40 Ply P-9 gas millage

[plym_46]

The step up erichment circuit depends on a vacuum signal from the intake through a slot in the carb to manifold gasket.  If that signal is not provided due to improper gasket alignment of improper gasket, the enrichmet jet stays open all the time rather than at time of low intake vacuum.  Did you pull you plugs to see how they are burning??? 

A friend had a 54 wagon that suffered from this ailment with milege figures of 10 to 11 mpg.  Once the vacuum signal was restored the car immediatly went to 17mpg.  I run dual carbs stock 3 speed and 4.11 rear end and average 17 and get close to 20 on road rips.

[bigaadams]

number of minor things could jointly be  causing your low mileage situation..timing, plug gap, dragging brakes, low tires, but do look real close at the step-up enrichment circuit for failure and that the choke is proper with the plate true vertical at temp..poor fuel air ratio adjustment and high float level or partial submerged float due to pin hole (causing boil over/perking)..inspect your fuel pump to ensure fuel is not being pumped into the crankcase due to a bad diaphram...basically read the section on fuel and follow the adjustment/tests


also test for vacuum and the actual vacuum advance diaphram for proper operation to advance you timing..

[Don St Peter]

I have a newly mfg carb, complete tune up, and completely checked over by known old Ply mechanic. still can only get avg. 10 to 10.5 mi per gal. Feel I should be getting around 15. I have recorded mileage for about 10 tanks of regular. I've exausted my list of items to check.
Any thought would be appreciated.
Don