Hello,

I have been having more fuel related drivability problems this year than I had last year. When I say "fuel related drivability problems" I am referring to severe stumbling, severe hesitation, engine shutting off, etc. I know it is fuel related because I can smell fuel when the signs start. One of the things I did over the winter was paint my aluminum M1 intake with the Mopar Chrysler red paint. The other thing I did was remove the Holley heat shield; didn't think it was doing much. The Carter mechanical fuel pump, feed line and return line are all the same as last year. Same carb, air cleaner, headers, timing (36 total), radiator, etc. The car runs at 185 - 195 degrees according to my temp gauge and my Craftsman laser temp gauge (pointed at timing cover and thermostat housing). I am wondering if the issues that I am having are due to the painted intake not allowing the heat to be dissipated.

This weekend I drove my 68 Barracuda up into the foothills and mountains of Colorado (Peak-to-Peak byway). I had put about a half-tank of ethanol free gas in it prior to the trip. The temperature for the day was in the mid 80's in Denver and got progressively cooler as I climbed in altitude. I had the drivabilty issues occur several times, even at higher altitudes where the temps were much cooler. Two of the issues resulted in the car shutting off. The car started again, but I had to have the carb throttle blades wide open to get it to start. Once I started to descend, I did not have the issue again. The temp gauge, which reads coolant temp from intake, never hit 190 during the entire trip. I drove the car home in the evening and had no further problems.

Is the fuel worse than it was last year or did painting the intake and removing the Holley heat shield have that much of an effect?

I forgot to mention that I participated in a poker run from Woodland Park to Cripple Creek, which included going over a mountain pass (11,000 feet) around the same time last year without a single hiccup.

Also forgot to mention I have a 1/2" phenolic spacer in between the annular discharge carb and intake.

I'd vote for heat shield over the painted intake.

You performed two changes, painted the intake and removed the heat shield. I'd say you know the value of the heat shield now.

I've read tests done on paint as an insulator and the results are so small as to be insignificant.

Modern fuel overall is crap, especially the E10 predominately available in Colorado.

The altitude is also a factor as there is less atmosphere to absorb heat from components in the engine bay. So while the ambient air at altitude is cooler, there is less of it and it tends to create heat issues not experienced at lower elevations.

I don't feel you did anything that would put you further into the heat soak area. Especially given the non ethantol fuel. It sounds more like a carb related issue. Have you checked float drop on it? Or pulled the air cleaner and looked down the barrels or at the levels when it's giving you trouble? Holding it wide open is too much fuel. Smell is too much fuel.

put the heat shield back & if it ain't right then what Moper said & (as you know) something drastically changed, keep after it

My neighbors truck is getting hit with the fuel boil over now. He has had it 4yrs now with no issues and then in the last 60 days, whap! Fuel boiling over. It crapped out on him as he pulled into his driveway. Checked it out with a flashlight [dark outside] and I could see it boiling out of the venturi clusters. I checked the float level and drop, AFB btw, level was fine drop was off. Manifold raw Edelbrock aluminum. Summer temps no different for the last few months. He is going to get a heat shield from Classic, reproduction unit on bowtie stuff, like what I've used in years past that works quite well to keep heat off carb. 3969835, OE GM #, in case someone wants one for standard flange [3969837 for spreadbore]. But I think the main issue on his is that the fuel composition has changed without any notification of what you are buying at the pump. Too high of a concentration of alcohol. On my Coronet, the fuel can be heard boiling in the tank with just a 15 minute drive. Makes the exhaust run hotter netting more radiated heat to heat soak components.

As far as color affecting temperature, the key is heat absorption. White absorbs the least (coolest), black absorbs the most (hottest). The rest of the colors fall in between these two extremes. I have no idea where red would fall.

I don't think colors are relevant to underhood temps,
if you are in the shade with a white or black shirt, you aren't going to feel a difference between them, in the sun though, yes.

Convection/radiation/conduction are different

Joe

I think I am in the majority ( for once) here, painting played no measurable part here, unless we are maybe talking pick up bed thick paint. As mentioned, black color absorbs most heat, also emits the most heat, opposite for white, issue is the environment/heat sources and paths, radiant heat finds a reflective surface best for rejection like shiny alum or gold foil. Why all my PS boxes are painted silver.

He said it was non-ethanol fuel too.

I put the heat shield back on and insulated the fuel line that exits the mechanical fuel pump and feeds the carb. The fuel line that enters the fuel pump, including the return line, is already insulated with heat sheathing. Next, I re-routed and insulated my heater hose to get it away from the carb and fuel line. Then, I put the factory metal air cleaner assembly away and went with a K&N "XStream" open air filter assembly. Finally I adjusted the float level on the primary bowl (secondary float level was good) by increasing the fuel level to spec; it was low.

After all of that, it still acted up yesterday during a long (hour) hot drive (mid to high 80's in Denver yesterday).

So, I filled it up (7 gallons) with non-ethanol fuel (so still has about 8 gallons or E10 in it) in the evening on my way home. I will continue to fill it with non-ethanol fuel for at least another fill-up (to get to 100% non-ethanol in the tank) and see if that helps. Since it will start getting cooler here, my test may not reveal much. But I have a big cruise to do this coming Saturday, so I'll see what comes out of that.

This issue completely ruins the hobby.

I forgot to mention, that once the outside temps cooled down (in the evening), I had no further problems. The issue that I am experiencing is DEFINITELY heat related.