16-10 on the other hand is starting to get into high pitch speed/low thrust area. That's good for planes that want to go fast.

    Jim


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