Farm Boy guidance please!

[Iampappabear]

My recently completed farm Boy hit and miss engine stubbornly refuses to run longer than about 45 seconds, starting is achieved by placing my thumb over the air intake and varying the amount of air that I allow past. When the engine is started RPM increases for about 20 seconds then diminishes until the engine stops completely. Removing the spark plug and giving it a clean usually enables me to start the engine again.

Currently the fuel is Coleman camping stove fuel ( I cannot get it to start on Methyl Hydrate), compression is good and I feel if the timing was out I would be unable to get it to start at all.

I guess my questions to those so more experienced than I is:

- Why does the plug become fouled after such a short period?
- How to I set the engine up to run on Methyl Hydrate as opposed to Coleman fuel?

Thanking you in anticipation.

Colin

 

[Iampappabear]

My recently completed farm Boy hit and miss engine stubbornly refuses to run longer than about 45 seconds, starting is achieved by placing my thumb over the air intake and varying the amount of air that I allow past. When the engine is started RPM increases for about 20 seconds then diminishes until the engine stops completely. Removing the spark plug and giving it a clean usually enables me to start the engine again.

Currently the fuel is Coleman camping stove fuel ( I cannot get it to start on Methyl Hydrate), compression is good and I feel if the timing was out I would be unable to get it to start at all.

I guess my questions to those so more experienced than I is:

- Why does the plug become fouled after such a short period?
- How to I set the engine up to run on Methyl Hydrate as opposed to Coleman fuel?

Thanking you in anticipation.

Colin

Short video now attached.

 

[danallen]

What is the fuel level in the tank relative to the mixer. Mine likes them about the same.

 

[Brian Rupnow]

Your engine is running out of gas, not fouling the plug. The top of the fuel tank should be about 1/4" below the center of the carburetor throat.

 

[Jasonb]

Is that a clear top on the fuel tank? if so have you got a breather hole in it

Having the fuel level below the carb is not a problem, I've built a few that way but you do need a non return valve of some sort so the fuel does not drain back when the engine is missing.

 

[Vietti]

I think I wrote before but Randall Cox showed me the trick of using small to very small id nylon tubing for a fuel line. Capillary attraction keeps the fuel from falling off the needle and obviates the need for a sometimes troublesome foot valve. Got mine years ago from MSC but other sources probably cheaper.

 

[Iampappabear]

Well thanks to the input received here, I managed to get a 10 minute run tonight. Changes made were an increase in the level of fuel in the tank and remove the tank lid as it fitted very tightly and may have been causing a slight vacuum in the tank.

To keep it running, I had to keep my thumb over the air intake and only allow the slightest bit of air to enter the fuel mixer, if the engine started to slow down, I closed off the air completely and the engine would pick up. Adjusting the thumbscrew to allow more fuel in appeared to have no impact on the running of the engine which leads me to suspect there is a partial blockage in the mixer.

Thanks for all your input, you were all pretty much of one voice in that my problems were fuel related.

Colin

 

[Master]

My plug fouled with Coleman fuel. Works fine on acetone.

 

[Harglo]

Your engine is running out of gas, not fouling the plug. The top of the fuel tank should be about 1/4" below the center of the carburetor throat.

When the engine stops an you take out the plug make ((sure}} you do have a spark. If its blue your good a soft yellow means something a-ray. Yes sounds like you have some fuel level issue. Mine runs so smooth with a long miss that made a 20% larger on runs equally. I run mine on propane.
Harvey

 

[William May]

Another factor may be that, being newly completed, there has not been enough run time on it to get the rings to fully seat.

I have watched Model T's on the assembly line, and when they got to first engine start, they smoked like crazy. But after a few minutes of running, they were much better.

I think your engine's behavior will get better the longer you run it.