I have US 35 cc engine with Ch igniton set at 29 degree BTDC. I rebuilt the carb. the carb is pumping fuel to the carb just fine when we are flipping the prop. when you stop flipping the engine, the fuel will go back down the fuel line in the tank. When we get it running it will run for a short bust and it will quick we took the fuel line off to run out the fuel and it ran fine for 30 seconds. correct me if i am wrong but the engine should run better with the fuel line on then off.

when I was flipping it to clean out the carb it would kick back a lot it snapped my fingures bad.

give me a idea on what to do now??

Paul

Could be 2 things...
Take the sttel cover (4 screws) off...Check the lever in the center, it should be flush with the casting next to it...Put the gasket on first, then the diaphragm...Take the other cover off, put the diaphragm on first, then gasket...
If the ignition is NOT a syncro spark it will kick back when starting, flip the prop harder with a glove...If it IS a syncro spark, the first flip retards the spark..Turn the ignition on and give it a good flip before you choke the carb......Can't kick back when there's no fuel in the cylinder..

This one is syncro spark. I had it on a engine before with no probs. I just rebilt this engine.

I was thinking about the kick back. I wonder if i have the timming more the 29 and not know it. I mite not have had it a TDC when I set it. Would that make it do a good kick back?

I will take the carb off and do what you said. I will let you knoe what I find out.

Paul

Too much advance will generate kick back. If the piston was not at the exact high point center when the timing was set you could be several degrees advanced or retarded from 29.

If the fuel runs back down the line after the engine is shut off, you need a carb repair kit. The pump flappers are warped and not stopping the return flow. The carb cannot function well like that. The engine might run some, but it will not be dependable.
The rest is covered by Pat.

He said the carb was rebuilt...
The pump flappers don't keep the fuel in, they're on the other side of the carb..
The fuel in the carb is contained in the other side, under the diaphragm..If fuel leaks back out it's because the needle is leaking, not the flappers...

Hey...your pretty good for a Antique!!!!!!!!!! Take Care, Capt,n

I looked at it again. The timing is right on 29. The needle was up NOT flush by 1/8 of a inch. That is a lot. I reset the needle and now it is working. the fuel is pummping and it is now staying in the line. I did not have the time to test run it yet. I will try it tomorrow.

I Think it was kicking back from having to much fuel in it.

Thanks for all you info

I will let you all know if it works

Paul

If the pump flaps can't control the direction the fuel is flowing how are they "supposed to work"?

A poorly seated, improperly installed, warped, or dry pump membrane most certainly will permit fuel to flow back into the tank. If the metering needle was too high I'm surprised the carb wasn't dripping out the venturi onto the ground. A bad pump can lead you to think it's working because fuel can move through the line, but in an amount greatly reduced from what it should be. If the pump is working like it should fuel will remain in the line.

Since the carb had been "rebuilt", but the metering needle set to an incorrect height, who's to say something else wasn't also done wrong during the rebuilding? I can think of about 6 places in the carb where something can be improperly installed, screwing every thing up.

The fuel was not dripping out of the carb cuz the tank was 2 feet below the carb. I do all my test run with my fuel line comming from my gas can and not the tank in the plane. That way I know if the pump is working or not. Like I said before the fuel would pump to the carb but then it would go back in to the can. The engine ran like crap. It was just fludding out. I went back in to the carb and saw that the pin was way to hi. I put it were was said up top and now it will bring the fuel out of the take that is 2 feet below the engine and stay there.

When I get up in the am and if I have time I will try to do a test run to see how it runs now.

Thanks for all the info

Paul

So it appears that you just identified why the fuel would run back to the tank. Low tank location, incorrect metering needle height, and still likely a weak pump membrane. Nice when you provide all the deatils to arrive at a conclusion.

Looks like Antique had the right answer!!! Way to go! Capt,n[)]

Cap, Figure it out, if fuel is leaking back past the flappers the pump isn't working right. The carb is ixhibiting multiple problems. The fork height was too high allowing fuel to flow back through the pump. And the pump diaphram is not seating correctly. The flappers act as check valves to control the direction of the fuel flow. The fuel flows from the tank to the pump to the metering diaphram. There is no provisions inside the carb to allow fuel to return to the tank if it is working correctly. The flappers work in conjunction with the pump diaphram. Unless the owner of the carb finds out why the fuel is flowing back through the pump he is going to have problems with his engine.
The metering needle will shut off fuel from flowing back to the carb and hide a faulty pump diaphram. Ki8FR should remove the metering needle, pump fuel to the carb then see if fuel flows back to the tank. If it doesn't flow back to the tank now perhaps he can say what fixes he did to the pump diaphram to fix it.
The meetering needle has one purpose, It opens and closes the flow from the pump to keep the fuel cavity full of gas.

That is true what you say. My bet there was a tiny piece of crud under one flapper valve with the combination of the a un seated fuel metering valve (or set to high) letting in air so drain-back would be faster or more apt to happen. I have took the cover of and sprayed silicone spray on all the rubber parts....on any carb I store to use later. It works great to keep those parts flexible and ready to do their job! Capt,n[)]

Even if the flappers on the pump side are perfect, all it takes is for the metering needle to leak from crud or not seating etc and fuel will flow back wards or for wards depending on the tank level. The metering needle is the cork so to speak Seen it happen too many times, fuel always seems to find it's way thru the pump side.

I did a little test to see just what it was. I put the needle back to were it was when the fuel went back in to the take. Hooked up the fuel line from my tank that is 2 feet under the carb. and put my finger over the carb and flipped the prop. the fuel went to carb. When I stoped flipping the fuel went back in the take. Put the needle back were it should be and did the test. The fuel went to the carb and stayed there.

terned on the power gave it a flip and she took off running. I let it run for about 15mi. and shut it down. let it sit for about 20mi and started it back up. I ran about 1gl of fuel though it with the tank 2 feet under the carb. I will run 1 more gl though it before I put in on the plane. The egnine is running great. Not broke in yet but will be soon.

with this test it is clear that the deedle was why the fuel went back in to the tank. Thanks antique. and every one that helped me out here. I leard somthing about carbs I did not know.
YOU HAVE TO SET THE NEEDLE..LOL