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Fuel Sucks! Or doesn't as the case may beQ:I have been playing with a carb problem on my '29 Economy XK 6 h.p. (Iam 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 mclarem1@rochester.rr.com 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... Goatboy237@aol.com 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 mclarem1@rochester.rr.com 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 overGoatboy237@aol.com ... This article is part of the Stationary Internal Combustion Engine Frequently Asked Questions (FAQ). This series is a combination of my views and knowledge and the views and knowledge of other people - most of them members of the Stationary Engine Mailing List (More info on ATIS). Those articles which were written by others are © Copyright to the author. Those articles written by myself are © Copyright to Paul Pavlinovich.
Got comments?If you would like to comment on any part of the FAQ please do so by using theDisclaimer:It should be noted that the information given in this document is considered to be good advice by the people who give it, however any legal liability lies strictly with the reader. The contributors are hobbiests not professionals. |
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Last modified Sunday, 06-Aug-2006 12:15:09 BST |
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