Carburetor, starvation, newbie asks help

[jay1922t]

'29 A pickup.

Engine is starving for fuel while riding, then engine dies.
Will start again and repeat dying condition.
Repeat cycle again.

I was able to get home after discovering to pull out and then push in the choke rod every time the engine would be at the verge of dying.
Seems this action adds fuel to the carburetor and keeps the engine running.

What might the cause be for the starvation/dying condition?
The carburetor is a restored Zenith.
Thank you. All input appreciated.

[BILL WILLIAMSON]

Is gas cap venting?
Is fuel line set too deep in carb?
These were suggested by my Dog.
Bill W.

[Big hammer]

I will add check fuel filters/screens, fuel flow from carb drain!

[H. L. Chauvin]

Hi Jay,

Very common Model A problem. Just try this "quick", intelligent fix, recommended often herein, & live happily ever after.

1. An in tank screen is an excellent start for filtering 80+ year old gas tanks full of carburetor harmful scaling rust, coarse sand, etc.

2. The NAPA "Gold Filter" #3039 in your glass sediment bulb will filter all of the fine silts & rust in tanks so it will not settle in your carburetor bowl and get stirred up every time you hit a bump.

3. Few living today remember when window & door screens were "first" introduced.

4. Intelligent people provided screen on their windows and doors and no longer had malaria.

5. The hard headed idiots tried to cling to the old & did not install screen ..... drinking hooch and smoking was more important ...... so they kept inhaling the poisonous fumes from their flit guns and kept nasty fly swatters, and stayed up half the night swatting flies and mosquitoes.

6. Some people try things that work, others stay miserable ..... just choices in life.

Hope many in the future with dirty fuel will remember this screen & insect story.

[Tacoma Bob]

First thing As already mentioned is the gas cap. They have internal venting and rust and scale will clog up the vent. Next time it dies remove the gas cap. If you hear a "swoosh" bingo. If so use an air compressor and try to blow out the crud. I eventually went with a new cap.

[abachman3]

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Open the GAV valve 1/4 to 1/2 turn counter clockwise. After starting, pull down on spark advance about half way.

[H. L. Chauvin]

Hi Jay,

Another point to consider is, because of limited Model A fuel filtration, fuel starvation can occur with a totally restored Model A right after filling up at a gas station that "may" have bad gas containing harmful deleterious material.

Fuel starvation on today's 2016 highways with today's 2016 texting drivers can be most dangerous when a Model A is "stopped" in any of today's highway lanes .....

If you ever get rear ended, just once, because of your present carburetor fuel starvation problem, you will never forget the reason for having window screens and flyswatters ......

[ian Simpson]

Bad gas, water in the tank?

Empty tank and refill with fresh, and if obtainable - non-ethanol, gas.

Don't forget to install the filters per post #4.

[Brentwood Bob]

newly installed rebuild, or has it been functioning ok, and then suddenly started causing problems?

[jay1922t]

Thank you for your advice.
Gas cap is good.
Fresh gas.
Fuel line tube properly set.
Filters clean.
Coil changed per previous advice.
Zenith rebuilt about a year ago.
Runs fine for a long time, then acts starved, then dies.
Starts right away, runs a bit, then dies....cycle repeated.
Zenith leaked once, tapped the bowl, leak stopped.
Going to unscrew the needle housing and see if the needle is seating properly.
Going to unscrew the drain plug to see if there is a clog with the main jet.
I've never fooled with a Zenith or a Model A, so, I'll risk and learn.
Worst case is if I screw it up good...then off to a pro for repair.

What I don't understand is that whenever it acts starved, I pull up and push down on the adjustment rod and fuel gets to the carburetor and keeps the engine running for about an 1/8 mile. Then I pull/push the rod again to keep the engine running. Repeat. Repeat. Just to get home. It is like I am pumping gas into the carburetor.
Can anyone explain why this is?

