GAV Adjustment + Choke flood

B

bautiprea

New member
Hello people. This is my first time on the forum. I have now fully serviced my 31' Model A, and now everything is running correctly I would like to further understand the car. I usually use the Gav at 1/4-1/2. However, it backfires, meaning there is fuel left to ignite. So when I open it just a tiny bit more than 1/2 turn(usually 1/2 turn will not backfire), engine will idle pretty bad to my taste. It feels more jerky, not as "harmonic". So how should I balance the backfire-idle problem, can't seem to find a spot where it wont backfire AND idle nicely.
Another thing, when starting this last couple of times, it was more difficult than usual. I usually start it retarder, and gav 1/2 open, and with the choke lever up from the point in which I press the starter, until it starts. Problem is, lately its taking longer to start, even have to try 2 times as it may start, and then die after a second(it feels as it didnt have fuel, slowly dies even though I accelerate it) So. Am I flooding the engine with too much choke? Should I advance the throttle a bit so it starts more easily? A couple of months ago, it would start after the engine turned a couple of times, now I even need a good battery on it for it to start(my battery is pretty discharged, I might need to change it, point is, I ve had it started in 4-5 slow turns, now it needs more and faster turns, cant seem to find the problem)
Thanks a lot for taking the time to help. Understanding our cars and having fine control on them is essential. Cheers!
 
I think there's a fine line between enough choke and too much. What I do on a cold engine is


  • spark fully retarded
  • throttle down a couple of notches
  • GAV 1/2-3/4
  • choke out for no more than 4 revolutions.

If the engine catches before 4 revolutions then I put the choke in, but sometimes it will start to die. So I pull the choke out quickly but very briefly to re-establish the rich condition to keep it running, and pull the spark advanced. Almost always it will keep running. But if it dies at that point I crank it a couple of revolutions with the choke open, then pull the choke out while cranking but only 2 revolutions. It's easy to flood by overchoking.

One of my cars is very sensitive to spark position, the other not so much but is much more sensitive to GAV (needs to be opened more until it's warm). You just need to learn your car.

Know your fuel supply situation, too. If you turn off the fuel valve at the tank and then continue to run to draw down fuel in the carb before stopping, upon starting it will need a bit of time to reestablish the fuel level after you turn on the valve. So it might seem to be harder to start for some other reason, when in reality it's just fuel starved.

And a weak battery will not help, get it charged!

JayJay
 
Do you have the right size battery cables? I presume you are 6 volts. Undersize cables will cause slow cranking. Elsewhere in this forum the recommended size cables are discussed...........i just do not recall right now.
 
I recently acquired my first A also, and am new to this forum. I want you to know that I am going through the same learning curve to start the vehicle. My main complaint is I can't get it to keep running on the first crank try. It ALWAYS FIRES AND DIES. I got some advice here also and I am still finetuning the car. Have worked through carb, points, timing, plugs, etc. Still won't stay running on first try. I have tried every conceivable combination of choke throttle, timing, and GAV. All I can add is keep working on it till you are satisfied with its condition, then learn to work around its quirks and just enjoy it. These are not modern engines, so maybe we should not expect them to act that way!!
 
Good Evening...Model A six volt battery cables should be 00 size. The cable which is rubber covered is about the size of your ring finger. The major suppliers have them, NAPA has the cable and end fittings. They should be attached by soldering. Many of us use two ground straps...off of a marine terminal on the positive battery lug. One goes to the transmission and the other to the frame...Your A will crank like a champ. Ernie in Arizona
 
Why is it that internal combustion engines need a higher idle when cold and the choke is closed ? When I start my A when cold #1 retard the spark,#2 hand throttle 2 clicks down,#3 gav 3/4-1 turn richer,#4 gas valve open,#5 ignition switch on,#6 pull the choke,#8 hit the starter, #7 release the choke after 2-3 turns and then it starts. IF it doesn't start after trying 2X I look at the points check the gap and or clean the points. IF it starts and then dies I check to make sure that I've not forgotten to open the gas valve ( it happens)

Your idle issue; after its warmed up #1 retard the spark lever, #2 close the gav,#3 adjust the idle speed to a nice slow speed as to not die,#4 then adjust the idle air screw in and then out finding a middle ground to where it runs smooth. If after this you still cannot get it running with out backfiring you may need to go though your carburetor .
 
First off, Welcome Bautiprea. Good to have you onboard. I've had my A for 28 years and I've found that what works for me is all of the above but I'll turn the engine over a couple turns with the choke out and the ignition key off. Then put the choke in and turn on the key and I'm off. Works for me.
Marty
 
Let's look beyond the carburetor.

1) Burned or worn exhaust valve seats will cause backfire.

2) Intermittent electrical connections will cause backfire by causing spark misses that pump unburned fuel into the exhaust. Check:


  • Upper to lower dizzy plate connection

  • Armored cable internal wire and dizzy body contact

  • Ground connections in multiple places

  • Did you add a ****** bolt to frame ground? That will help with both cranking and intermittent issues with ignition and generator/alternator
 
Good afternoon...Model A's are very much their own, machines...If yours starts always on the second try...just let her do that...frequently the GAV needs to be adjusted after a couple of minutes as the engine warms up. I was taught in the 1960's by an OLD guy at the time, to set spark up, throttle about half down, step on the starter and give the choke a quick pop, out and back in...at start move the throttle back up a bit and move the spark down 2/3 of the way...ours might turn over five or six cylinders depending on how long I let her run after I turned the gas off...the last time out...these girls are much like your first girlfriend in high school...you have to figure out what THEY like...not the other was around...Ernie in Arizona
 
When its cold I need to give one quick choke pull plus open the GAV 1/2 to 3/4 turn for a couple minutes. If I don't richen the mixture via the GAV for a couple minutes, I find that it will probably die and need to start again. Oh, and yes, .... a faster idle for a couple minutes helps too.
 
If adjusting the GAV changes your idle, then the idle is too fast. The gav feeds the cap jet only, which is used only in mid to high speed use. The idle mixture can be adjusted at the carb, but remember it is an air mixture screw, so opening it, will lean it out. The gav is used to richen the mid speed mixture until warm up. A lot of folks open it 1/2 to 3/4 of a turn, then as it warms up close it for better mileage. It's something you kind of play with, but as I said, it should not affect idle at all.
 
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