BobBurns

I recently bought a 1982 that has a stroked 351 (399), 4 bl Holley, 4 speed manual w/exhaust headers. I'm only getting 4mpg and suspect something is seriously wrong. I don't see or smell any gas leaks. Any suggestions?

DrinkinGasoline

First of all...is it a Windsor Family engine or Cleveland? Secondly, has the carb/choke been adjusted to the climate in which you live? Thirdly, I would be concerned about Differential gearing matching engine/trans input to it..Not sure why the 351 was stroked to 399 when 400's are a better choice to start with, but....ok.

BobBurns

It's a Windsor, and has a manual choke. It runs smooth and gives no indication of any problems other than the mpg.

DrinkinGasoline

From the on-set, I'm assuming (correct me if I'm wrong) that the differential gearing remained stock after the engine punch out. That in itself spells poor economy when rear gears are not matched to engine/trans. Which brings up another valid point. Is the trans stock? I would also look closely at the Holley as they are notoriously "fussy" carbs. If the engine cannot handle the CFM of the carb, it will either choke on the fuel or at best give poor results in MPG's. What CFM is the carb?

BobBurns

Thanks for the response. I will check the carb tonight when I get home from work. Checking the gearing will have to wait until this weekend, but my guess is it's a high gear set given it's quickness.

burnthelight88

You sure you're good at math? Lol.

I'd venture to say that your carb is too big. Too big is much worse than too small. Not saying you necessarily have to ditch it, but it may be an economy killer. I'd start by doing a re-tune of the carb. When was the trucks last tuneup?

BobBurns

OK it's an 800cfm double pumper (List# 4780-4) much too big. I should consider switching it out. I'm fairly handy, but not sure I should take this on myself. Any suggestions on which carb is better suited?

BobBurns

I've been asking around and have been advised my best bet is to switch to a Holley 3310S Model 4160.

burnthelight88

Yeah that's way too big. Swapping the carb is a very easy job. Tuning it is a little harder depending on your experience and what instructions you're using. If you're gonna pay someone to do anything, have it be the tuning part not the swap itself.

I've got a pretty good tuning guide I always use, I'll try to post it later.

DrinkinGasoline

I would bolt on a 550 cfm at the most for economy reasons. Even stroked to 399, I would even consider going 2v if you are looking for MPG's. I ran a 63 Galaxie 390 3 spd with a swapped 2bbl intake and Motorcraft 2100 2v for quite a few years with very decent mileage (15-16 avg).