All Small Six Plug fouling

[kaden_.adams]

Hey! Recently rebuilt 200, my plugs are getting fouled after about a month of driving, old motor had this same problem. Im wondering, I have an electric fuel pump on the car because the last motor had a wiped out cam lobe for the mechanical one, its a 27gph pump, im wondering if this is the problem? It doesn't have an inline regulator, wondering if too much fuel pressure is pushing past the needle? And help it appreciated!

 

[pmuller9]

Yes, you should have a bypass fuel regulator, and the regulation pressure depends on the carburetor.
Which carburetor are you using?

 

[aussie7mains]

Quite possible, but you should have other symptoms like:- black smoke, excessive fuel consumption. the flow rating of your pump is more than you will ever need, but you might need a pressure regulator. What carby?

 

[kaden_.adams]

It is a holley 1904 I believe, and it is using quite a bit of gas, more than I feel it should be, havent noticed and black smoke though

 

[pmuller9]

It is a holley 1904 I believe, and it is using quite a bit of gas, more than I feel it should be, havent noticed and black smoke though

The Holley 1904 should not have more than 4 psi of fuel pressure to prevent flooding.
You should install a regulator that has a return line back to the fuel tank and a fuel pressure gauge right at the regulator.

Certain electric fuel pumps cannot be dead headed at the carburetor and must have a return line regulator.
Which fuel pump are you running?

 

[alwill923]

• Post #13
• Oct 10, 2025
• Forum: 144-250 "Small Block" Six Performance

I would always install a return regulator with an electric pump. Pick a pump with slightly more flow and pressure than you need and use the regulator to control the pressure. This will give you a steady pressure and by always returning fuel to the tank it keeps the gas to the carb cool, no vapor lock. Always put the regulator close to the carb. I have pictures of this in my build threads in the truck stop.

Also run the fuel line in front of the engine to keep it cool.

 

[kaden_.adams]

The Holley 1904 should not have more than 4 psi of fuel pressure to prevent flooding.
You should install a regulator that has a return line back to the fuel tank and a fuel pressure gauge right at the regulator.

Certain electric fuel pumps cannot be dead headed at the carburetor and must have a return line regulator.
Which fuel pump are you running?

Its just one from orileys, after spending 139 on a holley one and it took a crap i decided it wasn't worth it to put another on, how would I go about putting a return to the tank? It's a 1960 ford falcon

 

[DON]

Make sure the regulator has a port for the return line. The best thing at the other end is to get a sender unit that has a barb for a return line. Like this one:

https://www.cjponyparts.com/cj-classics-fuel-sending-unit-with-return-line-stainless-steel-mustang-1965-1968/p/FSU65/?year=1967&utm_source=bing&utm_medium=cpc&utm_campaign=Core%20Vehicles%20Shopping%20(Tier%202)&utm_term=4583451683749157&utm_content=Core%20Vehicles%20Shopping%20(Tier%202)

This method keeps the fuel to the carb cooler. You can just put a tee in out side the tank and feed the return into it, but then you have the heated fuel returning to the pump/ carb

 

[kaden_.adams]

Make sure the regulator has a port for the return line. The best thing at the other end is to get a sender unit that has a barb for a return line. Like this one:

https://www.cjponyparts.com/cj-classics-fuel-sending-unit-with-return-line-stainless-steel-mustang-1965-1968/p/FSU65/?year=1967&utm_source=bing&utm_medium=cpc&utm_campaign=Core%20Vehicles%20Shopping%20(Tier%202)&utm_term=4583451683749157&utm_content=Core%20Vehicles%20Shopping%20(Tier%202)

This method keeps the fuel to the carb cooler. You can just put a tee in out side the tank and feed the return into it, but then you have the heated fuel returning to the pump/ carb

So my new tank has a little drain on the side of it, im wondering would it be dumb to run the return line through that? Or is it just better to get a new sending unit? Whole fuel system is already new

 

[aussie7mains]

That drain will do. It might be an idea to fit a tee, with a valve one one side to drain fuel, small suitable ball valve with a screw in plug and the regulator return on the other leg of the tee. A return filter might be a nice idea too. This could be mounted inside the "boot" trunk for you, to keep it out of the weather.

 

[Frank]

So my new tank has a little drain on the side of it, im wondering would it be dumb to run the return line through that? Or is it just better to get a new sending unit? Whole fuel system is already new

Sending return fuel into the tank as low as possible is safer.

 

[DON]

It’s curious: a drain on the side??
Maybe it’s intended for a return?
I wouldn’t want a return on the bottom of my mustang tank

 

[aussie7mains]

It’s curious: a drain on the side??
Maybe it’s intended for a return?
I wouldn’t want a return on the bottom of my mustang tank

Drain at the side is to reduce the chances of it being knocked off. If the return line is at the lower side of the tank, there is more chance of mixing the warm fuel with the cold fuel, and it doesnt splash like a top one would.

 

[DON]

So how do you fully drain the tank when the drain is not at the lowest point?

 

[Frank]

It took semi manufacturers till the late 90's to figure out to run the return line into the top of the tank, and pipe it to the bottom. With the old system of releasing hot return fuel into the top of the tank the tank was FULL of thick white, hot fuel vapor when the cap was removed after a run. Incredibly dangerous- and that's diesel. Gasoline is that much more volatile. The homemade return on my f150 is also piped into the top, to the bottom of the tank. At the bottom, the pipe turns 90* so the fuel is released parallel to the bottom (same as semi). After seeing the diesel vapors for years, there is no way I would route a gasoline return that doesn't release into the liquid fuel in the tank.