31 AA - Won't Start When Hot

RustyWiring

RustyWiring

Member
Hi folks,

I have another issue with the new hobby and would very much appreciate your input: Truck starts quick and easy when stone-cold. Runs great, driving as long as I want. However, if I turn it off and try to restart, it will not restart without choke; and, even then, it's a challenge to re-start. Once re-started, it idles and drives great.

This began, like a light switch, about 30-40 miles ago (I'm at about 130 miles now). Before that, just a touch of the starter and it would re-start. To me, it seems like an obvious carb issue: not enough gas or too much air. I checked and tightened every bolt in the vicinity (manifold and carb). No joy. I had my son remove the lower carb half and clean out the jets but that made no difference (assuming he did a proper job). I removed and blew out the idle jet today. No change.

I will be removing the whole carb and examining it tonight. For the experienced, this seems like one of those 'Oh, yeah. This is your problem...' problems. Any ideas where to start?

Thank you!
 
If it was the carb it would not run well. Points condenser or coil or loose connections. Maybe the engine is tight and the starter is not turning it fast enough.
 
@George & Dave - Thanks for the insights, guys. I will look at the points tomorrow. I had trouble early on with smoking the distributor and it caused the points lobe to melt a bit. I did some filing, re-timed it and away it went again. It certainly could be the points acting up. It would be great if it was that simple :)
 
What do you mean smoking the distributor. If it got that hot to melt the rubbing block that is not good. Do you have lube on the rubbing block. When it acts up see if you have spark at the coil wire. If not then you have a elec. issue not carburetor.
 
Make sure the wire from the lower plate to the upper plate is not touching the side of the distributor via its attachment "flag". Ensure also that the nut securing the wire to the bottom of the ignition points is tight. Smoking probably happened when the connecting wire touched the metal distributor body. If it is now in contact with the body, the engine will not start.
I am guessing that if this is the problem, the wire connector must be in very close proximity to the distributor body. When cold, there is enough of a gap so that the ignition points still function. However, after the engine is warm and transfers this heat up to the distributor, the distributor's metal body expands with the heat and closes the gap between it and the wire's connector = shorts out.
Before taking out the top plate, look down the gap cutout where the wire connects to the points. You should be able to see the wire's connector. Gauge how close it is to the distributor. If too close or it seems loose, locate the distributor cam's open notch (or rotor tip) to some easily replicable spot in its arc of travel, such as at the 3 or 6 O'clock position. Note how much free play there is and then take out the cam's screw and lift off the cam. Take off the spark rod from the upper plate's arm, and twist the upper plate until the three ears come free and the plate can be lifted out. Inspect the condition of the wire. If the coating is charred and the brass wire strands are visible, replace the wire with a longer and more flexible one available from vendors, or make your own. The original wire is too short and too stiff. Once the new wire is in place and the nut tightened, replace the upper plate and ensure that the flag does not touch the distributor. Don't forget to put the tension spring back in place beneath the upper plate! Set the distributor cam's open notch at the position you determined before disassembly. This will ensure that the timing has been retained. Put the cap and connectors back on, and the spark rod. Then try to start the engine. Let it warm up or drive it around some. RETURN HOME before shutting off the engine to see if it will start hot.
Let us know what you find, please.
Marshall
 
On our '29 tudor, I had a similar problem. It started great when cold. It would not restart when hot though. Sometimes it would miss at the higher road speeds. I found a wire end in the firewall terminal box that had developed a poor current connection over the years. While in use the wire end developed heat and then it had a huge resistance to current passing. After clipping off the burnt wire, I resoldered the wire end and it is now working great once again. Took me a year to find it. I inspected one wire at a time until I found the problem.
 
:) Thanks, "tbirdbird". Let's hope it helps! We all know from bitter experience with our Model A's that the problem experienced by the OP could be caused by a hundred different things. Sometimes we cyber-armchair diagnosticians get it right, sometimes not. But smoke coming from a distributor pretty much rules out the carburetor. :)
M.
 
Hi Rusty,

Your mentioned detail is interesting:

" if I turn it off and try to restart, it will not restart "without choke"; and, even then, it's a challenge to re-start.

There was a 50/50 time honored "quick" vintage Model A Test used by "all" vintage vehicle mechanics years ago that today's Model A part changers refuse to try:

When engine "hot" & definitely will "not" start:

1. Switch OFF, choke pulled out , rotate engine several revolutions, remove spark plugs and smell & look for wet plugs or dry plugs.

2. With plugs removed, switch ON, rotate engine several revolutions, look for spark at tips of "grounded" plugs laying on their side and connected to distributor.

3. The quick 50/50 Chance: Dry plugs, usually fuel problem ...... no spark, usually electrical problem ....... dry plugs & no spark, usually fuel & electrical problem.

