I have tried a few 4 bbl carbs on my warmed up 360 I get the same problem.
when it is cold to just warm it is perfect. Once it is hot like you come off the
hiway the throttle response is a little sluggish and tends to idle rich. if you give
the throttle a quick light snap I get a little bit of black out the pipes.
keep in mind this is only when it is hot. I have tried motorcraft 4300,
Holley 600's (3 different ones) , holley 750, and hell even a GM "evinrude"
Q-Jet 4BBl. same thing.

Should I add some aftermarket heat shield.
should I add a cool can to keep the fuel colder?

it is also a bit of a bugger to start when it is hot.

This is not a serious or show stopping problem just more of an anoyance
than anything.
Any advice is greatly appreciated.
Thanks guys.

 

Cory,

I wonder if you are having a fuel perculation problem. Are you running any kind of spacer under the carb? I would consider putting a phenolic 1" spacer in and see if that helps. Sounds like you may have a heat transfer problem from manifold to carb.

Also make sure that your fuel line from pump to carb is routed away from any hi heat source.

Good luck,

 

I do believe that is the problem. I have a the 1" aluminum spacer that came with the manifold and also I threw in for extra height a
1/2" spacer hoping that would help. still seems to have the same problem. The motor does not seem to run hot only when left idling for long period of time (which is not required). Sometimes
people just love to hear the sound of an agressive cam when idling. I know i love it. hehehe

 

Please define "Hot"? What does the temp gauge read? What temp is your thermostat?

I know with my 390...the thermostat that gives me the best results in both summer and winter is a 180.

Sounds to me that after putting on 1.5" of spacers the carb should not be getting "hot".

If you find a resolution...please post.

Thanks.

 

The temp guage comes up about 1/4 - 1/3 from the cold mark. and stays there
unless I sit and idle then it will rise a little past 1/2 - 3/4 towards hot.
I have never seen the guage go higher than 3/4. The stat is 180.
I had similar problems with my other 390 in my old car as well. Just didn't
notice it as much because it was automatic as my truck is 4spd manual.

Should I route the fuel line farther away from the motor as well like in a
cool can or something?
Does the phenolic spacer disapate or reflect heat better than the aluminum ones?
I am really looking for ideas here.
any info would really help. thanks guys.

 

I would try retiming it when Hot. Heat makes things exspand and your timing could be off just a little bit, somtimes a little bit goes a long way.

 

Hi,

Aluminum transfers heat very well. The phenolic spacer will not conduct heat anywhere near like the aluminum will.

 

So I should definitely use the phenolic spacer instead of the aluminum one right?

 

yeah it would be better than the aluminum one

 

I will try that. I think this spacer I have is about 3/4" thick phenolic.
So that should prevent the heat from getting to the carb.
Should I also re route the fuel line away from the block a little better?
I always thought it was wierd with the fuel line running right up near the
block up to the intake? I will try these tricks.
I do not beleive timming to be the suspect.

 

it wouldnt hurt to re route the fuel line but i dunno if it would help much.

 

Ok...the carb and fuel really are not the problem (although a spacer is not a bad idea). It seems to me that the problem is that the engine is getting way to hot. Having a 180 thermostat should not be causing this. Sitting in traffic and the temp gauge going 3/4...in my opinion is the problem. The effect is the carb and fuel getting hot.

Timing is definately something to think about. But what type of Radiator do you have? You should have a minimum of a 3 core but prefer the 4 core. If you open the cap and look in...what do you see? Do the tubes look nice and clean/clear? If not, then flush and clean the radiator. What about the radiator cap? Should be a 13psi...and remember these go bad too.

What about your fan and fan shroud? They stock for a 390? You could always upgrade your fan. http://www.flex-a-lite.com/ has great products at reasonable prices. Upgrading to a fan that pulls more air will certainly help during idle time in traffic. Also make sure your belts are in good shape and fit proper (tension).

It would be hard for the 390 to have pockets of air trapped in the system since it is "open", but that too could be a possibility.

Please let us know how it goes...

//biz

 

If the exhaust system is too close to the fuel lines or the gas tank then the gas is getting warm enough that it can multiply the problem of the gas percolation by the time the already warm gas gets to the carburetor. This is common when a dual exhaust system is installed by a muffler shop that isn't familiar with the best layout for a system in trucks like ours. Often the left side exhaust pipe will be the culprit, but don't overlook a problem around the gas tank area.

Just as the phenolic spacers are needed so as not to transfer or conduct heat to the carburetor, so does the gas line that hugs the engine between the fuel pump and the carburetor need some heat shielding material or just reroute it to a cooler location. Every amount of heat that the gas picks up on it's way to the carburetor is potentially adding to the carburetor percolation problem.

 

Exhaust pipe not the issue as the tank is inside the cab (65) the fuel line in nowhere near the exhust pipe.
I do agree that it does warm up a little when idling. I also will be changing to a 4 core rad. the one in there now is a 3 core with only 1 damaged and sealed off.
The problem does not only exist when idling hot (3/4) is exists just barely after is is warmed up.
The temp guage is only about 1/4 way up. it still does it.
I will definitely do the rad and have a 7blade clutch/flex fan for it.
I could get a shroud when I get the 4 core rad. anyway thanks for the ideas.

 

One last thing...

What type of carb spacer do you have? Keep in mind that different spacer's effect the performance differently.

1. A spacer with the 4 hole setup (they align underneath the 4 barrell carb) are usually used for a more torque feel.

2. A spacer without the 4 holes, but one large opening is generally used for high end power.

Also, a fan shroud is pretty much a "must" have for keeping your truck happy.

Good luck with your truck!

\\biz