Jartanyon

So my newly rebuilt engine was boiling the fuel in the carb for some time after the cam break-in. Engine temps never got past 200 degrees, but I think the aluminum is transferring the heat more easily to the carb than the iron was. I used the MRG-56A gasket between the carb and the intake. So, my question is twofold. First, out of the following, which is a better solution:

Insulator Gasket: FEL-1905
Carb Spacer: MOR-64941
MRG-86
MRG-86B
Mr. Gasket 3406
Trans Dapt 2109

If a spacer, what is the max height I could I get away with a Summit Stage 1 and a drop base on a stock '78 L48 hood? .25", .50" or 1"? Thanks for the help!

7T1vette

Use 'block-off' inserts to prevent exhaust passage in the intake heat riser channel. They get inserted when the intake manifold gaskets are installed.

Are you sure that the heat riser valve (right-side exhaust outlet) is actuating properly? If not, all of the right-side exhaust will try to flow under the carb to go out the left side (whether single exhaust or dual).

69Vett

1/4 isolation gasket will be suffeicent to kill the heat transfer, and your gonna be tight on clearance, like 7T1VETTE said be sure to block off heat passages.
I block them with intake gasket inserts, and then block the heat passages under the carb. also.
before the islolator after engine warm up, I could not keep my hand on the carb. body it was so hot,
after Isolator gasket, standard GM 1/4" thick, the carb was actually ice cold, almost forming condensation on the outside of the carb.
...hugh differeance.

Jartanyon

A little late for the block-off, no? I don't have the heat riser any more - upgraded exhaust to 2.5"

I used Fel Pro 1256 intake gasket - doesn't that block it enough?

So go with Fel Pro insulting gasket or the 1/4" Mr. Gasket spacer?

bluedawg

1" 4hole phenolic spacer.

scottyp99

Enough? Look, it's either blocked off, or it isn't. And with a 1256, it's not blocked off.

I think a 1/4" insulating gasket should be sufficient for your intent. Make sure it's a 4-hole gasket, you want to keep the two planes separate, anyway.

I wonder if there might be some advantage to having the carb cool, but the intake manifold hot, like maybe it will help atomize the intake charge. Could someone who knows about this kind of stuff comment?

Scott

REELAV8R

I'm using this gasket on mine;

http://www.summitracing.com/parts/fel-1908/overview/

Seems to work well with my Q-jet.
The crossover heat was there originally to help atomize the fuel on cold days and starts.
Most of us do not run these cars at 0* F so it probably is not needed.
As the engine warms to operating temp the fuel/air can actually be over heated and create not only a less dense fuel/air charge but also a hotter one getting you closer to detonation vs not having the crossover heat.
If you have an aluminum intake with no oil baffle on it this may be even more so as the engine oil splash/mist in the lifter valley also heats the bottom side of the intake on the lower runners.

Aluminum gives up heat easier but also absorbs it easier.

It would depend on how hard your running it, how hot it is outside and how high the water temp is running as to how hot the intake manifold will get. But it will definitely be hotter with the crossover heat present.

MelWff

Do you have a fuel return line hooked up?

ddawson

Before I could not touch my carb for more then a sec before it hurt.

Plugging the intake manifold crossover I can now hold my hand on the carb with out pain. In fact it's barely warm.

gkull

The wood spacers do the best job of blocking carb heat. You can buy 4, 2, and one hole 1/2 inch spacers

bluedawg

I've seen the wood, but went phenolic mostly to space my accelerator pump off my intake.

Jartanyon

Thanks for the responses everyone.

@REELAV8R - I originally had that one on the car before the rebuild. When I pulled it off, it ripped (despite the lithium grease). Maybe I will pick another one up.

@MelWff - yes, there is a fuel return on the pump.

I wish I would have known about blocking off the crossover when building it! Oh well, now I know. I am wondering if I should pull off the intake and put them on now. Otherwise, maybe I can run the 1/4 gasket until the winter and add that to the next project list.

69Vett

here is how I blocked off the heat passage under the carb. after the intake was already installed.
this will depend upon your manifold this works for stock manifolds.
the heat passage under the carb is connected via holes on each side, about 3/8" dia,
which go straight down, I took 3/8 stainless tubing about 2" long, pluggeg the ends.
and wedged them into the heat passage holes going up, make sure plugs do not stick above the carb base,
the way it is made, they cannot move anywhere. Good Luck !

lars

The solution to the problem depends on what type of carb you have. Is this a Holley or a Q-Jet?

Lars

Jartanyon

Quadrajet

REELAV8R

Jartanyon, I forgot that I also added this Mr gasket spacer;
http://www.summitracing.com/parts/mrg-86/overview/
in order to insulate the carb from the intake.
I'm using a edelbrock 2101 intake and it has an open plenum.
I wanted to duplicate the stock 4 hole plenum design for off idle performance.
So I use that gasket set with two of the aluminum spacers and two of the gasket spacers then added the previously mentioned open style 1/4" gasket on top of that. It comes with 3 gasket type spacers and 2 aluminum spacers all told 1/4 inch. With this set up and the open 1/4" gasket I have about 1/8" to 3/16" clearance from the hood.