Need help near Atlanta diagnosing motor issue

H

Humperhill

Member
New to Ford Model A's and older cars in general. Picked up a '31 model A based speedster that has a miss, and I am afraid its getting beyond my experience. Have ruled out fuel delivery and electrical/timing. Installed an electronic distributor and have checked timing at idle and at speed to confirm it's advancing properly. Rebuilt carb, and have completely rewired everything and have checked my ground. Miss is apparent at all speeds except possibly at idle. She fires right up, no backfiring or completely cutting out. I have not been able to do a proper compression test because I don't have an adapter large enough to screw into the spark plug hole. I have tried with a rubber stopper and holding it by hand, but I have to question the validity of this method. At this point I really need someone that knows what they are doing and has experience with the Model A. I am north of Atlanta in Woodstock area. I can easily trailer the car to Atlanta or north Georgia area. Any suggestions of anyone to contact?
 
Could be a sluggish valve. Might try some Marvel Mystery Oil in the gas. Four ounces per ten gallons is pretty standard. Routine use of MMO is pretty common. Good Luck.
 
Glug-glug-glug-glug-glug with the MMO. Not going to hurt anything, maybe a little smoke.
Some mix diesel in with the gas.
Paul in CT
 
What compression numbers are you reading using the rubber stopper? I suspect sticky valve or burnt/leaky valve. This would show up in the compression numbers.
 
With the rubber stopper and holding it by hand after the engine had warmed up I was getting 55-60 on all the cylinders. But I don't have real confidence in this method. I am going to purchase an adapter to 14mm to I can use a fitting to check compression. She fires right up and seems to idle fine. And when I say it starts right up we are talking no choke, no waiting to catch, its immediate. But raising the rpms fast or slowly it still seems to miss, and definitely lacking power under load but no backfiring. Would a leaking head gasket contribute to a valve leaking or getting burnt?
 
Humperhill said:
With the rubber stopper and holding it by hand after the engine had warmed up I was getting 55-60 on all the cylinders. But I don't have real confidence in this method. I am going to purchase an adapter to 14mm to I can use a fitting to check compression. She fires right up and seems to idle fine. And when I say it starts right up we are talking no choke, no waiting to catch, its immediate. But raising the rpms fast or slowly it still seems to miss, and definitely lacking power under load but no backfiring. Would a leaking head gasket contribute to a valve leaking or getting burnt?
Click to expand...



When you suggest that I starts easily without using a choke, that would lead me to believe that the fuel mixture is rich enough that it should accelerate properly. The miss at that point would make me want to look towards ignition. A weak ignition coil, -or possibly a condenser would be possible culprits. So many variables & unknowns to try to diagnose from the internet. I would offer an opinion that it is not valve or gasket related if you can get 55-60 psi on a compression gauge. If you had one cylinder that was leaking compression, -either thru a burned valve or a blown headgasket, you would see a lower compression reading.
 
One other thought since this is a speedster that has likely had several modifications away from stock, have you checked the ohms rating of the coil and compared it to your voltage system? Also, have you checked the coil polarity?? All the electronic ignition has done is provided you with a triggering system to fire your coil. It does not make a hotter spark other than possibly a tad longer coil saturation time. For the compression ratio that you have, the performance increase using the electronic would be negligible over a kettering points system.
 
I agree with Brent, now that I see the compression numbers. They are all high enough and close enough to each other to make a valve problem unlikely.

As he said, incorrect coil polarity can cause what you have. Or running a 12 volt coil on a 6 volt car. Is this a 6 volt car?

If it starts that easily with no choke(!) it is way too rich. What are you doing with the GAV in all this? How far open is it? If a Model A will start and idle and run with the GAV closed when the engine is cold, the carb jets are too rich. Most reproduction jets are too rich; it's a known problem. You may have a jet missing in the carb that you can't see, giving you way too much fuel.

How much slop is there in the distributor rotor shaft? Using just your finger tips, rotate the rotor clockwise and counter-clockwise, stop-to-stop. How much does it move? If excessive, you may not have the timing right, despite best efforts.

Also check the condition of the wire that plugs into the nose of the coil and runs down to the distributor cap. Is it in tight at both ends? Are the metal ends in good condition? Is the little center wire soldered to the metal end clips?
 
EHERRICK;]Contact Benny Bohannon at Bentley’s
antique Auto Maysville Georgia
He specializes in Model A’s
Good luck



Taking my car to them Friday. Sound like nice folks.
Thanks for the referral.
Eric
By the way where are you located that you know of them? I am in the Woodstock/Roswell area
 
Thanks for all the input. The ignition is a new FS Ignition for 12 volt negative ground. It comes with its own coil and I purchased their wire. I cleaned and rebuilt the carb using Synder's kit. GAV is set at about 1/4 turn out and the float level is about 3/4 inch. At this point I feel confident the ignition is working as it should. Once warmed I tried disconnecting a spark plug at a time to see if a particular one disconnected made less of a difference than the others. It seems as if when number one is disconnected it made the least amount fo difference but I cant say for sure.


Its a learning curve for sure, and I know trying to diagnoses over the internet can be futile. I am planning to take it to a shop here in GA that specializes in Model A's Gaining some knowledge from them will be well worth the investment as they can fine tune my carb if I have something out of whack there. And I am sure they can run a proper compression test. I'll let you know what we find out.
 
You must log in or register to reply here.
Back
Top