I absolutly LOVE this combo. Slant six in a chevy truck with a ford rear and no freakin' window! This has me written all over it.

The missing window will make a substantial difference in mileage, but probably not to the tune of 8-10mpg. It's a factor, but not the culprit. If it was, you probably wouldn't be able to get up to 60mph - the motor would run out of steam before that happened.

You don't need a GPS to check your speedo. You need an interstate and a stopwatch. Go 60mph per the speedo, use the green mile markers on the shoulder, and start the watch as you pass one. If you pass another at exactly 60 seconds later, you are doing 60mph. If not, you can calculate the margin of error. My guess is that even without the windshield, you are getting about half of the mileage (highway) you should be. This means you'd be doing about 30mph on the highway - not likely.

The weight you give for the truck sounds a tad low to me. I could be wrong about that, but how do you know that is the true weight?

Are you able to see the exhaust pipe at speed? Or have someone follow and watch for smoke?

Does this thing have a tach? Are we turning 5000rpm at 60mph? 1000 rpm @ 60mph?

I'm guessing the carb issue is the one causing the problem, but it can't hurt to time it, do a compression check, plugs and wires. One or two dropped cylinders would cause those symptoms, but the truck probably would run crappy and smell like a gas station. But we can't rule out a mid-speed ignition miss without knowing about black smoke. I'm curious to see what the final answer is.

-Kip on Truckin'

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1965 Valiant wagon Turbo slant (work in progress)
2000 Chevy 155" cargo van - The Abductor
1970 Newport convertible
1996 Buick Roadmaster Wagon
1966 CruiseAire motor home
1990 Toyota 1 ton box truck TURBO slant (scraped)

I went to a tractor trailer wieght scale and 3080lbs was the total, it could be because some metal was removed from the radiator support area since I performed a six inch channel on the cab. Also the slant six might be lighter than an original six. I dont have a tach yet. I guess I could stick my head out the window and take a look at the exhaust.

That truck is so cool it actually HURTS me. I am so jealous! Don't ever paint it EVER or I will find you and smack you.

Truck scales don't lie. The ones at the weigh stations might, but the private CAT scales don't. Channeling, slant versus stock engine, missing bits, I believe 3000lbs.

Making some assumptions (brakes not dragging, wheels actually round, engine not running at 5000rpm, fuel leak, etc) we can deduce two possibilities.

1. That fuel is going somewhere. Either it is going out the tailpipe unburnt, or it's getting burnt but at the wrong time.

Did we test vacuume advance? Pull the hose, if mileage doesn't change then we know it's not working right.

2. Something is massively wrong internally. Like, a piston shattered or a valve got sucked or the cam jumped a tooth. Something really weird and unlikely.

Keep at it.
Kip On Truckin'

_________________
1965 Valiant wagon Turbo slant (work in progress)
2000 Chevy 155" cargo van - The Abductor
1970 Newport convertible
1996 Buick Roadmaster Wagon
1966 CruiseAire motor home
1990 Toyota 1 ton box truck TURBO slant (scraped)

You hit the nail on the head!
First off, there are some suspicious decals on the top of the carb leading me to assume that this is one of those nasty rebuilts.

After removing the float bowl, I discovered a check ball on the bottom. There is a plastic lever that operates two balls when vacuum is lost(full throttle I assume)

The brass ring that hold the ball had work out of the block

I am going to attempt to nick the sides of the ring and see if it holds.

It currently has a 55 main jet. Would going up a couple of sizes help performance Any?

Thanks.

Yep, that's your power valve. When those check balls and retainers fall apart/out, you're dumping tons of fuel into the engine all the time. Real easy to start from cold, but it'll drink down the contents of your bank account through the carburetor!

Don't mess with this remanned-to-death 1920; send me a PM for a brand-new Carter.

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Too many people who were born on third base actually believe they've hit a triple.