Small carbs

[Toe_cutter]

Anyone know much about the old Rochester Monojet carbs? I just acquired a Chevy k20 with an 8 ft service bed full of old tools and a 292 engine. I got it super cheap because the rear main is leaking, the gas tank is leaking and it has some rust, I was planning on using it to haul firewood and scrap metal from work, but the thing just has insane torque and ok economy. Starting with the tank bone dry I put one gallon in and drove it home, 37 miles total, I made it 14.8 before I ran out, 13.2 the next gallon, in 30 degree weather with what im guessing is 2500 pounds of tools, snow plow rigging on the front, and the massive tool bed. Im curious to see what it would pull without all the weight. Anyway, are ther any tricks to tuning these old carbs to get better mileage other than just turning the mixture screw? Everything I have read says chuck em and get a four barrel but the intake required to do that is almost $400, and thats alot of gas.

[ex-x-fire]

You could rejet it, but thats a hit & miss deal, might make it really under powered. I think a tbi junkyard swap is worth looking into, I'd sart by getting a 305 tbi unit out of a chevy truck, caprice, or camaro. Get the harness, sensors, ecm,ect. You'll need to find a computer controlled distributor, or you might be able to make one using the guts of another distibutor & putting it into your original one.

[ecomodded]

Buy a jug of kerosene to soak the carb's in and put a quality rebuild kit in it.
smaller intake= less hp = less gas consumed,unless its running rich or out of carb tune. Set the carb up to factory spec , something like 2 1/2 turns out from seated , so on and so fourth,then connect a vacuum gauge to the running motor and tune till its somewhere around 15 lbs, I forget, your manual will know.
your Truck sounds really cool, loose some weight from it ! sounds like your carrying a lot of crap!

[JRMichler]

Small carbs get better mileage than larger carbs because higher air velocity through the carb does a better job of atomizing the fuel. A four barrel carb can do better if the primary venturies are small AND you drive so the secondaries never open.

A beater truck used only a little will never pay off $400 upgrades. Do the cheap stuff - carb rebuild, rear main, tire pressure, driving habits.

[bandit86]

Keep the 2 barrel. You won't like the 4 for Economy. Tune it up and let the engine work. Get A 700 r4 tranny. Has overdrive and more efficient. Easy to wire in. Has different first gear options get nice and low (numerically higher gear ratio) to get that beast moving. A diesel torque converter will get the tranny working at lower rpm and make it even more efficient

292 or 392 engine? Small block or big? 4x4 then get some manual locking hubs. Gonna work it hard? If so keep stock size tires if not get some taller skinny commercial tires. Blow them up nice and hard to 80 psi

[Toe_cutter]

292 inline six, just under 4 inch bore and 4.125 inch stroke, one barrel carb, 4.88 (ouch) gears, it is an old school truck so it has a solid front axle and manual hubs. I'm toying with the idea of propane, I have an old sytem that came of another truck, if I can find parts to rebuild it properly I may switch over to it, bump up the compression and have a much cleaner burning beater truck.

[blimo]

Monojets work pretty well. They have good booster venturis. Re-build it to specs and make sure the jet needle's piston isn't binding in it's bore. Make sure the needle isn't worn flat on the side it rubs on the jet. Where you would go to get a new needle and jet to match your application is beyond me...

If you think it has torque now, just put a long tube exhaust header on it.

And if that isn't enough get an old intake manifold and split the siamesed intake ports into individual runners. (web search).

I had very good luck replacing the ignition points with an electronic ignition converter that retained the stock distributor cap (upgraded to one with copper posts - Standard Blue Streak..).

You could mess with the distributor curve, too.

Then you'd need a taller rear-end, or taller tires.

[Toe_cutter]

A gearing change would cost about $1000 in parts alone unless I can manage to find a donor, and the tires are already 235/85/16's so any taller and I would have to go way wider.

[ron]

run it, best I ever got out of a 62 was 18mpg on flat 250 mi trip,best advice is (blimo) the pertronix distributor mod makes it start(faster) and run(leaner)just throw the points and cap in the glovebox Just in case!