Hot Starts - Holley Carb???

[Silk]

I’ve got a Holley HP Pro – no choke and mechanical secondaries. On cold starts, couple of pumps and it always fires right up. Never a problem. Once hot, I can always restart with no problem if the car only sits for 5 or 10 minuets. If it sits much longer, I have to crank it for quite a while before it fires, and always has a strong smell of gas. I never pump the accelerator on hot starts. Any thoughts on what’s going on here and what the cure might be?

[TerribleTed13]

Silk, The carb boils over,engine is flooded. Do you have winter fuel?I have the same kind of problem with my Holley carb. Try a spacer between the manifold and carb,to help disapate heat. Is your fuel pump manual or eletric? Does the electric have an "on" toggle switch? Turn off the fuel pump 1 block before your destination.

[Silk]

Mechanical pump, and a 1/2 inch spacer - which is as large as I can go and still close the hood. No winter fuel.

[Rick Parker]

Lower the fuel level in the bowls a minor amount, it is spilling over through the down leg boosters as the fuels boils/expands from the heat while setting.

Rick

[Mr.Fixit]

What is the carb spacer made out of? Try phenolic.

[Jerry Cowing]

Silk,

I had the exact same problem. If you were to remove the air cleaner and stand beside the car for a few minutes, pretty soon you would see the gas jetting out of the accelerator ports near the top of your carb. This is because when you shut the car off, the cold gas from your tank expands after it is heated by your intake, etc. The mechanical fuel pump won't let the expanding gas go backwards into the tank, but the gas has to go somewhere so it pushes through the accelerator pump ports and floods your engine.

As Mr Fixit said, use a Phenolic spacer, not a metal spacer. The half inch phenolic spacer solved my problem.

If this doesn't work, you could place a T fitting in your carbs fuel line and a T fitting on your tanks vent tube. Then run a line off this carb T back to your tanks vent tube T. Place a small valve in this line to let the excess pressure bleed back into your tank after you shut the car off. The valve could be an old jet that has a small hole in it stuffed in the line. This small hole won't interfere with the gas going to your carb, but will allow the expanding gas to be bled off.

[Silk]

I appreciate the responses. Looks like I've got a phenolic spacer in my future.

Just curious - what are the properties of phenolic materials that make them suitable for these applications? Significantly better heat dispersion?

Again, thanks for the suggestions.

[scootter]

I had the same problem with mine. After talking to the prior owner, you have to open the throttle a little when you start it to let some air in. Mine will fire right up now wether it sits for 10 minutes or 1 hour. It took some practice. As soon as I hit the key I hit the throttle about an 1/8 to a 1/4 and it starts right up. As for the bubbling gas in the carb, I get that to some times. I keep the gas level about 1/16 below the float holes. I just installed a new black Holley pump with a regulator. I am hoping the regulator helps some, because there wasnt one before. Holley also recommends keeping the pressure down.

[Zoom This]

I had the same problem on my 418. I put a 1/2 inch spacer under the carb and drilled .014 anti-siphon holes in metering blocks to allow gas to reenter the carb as it starts to boil up to the jets. Works great, no raw gas smell in the garage and starts up on 1 crank after sitting for 30-60 minutes.

[joea]

You can run a return line back to the fuel tank...like you would run in a fuel injected system. The pressure in the fuel lines when the engine is hot has no where to go so it floods the carb(s).

Don't take my word for it though...I'm just repeating the Gospel George Anderson from Gessford told me.

[mr0077]

Silk, the phenolic spacer has very good insulating properties...it conducts less heat from the manifold to the carburetor, so less liklihood of a boilover during the shut-down heat soak period. I have a similar problem, I just hold the throttle wide open during hot starts, it clears the rich condition pretty quickly.

Also, regarding the return line...with a mechanical pump it seems that you could run from the carb tee to the suction side of the fuel pump and keep all of the line in the engine bay rather than run it all the way back to the tank, just to simplify things...that way, the excess fuel could bleed back on the the tank supply side of the pump...it would be best to use small diameter steel line where possible for safety reasons, and be careful how you route it...maybe just parallel the supply line from the pump to the carb?

[Silk]

Ken,

Thanks for the explanation. Makes perfect sense once you think about it. And of course a side benefit of this newfound knowledge is that I can be absolutely scintillating at cocktail parties. "Hi there, what do you think about phenolics . . . . "