Dashman72

Hi,
Today I finished installing the Evolution 33 into my Hangar 9 Spitfire. This is my first gas engine, but have been flying for many years with glow and electric. After several attempts at starting it, I could see that it is not getting fuel. The strange part is that I can't even blow air into the carby through the fuel line. The lines are clear as fuel flows through freely when I blow into the overflow line. I checked and I am getting a spark, so it seems a carby issue. Any ideas??
Thanks
Darrin

av8tor1977

My Feedback: (6)

It is normal to not be able to blow through the fuel line to the carb. It is part of how a pumper, self-regulating carb works.

Sounds like you have "Dry Carb Won't Draw Fuel Syndrome". Try priming the engine through the carb or the spark plug hole with 4 to 6 drops of gas. It should start, and possibly stop again. Do this a few times if necessary to see if it will start drawing fuel. If not, you might have to pull both covers off the carb and shoot some fuel in them, and re-assemble. It should work then. This, of course assumes you don't have any other problems like kinked fuel lines, etc.

AV8TOR

Dashman72

Great, I'll give that a try. Thanks av8tor1977.

av8tor1977

My Feedback: (6)

A pumped carb is also very sensitive to air leaks in the fuel lines, and won't draw fuel if any exist. Each tubing connection should have hose barbs soldered on, and be secured with tie wire around the tubing like a hose clamp.

AV8TOR

Dashman72

Wow, much more different to glow than I thought. Thanks again.

av8tor1977

My Feedback: (6)

The good news is, once you get it all set and dialed in, you're done. You won't have to fiddle with it to keep it tuned like you do a glow engine. The even, steady metering of the pumped and regulated carb is a definite benefit of gas engines as well.

You will likely also be amazed at the torque of a gasser. They pull like a tractor compared to glow! (But I still like glow too, and have kept a few in my fleet, though my fleet is mostly gassers now.)

AV8TOR

BarracudaHockey

My Feedback: (11)

On that model I had t make an air dam in front of the carb because the air would come in, hit the choke plate and make the engine run lean at high speeds. It wasn't anything but aluminum foil folded and attached to the front lip of the carb inlet to prevent air from hitting that choke plate directly.

av8tor1977

My Feedback: (6)

I've had to do the same thing on other airplanes. The airflow can cause the reversion, or "spit back" to be blown away instead of being sucked into the engine, and cause it to go lean. Another problem is ram air in the cowl forcing on the carb regulator diaphragm, causing the engine to go rich.

Sometimes those maiden/test flights go smoothly, sometimes you have issues and/or tuning to sort out. The only first flights that ALWAYS go perfectly are in the magazines! == ;~)

AV8TOR

BarracudaHockey

My Feedback: (11)

I document any problems I have when I write my articles.

av8tor1977

My Feedback: (6)

I was just teasing...

Years ago, I was published as well. In RCM and others.

AV8TOR

av8tor1977

My Feedback: (6)

Well, a glow engine won't work properly with air leaks either, but it is slightly less critical about it because of the muffler pressurizing the fuel tank in a glow fueling system. The problem is, depending on what size gasoline proof tubing you are using, it isn't always a nice snug fit on the brass tank tubing. In addition, the gas often swells the tubing slightly, making that fit even more suspect. Since most any pump will be problematic if it sucks air, this is an area that needs close attention.
AV8TOR

Lifer

My Feedback: (1)

I was dealing with a 55cc gas engine that took something like 70 flips of the prop to draw fuel when choked. Really wore my arm out. Once it popped however, it started and ran normally. The engine is in a Howard Ike and it sits at a pretty steep angle. I assumed that the issue was due to the latter. On a whim, I replace the pump diaphragm and it popped after 5 flips with the choke closed and started after a few more flips. Seems like even with the diaphragm working, it can be improved upon. I think I'll keep a few spare diaphragms on hand.

Hope this helps somebody.

av8tor1977

My Feedback: (6)

It can also help to resurface the carb body where that diaphragm seals. Sometimes the machining is rather rough and the diaphragm doesn't seal well.

Take a piece of 220 wet or dry sandpaper and lay it flat on a piece of glass. Then while holding that surface of the carb perfectly flat on the sandpaper, use an "X" pattern to sand and clean up that surface. Rotate the carb in your grip every few strokes to make sure you are sanding evenly. If you want to be anal about it, you can follow up with #400 sanpaper, then 800. This helps the pump seal and perform optimally.

The black rubber diaphragm pumps the most, followed by the brown composition one, with the blue plastic one pumping the least. Their order of fuel and additive tolerance is exactly the reverse, with the Black one performing the worst. I always just compromise and use the brown one.

Another trick to get max fuel draw for cold starts is to solder the hole in the choke butterfly shut. (Be sure of your solder skills and use a good hot iron if doing this.)

A properly working system will draw fuel 3 feet straight up, and when firmly choked you should see the fuel move towards the carb with every flip of the prop.

I don't generally have problems getting my cold engines to start, but I do have some engines that sit many months, (years sometimes!), between uses. It would be nice to be able to flush fresh fuel through the carbs on those, so I have seriously been considering adding a hidden primer bulb setup on those planes, like those found on weedeaters, etc. Read my post at #38 here:

http://www.rcuniverse.com/forum/gas-...rmation-2.html

AV8TOR