Model A Lagging and Popping when Accelerating

T

The "A" Team

Member
Hi everyone,

The past few times I've driven my Model A, I noticed it loses a little power and pops a bit when accelerating. It idles ok.

I'm wondering if there might be a couple of reasons why it might be doing it. I'll give you the scenario from starting to driving in the morning.

I retard the spark lever all the way up, pull the throttle lever about 1/3 to 1/2 down, open the GAV to about 1/2 to 3/4 open, open the gas valve, pop out the ignition, pull the choke and start the car. It usually starts right up on either the 2nd or 3rd crank. I then pull the spark lever down about 1/2, push the throttle lever up to idle and turn the GAV to about 1/4 open. I let it idle for a few minutes while I move my other cars out of the driveway and get my stuff together for work. I then back it out, and start driving. As I accelerate out onto the main road is when I notice it lag a bit and pop a couple of times when accelerating. Most of the time, after a little while of driving, it starts picking up the pace and stops popping.

Could it be any of the following?

  • Am I starting to drive it while it's still a little cold and should let it warm up longer (the outside morning temperature here in Jersey is around 55 degrees right now, but it has happened when leaving work and the temperature is in the 70s)?
  • Am I forgetting I'm driving a 93 year old car with a 40 hp and just expecting it to accelerate like newer cars and giving it a little too much gas?
  • Should I pull the spark lever down more than 1/2?
  • Am I running too lean and should open the GAV more than 1/4?

Thanks as always in advance.

John
 
It sounds like it's running lean while it's cold. Try opening the GAV another 1/4 to 1/2 turn while the engine is still warming up. You can then try closing it a little once it's warm.
 
Too lean. Open the GAV more for the first few miles.

You can put a can of injector cleaner in your tank. It will clean out the gum in your fuel system, including the carburetor. Buy that at your local auto parts store. It does not have to be specifically for carburetors, any injector cleaner will work, like Gumout.

Play with the ignition lever. Try advancing it more. Advance to the point where further advancing will not increase rpm or power then retard one notch. Use different ignition advance under different conditions. Retarded one notch in town or under heavy load at low rpm, advanced one notch when driving on a level road at a constant speed.
 
ddweave said:
It sounds like it's running lean while it's cold. Try opening the GAV another 1/4 to 1/2 turn while the engine is still warming up. You can then try closing it a little once it's warm.
Click to expand...

I had a feeling that might've been the problem. I'll do that from now on.
 
nkaminar said:
Too lean. Open the GAV more for the first few miles.

You can put a can of injector cleaner in your tank. It will clean out the gum in your fuel system, including the carburetor. Buy that at your local auto parts store. It does not have to be specifically for carburetors, any injector cleaner will work, like Gumout.

Play with the ignition lever. Try advancing it more. Advance to the point where further advancing will not increase rpm or power then retard one notch. Use different ignition advance under different conditions. Retarded one notch in town or under heavy load at low rpm, advanced one notch when driving on a level road at a constant speed.
Click to expand...

Ok, that sounds good, I'll put that in today. The instructions say to add one bottle to 20 gallons of gas, should I only put half a bottle in the 10 - 11 gallon tank?
 
What works for me on cold starts is:
Ignition advance fully retarded
Throttle lever pulled down 2 or 3 notches
GAV valve 1/2 turn further than it's normal position

Then pull the choke and hit the starter simultaneously. It fires up and I release the choke. Then pull timing down about halfway but leave the GAV/throttle lever alone.

I Then adjust the GAV until the engine runs as smooth as possible and let it "fast idle" like that for a minute or so. Usually that means I'm adding a little more fuel via the GAV to smooth it out

Then after a minute or so after that drop the idle back down and take off. I've got a temp gauge, so once engine temp hits about 130*f, I back the GAV down to its normal position

No pops or problems with that method. Engine runs nice and smooth from cold start
 
Follow the instructions on the bottle. Some additives say to add more initially and then less after that.
 
Thanks for all the great advice everybody! I'm going to keep the GAV open more and the spark rod little further down when I drive it home from work and see how it runs. Even if I don't get any popping, I'm going to put the gumout in and double-check the distributor shaft and points when I get home.

I'll update you all after I perform all the checks.
 
Ok, update time.

I checked out the instructions on https://modelabasics.com/Ignition.htm that gave instruction on the ignition system. First I checked the gap from the rotor to the contacts on the distributor cap. One or two gaps were a little too wide, about .030, so I adjusted the gaps. I then removed the rotor and distributor cap and checked the shaft, which was fine. I then checked the point gap and that was pretty much at .020.

The site also mentioned that the spark arm on the distributor shouldn't be hitting the distributor body at all, and it was, so per the instructions, I loosened the steering column clamps and slightly rotated the column until the arm wasn't hitting the distributor anymore (a much bigger difference than before).

Lastly, and this was the weirdest thing. I decided to replace the fuel line because the nuts on the old one are a little stripped from when we were first getting back together about a year ago. The funny thing was, when I started the car with the new fuel line, it ran and then stalled, and wouldn't start again, like I didn't open the gas valve or something. I was contemplating putting everything right back where it was, but then thought what if I put the old fuel line back on? I took the new fuel line off (it DID have gas in it), put the old one back on, and it started and ran, so I don't know what the problem with that was. I took the car for a drive and it didn't lag or pop, so maybe I did something right.
 
Do any of you think I should look at the timing or anything after doing that work on the points and rotating the steering column to line up the distributor arm correctly? It seems to be running ok, but it did feel like a little bit of a rough idle last night and stalled (maybe it was the GAV again).
 
The "A" Team said:
Do any of you think I should look at the timing or anything after doing that work on the points and rotating the steering column to line up the distributor arm correctly? It seems to be running ok, but it did feel like a little bit of a rough idle last night and stalled (maybe it was the GAV again).
Click to expand...

Deffinattly check the timing, reset if necessary.
 
A past member Tom Wesenberg always said “ set the timing and forget it “ unless you mess around with the distributor cam. The points follower can wear and change the timing, resetting the points will bring the timing back. Have you adjusted the idle speed and idle mixture yet? Only adjust the carburetor after your engine is fully warmed.
 
Do you have someone nearby that can help you. Easiest way to learn sometimes is watch someone who has experience.
 
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