Carb heat soak ideas

[oldiron]

So I'm trying to come up with a good plan to minimize heat soak on the 2bbl autolite 2100. It's on the '72, basically stock everything. First off let me say that it never overheats, even on 100 deg. days with the a/c on. Engine temp stays around 190-200 no matter what. The issue is starting after a hot shutdown i.e. 10 minutes or so. Checked yesterday with an ir thermometer and the carb gets to 175 after the 10 minute period with the hood closed. Temp at the screw in filter on the carb was 200.
My ideas are. 1: would dropping to a 180 degree t-stat from the 195 improve heat soaking? 2: would adding a return fuel line offer any benefits?
Anyone ever experimented with these ideas?
Greg

 

[blubuckaroo]

A return line would only help with vapor lock. It wouldn't help when the engine is shut off.
Yes, of coarse a 180 degree thermostat would help. Even though I like the way a 194 degree makes mine run.

The two biggest improvement I've made, concerning heat soak, are adding a thicker carb spacer and blocking off the heat riser exhaust port under the carb. My heat soak is now eliminated on all but the hottest days.

 

[oldiron]

Since this is a daily driver I kept the ex crossover open under the intake. Did blocking it off affect cold weather driving? And it runs perfectly with the 195 in it now. Just kicking around ideas.

 

[Broncobowsher]

Holley makes a 2-barel Sniper that will fix the hot start issue.

 

[blubuckaroo]

Since this is a daily driver I kept the ex crossover open under the intake. Did blocking it off affect cold weather driving? And it runs perfectly with the 195 in it now. Just kicking around ideas.

Of coarse. Blocking off the heat riser makes for a longer warm up.
Also, the 195 thermostat will heat up the engine bay more than a 180.
It's all about whatever you can live with. Back in the day when these cars were made, gasoline had a higher vaporization point. You do what you can live with.

 

[Rustytruck]

need to use motorcraft G979 which is a thick insulator carb base gasket.

https://www.carburetor-parts.com/g979.html

it is a thick gasket with plastic spacer rings around the studs. its a little over 5/16" thick. you may or may not need longer carb studs.

 

[MS73HD302]

Cured mine with some amazon heat sleeve on the fuel lines inside the engine compartment, 1 inch spacer, removing pressure regulator (stock pump) and a smaller air cleaner — went from 14 down to a 9in. Wanted to go with return line but I have two tanks seemed like a headache

 

[jckkys]

Holley makes an insulating gasket that includes a shield under the float bowl here;https://www.summitracing.com/parts/hly-108-52. This would block more of the radiant and convection heat from the top of the intake. The 2100 is already the best carb for resisting percolation and in my experience usually only requires a different starting procedure. If it won't start immediately, I floor it then crank to clear excess fuel and fumes that have effectively flooded the engine.
Blocking the cross over makes cold start ups a PITA and increases engine wear. Cooler thermostats do the same. Neither were ever recommended by Ford or any other car/truck maker. I've tried both over the years with 0 success.

 

[MarsChariot]

Here are a few things that I have done on my Autolite 4 barrel that appear to work well. First, a one inch phenolic spacer. Second I have a 2.5 inch wide approximately 8 inch long strip of header wrap (with the ends nicely trimmed in high temperature aluminum tape on the ends to avoid it unraveling) laid across the top of the intake just beneath the main front fuel bowl. Third, for when I return to the garage on a hot day I have a large fan in the garage on the corner near where I park; I open the hood and get that fan going to help bring the under hood temperatures down as quickly as possible. These work well and even when I can't do the last step above, I have no real problem starting, I just keep my foot off the pedal until it starts as it does not seem to need ant additional gas to start.
I have been mulling over making a nicely bent and otherwise shaped aluminum shield to forma heat tray beneath the carb to help deflect some of the radiant heat. But I haven't messed with that just yet.

 

[blubuckaroo]

Since this is a daily driver I kept the ex crossover open under the intake. Did blocking it off affect cold weather driving? Just kicking around ideas.

Most of the aftermarket cylinder heads come without the heat riser ports drilled out to the exhaust rail. I don't know of anyone who has gone to the trouble of drilling them out, and I haven't heard any complaints.

 

[chuck1022]

I cant explain why , but I started running 4oz of Marvel Mystery Oil per 10 gallons and my truck stopped vapor locking.

