1931 Model A no start/ run issue

FromRagsToRaces

FromRagsToRaces

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Hey guys. My name is Chris. First time posting here. Modern Auto Master tech. Avid intermediate level antique/ classics tech.

I've got a client's 1931 Model A. Here for a no start/ no run condition. Cranks all day.
I have put in new ignition coil, ribbons, and champion plugs from Snyder, gapped to .035. New 6v generator with new regulator, both from Brattons before they closed down. Has a known good 6v battery (was hooked up reversed by a previous tech that did not know what positive earth is) ignition coil, and generator replacement were done after battery was correctly hooked up, to account for polarity "damage". I have rebuilt the carb (being a 31, the GAV valve seat is not replaceable without replacing carb body) with a full carb kit from Snyder. Unfortuantely they do not machine or etch jet designations on their jets in these kits, but it is supposedly a factory equivalent replacement. Because of this I can only assume/ hope that they are correct. I have adjusted float level to be correct.
Their is no damage to any of the wiring that I can see, any where in the harness. I have pulled the dizzy cap and cleaned the points up. Confirmed that timing gap is correct for the condenser bits, at .022. As far as I can tell, the engine is in time. It was running off and on for a while before I started on replacing things and doing some maintenance. Oil level is good. So far the only issues I have been able to find, is that the throttle shaft has a some amount of play, does leak gas when attempting to start. (minor level leak, though I know any gas leak is to be taken seriously). I have been able to get it to run for all of 1to 2 minutes tops. Stumbled the entire time, and would randomly "catch" and idle fine, then go back to stumbling. Carb setting was 1 full turn on AF screw, 1/4 turn on idle, and 3/4 on choke. Pulling choke has no affect on getting it to start. After the 1-2 minute run cycle, it has not run since.

It is worth mentioning that the radiator did dump all the coolant while being driven, and then died a short bit later. According to client, vehicle would continue to start up and run for brief durations, and then die and not start for a while. I cant visually see any indicators of an overheat condition anywhere. I did a temp seal on the radiator, and ran a pressure test. It holds, no pressure drop below .5psi over the course of 45 minutes. Passed leak down test on all 4 cylinders, with no more than 15% leak down, which i believe is fine for an engine like this. Have not done a compression test yet.

I'm honestly at a loss as to where I should go from here. Have been tackling this on the weekends for 2 months now. Still have to do other things unrelated to engine. Still waiting on new radiator from Brass works.
 
Do you have good compression, nice blue spark from coil wire when the points open, good fuel flow to carburetor.
 
Bob C said:
Do you have good compression, nice blue spark from coil wire when the points open, good fuel flow to carburetor.
Click to expand...

I believe i have good compression. Only mechanical test I've not run. I can only assume it does, given the leak down testing results. Yes I have blue spark. Yes I have good fuel flow, filter screen is completely clean.
 
Install a stainless finger screen in the bottom of the gas tank.possibly rust plugging the fuel output. That doesn’t help at least you have eliminated that possibility
 
FromRagsToRaces said:
I believe i have good compression. Only mechanical test I've not run. I can only assume it does, given the leak down testing results. Yes I have blue spark. Yes I have good fuel flow, filter screen is completely clean.
Click to expand...

Verify compression with compression tester. A good spark should be 3/8'' from coil wire to ground when shorting + coil term to ground. If not, possibly bad condenser. Then same good spark from plug wire to ground when cranking.
Good fresh fuel?? Possibly try known good carb.
 
Try replacing the condenser with 1 of the burn out proof condensers many of the older condensers once heated up short out and you lose spark then after they cool down they still test good!!!
 
You said that "As far as I can tell the engine is in time." Did you check the timing using the timing pin in the front of the engine? The points should just be opening when the #1 piston is at TDC and the ignition lever all the way up.

The engine needs air, gasoline, compression, spark, and correct timing. If it has all these things it should run. Is there any possibility of a manifold leak or a plug in the exhaust system?

