1977 DodgeM880 engine tuning

[Bob'sM880]

I have a 1977 Dodge M880 with a 318 and new rebuilt carter 2 barrel carburetor. How do I go about correctly setting the mixture on this carburetor? It also has trouble warming up, the thermostat works fiine, but it takes almost half an hour before the choke thermostat(also new) opens the choke enough to make it driveable. Just chugs and acts like it is fighting just to stay running with the throttle floored.

Also, what can be done to improve fuel economy and what MPG should I expect to be getting?

And lastly, is there any advice on a different manifold and carburetor(4 barrel ) that can be installed on the 318? I really like this truck and earlier this year drove it to Biloxi, Mississippi from my home in Kansas and back(aound 1900 miles) to attend technical training in the Air Force.

Thank You very much for any advice,

Bob Wilson

New Dodge Enthusiast :gr_patrio

[Dodgevanman]

Usually the mixture screws are pre-set from the rebuilder...besides the mixture screw are only for idle anyhow. But most of the time anywhere from 2 to 2.5 turns out is sufficient.

The reason you choke isn't opeining up correctly is because 1.) The heat riser assembly on the exhaust manifold (usually on the passenger side) is frozen open and won't allow the exhaust gases to crossover the intake and open the thermostat or 2.) The crossover passages in the intake and heads are so gummed up with carbon it also wont allow the exhaust gases to crossover the intake.

A bad EGR valve can make the engine run bad as well

The easiest way to fix this is to trash the 2bbl. setup and get yourself an Edelbrock Performer intake (with EGR of course) and an Edelbrock 500cfm or 600cfm carburetor with electric choke. You can go with a set of headers or retain you stock exhaust manifolds..you'll just need to eliminate the heat riser.

[Banfiadh]

hhrrrmm, I believe holly has an intake that will fit a 318, and 318 heads.
Edelbrock intakes are good, but you need to have either 340 or 360 heads on the engine for it to fit. The difference is in the head to intake bolt pattern.
Ive got(had?) a '74 318 with the holly intake, and an edelbrock 1405 (600 cfm, 4bbl, manual choke) and a 340 camshaft.
the combination was pretty good, and at times I could tune 17 or better mpg out of the combo.
I could also (clocked) pull 140 mph out of that '73 W200 power wagon running a dana 60 rear 4.10, an NP 445, and an NP205 transfer case on 31 inch tires (stock, basically).
with a similar combo, you should be able to pull similar numbers, as the M880 is pretty much the same truck, give or take a few minor changes. Well, maybe not quite the torque, as the M880s are/were generally automatics, using either an NP 208 or NP 203 transfer case.
I couldnt quite spin all four on pavement, but in 2 high it was a blast, I actually pulled about 1.5 feet of air for about 30 feet one time when I flat flooored it, and dumped the clutch. (whups, I went home and hid before the cops showed up)
Note, while I believe hollies to be good, I preffer the Edelbrock, because theyre much easier to fine tune, and in the long run less expensive to upgrade. (offroad seats and such, and needle sets are about $20 bucks).
I pulled mine out of the box, bolted it on, checked the timing and tweaked the mixture screws about 1/8 turn, and then went out and pulled the 140 mph reffered to above.
The worse mileage I ever got, was pulling a box/PU bed trailer (loaded with truck parts, car parts, two roll aways, 3 top boxes w/tools, plus the truck was loaded as well guesstimated weight of around 11,000 lbs) at speeds of up to 100 mph (averaged 75 to 80) across country, My mileage averaged out to around 12 mpg on a 2800 mile trip.