Hello again,
Been awhile since I have been here. Trucks been running good for awhile but it has started acting up again. It's a 79 D100 with a slant six, single barrel carter and a three on the tree. Engine has about 20k since rebuild. Problem I get is that at highway speeds of about 70 mph holding about 1/2 throttle, the engine intermitently cuts out. Its not a miss but more like the engine shuts down for about a second at a time like it is starving for gas. If I try to accelerate past that point it gets worse. It does it up or down hills. I have tried to see if it will act the same in second gear but it only happens in third. It seems to have started when the weather turned colder (no idea why that have anything to do with it but I mention anyway).
I have already done the fuel line mod so I really don't think it is a heat soak issue. Now the carb has been rebuilt at least 4 times (I have a had this truck for 14 years). I think it may be time for new carb but all I find is remans. Furthermore, I only find holley's and no carters. I haven't been looking really hard yet though since I am not convinced this is even the problem. My question for you guys is what do you think may be the problem? If you think it is the carb, what do recommend? Another Carter 1 bbl or the holley 1bbl? Not really looking to go 2 bbl at this time but who knows. I appreciate any advice.

Thanks
Frank

Clogged up exhaust........

Don't happen to have a cat converter?

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Don't think it's a clogged exhaust, or it would be worse in 2nd gear. Sounds like probably a fuel problem, but it can't hurt to recheck the ignition system, too, top to bottom and front to back. Reman carbs tend to be junk. I have some new-new ones remaining on the shelf; send me a PM if you'd like one.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Cat converter is gone and the exhaust has pretty much been ruled out. Nothing but pipe and muffler now. I have considered the ignition but it is running eletronic ignition, I can't see it missing at 3500-4000rpm and only in third gear. Second gear at 4500 rpm it runs fine.
The reason I am thinking fuel system is the conditions that have to be present for the problem to occur. It only happens at certain speed or rpm and under certain load characteristics or third gear only. I almost get the feeling that what may be happening is that the little 1 bbl carb just can't push the amount of fuel needed to sustain that speed and is acting as if it were a governor. God knows this truck was not designed for highway use. When I first got it I had to change rear ends and put some taller gears back there just to break 60 MPH. It has run well with that setup but then I have never really pushed her this hard and fast. I am almost starting to think that a 2bbl is the answer. any thoughts??

That's not it. The 1bbl carb certainly isn't the world's biggest, but they're not too small and they work fine. These vehicles (and others much bigger/heavier than yours also equipped with slant-6 engines and 1bbl carburetors) do not have driveability problems such as you describe when everything's working correctly.
A 2bbl setup would be an upgrade, not a repair. A repair would be a properly-working carburetor (if your problem is in the carburetor, which I agree with you seems likely.)

Got your PM and responded, by the way.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I have had the same problem. In my case, it turned out to be a float set too low. This typically would not all of the sudden happen but it may indicate that at high, sustained engine speeds, you are running out of fuel. I would be interested to see if your plugs show an indication of lean running conditions. Is it running a little warmer than usual?
If it is being starved of fuel, I would check the float level, partially clogged fuel filter (Rust?), partially clogged fuel line all the way back to the tank (rust?), and for a weak fuel pump.
Good luck and keep us posted.

Just changed the fuel pump and recently performed the fuel line mod so I don't think the problems could lie there. I would tend to agree with the assessment that I am not undercarbed since I am running totally stock. I can definately see some validity in the floats being set to low. That idea make total sense to me at this point. Although it seems that the problem would also occur in second gear, I have not sustained that level of demand for the same extended periods of time as I have in third. I am leaning towards a new carb though sinse this one is about thirty years old and has been rebuilt many times. Thanks for the advise guys. I'll keep you posted