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Fuel flow problems

I have two very different planes that both have the same problem. I can't get fuel to the engines. The common denominator is that both planes are designed with the tank setting below the carburator. The first plane is a Clancy Lazy Bee. I've mounted both a used (and well broken in) MRC .15 and a brand new ThunderTiger .15 on it with the same results. I prime the line, start the engine, and watch the fuel line go dry. The fuel tank is assembled properly and the lines are new and properly installed. If I remove the tank and attach it to the top of the plane (above the carb) the engines run fine until I tilt the nose up to the point that the tank goes below the carb. The second plane with this problem is a Cermark Extra 300S with an ASP .91 on it. Once again, I've replaced the fuel lines, thinking that a small hole in one was the problem. I open the throttle to full, put my thumb over carb air intake, flip engine over a few times and watch the fuel line fill. I then remove my thumb and watch the fuel drain back to the tank. This plane and engine are a few years old (though new to me). Can anybody give me some idea what I should look for to solve this problem? Since it is happening to two planes with a total of three engines, I have to wonder if I'm doing something wrong. BTW, I also have a GP PT-40 that the engine (Tower Hobbies .46) runs fine, so I'm sure that I know how to install a fuel system. The difference is that the PT-40's fuel tank sets even with the carb, perhaps even a little above it. Any ideas are more than welcome.

Reply to
dredhea
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Are the fill lines connected to a muffler tap to pressurize the fuel systems?

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Reply to
aeropal

Are the vent lines connected to a muffler tap to pressurize the fuel systems?

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Reply to
aeropal

You have at least 4 possible problems.

  1. The clunk is too close to the rear wall of the tank. Be sure you have at least 1/4" clearance. If it's too close, the engine can't draw fuel.

  1. You do not have muffler pressure attached. Most glow engines need this to run smoothly and draw fuel effectively.

  2. You state the tanks are below the carburetors. The centerline of the tank should be within 3/8" above or below the carb. Our engines are, at best, marginal on fuel draw. If the tank is too low, the engine simply can't pull the fuel.

  1. You are trying to run your engines too lean. Readjust the high speed needle.

Dr.1 Driver "There's a Hun in the sun!"

Reply to
Dr1Driver

Let's call it 4 and a half. :) Just today I was out to the field to check out a new ARF Trainer that I bought just to have a machine to give newbies some stick time as we usually have a bunch drop by for the first couple after-Christmas months. I had taken out an old ST .40 from as drawer where it probably laid for at least 5 years. Well, I could not make it rich enough, no way. Then after about all my patience was used up, I noticed no little bubble-like flow indications in the clear pressure line. What-da-know? Scientific exploration with a large straight-pin and the pressure nipple clog was removed and another earth-shattering problem was solved. Drats, DR, I had it attached like you said, but it just wusn't workin'. OTOH like you said, I also needed some flowage there.

Reply to
CainHD

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