[Tim Corcoran]

I have a 473 with an 850DP on top of a Performer RPM. I think the fuel is boiling out after shut down I want to put a phenelic spacer either a 1/4 or 1/2 inch. My question is should I use an open spacer or a 4 hole? Not sure if I can find a 1/4" spacer or if it would provide enough insulation to prevent the fuel from boiling. Thanks for your thoughts.

[JLMounce]

I'd probably go with the .25" phenolic open spacer like this one here.

https://www.summitracing.com/parts/s...BoCyJ8QAvD_BwE

If the .25" spacer doesn't provide enough heat shed from the intake to the carburetor to stop your issue, I doubt that a 1/2" spacer would either.

I'm assuming you're using E10 fuel, straight out of the pump? E10 is simply more volatile than pure gasoline and boils at a much lower temperature. Depending on your specific altitude, boiling points for E10 can be as low as around 170 degrees. With under hood temperatures climbing to around 200 degrees or more, as soon as fuel stops circulating in the carb, it's only a matter of time before the ambient temps sink through the carb bowls and boil out the fuel. No heat shield or spacer is going to protect against that condition.

I'm not certain what your fuel setup is, but this is why I believe carb'd vehicles that see regular use and pump fuel need electric pumps in the tank. You can prime the bowls before starting because they will be empty. Or, you just understand that if you're using a mechanical pump, you're going to need to use the starter to get the bowls primed.

[Skip Fix]

Do you have the 50cc accelerator pump on the front of the 850? I just put one that had that swap on an RPM and it needs some spacer to clear.

[steve25]

Is your motor hard to restart due to fuel boiling over and flooding the manifold, or has the fuel just boiled away out the vent tubes?

Do you have a mechanical pump and no return line?
Do you have a seperate regulator?

What’s heads do you have and is the exh crossover open ?

Many times at shut down it’s the fuel in the pump that starts to expand and or boil.

When this happens the fuel has no place to go but up the line and into the carb and overwhelm the fuel bowl(s) .

[Skip Fix]

I'm not certain what your fuel setup is, but this is why I believe carb'd vehicles that see regular use and pump fuel need electric pumps in the tank. You can prime the bowls before starting because they will be empty. Or, you just understand that if you're using a mechanical pump, you're going to need to use the starter to get the bowls primed.

I agree one of my best friends a Mopar guy gave up om carbs and went EFI as the evap and how each different fill up the blend was just a hair different and AFR would be off.

[chiphead]

Going through the same thing. When its hot out and my engine is about 190F, the AFR on the gauge goes into the 12s-11s during an interstate cruise. The damn fuel vapor makes it go rich while it's running. I blocked off the heat crossover with 321 stainless. That helped a lot but not completely.

I'm trying a 1/4" open spacer between my 750DP and RPM. If that ain't enough, I'm going 1/2" open phenolic spacer. I ran a 1/2" nitrous plate under a Q-jet on the same intake on my previous motor. A nitrous plate is basically an open spacer with the spraybars in the middle. That engine was 9:1 400, XE274 cam, mild ported 670s. 10" converter and 3.90s. It loved the open spacer. The idle vacuum was 10-12", but otherwise the open spacer worked. Especially when the solenoids opened, LOL.

[65 Lamnas]

Originally Posted by Skip Fix

...carb'd vehicles that see regular use and pump fuel need electric pumps in the tank...

I agree 100%.

I run an "overkill" fuel system for my ugly old Qjet, on purpose and in part to help to eliminate hot start issues. Besides, the sh*t gas that's available just makes the symptoms worse.

Tim, I don't know if you're running a mechanical pump or not, but the heat transfer from the pump to the fuel doesn't help any. If you DO TRY a spacer, I'd go with the 4-hole 1/2" phenolic....1/4"seems too thin to me. https://www.summitracing.com/parts/aaf-all25983

I run a resto-mod tank (www.rickstanks.com) in my '65 Lamnas. I chose an Aeromotive 340 pump in the tank with -6 supply and -8 return. I've got the regulator (https://www.robbmcperformance.com/pr...ulator_bp.html) set at 7psi, so there's A TON of fuel being recirculated at all times other than WOT blasts.

It also helps that my 462 runs cool....not a lot of heat underhood and I can hardly get my engine to run at t-stat temps....except on super hot days. If you're able to run a cooler stat, that "might" help too.

[Tim Corcoran]

The car has D-Port Edelbrock heads and a mechanical fuel pump with no return line. The reason I think the fuel is boiling out of the carb is after a drive then parking the car in the garage, the garage smells like gasoline very strong. Plus after the car was cool I advanced the throttle and noticed the rear squirter was not discharging fuel which leads me to believe the rear bowl was empty. It's not the starting issue that I am trying to solve, it's the strong smell of gasoline that bothers me. If I pump it several times it does start OK. I thought about adding a 50cc pump on the front and I did notice it would require a spacer to fit.