 

[jckkys]

The after market heads are either made for racing or EFI. Racing has very limited application for 4X4s and EFI atomizes the fuel with high pressure through tiny orifices placed at the intake port. The cross over is upstream of the injectors so no fuel touches the heated bottom of the intake. You'll notice that EFI intakes don't have cross overs. I installed the cross over blocking intake gaskets on a 460 only to find the cold starts took a lot longer to warm up. The full throttle HP may be a little higher but the 351 has far more HP than I need.
The vapor recovery system on the last of EBs helps remove excess vapor from the intake reducing the engine flooding. Some emissions equipment is good.

 

[blubuckaroo]

The after market heads are either made for racing or EFI. Racing has very limited application for 4X4s and EFI atomizes the fuel with high pressure through tiny orifices placed at the intake port. The cross over is upstream of the injectors so no fuel touches the heated bottom of the intake. You'll notice that EFI intakes don't have cross overs. I installed the cross over blocking intake gaskets on a 460 only to find the cold starts took a lot longer to warm up. The full throttle HP may be a little higher but the 351 has far more HP than I need.
The vapor recovery system on the last of EBs helps remove excess vapor from the intake reducing the engine flooding. Some emissions equipment is good.

The exhaust heats the area under the carb a lot hotter than the engine would without the crossover. When you shut off the engine, that exhaust heated intake manifold can cause the fuel to boil with modern fuel.
Warm up is affected, but I'll take that over the cylinder washdown and contaminated motor oil caused by boiling over the carb.

 

[OsideDave]

Phenolic is a good material to isolate the carb. Here's an example but not sure if fits
https://www.summitracing.com/parts/ctr-85-032

 

[ntsqd]

This thread popped up at the bottom of another thread and I thought that I'd share my experiences with this. I first tried the insulating spacer on my '67 Ranchero (302, 4V) and while that worked it was far from perfect. Then I was playing around with porting coolant from the rear of each head to the front in an attempt to get the rear cylinders to run at the same temp as the front cylinders (I got closer to that, but never made it happen). This required a pair of SS tubes that laid across the top of the intake manifold bolts. And as you might expect that made boiling the fuel out of the AFB carb (with it's fuel bowls located on the sides of the carb i.e. RIGHT above those tubes) a LOT bigger problem.

The insulator wasn't enough so I made a shield like linked above. My shield was the width and length of the intake manifold and made from 1/8" aluminum. I ran a thin insulator between it and the gasket, and another thin insulator between it and the intake manifold. Except for when I ran ARCO fuel in that car the shield nearly fixed the boil-off problem and I never experienced vapor lock.

Something to keep in mind, the fuel we burn today is nothing like the fuel used in the 70's. "Gasoline" is an amazingly complex blend of different hydrocarbons and other components, and that blend varies with the time of year. There are certain specs that it meets that our fuel from the 70's also met, but there are other attributes of this current fuel that the 70's fuel did not have. Today's fuel is made with EFI and mildly pressurized fuel tanks in mind. The makers expect the fuel to be under some pressure everywhere in the vehicle. Put it a carb'd vehicle and of course it's going to misbehave and not perform as well as it could.

 

[TX-ZACH]

School me on heat soak. Any new tech advancement in this dept? The heat this year in tx is historic and seems to be really taking a toll on starting after the 1st run even a couple hours later in the 100+ degree heat. If I open the throttle watching the fuel in carb, I can hear what sounds like water on a hot pan. Almost flooded it last night after just a 5 mile trip restarting to garage it for the day. Carb seems super hot. Park idle is 600-700, drive idle is at 500-600, carb tune and timing is near perfect. Cold start up is crisp and instant runs phenomenal. I believe I have clearance for a spacer on carb as I am running the WH Proflo Delux hood.

I have a holley 600 on top of EB RPM Performer intake and heads, 190* tstat, fuel line is flex hose near motor. ATK 351w roller.

 

[hsach]

I have been dealing with heat soak on my 78 bronco for years in the Nevada heat. Started with a Carter 625, then Edelbrock 600, now AVS2 650. They all act the same in 100 degree heat. The only things I have done that seem to lessen the affects of the heat are wrapping the fuel line coming from the mechanical pump to the carb, in DEI Fire Sleeves. Most of my line is steel and runs close to the front of the block. I think the biggest help has been the 1" phenolic spacer. If you have room for a spacer, give it a shot since they are pretty cheap.