[Mitch//pa]

When choking the carb your blocking off some air entering the carb air horn by the choke plate. So if your running a lean mixture due to lack of fuel or a blockage it's richening up the mixture somewhat compensating to keep it running. You may also find by holding the choke halfway it may help also instead of returning it back to the open position...
A vacuum leak at the intake can also give you similar symptoms of poor fuel flow

[Fred K-OR]

I hate to admit this, but I had this problem once when I went for a drive. I had just worked over the carb and took off for a check out. After awhile I had to keep the choke pulled to keep it running. Problem, I did not tighten the bottom drain plug and it dropped out.

But a more similar problem I had that sounds almost like yours, was caused by a bad coil. But you said you had changed the coil so may not be the problem unless the "new" coil you used is bad. What the problem I had was similar to yours in that I would be going along then the car would quit just as if you had turned off the gas. I would pull to the side of the road, try to start it and it would start up just fine. Run it a little further, same problem and same solution to get home. I then put on a "new" coil and have had no problem since.

[Tom Wesenberg]

Sometimes you can unblock a carb passage or jet by opening the throttle wide open, then slap you left hand over the intake. Remove your hand before the engine dies and let it clear and rev up again, then repeat once or twice more. This was a common practice on customers MoPar 2.2 and 2.5 engines in the 80's.

If this doesn't clear the carb, then take it apart and blow through all the jets and passages with compressed air.

[H. L. Chauvin]

Hi Jay,

As you already mentioned and questioned when you pull out your choke:

"It is like I am pumping gas into the carburetor. Can anyone explain why this is?"

YES ..... A Simple Physical Experiment !!!!!!!!!!!!!!!!!!!!

1. Get two (2) drinking straws & label one F for Fuel and one A for Air.

2. Place one end of the F straw in a 10 quart bucket full of water and allow one end of the other A straw to remain in open air.

3. Place your mouth on the opposite ends of the F straw and the A straw.

4. Like your Model A engine's strong intake valve suction force, form a suction with your mouth & draw in both F straw water from the bucket and A straw air from open air.

5. To simulate a "possible" reduced flow of fuel from inside the bottom drain in your possibly dirty Model A fuel tank, (rust, dirt and/or mice crap), squeeze your F straw to reduce your water flow 75%; e.g., now ...... too much air & not enough fuel to run an engine.

6. To compensate for reduced F straw water flow, (like with your choking intake air with your choke), you squeeze your A straw an amount to reduce air flow; e.g., now you have similar proportional amount of water flow and air flow as that of 4. above ........ and ...... because you are like your engine with the same "strong" suction force; the water velocity increases and the air velocity increases such that you are getting both enough balanced air & gas to operate your engine.

7. Getting back to screens, mosquitoes and fly swatters, an in tank screen is a tall cylindrical screen as opposed the flat screen near your carburetor.

8. The mice crap & rust that settled to the tank's bottom which clogs a tank drain can usually clog the bottom of the tall tank screen cylinder ...... but not the top of the screen; hence, fuel is allowed to "freely" flow through the unclogged "top" of the cylindrical tank screen down through the interior of the screen to the gas line.

9. Not to be facetious; but, if you experiment with straws F & A, please do not place mice crap in the bucket to prove this fact; however, "if" a dirty tank is your problem, you will see that in tank "screens" actually work just like keeping out mosquitoes out of a house & mice crap out of a carburetor.

In accordance with reply #4 & #7 ........ just hope this helps not to forget Model A Carburetor Choking Physics 101 and those who continue to ignore in Model A tank screens, & "possible" often occurring gas tank clogging mice crap, rust & such that stop engines ... but re-start after choking.

[tbirdtbird]

Pulling the choke rod out decreases the amount of air going into the carb, thus richening a lean mixture.
Whereas the GAV (this is the same as the choke rod....only it turns CW and CCW for the GAV function) increases or decreases the amount of fuel going into the carb.
How do you know the cap is 'good'?
Drive around with the cap loose and see what happens. My guess is either the cap vent is plugged or the GAV is not open enough (turn it more CCW). The GAV was put there to be fiddled with until the engine runs well...don't be afraid to play with it. Start the car cold with the GAV open 1/2-1 full turn, and as the car warms up close it down to about 1/2-1/4 turn open. Every car will be different regarding this adjustment
yrneH, hguone

[H. L. Chauvin]

Again, sounds like a very "possible", very common occurrence with vintage vehicles, trucks, tractors that are 60+ & more years old.