[PAUL K]

Originally Posted by Tim Corcoran

The car has D-Port Edelbrock heads and a mechanical fuel pump with no return line. The reason I think the fuel is boiling out of the carb is after a drive then parking the car in the garage, the garage smells like gasoline very strong. Plus after the car was cool I advanced the throttle and noticed the rear squirter was not discharging fuel which leads me to believe the rear bowl was empty.

Check the bowl screws and accelerator pump diaphragm for leaks. The diaphragm will hold fuel for a long time. There's too much fuel in the bowl to "boil out" and even if it did it'd still remain in the accelerator pump.

[Tim Corcoran]

There is no evidence fuel is leaking onto the intake manifold.

[PAUL K]

Don't check the manifold, check the bowl screws and diaphragm. I'll start the car when cold and feel the bowl area and screws with my hand, if it's wet and smells like fuel I know it's leaking.

[steve25]

If fuel is boiling or evaporating out of the carb you could have a 80CC front pump and it would not matter.

[chiphead]

Originally Posted by Tim Corcoran

The car has D-Port Edelbrock heads and a mechanical fuel pump with no return line. The reason I think the fuel is boiling out of the carb is after a drive then parking the car in the garage, the garage smells like gasoline very strong. Plus after the car was cool I advanced the throttle and noticed the rear squirter was not discharging fuel which leads me to believe the rear bowl was empty. It's not the starting issue that I am trying to solve, it's the strong smell of gasoline that bothers me. If I pump it several times it does start OK. I thought about adding a 50cc pump on the front and I did notice it would require a spacer to fit.

I think it's the nature of the beast. This E10 stuff evaporates very easily. There is no fuel visible in the bowls 24 hours after I drive it in the summer. I park the car in an attached garage. If I leave the door to the laundry room open, the whole house smells like Cooter Brown's garage in about 10 minutes. The wife asks if the house is going to explode. The kids dance in a circle and scream "dads in the garage, dads in the garage and left the door open" like they're telling on me. The dog goes out for fresh air. Its BAD. My only suggestion is to try a vent fan. I'll leave the garage door open for awhile after driving it, it seems to really help. The smell in the garage goes away a few days after the last time the engine ran. So it seems to be from the float bowls rather than the fuel tank, unless I recently got gas, the smell lingers.

[HWYSTR455]

Drop base air filters trap heat, the deeper the drop, the more heat is retained.

The rad fan blows right on the front bowl, that too doesn't help.

If you have a mech pump and the carb feed line is in roughly the OE position, the fan heats that too. Add a filter before the carb, more area to soak with heat. (And hopefully no one is running a plastic filter).

Bypassing fuel does help keep things cool(er), but you can still suffer from heat soak, especially if it's under a 1/2 a tank of gas.

In traffic, radiant heat from hot asphalt can super heat the bottom of the tank. It's more common than you think.

Pump gas additive formulas change per season, summer getting anti-vapor additives, which is generally added in the spring, and anti-moisture type additives for winter, added in the fall.

Transition for those take time for ground tanks to get to a proper level of seasonal additives, so spring & fall are tough to get 'proper' gas. So you will see 'rich' conditions in spring, and lean conditions in the fall.

E-pump/bypass systems help a lot, but you can still suffer some. But in general, it cures many issues, or at least makes them 'less of an issue' and manageable.

You think it's tough now, in a few years, the baseline pump gas is going to be all E85.

E85 and High-Ethanol Fuel Timeline (2025-2027)

Late 2025–Early 2026: E15 (15% ethanol) sales began expanding rapidly, with ethanol blend rates topping 11% for the first time in late 2025.

May 1, 2026: EPA authorized emergency waivers to allow nationwide sales of E15 through summer to lower gas prices.

June 15, 2026: The EPA's "Set 2" rule takes effect, establishing the highest biofuel blending mandates in U.S. history (25+ billion gallons) for 2026 and 2027.

2026 Trends: California alone is projected to see significant growth in E85 consumption, with usage estimated to reach 160 gallons per Flex Fuel Vehicle (FFV).

2027: Fuel ethanol production is expected to expand to 1.08 million gallons per day, with EPA mandates for 27.02 billion gallons.

Stock up on carb parts now. I suggest moving to 1/2" lines to and from, and going to E-pumps now.

I predict many will be converting to TBi setups....


.

[Tim Corcoran]

I just bought this car and it still has the fuel it came with. In the future I will use ethanol free gas in this car and see it it helps. As a side note I use mid grade regular pump gas in my 67 LeMans it has a Q-Jet and I don't have this issue.

[Tim Corcoran]

.[/QUOTE] (And hopefully no one is running a plastic filter).


What about a plastic filter? There is a plastic filter back by the tank but what does that have to do with the subject.

[73ta]

Im still quadrajet carbed but went with Walbro intank pump in baffled tank. 1/2" lines with return regulator. Got rid of my top end fuel issues, no heat issues with circulating fuel, even with a transverse muffler! Future proof.

[slowbird]

If you put a spacer on it, 100% go with open

[TXSTARFIRE]

A plastic filter on top of a hot engine is a fire hazard.

[steve25]

With a mechanical pump the only thing you want it to have to suck thru is the stock sock on the tank pickup.

If that in line filter back there is in addition to the sock then remove it.