Q:

I have been playing with a carb problem on my '29 Economy XK 6 h.p. (I
am NOT convinced that it is the original carb for the engine, BTW)

It simply refuses to suck fuel up from the tank.

Upon taking the carb off and apart today, I found that the rubber O-ring
on the fuel pump "piston" was shot. I am sure that is a part of the
problem.

However, there is supposed to be some kind of a cover on the underside
of the carb that is held in place with a screw. It is shown in the
pictures at the following page:

http://www.missandhit.com/arcade/EconomyCarb.cfm

Over the years someone has replaced the original cover with a piece of
tin, which seals VERY poorly. If I push on the cover while the engine is
running it immediately changes the speed by controlling the amount of
air intake. I am wondering if this would affect the amount of fuel
suction as well?

Does anyone know where the correct location is for the check ball? What
about the size?

Thanks,
Tim This email address is being protected from spambots. You need JavaScript enabled to view it.

A:

Absolutely! The fuel is sucked in by the vacuum formed in the fuel pipe because the carb only sucks so much air through the intake. Some of the vacuum is "spent" sucking in air past a resistance and some of it is spent sucking fuel out of the tank. Especially with an engine like an Economy (ok, most horizontals) where the tank is under the engine so there is no gravity feed). Make that cover seal as tight as the original. Did you say yours has a pump?

Air is easier to suck than fuel - if you make the job of sucking air too easy, the engine will not suck any fuel.

You might also check to make sure any check valves are nice and free moving and only work in the direction they're supposed to - ever put one on backwards? I'm ashamed to say I have.

A:

the piston assembly,,,(hollow perforated tube/check ball) sits on top of a spring,,,there is another check ball under this piston assembly,,,to seal the hole in the carb casting,,,this prevents the pump from losing its prime back into the tank,,,a possible problem might be that the carb body check ball seat is pitted or out of round,,,take the piston assembly out,,,and take a punch that will reach down to the ball,,,and squarely strike it several times to seat it better,,,then there should be a cast iron/steel plug on top of the brass pump assembly to keep the check ball in,,,take it out,,and seat the piston ball,,,now the balls might seal a little better and you can get a little more suction,,,make sure the spring is stout enough to ensure the plunger makes a sharp upward stroke,,,but not too stout,,,if the plunger/bore is worn too bad,,it may have to be machined out and a new one built,,,I used 1/4 inch steel bearing balls,,,and I'm no expert,,,but that kinda looks like a !
fairbanks carb,,,I have a '29 6 horse XK also,,,need anything else,,i'd be glad to help... This email address is being protected from spambots. You need JavaScript enabled to view it.

A:

Thanks for the help.

I have taken things further apart, and I find only one checkball. I have
the one immediately under the piston assembly.

Are you saying there is a check ball WITHIN the tube, as well as the
check ball below the tube (with the spring)?
Tim This email address is being protected from spambots. You need JavaScript enabled to view it.

A:

yep,,,there should be on inside it,,,when the plunger gets pushed down,,,it forces air inside the pump bore out past the ball in the plunger,,,on the up stoke,,it seals,,,and causes a draw from the fuel tank,,then on the down stroke again,,the ball in the bottom of the carb seals, preventing the newly drawn fuel from seeping out,,,giving the plunger something to grab on it's next stroke,,,this happens over and over
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