Tuning; where to go next?

[Rick Finsta]

Gentlemen-

I've just started taking care of a 1930 A coupe, which is mostly stock. The engine loves first and second gears, and then lugs down a lot from about 25mph (after 2-3 shift, obviously) until about 35mph, where is smooths out and pulls strongly to about 45mph, where is lugs down again and doesn't like to pull much past 50mph. Vacuum guage shows it bouncing around from about 15-18" at idle, and it responds as it should when throttle is applied and removed (I have not run the car down the road to monitor the gauge yet - haven't figured out how to hook it to my bluetooth and datalogging system... ). Timing is dead nuts, plugs are good, and fuel system seems to check out (GAV is 1/4 turn open for best driving). I advance the spark about 5* per 5mph (so at 45-55mph I'm almost all the way down), and I've played with the spark and fuel while driving to try and find a sweet spot in these low-power areas.

Should I continue looking through the ignition system (condenser, coil, etc.), or should I start going through the carb? I'm used to Holley 4150s and EFI, with HEIs or DIS/COP, so this is a bit of a departure for me...

Thanks in advance for the help, and for this great resource!

[Kevin in NJ]

Originally Posted by P.S.

First of all, a stock Model A with stock gears in the rear end isn't good much past 45-50 MPH. Most people run their A's around 45 MPH. Seldom would you even come close to 50 MPH.

Hummm

Let us nip this in the bud.

From the factory you would expect the Model A to run at least 60 MPH comfortably. In fact the dealers were told to show the customers how well the car ran at those speeds (see the service letters).

From 40 years of experience. A properly restored back to factory A runs nice at 55 to 65 MPH all day long- and NO they do not feel like they are beating themselves to death!!! I have many hours of staring at a speedometer from a rumble seat at 50 MPH (which reads low by 5 MPH). Cars from the 50's complained we went too fast over the Delaware Mem bridge and they could not keep up on a car club outing. The only problem we tended to have was the condenser going bad. This does not happen with the new burnout proof condensers.

Many A's are not properly restored so there is good reason why people have the false belief on the Model A performance. You have to understand that if you took the A engine prints to a machine shop and said bring it back to factory they will tell you that you want the engine built to racing engine specs.

To be honest most of the local cars where the guys say 45 is the top end is a stretch. I would not run the cars over 25 MPH as I would not consider them safe. They do not hold the road and the do not stop. You have a good clue when you can see the front brake lever leaning rearward from 30 feet away and no shocks.

Now for those who say they would prefer to slow down and enjoy the drive. Well once you have driven a properly restored A you will find that they are comfortable to drive at any speed. Many are horrible to drive at 45 MPH.

[P.S.]

Yep, and I agree.

You may notice that my comments included the following: "I have heard some of the "old timers" mention that a Model A motor redline should be considered to land somewhere around 3,000 RPMs. "

Personally, I somewhat agree with you. However, from what I have read so far, a lot of people here do not.

As for my own car, I feel a whole lot safer now that the front end is perfectly tight! And, I echo your comments about the brakes. After redoing the brakes, the Model A stops just great with the stock brakes. If properly done, I don't know what gripe people would have about the brakes.

Back to the post above, I stand by the previous post. We'll see what some of the guys here with way more experience than me (and that comes down to 99.9% of you here) has to say.

[fordfixer]

First I would do a compression check to see how tired this engine might be. Next I would pull the head and check the valve seating. Also pull side cover and check valve clearances. Also would take a look at the valve springs. If you have nice compression, then the valve train is where you need to be looking. This is assuming that the carb. is rebuilt properly and the electrical part is up to snuff.

[Tom Wesenberg]

Are you comparing this Model A to other Model A's, or to a modern car, when you say it bogs down? Model A's have good low end torque and even mine with only 50 lbs. compression pulls up to speed without bogging down. I like to keep it 45 or less, but it will do 60 if I want it to. Your engine could have worn cam lobes or weak spark, both of which will be noticed at higher speeds, when demands are greater.

