Odd fuel problem

[Ottmundr]

New problem just started happening. This has happened when the engine has been running for fifteen minutes, and happens almost every morning as well.

I live in the bay area so air temps in the morning have been in the 50's and 60's. I let the engine warm up and wait about 2 minutes before driving.

I have no problems driving on surface streets, or putting a load on the engine getting on the freeway. After I am on the freeway, and cruising for about a half mile, it feels as if I am running out of gas. I then play with the throttle, flooring it, letting back off to part throttle, get some response, it goes like this for half a mile or so, and then the problem goes away, and the car runs great for the rest of the day.

I am running the summit M2008 carburetor
https://www.summitracing.com/parts/sum-m08600vs
Fuel pump and filter are 5 months old, same as the carb.

What do you guys think this could be?

 

[AJ/FormS]

Well it's a 4bbl, so I guess it's a small block Mopar?

It's going lean.Or it's icing up.

 

[Ottmundr]

Yes, sorry didn't include that info. 318.

Also, that makes a lot of sense, the relative humidity has gone up in the same time period. Wretched clouds.

 

[AJ/FormS]

Carburetor icing occurs at air-temps below about 60*F and under high humidity conditions; ie this time of year. And is usually worst while cruising with the butterflies nearly closed.Atmospheric moisture freezes on the edge of the butterflies and chokes the venturies down. Slapping the gas-pedal breaks it off.But it reforms almost instantly. The usual cure is to provide heat to the underside of the carb or to the air entering the carb.It is very hard to diagnose on account of by the time you get stopped, and look, the ice has melted.
Once the intake manifold has warmed up, and the carb on top of it;then usually the problem goes away.
Too much ignition timing will cause the butterflies to be open just a very small amount at steady speed cruising,exacerbating the problem.
As to running lean;
Cold engines like extra fuel while cruising,on account of some of that low-speed fuel will condense on the intake floor, the port walls, and even inside the chambers, passing through the engine unburned.It is the job of the choke to enrich the mixture until this phenomenon stops.
Perhaps your choke needs to stay on a little longer?
Or perhaps the fuel level could be a tad higher?
Factory heads and intakes have an exhaust-crossover passage under the carb to heat it up quickly.A heat-riser valve in the exhaust forces some of the exhaust to flow from one side of the engine to the other,through this passage.
Of course with headers, the exhaust in this passage is more or less stagnant. Air-gap type manifolds are designed to run cold.