You said you did a leak down test and that was good. But check the compression with a compression gauge too.

Check to see if the coil is wired correctly. Negative to ignition switch, positive to points. A modern coil will have the Bat terminal going to the points.
 
As far as fuel is concerned, I have completely drained the tank, and boroscoped the tank interior. Not a lick of rust to be seen anywhere. I have not inspected the timing directly. I have to install a new door frame and door on my house today, so if I get enough time this evening, I'll brave the cold and mess with it again.
 
Kurt has a good suggestion. If the timing gear is bad the engine will not run. It may have skipped a couple teeth or continuing to skip teeth. Valve and ignition timing is fundamental to every engine and the Model A is no exception. To check take the spark plugs out and watch the valves in respect to the piston position. At TDC with the crankshaft 360 degrees out from ignition the valves should just be changing. The exhaust valve should be closing and the intake should just be opening. Very easy to check.
 
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Good afternoon...Just a few old school things to check from a guy who spends time in a Model A Shop in the wilds of Arizona...If there is a fuse block on the side of the starter...those things can short out by engine vibration...now it works, now it does not. Remove it. Check the wire from the bottom of the distributor to the upper plate. The insulation has a habit of coming off and the strands of the wire can short to the case...Check the connections on the back of the Amp Meter and the Ignition Switch...they can come lose and sometimes short to the gas tank. Clean the area and cover with black tape...Run your hands over all the wiring looking for breaks in the insulation...vibration sometimes allows these wires to work and other times to short out. Prehaps these old school suggestions might help. Check the battery cables carefully...They can look OK and have mostly broken strands inside the covering and also the end fittings can be lose or full of corrosion inside the fitting where you can't normally see it. Car might start, run for a minute or so as you have stated and then the vibration causes the short to re-appear...One additional thought...Check the Gas Cap to make sure the vent is not clogged up. An open system with a clogged gas cap will run for a minute or two and then quit...Please do let us know what the final answer is...You most likely have checked the gas shut off valve under the tank to make sure it is not clogged...It could cause an issue just like the Gas Cap...Even if it's just that the old girl is in a bad mood! Ernie in Arizona
 
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I haven’t seen in the post that you actually have spark. I had a no spark issue last year. This was discussed in a similar post not that long ago. Both P.S. and nkaminar suggested a good way to confirm that the electrical system is as it should be.

With the key on and the points open, use a digital volt meter and with the positive lead connected to a good ground (preferably right to the + battery post) measure the voltage between the following points, in order:

1- Battery negative post. Make a note of the exact voltage.
2- Fuse block or lug on the starter.
3- The terminal box lugs (both sides)
4- Both sides of the ammeter.
5- Ignition switch terminal with the wire from the ammeter or terminal box going to it.
6- At the points.

If any of these test points measures more than 0.2 volts different than the battery post, you will have isolated the issue.

You also need to use the timing pin and make sure the engine is in time before getting too far along. With the pin in place make sure cylinder 1 is at top dead center and both valves are closed, you can see all of that through the spark plug hole. If it all checks out you should be able to focus on the fuel system. You can do a fuel flow test at the carburetor if you get that far.
 
Maybe not your problem, but it is a problem. That being said, a sloppy throttle shaft will leak air and not idle right. A simple fix is to remove , solder up, and sand down for a tight fit. Install with fuel resistant grease.
 
Ernie Vitucci said:
...Check the connections on the back of the Amp Meter and the Ignition Switch...they can come lose and sometimes short to the gas tank. Clean the area and cover with black tape
Click to expand...

Yes, yes... Exactly the issue I had, with very, very similar symptoms to FromRagToRaces - and - very similar, head scratching troubleshooting.
 
All of the issues with intermittent shorts and opens can be bypassed by disconnecting the supply wire to the coil and running a temporary wire from the battery to the coil. If the engine starts and runs well then start an investigation along the normal electrical path.
 
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