1. Carburetor reported rebuilt, & "everything" clean from tank drain down.

2. Start the engine with a "full" gas line filled over time with vintage gravity flow of fuel, as opposed to gas pumped through a more modern fuel pump.

3. If there is a partial blockage present near the tank drain, with gravity flow, it cannot allow enough fuel to get to carburetor after the engine is running & the carburetor bowl & the fuel line is now getting close to empty.

4. Choked carburetor causes less air; however, it also causes more fuel to be drawn out of the tank, through a possible partial tank drain blockage ..... then, as this blockage is increased, not enough fuel flow, & engine dies.

5. Then, wait a few minutes with engine not running ......... no suction on fuel line ..... crud relaxes & is not jammed against drain because of engine running suction .... but, with gravity flow, carburetor bowl and fuel line fills again ...... then, engine starts and later repeats fuel starvation.

6. All above multiple advice is wonderful & also happens often, ..... but it is good to keep looking "everywhere" & not giving up ..... it will always be something so very simple.

[jay1922t]

I previously posted and tried all the recommendations: venting, filters, gas line, gas, spark plugs, etc.
Still have the engine dying problem.
I now believe it is the 12 volt conversion.
Killed 2 coils.

Need help in converting back to the 6 volt system.
Am not experienced but willing to learn and proceed.
Or perhaps I can pay a local member or mechanic.

But a more similar problem I had that sounds almost like yours, was caused by a bad coil. But you said you had changed the coil so may not be the problem unless the "new" coil you used is bad. What the problem I had was similar to yours in that I would be going along then the car would quit just as if you had turned off the gas. I would pull to the side of the road, try to start it and it would start up just fine. Run it a little further, same problem and same solution to get home. I then put on a "new" coil and have had no problem since.

From Fred K in Oregon.

[wmws]

If you are able to make the engine run by intermittently pulling out the choke, I don't think you have an electrical problem. The one think I don't think anyone has mentioned is maybe you float is binding up. I would take your carb apart and make sure everything is in order. If you don't know how to do that get help from a club member.

[Mitch//pa]

Posting an approximate location in your avatar will certainly help

[BILL WILLIAMSON]

Did anyone mention the PENCIL FILTER that goes in the top of the fuel valve?
Bill W.

[Patrick L.]

Will the car run at certain speed [ say 35-40] and then die at a higher speed [45 or over] ? If so, that still sounds like a fuel flow issue.

Just loosening the fuel cap and going for a ride, or, reaching thru the windshield once it starts to die and opening the fuel cap will rule in or out the fuel cap. I know you said it was good, but, they can fool ya.

Sediment plugging the inlet can be a royal PITA too.

The other info is good. There are quite a few issues that can cause your problem.

[BILL WILLIAMSON]

Remove the carb drain plug, turn on the gas & let it drain for quite awhile into a container & see if the flow is CONSTANT. You can also see if there's water in the gas.
Bill Test

[jay1922t]

Many thanks for the recommendations and tips...I'm learning.

It dies at idle and at 25-35 mph speed.
I even drove with the gas cap off.
Turning the choke rod a bit ccw also caused back firing at the muffler.
I'll remove the drain plug today.
I removed the tube at the carb and the fuel flows out consistently steady.
Haven't investigated the float, but will do so after I search the Forums for instructions on taking it apart and reassembly.

I like the truck although it frustrates me.

I really would like to convert back to 6 volt for the sake of perceived originality but I don't know how.

I live near Fort Wayne IN, perhaps an experienced Model A'r is nearby.

[George Miller]

sounds like a lean mixture, you might have a leaking intake gasket, or carb gasket.