Rebuild Holly carb or replace with Zenith

[dfanders]

Gents,

I have an 1957 M52 with a holly carb on a gasser engine. This is Armyman30yearplus's old truck. Just did a run and for the first half (about 30 minutes) she ran fine at 55mph. After going thru tolls( slowed down, shifted,etc) i made the second leg of about 40 minutes. On this leg i could only get 45 mph due to backfiring and loss of power when pushing the pedal down. At 45 mph she runs steady with a slight hesitation at times and occasional backfire.
I had already planned on rebuilding the holly carb, and have the kit to due it. I am wondering if i should just buy a zenith and replace the holly? I have read that folks are happy with the zenith and was wondering if it is a true bolt on replacement? If the zenith really does get 4 mpg as opposed to 2 mpg on the holly - it will pay for itself on my first run!
I plan on using the truck to pull a 45 foot semi trailer hauling a ww2 M3 white half track and 2 ww2 british Dingo armoured cars. The main use will be making 4 hour over land runs to ww2 events.Having something for highway use was the plan. I went with the M52 for field recovery if needed , as it has a front winch. It is also a gasser , and righ tnow gas is cheap !

 

[m139h2otruck]

You can try to rebuild the Holley, but when we did, it made no difference in fuel use. Call Saturn and get a Zenith, it is a true bolt-on. Just have to turn or reset the air cleaner to hit the carb entrance fitting.

Be sure to check the following items:

1. No mice in aircleaner!
2. Fuel pump is working right and fuel filter not plugged. We installed a WIX fuel filter adaptor and use a large 30 micron filter w/ drain in place of the little original unit.
3. Check points and cap/rotor for pitting and crud. Make sure dizzy advances right, and is not stuck. Went through this with ours, "rebuilt" unit was retarding spark with increasing RPM!! Advance static timing at least 5-7 degrees, truck will run better and fuel use will decrease.
4. Clean, fresh gas. New gas is a pain, and likes water!
5. Governor is working right. Zenith carbs have a very thin diaphram for the governor pull-off, and we blew ours. Holley unit is multi thickness, but if the governor is not right you can't rev to 2,800-2,900 RPM. Don't go over 2,900-3,000 RPM as these motors will fail at high speeds (think Cummins 855). We shift at about 2,700 or so.

Empty, your truck will fly, but be prepared for slow speeds loaded.

 

[m139h2otruck]

Also, still looking for Zenith parts, gaskets, kits, etc. Anyone? Thanks