Here are another couple pictures of My L4 conversion from this World Models 119" Cub. At this point, I've done some engine testing with the engine mounted on the plane. As usual, there are issues. On the test stand, the engine ran fine. No so much, once in the plane. Even in a perfect world, glow carbs don't handle gasoline very well. I thought this one, on the OS Pegasus, maybe was an exception because the bench testing was so trouble free. However, in the plane, the stock gas tank location was so much higher than the OS's carb, that gas was constantly siphoning from the tank, onto the ground from the carb. Also, I couldn't get a decent transition from idle to WOT, probably because the engine was drowning in gas. Good RPM at the top, about 7200rpm with a 19x8 Zoar. 18lbs static thrust, 25lb model. Not bad for a Cub. So, I lowered the tank to the bottom of the area just behind the firewall and gave it another try. Less siphoning for sure, and a better transition, especially when the prop was backed off to a 18x8 pro Zinger. RPM was now 7800, but the thrust was less (didn't measure it, but I could tell). But there was still that carb-needle valve sensitivity that could kill an engine once things change in the air. So, I'm biting the bullet and I've installed a Walbro. See one of the new pics. Pressure tap is right off the crankcase--not sure why that works but it seems to be pumping. I'll know for sure tonight when I do the first test run. I made the carb mount myself on the lathe and milling machine. Bottom line, glow carbs don't work for gas because the needle valve angle is way too blunt (or course) for gasoline. Nitro fuel carries much of it's own oxygen right in the liquid unlike gasoline. So, the fuel air ratio mixture adjustment is only regulating a small part of the overall oxygen getting into the engine. Thus, glow carbs provide much more fluid to the engine than what is appropriate for gasoline. The free passage of fuel through a glow carb is too unregulated an environment for gasoline, where the fuel air mixture must be controlled externally. That's why walbros have regulators that sniff the outside air pressure as a reference. I'll update the site after tonight's test run with the walbro.
