OS Gemini twin rear carb gas conversion

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Fernando, your parts look great to me. I found out the hard way that those venturis look simple but they are hard to get right.

As for the Walbro 962 keep this in mind: it is what I’m running on my Gemini 160 which is 27.5cc’s and it runs GREAT. So don’t worry. Your 240 will run just fine - if you get everything else right.
Great! thank you Mitch.
Next I need to make the ignition rings and I'll be able to give it a try!!
Got it!!!
The other thing is kind of stressing me out is that my engine came with the "infamous" conrods. The sencond engine I don't know it looks unrun so I don't feel like opening it but the serial# is lower than the beated one so I guess conrods are the same.
So I have mixed feelings about this, on one side my brain tells me "if it's not broken..." on the other hand it repeats me "when it WILL fail the damage will be catastrophic".
The few videos I found that they mention this issue are very insistent that replacing original conrods is a must, while the rest of the videos don't even mention conrod issues.
Fernando, this is a decision only you can make HOWEVER, if it was me I would not change out the rods (unless they can be had for a reasonable price?). I'm not very knowledgeable about past failures of these rods but I suspect that if properly lubricated and not pressed too hard they would survive.

My Saito FG61 (4-stroke gas) radial requires the user to squirt a few cc's of raw oil into the crankcase before flight in addition to a 20:1 oil mix. I suspect that if you did the same, and also ran an oil-rich gas mix AND kept the revs down to a reasonable level your engine would be fine.

You have one thing in your favor - your gas conversion will decrease power output and thus the load on your rods (generally speaking).
That makes sense, thanks Mitch.
I'm one step closer today. I made the sensor/ magnet/magnet rings, Yes that's right is not a typo I had to make two magnet rings because I made the first one really nice, straight flush with the sensor one and then realised why the ones they make commercially have a "step" if you don't raise the surface where the magnet is the gap is too big to the sensor so the second ring I left a bit of a shoulder on the magnet.

So today I got my first mouthfulls of CO🍿🎉🎊
EDIT: Apologies for the audio on the video. I took it for my friends over here:oops::oops::oops:


  • WhatsApp Video 2022-10-17 at 13.01.13.mp4
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  • WhatsApp Video 2022-10-17 at 13.56.07.mp4
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I was having a fuel issue that after few seconds of idling it would rev up and die like it was using all the gas in the carb and starve to death, it took me some time (too long) to realise what the problem was. The second spigot that most of the rc engines have it crimped (where the priming bulb connects) I put a hose there to be able to prime the carb and that was the culprit. I plugged it up and now it idles steady and does not die.
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I tried to upload the video with the issue fixed but I think it's too heavy. I'll upload it to Youtube and then edit this post with the link to it.
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Can any of you guys who ran the CH twin fire ignition on the boxers tell me about the magnet used (diameter x thickness) & spacing distance to hall sensor pickup? I'll be improvising my own when the time comes (as opposed to buying a conversion drive washer collar thingy). I have all kinds of little neodymium? magnets, guessing they are generically similar in terms of magnetic strength for a given size? Anything else I need to know?
1/8" diam x 1/16" high neodymium magnets work fine with the Hall Sensor specified in the Sage-Gedde ignition circuit (I've been using a "us5781", you can use any sensor with a similar triggering field strength rating). the difference in field strength of various grades of neodymium magnets isn't significant compared to the differences in the triggering field strength of various sensors available. IMHO, YMMV, VWPBL, yada, yada, yada...