I have a '53 F100. It has a highly modified 400 engine w/ 351C-4V heads and C6 tranny. I have been running this setup for a couple of years. I take it to shows and drive in parades.

It has a 750 CFM Carter carb, and Carter electric fuel pump. It also has a Mallory Unilite Dist. and a Holley Annihilator CD unit.

It runs great, until the hot weather starts. If I am in a parade, I try not to run the engine until the parade starts. All along the parade route I have no trouble at low throttle. It runs fine and idles fine. After the parade is over and I head out onto the highway it get very rough when I give it some throttle. It feels like fouled plugs, but it doesn't clear itself after running a while, and it idles and runs at low throttle fine. The engine temperature stays at 180 -190. If I park it for a while and let it cool, it is OK again.

I have been all over the ignition and changed plugs. I contacted Autolite and they recommended the plugs that I am using. It has 10.3:1 CR and requires colder plugs. Autolite suspected unvaporized fuel, but that would be more likely at colder temps. not the hot temps and it would tend to correct itself after running and also affect the idle and low speed operation.

I suspect boiling fuel. My fuel line is rubber hose, from the pump to the carb inlet. The steel line from the tank to the pump passes buy the left header outlet. I have a GM type metal in-line fuel filter in front of the fuel pump. The carb sits on a 1" Aluminum spacer on an Edelbrock Performer(Aluminum) intake, but I am mystified why it runs OK at low throttle.

It may be a partially blocked fuel filter, but why does it run OK when cool?

What is the proper method to prevent boiling fuel?
If I could measure the carb temp, what should it be below?
Should I get an insulating spacer?
How about metal fuel lines or do they make it worse?
Changing the fuel filter is an easy thing to try. but it requires a hot day and a lot of low speed running to reproduce the symptoms.

Dan

 

Sounds like pre-detonation. But I'm sure someone with more knowledge here could help you.

 

Sorry not pre-detonation. Just detonation.

 

Hey Dan, welcome back! Haven't seen your name in the forums for quite a while!

I think you're onto something with the overheated fuel unless you have a problem in your ignition box which only manifests when it gets hot. If you have a heat gun you might try heating up the ignition box and seeing if you can reproduce the symptoms.

As far as the fuel goes, I'd start by putting in a phenolic spacer and trying to insulate the fuel line where it passes by the header.

 

Bill,

I sent the Ignition Box back to Holley. They checked it and said it is OK. The problem is not detonation, but a misfire.

The engine does not run excessively warm, but aluminum is a good heat conductor.

If it is boiling fuel, then I would have trouble at idle and low speed as well once it started to boil.

They only thing that fits is spark plug fouling. I am hesitant to go to a hotter plug because of detonation. I think that I will try the plugs first.

I came to this forum because I know that I will get knowledgeable replys here.

Thanks,

Dan

 

I pulled the old plugs. They were Autolite AP24's. They are a milk chocolate brown. I replaced them with Autolite 25's. I wanted AP25's, but they didn't have them in stock. The plain vanilla plugs should be OK, because I don't put much mileage on this truck.
I took it for a ride with the new plugs. It seems OK, but I didnt go that far or very long, because of the rain. Also due to the traction, I couldn't put the pedal down. I should have a good run on it this weekend, if it doesn't rain. I am going to a show about 10 miles away.

 

From the color it sounds like those plugs are running about right. I still think you have a fuel issue which only occurs when the truck comes off of the idle circuit.

 

Tell me about the cam. Is the original cam? If so, and if you are not using EGR, you'll want to advance the cam.

I recommend using a 195 thermostat for at least three reasons; it will help with fuel vaporization, it wil help keep the oil clean, it will reduce friction.

Is the exhaust cross-over in the iron intake manifold clogged? You'll want the intake to be nice and warm to vaporize fuel. If it is clogged, get a pan with a cover big enough to immerse the intake, put some water in it, dump a bunch of Red Devil lye in there and let the lye eat the carbon out of the intake. Repaint and go.

I know that all the magazines say you should run as cold as possible to make the maximum power, but you don't need power in a parade.

 

Paul,

Your advice is in line with the Autolite tech support person. He recommended a 195 degree thermostat for the same reason. I am running a 180.

It is not the original cam. It is a Crane H272-2. It has about 234 degrees duration on the intake. It is set to zero degrees.

I am using an Edelbrock Performer Aluminum Manifold, it don't believe that there is a crossover. I have headers and no Heat Riser to send exhaust through the intake manifold.

All these things are reasonable, but it runs fine when first started. This is when the engine is coolest and vaporization is more critical. I myself have thought it is a heat problem, but it could be just a running time problem, i.e. wet plugs. I will run it with the new plugs today and test that theory.

Thanks for the input, I may still go that route.

 

Dan, The original manifold has the heat crossover in it. (It also has a sheild under the manifold to prevent the motor oil from coking on that hot metal.) I suspect that the Edelbrock has a crossover, but that it's blocked. I'll bet that intake cools off when it's being run in a parade and the fuel puddles in the bottom.

The hotter thermostat would be one cure. Putting a small hole in the block-off of the intake manifold gaskets would be another. Make sure the hole is at the very bottom of the port so that any water that condenses can drain out. Attaching a heat sheild would take some work; welding on bosses for the riv-screws.

Iron intakes aren't a glamorous as aluminum, but they make the engine easy to tune and it will hold its tune. Of course the problem is that there are very few iron 4bbl intakes for a 400. Marine only if I recall correctly.

Nice cam.

 

I ran the truck a little today. It wasn't a parade, it was a show about 15 miles away. I drove in stop and go traffic with some places where I could cruise a bit. I spent the day at the show and drove home again.

The weather was cool and overcast on both legs and the engine temperature never got very high, but the electric fan did kick on in each direction. It ran beautifully. I will probably go in the 4th of July parade. I think that will be a good test.

 

I went to another show this weekend and the truck ran fine on the way (about 15 miles). I cruised around the a bit at low speed to find my group and then parked. There was no problem.

When I left, I got on the highway almost immediatly and gave it some heavy throttle. It responded great. A short way up the highway the speed limit drops to 45MPH and the cops were out in force all weekend. No sooner did I slow down than I saw the car with the officer pointing the gun right down the road.

I cruised at 60-65 (light throttle) the rest of the way after leaving the 45mph area. A few miles later I felt some roughness in the motor. The outside temperature was 80-85 degrees, the engine temperature was 170-180 degrees. It was only a temporary problem, because it began to run normal again.

This time it was not as bad as previous occurances and it cleared up by itself.

I have not had any preignition with the Autolite 25 plugs, but they didn't totally cure the problem.

 

I pulled the thermostat out of my motor. It is a Robert Shaw High Flow thermostat. The markings say 180. The shop that built the motor put that in. Now I want to find an equivalent at 195 degrees. The parts houses in my area all carry Stant. The Robert Shaw themostat is much better quality than the Stant. Does anyone know where I can get a Robert Shaw themostat online?

 

These guys carry the 195 degree model:

Rick's Specialties

 

I just received a Robertshaw Thermostat from www.flowkooler.com. It is PN 333-192. That is the recommended part for the 351C, 351M, and 400 engines. Ricks Specialties doesn't carry this part. They have PN 330-XXX. I'll run the truck this weekend to see if it behaves any better.