4. Or like recommended by many Model A owners on Forums for the past 20+ years:

Bounce around for the next several weeks changing out carburetor jets, carburetor floats, condensers, points, coils, electrical wire, manifold and carburetor gaskets, head gaskets, valve job, re-set timing, change fan belt, muffler clamp, inner tube tire valves etc., etc. until it starts.

Had a friend who had a doctor like that for a year ..... we buried him last month.
 
I think George was pretty close with those 3 possibilities of coil, points, or LOOSE CONNECTION. Dave seems to have zeroed in on the points and is my suspicion as well. When checking your points also check the adjustable point block. My lock screw on the top was real loose as well as the screws that hold it on. Points was very near closing at full retard and on the cam lobe high spot.....NOT GOOD........GOOD LUCK!!!
 
Well, it rained most of the day so I have not started the truck. However, I checked the points and, fully retarded, they appeared closed. Certainly not gapped to .020. So, at TDC, I gapped it again. If it dries out tomorrow, I will fire it up and retest.

@Marshall: Thank you very much for that detail. I will have to read it several times before I fully understand it.
 
RustyWiring said:
Well, it rained most of the day so I have not started the truck. However, I checked the points and, fully retarded, they appeared closed. Certainly not gapped to .020. So, at TDC, I gapped it again. If it dries out tomorrow, I will fire it up and retest.
Click to expand...

Gapping the points has nothing (well, very little) to do with advance, retard, TDC, etc.

To gap the points, the cam screw is loosened and turned so that the rubbing block on the points is on a high point of the cam. Then the points are set to .020.

Afterwards, of course, the engine will need to be retimed.

You can eliminate the retiming if you you use the crank to turn the engine so that the rubbing block of the points is on a high point of the cam and then set the point gap. Keep in mind, however, that one degree of dwell is equal to 1 degree of initial advance. If you change the point gap, you have also changed the initial advance.
 
If at first you don't suck seed...

I think I resolved the issue. So, last night I reset the points but only drove it today. No good. Still would not start hot.

Next, I replaced the points and condenser. No improvement.

Next, I pulled and inspected the carb. There was stuff in there other than air and gas. I suspect a trip down a dirt road must have gummed up the works. So, I fully disassembled it, blew it out and slapped it back on. Fired right up and ran much better - like it did early on but I had forgotten. More power, too. And, when hot, restarts better. Now, I say better because it immediately fires and slips the starter. Trying again, without choke, it will still simply turn over. But, with a quick dash of full choke (when hot), it fires right up. So, maybe the idle jet or the GAV needs setting. The idle jet is open 1.5 turns. The GAV was open a full turn (it idled, when first started, much smoother at this setting and not less).

That brings me to two questions:

1. I have an air filter; the upward elbow kind. But, I hear some say the carb needs some port opened up via the machine shop to prevent a too-rich mixture. True or false?

2. See the photos below. I have a hole in my Zenith-2 carb. Never noticed before. Is this normal?
 

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Thanks Bob. It seems to me to be a way of allowing dirt inside.

Any thoughts on question #1 regarding the air filter porting?
 
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Quite a few Model A air filters sold over the years did not have nearly enough air flow.

Many articles on the larger K & N filters which allow more than enough air .... the Hi-Boy arrangement is interesting if filters wet with fuel after choking the engine is a concern next to a hot manifold & exhaust.
 
If you push a thin short brass tube into that vent hole, then slip a hose over the brass tube and run it to the air filter side of the choke plate you will equalize the pressure over the fuel, so you can use an air filter without disrupting the gas to air mixture.
 
If blowing out the carburetor helped I would suggest pulling it off again and rebuilding it.
Get a kit from the vendors. If this is your first time going through a carburetor just take your time making note of where each jet comes out from paying special attention to where each gasket goes etc... Les Andrews volume one book has a pretty good tutorial to help with a re-build. Plus a whole lot of other information. If you don't have it, get it.
Buy a one gallon can/kit of carburetor cleaner from your local auto parts store to soak your carburetor body and parts and pieces. The cans come with a basket strainer in it to hold your parts. This really does a wonderful job of getting all the years of gunk out of them. Give the carburetor plenty of time to soak. Over night at a minimum. On really gunked up ones I will soak, wash, blow and clean and then give it another soak. Wash and blow the passages out well. Get some thin stiff wire to chase the passages to be sure they are clear. Doing this will also help you understand where the passages go and what they do.
 
@Tom: I was wondering if this could be used for that purpose. Glad you confirmed. Thank you.

@Dave: I fully rebuilt the carb over the summer - clean as a whistle. Before I began rebuilding the engine, I picked up Les' book. Great resource. I think I was just careless testing driving on dirt roads (trying to stay out of faster folks' way).

It still needs some fine tuning as well as either a new head gasket or head due to the compression problem in another thread. But it looks like we're going in the right direction this time.

Thanks everyone!
 
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