After re reading about the bent con rod,
I opened up my engines, and one of it( the ones i tried to run first time, but cannot get it work right) has bent conrod.

The ones that I posted here, I think it has a slight bent too. I dont have a way to measure it propperly, but by naked eye it looks slightly bent.

I ordered new conrod, but can I hammer the old one straight ? :)

I thought about trying to straighten mine out but I wasn't sure if it might have stress fractures in it or not after all the bending. Didn't want to take a chance on it breaking.

CR

I am interested in using one of these for Control Line Stunt (no throttle, just a venturi).
What is the weight with muffler?
Will this engine likely be able to be tuned to fly the favored 4-2-4 break? That is, take off and level flight in a fast 4 cycle, then when maneuvering (and nose up) pull into a 2 cycle, then when nose down, back into a 4 cycle?

I would think that it could, with a properly small venturi. And it would only need about 2oz of fuel to make the required 6 minutes of flight time.

What size venturi would come on a GX40?
Could I also get a "blank" venturi with just a small pilot hole that I could use to tune?

Has anyone run not on muffler pressure? A uni-flow tank setup is popular with control line pilots.

I hope there are still people watching this thread and I would love some insight... I have been considering buying the GX-40 for an rc trainer plane (aero-star 40). I have been flying rc airplanes and racing drones for a while but I want a slower rc plane to fly but I also want some extra power for basic acrobatics.

I have had some experience with tuning nitro engines (50 year old cox engines, weed trimmer engines, and a nitro rc car which I have converted to gasoline glow ignition), but I am still fairly new to tuning nitro engines. So I was wondering if I will have problems with tuning this engine and if you guys think it would be a good investment for me at this point.

Hi Bob,
For an Aerostar 40 you could use the GX40, the AX 40 as well as the Big Mig 40. and get the performance you wish. The Big Mig has slightly less power, but also less weight so the difference in flying is negligible. As to tuning, the Big Mig is the easiest, the AX would be next, then the GX, which requires a bit more care and finesse but the payoff is fantastic fuel economy and great power. If you are new to tuning nitro engines the Big Mig is pretty much no fuss right out of the box and let's you just concentrate on your flying. As a side note, when comparing it to getting a cox engine tuned right you might think the Big Mig was like electric. Most of us old timers learned how to swear just trying to get those cox engines set right 3 flights in a row. :)

Thanks, I do enjoy the rewarding feeling of getting that perfect tune in a nitro engine. I have had hours of practice tuning a gasoline glow ignition engine. (a stock nitro engine with a head shim removed). It was bad enough that 1/8 turn in any direction on the low or high speed needle would kill the engine. I feel like if I can sort of tune that engine I should be ok with a GX-40 engine that is optimized for gasoline... I could be wrong, but I like the challenge and don't want to pay the extra money for nitro fuel.

Inspired by the GX-40 I have sense increased compression on my gasoline/nitro engine, added a hotter glow plug, and mounted a diaphragm carburetor and it now tunes and runs almost as good as a nitro :) (just need to solve overheating problems)