Jet Flow Rates Using Crap Gas

[Bill Lee/Virginia]

I plan on flow testing several sets of Zenith carb jets this winter. Do you recommend increasing or decreasing the flow rates of the jets since all I can purchase is "crap" gas here in Virginia? If so, by how much?

Bill Lee/Virginia Peninsula

[Kevin in NJ]

Alcohol leans out the mixture. So a slight edge to richer.

That said, I just checked a pile of jets and found they tend towards richer.

While flow checking, also notice the stream. Some are kind of twisty indicating abnormalties in the flow. Some were very straight and did not break up for a very long distance, those I noted.

I am not a fan of redilling the jets. I believe some need to have their shapes and should be left along. I also have a large pile to pick from so I can be picky.

Inspect the long brass tubes on those jets. I found a couple with hairline cracks that leaked very slight drips.

[tbirdtbird]

Gasahol has less BTUs than non-polluted gasoline. I have had to increase jet size on several of my other marque vintage cars by about 10%, such as a '54 Packard I have, in order to get them to run properly. Also had to do this on my 2003 Harley, else it ran like total crap

However, the Model A has the advantage of the GAV so you can compensate for crap gas right at the dashboard. Thus, I personally do not mess with the stock jet sizes on an A.

[H. L. Chauvin]

OMG!

Will these pass today's Model A Judging Standards?

I can just visualize my new 2017 mailed, Model A catalogs having a New Ad in the catalogs' Carburetor Section: CRAP JETS.

[MikeK]

The stoichiometric ratio is independent of the fuel energy (BTU) yield. Leave the jets alone.

[H. L. Chauvin]

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Thanks Mr. Mike K.

[Tom Wesenberg]

Originally Posted by MikeK

The stoichiometric ratio is independent of the fuel energy (BTU) yield. Leave the jets alone.

Mike, I was waiting for your input on my overdrive thread.

http://www.fordbarn.com/forum/showth...ve+quiz&page=2

[Kevin in NJ]

Originally Posted by MikeK

The stoichiometric ratio is independent of the fuel energy (BTU) yield. Leave the jets alone.

The ratio changes slightly:

Discussion on gas vs gasohol ratios


The engine needs to run slightly richer with todays fuels. How much richer, well if you have a pile of jets for the carb and flow test them you will find some flow a bit more then others. Just put them in and adjust with the GAV. I would not drill them out bigger, in fact I would go out of my way to only use untouched original jets.

Truthfully, it is kind of hard to properly evaluate.

Everbody has different techniques to measure flow rate. This does not result in repeatable science. While I intend on using original jets that tested a bit high on the flow rates, that is not the 'cure'. You have more issues with how your car is breathing, how much valve guide leakage, and how the ignition is set up that far overshadow the effects of the gas.

If you are concerned then you must spend time understanding how you engine is running and carefully experiment with changes (you have a GAV and you must understand the left lever on the column). What works for your engine may not work for others engines.

My brother had experimented some with his car on an emission machine and if he chimes in he could elaborate much more.