I have a new K&B Sportster .65 engine. It is a light and reasonably powerful engine (APC 13x7 @ 10,200RPM). I am having problems with the mixture going lean gradually between 1/2 and 2/3 of the tank? I use a Dubro 8oz tank with all new hoses and pipes and as high in it's compartment as possible. Tank is surrounded by foam. The remote needle is rigidly mounted at the same height as the spray bar. There are NO bubbles in the fuel line while running (full or not). I have enlarged the hole in the exhaust pressure tap. I have enlarged the id of the pressure line. The spray bar is 3/8 of an inch below the top of the tank (I had to lower the engine).

If I start the flight sloppy rich then I get rather weak performance for about four minutes. Perfect running for four minutes and after that it gets leaner and leaner till it quits. This is a gradual change NOT sudden! My Goldberg Tiger 60 is easy enough to dead-stick but I love the power when set 300 RPM below peak.

Do I need a Cline regulator? Do I need a Perry pump?

Anybody try the fuel system in the attached drawing? Does it work?

Francis

yes u need pump. it will handle same mixture during full flight. u need pump. I use perry one and it's good one

I'm no engine guru but I do not think tank height is the problem.

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I know this is not specific to K&B, but here is a direct copy/paste from the OS 61FX manual:
FUEL TANK LOCATION
Locate the fuel tank so that the top of the tank is 5 - 10mm (1/4-3/8") above the level of the needle-valve.
Be sure to use a pressurized fuel system by connecting the muffler pressure nipple to the ventpipe of the fuel tank.
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Unfortunately I have no idea what the real problem is. It wouldn't cost anything other than time and a little fuel to try the non-pressurized system. Both needles will probably need adjustment to run without muffler pressure.

When you use a pump you actually use less fuel because you can set the mixture at optimum which is in your case about 300 rpm rich of peak, A Perry supplies about .25 psi without muffler pressure and is constant.

I am a total pump and regulator advocate. For your application the pump is fine. It's only $30 at Tower. If your tank was really far away I'd go with a Cline or Ironbay regulator. They make your glow engine run WAYYY better. And yes it will use less fuel, you will add a few minutes of flight time to the same size tank. One thing the Cline or Ironbay regulator are much easier to get working. The Perry pump takes some tweaking. Some people just plumb them up and the work fine whereas others (me) have a hell of a time getting it to run right.

By the way, that diagram you show has no pressure from the engine or exhaust. That means the engine must run completely on suction. I have my doubts about that diagram. I would only add one change to it: connect that vent line to the exhaust pressure tap. Then it becomes a Uni-flow setup which is supposed to work pretty good (control line).

Also, I understand that not all carbs will work with a pump, however the Cline is basically an "on demand" system that "should" work with any carb. I have two of them on different engines and the needles become very broadly adjustable.

Good Flying,
mike

you don't need a pump..... it's the mindless location of the pressure tap which is your problem.... why-o-why did they do that [&:] !!!.... if you were to measure your tank pressure you would find it varies greatly with speed and actuall can go slightly negative!..... plug it with a cut-off screw and put a tap into the muffler, where it belongs.... I bet you can find that the engine even runs better with NO muffler pressure [X(]....

[:-]

Tonight I tried that screwy three line system and It does not work worth *^%@#&&.


Perry Pump for me ---> but I will probly try moving the pressure tap as sugested.

Francis

Yeah move it to the crank case or the pump won't work either.

Perry Pump Installed !

The pump is finally installed and while it was a pain in the a#s it looks fairly neat.

I plan to try it out this sunday.

Francis

I have not seen a pump mounted this way. (vertically) Let us know how it works as the instructions say "for best results" mount horizontally.
-Tom

don't mount the pump that way.

I called Perry and they said that a vertical mounting is fine. There is no where else to mount.


Francis

Hello!
You sure don't need a pump! A pump is only needed when you have the tank positioned on the C of G.
Pictures show that you have the tank too low!!!
And for best results you better use either a Tettra "bubbleless tank from Dave Shadel, US Y&S importer or...the tank you have... set up in a "Uniflow" way with two clunks.
The picture you have shown is correct but the vent line must be attached to the pressure nipple once you are about to fly.
You would be much better off if you mounted your engine side-ways instead of right up the way you have now, that way the center of the tank could be positioned correctly at the center of the carb intake.when the airplane sits horizontal...which is very important.

Regards!
Jan K
Sweden

In your third picture , I don't see whats giving the tank pressure. Can you explain a little ?

I don't know if you will need the pump, but your plumming has got me baffled!!!. In picture 1 post #1 your muffler pressure line is connected to a low pressure area of the muffler. I would expect to see a smoke line here not a pressure line. In your second set of pictures you have the low pressure nipple connected to a high pressure nipple (the new one you have tapped), why?
If you connect your pressure line from the 'new nipple' to your tank - top line shown in post #1 picture 3.
Use line 2 (centre line) to fill the tank - then cap.
Use line 3 (bottom line) for fuel to carb.
I maybe 'off base' here but thats just the way I see it .

My $.02 -
If the pump doesn't help, consider this:

My K&B Sportsters never liked any kind of pressure - they prefer to run from a vented tank. The trick with a vertically mounted engine like your Super Sportster is to keep the carb throat as close to the tank center line as possible. If you have room, try moving the tank as far towards the top of the fuselage as possible. Or you could turn the engine on its side, but then the cheeks look terrible.

Hi!
Agree with Fencemagnet...the way you take pressure on the exhaust stubb area on the silencer is no good...much better to drill a hole and tap and place the nipple on the muffler...that way you get more even pressure. If you need pressure at all ofcourse..tha's not needed on engines like yours which put out low power and have small carb intake area.

Your drawing showing the tank set up is OK..It's what the Cl-guys call a "Uniflow" tank set-up and that's the best tank set-up you can have if you use an ordinary R/C fueltank. As I said earlier the Tettra "bubbleless" tank is even superior to the Uniflow tank though.
Regards!
Jan K
Sweden

Jaka,

The venturi in my engine is .342" ( small ??? 8.68mm ). My tank is as high as is possible. My engine has been lowered. The spraybar is 3/8" below the top of the tank. The tank is as close as possible to the firewall. I tried that screwy three line, special; clunk system and It does not work worth *^%@#&&. The pressure tap on the the exhaust stubb area on the silencer is where K&B put it. I moved it to the muffler body with no luck.


Francis

MerlinL14,

The plumming that has got you baffled is aeasy way to block off the now unused pressure taps.

Francis