Hello all, I've been getting crappy mileage for a bit..just now getting around to looking into it. I've got about 200 miles on a tank and I'm dry.
That's horrid.

My bird has a 305, tpi heads, stock tpi cam, eddy performer rpm intake, holley 600 vac secondary, no choke, point type dizzy set at 10° base timing, headers with true duals, no cats with one glasspack per side. 700r trans, no torque converter lockup, 343 posi rear and 31x10.5x15 mud tires. No ac, no smog. Gotta love non emissions states
Runs and idles fine under 2500 rpm.

Lightly blows white smoke, REALLY blows it on wide open throttle and deceleration.

Even with my motor running like crap above 2500, I should be getting better than 13mpg avg, yes? I don't hot rod in it much, tho it is a dd.

 

No

You will probably do better with it running right but without knowing if the swap was done correctly and there being likely coolant leak somewhere I am going to again say no.

Heavy tires are also not helping

 

I get 12/13 mpg in all city driving with the A/C. However; I do get better hyw miles into the 20's.

 

I'm fairly certain It was done right. I'm also guessing I have either a warped manifold or heads. I've changed intake gaskets 11 times, various thickness and materials. No change. No coolant in my oil either. Its actually got a blue tinge to it.

 

I live out rural, mostly highway. The 13mpg is my average. Highway I'm probably getting around 17.

I don't expect a lifted, carb'd, v8 anything with mud tires to get impressive mileage, but 13mpg average seems way too low. My father's avalanche gets 16..

 

I haven't seen one of those since the 80s except on original restos. Why?

 

I tried HEI, from stock vac advance as well as Accel. Every type of coil from cheapest Orileys has, all the way to accel and msd. Hei is cursed for me. I went though 14 coils and modules in 3 months. Switched to point type from a 69 camaro, set my point gap and haven't had an issue since.

 

if you're happy with it, that's all that matters I suppose. I'm sure your coil/module issue was not a result of bad coils/modules though.

 

I don't think so either, after that many, it had to be something I did and was missing

 

My carb'd 72 vette gets 14.6 mpg normal and 16.8 mpg highway. Dart 400, Demon carb, HEI, TH400 with yank 3200 stall and 3.08 gears.

Your 305 TPI should be able to get better mpg than my vette if your install, parts & tune are correct.

What do the plugs look like?

Sometimes a bad O2 sensor will hurt gas mileage.
Slipping transmissions kill mpg.
Bad alignment & under inflated tire hurt gas mileage.

I would have an expert mechanic check the timing, and ignition system. Something is wrong to lose 14 hei coils.

 

I don't have o2 sensors, no computer. My plus have a light carbon coating (despite being brand new), and..yeah..something is seriously wrong. My timing is dead on, I dunno the issue.

This motor is nearly dead, so I don't want to put more money into it. Just today went mudding, suddenly started blowing thick blue smoke. Had oil yesterday..yet today nearly empty with black media on the dipstick. Gonna venture to say I'll have a blown bearing here within a few weeks. Either way, I have a 350 nearly ready. Didn't fair too bad for a junk yard car/motor lol