View Full Version : Check valve in fuel line

brian Rupnow
03-30-2013, 07:25 PM
Today I seen something I had never seen before. I have had others tell me about the necessity for a check valve in the fuel line of a hit and miss engine. I didn't disbelieve them---I just filed the information away in the back of my head with 67 years worth of other "things worth knowing". This afternoon while attempting to run my sawmill with the Odds and Ends hit and miss engine I just finished, I actually got to see this happen. I have a transparent fuel line leading from the bottom of my fuel tank up to the carburetor. I would crank the engine with my electric drill, and choke it a bit with my finger over the carb untill it fired and ran. When the engine was "hitting", the fuel line would stay full. As soon as the engine went into "miss" mode, the fuel would all run back down the line into the tank. Then when the engine slowed and the governor weights allowed the exhaust valve to close, there would be a definite pause while the fuel rushed back up the line to the carb and the engine would fire again. This was a really great thing to observe, first hand. This week I will build a check valve and put it in the fuel line.

03-30-2013, 08:06 PM
I would think a check valve in the fuel would be a good idea for any non gravity fed carb, Else you might be cranking awhile before that fuel gets to the carb on cold starts.

Float valves and pumps (or gravity feed) are a wonderful thing :)

03-30-2013, 08:59 PM
You'll probably find that you will be able to start the engine by hand-cranking once you have that check valve installed. Choking will probably still be required.

You said, "attempting to run the sawmill".... implying that it didn't work..??

brian Rupnow
03-31-2013, 10:21 AM
I got up early this morning before hoards of egg hunting grandchildren descend on my house, and did a quick design of a check valve. This should do the trick.

Ron of Va
03-31-2013, 12:37 PM
I think I would cut the seat with a ball end mill, and add a small weak spring so the check valve would not have to be perfectly vertical at all times. (But I have never made one, so what do I know?) Yours looks good.

Weston Bye
03-31-2013, 01:17 PM
Your drawing didn't come up for me, but I learned from the steam locomotive books by Kozo H. that you make a nice crisp edge for the ball seat and then place the ball and hit it with a punch and hammer. This custom forms the seat to the ball.

I've had good success by following these directions.

brian Rupnow
03-31-2013, 01:29 PM
Got all finished up just as the gang rolled in. Weston---You're right, I read the same, so I placed the bearing in the brass seat and gave it a good whack with a 1/8" punch. That seemed to make a difference in the old "put it in your mouth and blow as hard as you can" test. The ball seemed to seat more completely after a good whack with a hammer. Will Loctite after everybody leaves this afternoon. I didn't put a spring in because these small bore engines don't create enough venturi effect to lift the ball off its seat against spring pressure.

03-31-2013, 05:57 PM
FWIW: we seat the check balls in our engines that way, also, it works well. You shouldn't need a spring.

brian Rupnow
03-31-2013, 06:48 PM
The check valve works good. I don't see any "run back" of the fuel in the line now. Of course, no good deed goes unpunished. Somehow, in all my screwing about with the carb, I have mucked up the gasket which seals the carb to the cylinder and the engine now doesn't want to run except in short bursts. By using the old liquid dishsoap trick, I see it blowing bubbles around the connection between the carb and the cylinder. Tomorrows job will be to replace my cereal box cardboard gaskets with some better gasket material.