well I just mounted a ryobi 31cc on my flybaby did a range check at about 50 ft got interfearance just was wondering what resister plug i should have in there the plug that i have in it now is a champion dj7y. it 's not marked resister anywhere.Thanks Dave .

I'm using the Campion # RDJ8J with good results. No radio interference. I picked mine up a NAPA.

I'm using an Champion RCJ7Y with excellent range checks on my Poulan.

Click on the manufacturer below to interpret their numbering system (from sparkplugs.com):
- Champion
- NGK
- Denso
- Splitfire
- Autolite

Reminder - Don't use a tapered seat plug on an engine designed with a flat seat and vice versa.

The last two Ryobi 31cc I bought came with RDJ7Y resistor plugs.

I've used both plugs in my Ryobi. I had to order them at the NAPA store but they came in the next day. They didn't have the "R" version in stock.

The engine ran the same rpm with either plug.

Jim

Same RPM, of course, but how was the radio reception? The "R" version (resistor) is supposed to reduce the RF interference from the spark plug.

???
My Ryobi came with the CJ7Y Plug but I never used a non resister plug in a converted engine in a model airplane. I wouldn't be able to comment as to the non resister plug's reliablity in a radio situation but I doubt if it would work without interference.

I bought a box of RCJ7Y's and another of the RDJ8J's at the NAPA store (I had to order them but they came the next day). I used both resistor types in the Ryobi. One worked the same as the other as far as radio interference and the way the engine ran.

The RCJ7Y is a gasket seat plug and the RDJ8J is a taper seat plug and is the smaller of the two.


Enjoy,

Jim

Sorry Jim, I misinterpreted your previous post. I thought you were saying you used non-resistor plugs.

Since I've never seen a Ryobi, what type of plug seat do they have? Flat, or tapered? My Poulan has a flat plug seat, therefore I use a flat, gasketed plug. If the Ryobi has a flat seat, try using the longer, flat, RCJ7Y plug. It'll increace your compression slightly (very slightly).

The Ryobi and Homelites have a flat plug seat and come with the CJ7Y but actually either plug will work and seal fine. The McColluch comes with a DJ8J tapered plug but you can run the gasket jobs in them if you want to. It doesn't seem to bother the head to swap back and forth.

But whatever or whichever, make sure its the resister version of that size that you use before having the engine in a plane.

I could never tell any difference in the way they ran with either plug but I've always flown them with the type the came with.

Enjoy

Jim

Jim - I've never tried swapping them. I figure since the plug holds in the compression, it would be best to use the plug which matches the seat. Their typically the same price. If my plug dies, and the only available replacement has the wrong seat, I'll use it till I can get the right one.

Most importantly, like you said, ALWAYS use a resistor type spark plug with RC equipment.

resistor plugs are hard to come by over hear so i just put a 1000 ohm resistor in the plug cap, same as 3w does in their plug caps. i also ream the plug seats to accept the taper plugs as they are a bit narrower and shorter. i also cut the threaded post off.

dave

how does one know what type plug to use for a particular engine? i have a poulan 46cc, with a husky 88 coming...

i know R for resistor now, thanks!

The two plug #'s listed above are the more common domestic USA plugs. One is a tapered seat and the other is a gasket seat type.

There are other plugs but I don't have the numbers in front of me right now. One is like a NGK plug that is not available in Champion. This was mainly for compatability with the shielded plug cap.

Jim

As Jim mentioned, the above mentioned plugs are the most commonly used plugs in North America for small, 2stroke engines like these.

Anything in the Champion RCJ?? or RDJ?? series should be fine, or a competitor's equivillant with 14mm threads.

Click on the manufacturer below to interpret their numbering system (from www.sparkplugs.com):
- Champion
- NGK
- Denso
- Splitfire
- Autolite

Thanks for the reply and good reference site on plugs .thanks Dave

I have the E3 spark plug with diamondfire
on my mac 28 engine