I hope someone can help me here, I built a G.P. Patty Wagstaff 1/4 scale extra 300s. I powering with the o.s.bgx-3500. I moved the fuel tank back over the c.g. During break-in I found if I try and tilt the plane vertical at about 45 deg the engine dies it stops pulling fuel. I am running large fuel line except for the piece in the tank to the clunk. I drilled the clunk out for fuel volumne and from about 3" in front of the tank out the firewall I am running brass tubing. The engine is mounted sideways with the needle on top.. Will a pump fix this concern? I richened the mixture to the point it hardly run level, no help. Thanks for any help you can give me.

Kurtis

I won't say that the pump will absolutely fix the problem, but I would say that I'm not surprised that it's not working without one.

I'm running an OS 1.08 with a Perry pump (driven by case pressure)... 20oz tank on CG and an 8oz header tank. No problems at all.
The Perry oscillating pump didn't help at all.

You're trying to draw fuel well over a foot... that's about 1/2 PSI you're drawing against.

I am a little confused, You tried 2 different pumps? I am new to 1/4 scale. Which pump do you recommend? My LHS says they have a pump that works of engine vibration and this may work. Is this the osolating pump you tried?

Thanks again

Ya... the oscillating pump looks like a cylinder on a bracket with two hose barbs, one on each end of the cylinder. It's intended to mount to the rear of the engine and as the engine "kicks", it forces the fuel through the one-way valve.
It does not work well on 2 cycle engines.

The regulated pump works very well. It does require that you drill and tap your crankcase for a pressure fitting. I put mine in the center of the backplate and made sure that the threaded part of the nipple didn't extend into the case. This one looks more like an old Ford starter solenoid. One hose barb (for pressure) on the bottom end of the cylinder, a very small hex screw on the opposite end, and two hose barbs in a "tee" pattern on the same end as the adjustment screw.
It's got a metal body with a plastic cap on the adjustment end.

Kurtis,

How large can the effect of fuel level be, with a 20 oz. tank in a 20 lb. plane?
at least 99% if all modelers have the fuel tank just behind the engine, well forward of the C/G.

Except for a click, or two of down trim, around two thirds of flight time, there is no problem.

Why bother with pumps and added expenses? Just put the tank near the engine, or use a header tank immediately behind it.

Even with the header tank, you are still drawing on the entire fuel column, which would be FROM the vent of the primary tank.
The purpose of the header tank is to always have an unquestionably covered pickup line.

As far as mounting the tank on CG, in the case of my Extra, it was a matter of flight time.
I think the stock tank was 12oz. Barely adequate for a .60, which was the bottom range of engines for the kit. Even 16oz will only run the YS 1.10 for 10 minutes. I found the plane to be too weak with a .61, and went to the OS 1.08. I would have been looking at 8-minutes or less, and believe me, at the field I fly at, sometimes it takes 4 minutes just to get a clear runway for landing.

I'm not flying competition where the idea is to launch, fly a few routines, and land. I fly to have fun, and part of that fun is not worrying about watching the timer or if I'll have to dead-stick it in. I spend a lot of time on the slope where I'll have a bird up for half an hour or more. Having an absolute cap of 10 minutes on a power bird is unacceptable (and one of the reasons I'll probably never go electric), yet with the tanks mounted in the stock locations, that's typically what we're stuck with. I cram the biggest tank I can get into the area behind the firewall, and if that's not giving me 15 minutes, then a bigger tank goes on CG with a 2-4oz header and a pump goes in.

BTW: A 20oz tank DOES significantly affect a small plane. Alcohol is lighter than water, but water is still 1 POUND for 16oz. Methanol is about 80% as heavy as water, so we can pretty safely say that 16oz of methanol weighs about 13oz, or more closely, 0.8oz per liquid ounce. A 20oz fuel tank would be pretty close to a pound... that's more than a 10% increase for my Goldberg Extra.
I carry 28oz or 1.4 pounds of fuel, plus another half pound or so of smoke fluid, so I'm getting up into the range of a 2 pound variance from takeoff to landing.

How well would your heaviest plane fly if you added/subtracted 2 pounds from the nose?

Well I tried a few things today without correcting problem. I put the tank in the stock location this is right up against the firewall. from the tank to the needle valve is right at 4". There is a light loop in line from tank to valve. The line is right at 5" long. I am running 1/8" ID fuel line from clunk to carb. Pressure line from muffler is 3/16 ID. With everything forward it will run vertical from idle to about 1/3 throttle anymore and it will die. This gets worse the lower the fuel level. The tank is stock 24oz. It appears to me that there is not enough pressure to draw enough volume of fuel. I thought about increasing the pressure line to match the feed line. I have not encountered a problem like this with my .60 size equipment. If I put a pump on it I think I will put the tank back on th C.G. Any help would be appreciated.

Thanks Kurtis

One thing I forgot to mention is I am running the bisson pitts muffler. I thing I read in a plane review that they were using an os 1.60 on with the pitts they had to block off on of the exaust ports to make it run correctly. I might try this and see what happens.

I had the opposite problem with my OS 1.08 and Slimline Pitts.
When I had the exhaust extensions on I tuned it normally, and in the air it REALLY ran badly. Didn't make power worth a crap (worse than a .60), I could occasionally hear detonation... I didn't even try vertical.

When I removed the extensions (they were only about 7" long) everything came to life.

Try plugging one (FIRST!) but be prepared to cut them shorter as well.

Well today I had some luck, I spoke with a gentleman who runs these bgx-1 engines and he told me he only uses standard fuel line. So today I removed the large fuel line and replaced it with medium which helped. I would run vertical but would lean out abit. So then I removed the standard vent/ exhaust line, drilled out the muffler fitting to 3/32 and installed the large line. Now it runs good vertical until the fuel tanks level gets down to about 1/3 of a tank and then it will lean out a little. It looks like I am going to put a pump on it and move the tank back over the C.G. and be done with it. I will update when done.

Thanks for the info