Gasoline Smell

[Large Arbor]

I have dual 4160's, 600's and after running the car, I always smell like fuel. wife complains and I have an odor. Would carb insulator plates help? Could it be the fuel is boiling somewhere. This happens even yesterday when it was 20 degrees out and I just idled the car. Any thought or suggestions are much appreciated.

Phil

[patrickt]

After you drive the car, and pull in the garage with the engine nice and hot and shut down, if you immediately remove the air cleaner and observe the boosters, do you see any dripping from them on to the butterfly valves?

[DanEC]

Good luck with that Phil - I have 3 old cars and they all stink. I've tuned them and adjusted carbs to within an inch of their life. I always set the idle mixture on the edge of the lean roll off but it doesn't matter. Some percolate fuel worse than others into the hot intake after shut down which really puts up a stink but even my GTX smells just idling. It's today's gas. Everytime I'm working in the garage on a car or I've been over helping someone else working on an old car, my wife tells me I stink when I get inside. Short of fuel injection, computer and Cats there's no good solution.

[patrickt]

Well what you can't do is just set the floats to where the gas is right at the bottom of the sight hole. That may have worked on an OEM engine, fitted in an original engine bay, with Sunoco 260 in the tank, but it doesn't work with most of our Cobras today. The gas is way crappier, and our engines often times sit at funky angles. You have to start with your float levels at the base of the sight hole and then keep adjusting them down until you find your sweet spot. An eighth of a turn on the floats can make a world of difference.

[Large Arbor]

Thanks Gents.

It seems to be from fuel leaking and then vaporizing on the engine bay or in the intake. I can see a few tiny spots where it leaks through the carburetors so I am going to pull them and take them in for an expert rebuild by a gent who told me this guy I am going to is supposed to be one of the best in the country on rebuilding Holley carbs. I will try that and see if it helps.

Phil

[sea2jet]

My fuel log for the dual carbs had a pin hole in it that was causing fuel to leak on the intake. Who would have thought.

[patrickt]

Originally Posted by sea2jet

My fuel log for the dual carbs had a pin hole in it that was causing fuel to leak on the intake. Who would have thought.

An easy way to diagnose that problem is to inspect your fuel lines with a Lucky Strike in your mouth.

[rodneym]

Aee you implying that it should be lit?

[sea2jet]

Originally Posted by patrickt

An easy way to diagnose that problem is to inspect your fuel lines with a Lucky Strike in your mouth.

The leak drove Jeff at Danbury Competition Engines crazy trying to find it. They took it off and soldered it up. We all thought it was the front carb leaking.

[DanEC]

Originally Posted by Large Arbor

Thanks Gents.

It seems to be from fuel leaking and then vaporizing on the engine bay or in the intake. I can see a few tiny spots where it leaks through the carburetors so I am going to pull them and take them in for an expert rebuild by a gent who told me this guy I am going to is supposed to be one of the best in the country on rebuilding Holley carbs. I will try that and see if it helps.

Phil

My setup is not too different - a LR 427 intake with two 1850 carbs on it. The exhaust is enough to get a cold shoulder from the wife but if I look down the primary throat on the rear carb about 10 minutes after shutting it down I will see fuel starting to drip from the accelerator pump shooter. That fuel on hot engine parts sets up a real stink that lasts for hours in the garage. I have heat shields under mine which helped somewhat but not a complete fix. I do have my floats set to hold fuel just below the sight ports and Patrick probably has a good point about taking them down a bit more. But I think the main issue is the accelerator pump sitting right above the intake and heat off the intake expanding and forcing fuel out the shooters. I've also cut a piece of aluminum faced insulation and put under the accelerator pumps but it hasn't been a complete fix either.

[Gaz64]

Originally Posted by DanEC

My setup is not too different - a LR 427 intake with two 1850 carbs on it. The exhaust is enough to get a cold shoulder from the wife but if I look down the primary throat on the rear carb about 10 minutes after shutting it down I will see fuel starting to drip from the accelerator pump shooter. That fuel on hot engine parts sets up a real stink that lasts for hours in the garage. I have heat shields under mine which helped somewhat but not a complete fix. I do have my floats set to hold fuel just below the sight ports and Patrick probably has a good point about taking them down a bit more. But I think the main issue is the accelerator pump sitting right above the intake and heat off the intake expanding and forcing fuel out the shooters. I've also cut a piece of aluminum faced insulation and put under the accelerator pumps but it hasn't been a complete fix either.

That can only happen with the late bowls that have the red umbrella intake valve in the pump chamber.

Early bowls have a hung unseated ball that vents the pump chamber back to the bowl.

Late bowls that have no venting can have a .013 hole drilled next to the umbrella outer edge, or a groove cut in the bowl under the umbrella edge.

Gary

[DanEC]

Do you have a picture of where to drill? I have new bowls on my carbs but I think both the prior ones and the new ones use the red plastic umbrellas.

[Gaz64]

A pic is a little difficult at the moment, but if you have a pin vice, you have two options.

Some bowls have a blind hole cast next to the outer edge of the umbrella.

A number 80 drill through there, or anywhere between the outer edge and the return spring seat will work.
The orifice allows any percolation to vent back to the bowl, and not pressurise the circuit after shutdown.

Gary

[Large Arbor]

So I got a call from my carburetor guy today and he informed me that my dual quads were sized differently. One was a 450 and the other a 600. I had never noticed before so I went to Jegs and bought a matching 600 so they both will match. I don't know how I missed this before, but it will be interesting to see if I see any performance differences.

Phil

[DanEC]

Which one was your primary carb (front carb)? That is strange - never heard of that before but maybe the builder thought the smaller primary carb would idle cleaner and be more responsive at part throttle.

[Large Arbor]

The front was primary and rear (450) was secondary.

Phil

[Gaz64]

Originally Posted by DanEC

Which one was your primary carb (front carb)? That is strange - never heard of that before but maybe the builder thought the smaller primary carb would idle cleaner and be more responsive at part throttle.

That makes some sense on the builders behalf, but completely wrong idea.

Originally Posted by Large Arbor

The front was primary and rear (450) was secondary.

Phil

And then even worse, the 600 is the primary?

Gary

[DanEC]

Yeah - I agree - that's pretty whacked. Hard to figure out how that happened - accident or some doped up theory.

I have an old fuel bowl with the umbrella seal. I'll take a look at it sometime an d see if I can figure out the .063" hole idea.

[Large Arbor]

I think it was just a mistake when the carbs were set. Its hard to see much difference between the 450 and the 600 if you don't look at the venturis. Either way, hope to have the carbs back later in the week and will put it back together, set the bowls and then mixture and should be good to go.

Phil

[Gaz64]

I've yet to hear of ANY dual quad setup where one carb is larger than the other.

Choose one size and tune it accordingly, 2 450s, 2 550s, or 2 600s.

Gary