A way to slow down Zenith gas evaporation?

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Steve Douglas
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A way to slow down Zenith gas evaporation?

#1 Post by Steve Douglas » Thu Sep 20, 2018 5:15 pm

The Zenith Carbs are prone to fuel evaporation, I think that the center vent tube is the only way that the gas vapors can escape the bowl. Has anybody tried to reduce the vent size? I installed the air correction jets in my carbs and the gas smell is a lot less after parking. Wondering if there could be problems, or anything??? The jets just thread in.
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Wes Bender
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Re: A way to slow down Zenith gas evaporation?

#2 Post by Wes Bender » Thu Sep 20, 2018 5:33 pm

Have you tried turning off the gas petcock two or three blocks from home? Most of the evaporation occurs immediately after shutdown when the heat proceeds up from the heads into the carburetors.
Some days it just isn’t worth the hassle of chewing through the restraints......

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Re: A way to slow down Zenith gas evaporation?

#3 Post by Steve Douglas » Thu Sep 20, 2018 5:55 pm

Wes, thanks for the reply. I turn the gas off after parking, but try to keep the float bowls somewhat full so restarting is easier. I drove the car yesterday, parked the car and today at noon it's 92 outside and 80 in the garage. Slight odor of gas, but far less than normal. I do run the gas out if leaving the car for more than a few days, but that doesn't happen very often. I could install an electric pump for restarts but haven't so far.

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John Brooks
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Re: A way to slow down Zenith gas evaporation?

#4 Post by John Brooks » Thu Sep 20, 2018 10:14 pm

Be sure to put a DAB of lock tight on that jet. Even brass will beat up a piston and head.
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Ron LaDow
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Re: A way to slow down Zenith gas evaporation?

#5 Post by Ron LaDow » Fri Sep 21, 2018 12:21 am

Two anecdotes, and a suggestion:
Way back when Alan was offering the dyno for experimentation, I got one of those huge "party" balloons that can be inflated to about 3' diameter, rigged it via some vinyl tube hose-clamped to a screwed-in nipple at the balance port, left it 'empty' off to the side, and started the pulls.
Sucker went flat in a New York minute, and the lambda told us real quick the mixture was *LEAN*. That was the first (and last) Pre Mat test for a closed Zenith fuel system. Maybe if you balanced the float chambers to the air volume in the tank, you might get somewhere, but that's never gonna be a Pre Mat product.
And then early Solexes had balance ports of 6mm (? - from memory), while the later ones got 8mm (again ? ). I think the carb designers were telling us something.
Without access to a dyno and something to test the exhaust chemistry, I'd be careful about restricting that balance port. A bit less gas smell today (and the same three days down the road) versus more today may cost more than you'd want to pay.
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Norm Miller
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Re: A way to slow down Zenith gas evaporation?

#6 Post by Norm Miller » Fri Sep 21, 2018 12:08 pm

Steve,
Tried that on the track in the 60's and needless to say it didn't work.
One lap and back to the pits!
 

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Ben Wainscott
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Re: A way to slow down Zenith gas evaporation?

#7 Post by Ben Wainscott » Sat Sep 22, 2018 1:11 pm

Don't know if it will effect evaporation, but after I installed an electric fuel pump for priming, and using Joe Gibbs Carb Defender (https://www.summitracing.com/parts/jgr-70040/overview/) at every fill up, I eliminated all my starting problem.
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David Jones
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Re: A way to slow down Zenith gas evaporation?

#8 Post by David Jones » Sat Sep 22, 2018 7:31 pm

There is only one way to stop the smell of gas in the garage and that is to use up the gas from the carbs before parking, though it will also depend on garage ventilation. Modern gas is more volatile than back before ethanol was added and modern cars do not vent gas to the atmosphere. As far back as the late 60's and early 70's as fuel injection systems were coming in car manufacturers were installing activated charcoal filters which prevented gas vapors from venting to atmosphere and also allowing the tank to breathe so it did not collapse from being evacuated. Unfortunately cars with carbs still have to reference the float bowls to atmosphere and as Norm alluded to they have to be able to have a large enough vent to not allow a vacuum in the float chamber. One could rig up a charcoal filter via a large diameter hose from the vent line through the charcoal filter to atmosphere but it would be easier, simpler and cheaper to just turn the gas off a few hundred yards from home and use it up before parking. Dick Weiss has been doing this for the last one hundred years, just ask him. I do not worry as my cars are not in an attached garage and it is unheated, though I do turn the gas off when I remember.
If I had known I would live this long I would have pushed the envelope a little harder.
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Re: A way to slow down Zenith gas evaporation?

#9 Post by Martin Benade » Sat Sep 22, 2018 10:07 pm

I have a small double exhaust fan in my garage window, always running. It helps keep my wife happier.

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Re: A way to slow down Zenith gas evaporation?

#10 Post by PaulAhnell » Sun Sep 23, 2018 7:37 am

Ah yes, the wife. Have you ever noticed that they have these hypersensitive noses? When mine complains of the smell in the garage I just tell her that's the smell of...Victory.
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Re: A way to slow down Zenith gas evaporation?

#11 Post by Martin Benade » Sun Sep 23, 2018 10:16 am

I am sure she finds that to be a satisfactory answer. :D

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Re: A way to slow down Zenith gas evaporation?

#12 Post by Steve Douglas » Sun Sep 23, 2018 11:05 am

I know that the current gas in California smog counties have a quick evaporation rate. I am going to try switching to the canister style air cleaners from the original mesh type, that may help. The mesh style do get a bit of gas splash back which eventually wicks to the outside, and a little bit on the carb top where the air cleaners clamp on. I replaced the two pieces of fuel hose earlier this year with good line and clamps. The carbs and manifolds are dry. So guessing the smell has to be from carb evaporation.
My shop is away from the house, so not a complaint from the wife, and does have roof vent fan, but still would like to lessen the fumes on hot days, winter days when the shop is in the 50-60 degree range is much better.

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