Carb Trouble On A 1948 Ef

[dutch25]

Hi, first time poster. Great forum here.

My dad has a 1948 EF Mack truck that has been in the family for over 40 years. It has the original EN290 motor with the Zenith 63AW12 down draft carburetor. He rebuilt the carburetor but it still will not run. The motor runs if you prime the cylinders so it is not a ignition problem. It seems like it is not pulling gas to the engine from the carb. We can not find any obvious vacuum leeks.

Does anyone here know about these carbs or have an idea what may be the problem?

Any help with this would be greatly appreciated.

[Mike]

Has he checked to see if it is pumping fuel to the carb? If so next check to see if the fuel is squirting down inside the carb. when you pull on the throutle to see if it goes down inside the manifold. You will won't the float bowl to be full of fuel to it's proper height.

mike

[Greg Rider]

Disconnect the line at the carb and see if you are getting fuel. It should be 4-5 psi at the carb. Make sure that the needle and seat are not stuck and that the float is free. The float lets fuel into the bowl where it is held till needed at the jets. Work your way back to the tank including the pump, filters, any bad hoses, kinked lines, etc. all the way to the tank. Take your seat out and remove the sending unit on top of the tank and be sure the dip-tube is not broke. It's a lot of stuff but it's all little things and wont take long, just frustrating.

[dutch25]

Thanks for the suggestions. and help.

Still not figures out yet. In the first post I said it is a down draft carb. It is actually a up draft carb that sits just under the intake manifold. We have bypassed the fuel lines and pump until we know the engine is running right. We are using a electric fuel pump and a gas can for a tank. Has anyone ever rebuilt one of these carbs?

[Firemack]

The updraft carb is little harder to diagnose than the down draft. I have rebuilt the updraft carb. I also used an electric pump to test the eliminate the possible issues with the fuel pump. First make sure to add a tee in the line to add a fuel pressure gauge, to insure that you are getting 3-5 psi at the carb. Once you establish that then see if it will run smoothly on the idle circuit. If that works then try to rev the engine and see if the engine will rev up smoothly, if it does good. If it backfires and then revs, you have a lean mixture from a bad accelerator pump, if it revs and stalls you may be running out of fuel from the float level being set too low. These steps will give you some basics to get started, once you have tried these then post the results and we should be able to help you on the next steps.

If you need a rebuld kit, Barry at Watts Mack was able to order that and is still available. aslo the entire rebulding instruction sheet and process is still available if you need it. I think Zentih still has it available.

Firemack