I had an idea I will try tomorrow with my Super Tigre .90, mounted in my Cap 580. I have mounted the tank on the CG which is about 2.5 inches behind the standard location behind the firewall.

The engine runs perfect with my new Perry carb, but on idle I get the lack of pressure driving fuel to the engine when she is in the vertical position. Eventually she leans out, and dies. I have a Fourmost check valve, and was wondering if anyone, and if not I will try putting the valve about an inch in front of the tank on the carb intake so the the fuel prime is held requiring much less pull from the motor to receive it in the carb.

If you put the valve in this location it would in theory act as a header tank providing a prime for the engine by locking the fuel in the line waiting for the carb to pull it in. This should make the engine only have to pull the fuel an inch before the prime is held providing consistent fuel intake.

If any one has tried this I would love to hear your result. Either way i will post my result tommorow.

A check valve doesn't have any effect on the change in head pressure with change in attitude.

What does work is a pressurized tank with a fuel regulator. The Cline regulator is popular and I have used them with very good results.

Greg

I agree with what your saying about pressure, but it would shorten the draw of fuel to the carb as it locks in the prime.

When the engine leans out it's because the engine lacks the fuel draw and weakens enough to let the fuel fall back into the tank, and lean out the motor till it dies, but my idea is with the check valve locking in the prime the fuel can't fall back into the tank making the fuel draw more efficient.

It makes sense in theory, but will it work.

You still have "head pressure" to deal with. Maybe not quite the correct term...

You only have so much suction. In a perfect world you can only draw water up about 30ish feet no matter how much suction you have, even if you draw a perfect vacuum!

Add in a check valve and you also have to overcome the pressure to open the check valve, adding to the problem. You either need to pump the fuel or have enough pressure to force the fuel to the carb via a regulator.

I suggest giving it a try though. I've been wrong before

Ken

No, it doesn't make sense in theory. Think about how a siphon works.

Greg

Nope , no free lunch here . Like Ken and Greg have said , especially considering the added cracking pressure forward drop across the check valve itself .

Then again it is easy with a YS

If you are running muffler pressure, i wonder if a check valve in the muffler line, keeping pressure in the tank, would help.

The check valve traps the peaks of the power pulses so the pressure is considerable which is fine at full throttle but when you pull the throttle back all that trapped pressure has to go somewhere. It pushes more fuel at the engine tahn it can handle. That's the reason a check valve pressurised system requires a regulator.

Well after practical testing today the engine ran PERFECT. I tilted the model completely vertical from idle to full throttle and never a hiccup for a whole tank.

The idea worked for at least my application, and I think some are a little confused as to how I istalled the valve.

I used the valve on the carb intake installed at about where the tank would be mounted if I had mounted it at the stock location. The valve locks the engines prime making the motor much more efficient as it isn't fighting gravity of the full length of the fuel tubing to the clunk.

The motor is only pulling the fuel a short distance (maybe an inch) before it enters the valve removing the effects from gravity at the longer distance of the tank, making the motor's siphoning effect much more efficient with my Perry carb. (throttle response is INSTANT)

I believe a pump or fuel regulator is another way to go, but this works just as well, and it might be worth a try before spending in excess of $50 for the other two.

Originally Posted by storm2313

Well after practical testing today the engine ran PERFECT. I tilted the model completely vertical from idle to full throttle and never a hiccup for a whole tank.

The idea worked for at least my application, and I think some are a little confused as to how I istalled the valve.

I used the valve on the carb intake installed at about where the tank would be mounted if I had mounted it at the stock location. The valve locks the engines prime making the motor much more efficient as it isn't fighting gravity of the full length of the fuel tubing to the clunk.

The motor is only pulling the fuel a short distance (maybe an inch) before it enters the valve removing the effects from gravity at the longer distance of the tank, making the motor's siphoning effect much more efficient with my Perry carb. (throttle response is INSTANT)

I believe a pump or fuel regulator is another way to go, but this works just as well, and it might be worth a try before spending in excess of $50 for the other two.

Looks Like I may ave been wrong again. Was this a flying test or only on the ground? In the air is the only true test.

I went through that on my CAP with a partially pinched fuel line. Ran all day held vertical. Leaned out in the air.

Ken

Actually the weather was rough so I ran her on the ground throught the testing today. I will post flight testing and pics of the setup.(maybe a video would be better) I hope it stays the same. I can't wait for the prop to unload to see how the Tigre performs.

I will say the ST likes to run slightly rich on the low end. The Perry carb is VERY sensative to low end adjustments, and I would rather be slightly on the rich side. The model only weighs 7.2LBS. so it should be a monster in the air.

It's possible it ran better, but not because it was easier for the engine to draw fuel. The check valve prevents back flow, but the suction required to lift the fuel is the same. The suction required is actually greater because there is a pressure drop across the valve when the fuel flows.

Greg

I don't quite understand what your saying.

If the valve prevents the fuel from back flow then your eliminating the gravitational force on the fuel making the siphoning force required to bring the fuel to the carb less. The amount is less, how much less I can't measure.

I look at it as a header tank's effect. I'm using the fuel tubing to hold prime via the valve, eliminating 3/4 of the lenght of the fuel line to the clunk. The difference is I'm using the fuel line as a header tank. It holds a small amount of fuel without the effect of gravity's resistence making the fuel that much harder to get to the motor.

I'm trying to figure out what you mean by it needs more siphoning force with the valve in place.??

What he's saying is that it takes pressure to lift the check valve off its seat which appears as drag/resistance on the carb side.

Sorry, a basic textbook in fluid dynamics is in order. The header tank is also a misconception. It does not reduce the lift distance, it eliminate bubbles.

Greg