Larry, the Fox .35 and the Ring are like a pocket on a T-shirt. Why is it not reliable? Aside from that, almost all the Fox's have the same bolt pattern 19's, .25's, 35's. The Evolution .36 fits with the exception of the nose being a bit shorter. The Double Star (Classic) .40 if you can locate one was the same bolt pattern and identical footprint and weight. That might be a tough find though. The LA .25 is close, but not close enough which allows you to use two sets of the holes. I have exchanged the EVO for the Fox. The EVO however is going to be in the upwards of 2.5 ounces heavier. All of the modern OS engines aside from the old Max-S will be heavier in and around the same as the EVO. The EVO is a ball bearing engine though.  The OS bolt patterns are much easier for swapping due to many fitting in the bolt pattern and case length. I personally would try and go with a Brodak .40 due to it's weight. It has the same bolt pattern as the LA .40, .46, Max-35, FP .35-.40. , Magnum .32 etc. If you decide to change, it will cover without the nose looking like a butcher job and it will leave many options. Ken

I don't think the L&J mod Fox engine has the burp stick installed.  All kind of info on this mod posted elsewhere.  However I had the same problem with my Ringmaster.  Cured it with a OS Max .25 FPS.  The OS Max fit by enlarging the mounting holes.

Just pulled the back off of my L&J, and there is JB weld in the bypass.
I do recall that there were various "stages" of rework they did, so perhaps not all got it?
But you would think that would be one of the first things to get done, along with the crank balancing

Mine was fully modified, crank, head, case, backplate, NVA

Can anyone provide an illustration or explanation of this "burp stick" thing? It would be much appreciated.

While Larry asked for a direct drop-in replacement, there was only the Double Star that I knew about.

I replaced a Fox 35 in an Oriental ARF with a Brodak 40. When assembling the ARF, I located the prop washer where Pat Johnston's drawing showed it. When I fitted the B40, it's longer but it fitted and the moounting holes were between and behind the Fox mounts. The small weight increase didn't affect the balance as it was a bit further back in the nose.

I can also vouch for the effectiveness of a Ringmaster powered by an LA 25.

Larry,

Before you toss the Fox aside, what tank, plug, and fuel are you using?

Uniflow is not needed on a Ringmaster, works better without it. Have you opened up the tank? Foxes vibe(as you know) and can detach a pickup and even crack fuel tubes.

Thunderbolt RC long is a must. I recommend 10/22, personal choice but thinner fuel helps it 4/2 better and also increases overall fuel flow. Many folks will run 25-29% full castor oil with success, I am just not sold on it. 10/22 has made a big difference in my runs. I have 100's of flights on my Ring with a '52 model Fox and it is still solid.

None of this advice is from me, but is a regurgitation of advice given to me by Ken Cook.

Good luck in whatever you decide.

Ron

If you can find it the OS 20FP is great, perhaps even more engine than you need.  I only have one, and it's aluminum piston, so I can't answer for the iron/steel version.

Brett Buck, who knows more than I do about engines, says that for a light Ringmaster a strong modern 15 (FP, LA, or, presumably, Magnum) would be enough engine.  I haven't tried it, but the mounting holes may be different enough that they won't intersect with the current ones.