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Need help choosing carburetor


Old Yesterday, 07:09 AM
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Default Need help choosing carburetor

Hi. I have an old .40 size nitro engine that came with a ROYAL AIR 40H. I wanted to convert it to a gas engine so I got a gas glow plug. That's given me a good start as I've been able to run it off gas and 2 stroke oil but it stops running at full throttle if I don't open the carburetor enough. But if I open it more it runs too rich and shuts off as well. I want to buy a carburetor made for a similar size gas engine because I've read that nitro carburetors can't work properly for this in some glow to gas article.
Someone in this article says that adding more oil to thicken the gas to make it be able to run with the nitro carburetor should work but I've filled the tank with 1/3 of oil and the rest gas but it ran the same. Seems like a lot of oil lol.
Oh yeah I also grinded a little bit of the head inside to lower the compression because I dont have anyakind of shim solution but it feels about the same. Maybe I should remove a bit more material?

I was wondering if I could get help choosing a gas carburetor that could fit this engine. And maybe any other tips.
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Old Yesterday, 10:47 AM
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Never done it, but it appears you have the compression thing backwards - to lower compression, you need to add shims to raise the head. Taking material off will increase compression, which in all likelihood will make it even harder to run. Having it stop while running at full throttle would seem to indicate being way too lean, and the heat build up is causing it to seize. You may have scored the piston/liner, which will make it even more unlikely to run right. Royal were "affordable" engines, so probably not the best candidate for conversion. Highly unlikely you will find a plug in carb for that size in gas. Be prepared to hunt down an OS GGT 10 carb, and then machine an adaptor to get it to mount. They are only $135 at Tower Hobbies right now.
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