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En 401 Carb Help Needed

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Hello. I bought a B42T with a EN401. (I will post pics ASAP). It starts right up but you have feather the throttle and choke it to keep it runnig and accelerate. I am in the process of running seafoam, new fuel, replacing fuel lines and plugs.

I have heard the increasing the fuel pressure can help this issue. How could I do that?

Who rebuilds these Zenith carbs?

How does the oil bath air filter work? Can I just install a K & N instead?

Any help would be great!!! Thank you in advance!

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We have a Zenith updraft on our B75 464 engine, it had similar problems and was caused by a bad accelerator pump (ball). We used a rebuilder that could also bench test the carb to make sure everything worked properly. Cost was about $400. I got it back and the truck actually runs better than when it was new, according to members in the company when is was delivered in 1954. I used Mark Buber Carb rebuilders in AZ. There is a list of suppliers and rebuilders on this site (from the Mack Museum) and Bubers contact info is on the list.

I also changed the air filter to a K&N and works great. I called K&N and they recommended the filter based on dispacement, Horsepower and max rpm. I modified the original carb filter arrangement to use the K&N and kept the top of the Mack filter to looks like original.

Good Luck


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