[Rick Finsta]

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I was going to run a compression check; I can do that next. I'm not expecting this to run like my 500hp Olds engine or my 2.0L Honda, but when I say it is bogging, I mean it feels like there is something wrong with the ignition or fuel curves where it is losing power in a certain range, and not pulling up to what I thought was redline (I wasn't going to ever take it past 60mph). It will cruise at 55mph, but it seems like I'm nearly WOT to maintain that speed. This motor has about 15K miles on it after a rebuild (done by someone known by the guys down in the Calumet or Joliet A clubs, so ostensibly it's a good build), but I did consider valves as a possibility (most shops can't run a Serdi to save their lives). I do not have any experience with other As to know what it "should" feel like, but there's a gentleman around the corner with a couple so I could have him take it for a spin and see what he thinks.

I can always pull the head and check cam lift, but should I try a new condenser or coil first? I replaced most of the wiring a few months ago (the ammeter shorted) so the rest of the electrical is in fine shape. It's still running positive ground, but it is a 6V alternator instead of the generator, and I didn't find anything wrong there on first look.

Thanks for the help; I really hope to not have to pull the engine apart, but I'm certainly willing to do what's necessary to keep this beauty in good repair and going down the road.

[Tom Wesenberg]

You can check valve lift by just removing the side cover and using a dial indicator,

I wouldn't replace anything yet, but just hold the coil wire near a head nut and check for a good blue spark, or you could lift it out of the distributor cap and do the same.

[fordfixer]

It always helps to know lots about the engine. Recent rebuild, helps to eliminate some things. Running the advance that far down the quadrant really should not be necessary. The position of the advance will be determined by the original timing. If to much retard it will take more advance to run nicely. Most definitely have a nother Model A owner drive your car and let you know what he feels is right or wrong. See if you can drive another Model A, and see if there is any differences in the cars.

[BILL WILLIAMSON]

Try this: To set the mixture control on the choke rod (GAV) Warm engine, Cruise steady at 20 to 25 MPH in second & adjust GAV for maximum, smooth RPM's. If it runs O.K. from cold startup & on up to warm, just leave GAV alone! And remember, GAV DOESN'T affect the idleing, unless the idle speed is TOO FAST. Bill W.

[[email protected]]

How good is the spring tension on your ignition points? Maybe at the higher rpms you are getting points float or bounce. Some of the newer repop points have weaker springiness.

[Frank Miller]

The bouncing vacuum at idle could indicate a manifold leak. Check distributor bushings also.

[Will N]

The higher the cylinder compression pressures, the greater the voltage required for a spark to jump the sparkplug gap. You would have higher pressures when the engine is lugging after the 2-3 shift, and also the load on the engine increases as you increase speed. I would try changing the coil. A weak or failing coil might not be supplying the voltage needed to consistently fire your plugs under these high load conditions.

[Rick Finsta]

Tightened up the manifold and carb base and it seemed to smooth her out; I also had to tune my idle back down as well as it seems to be giving me much better signal and more fuel pull. Drove her all day Saturday with no hiccups (other than slightly increased fuel consumption due to the higher and richer idle).

Thanks to all who took the time to give me ideas!

[1930artdeco]

Two areas to check on which would affect vacumm and idle. Check to make sure the steering column is rotated correctly. If it rotated CCW a bit that will retard the spark, which may be why you have to pull the spark arm down all of the way. I run mine between 9-10 o'clock. Also, the throttle shafts tend to be worn on the carbs. You can get an oversized shaft or bush it. That should correct some of the idle issues and gie you a bit more pep.

Mike

[Rick Finsta]

I set the steering column before setting the timing, so that's squared away. Maybe this build just likes a bit more advance. It doesn't want to die at full retard at idle anymore, and it seems to like the mid range of the timing a bit more, so I'm thinking the manifold was loose.

I'll take a look at the linkage for sure, but I thought these might be fly-by-wire...?

[green30coupe]

With engine running, spray carb cleaner around the manifold and carb base to check for a vacuum leak. (be careful to not spray into carb intake) A leak will result in a noticeable change in RPM. Also check lines and hoses to the wiper for leaks.

Also, try putting some Marvel Mystery Oil in the fuel tank to see if it helps with the bouncing vacuum gauge needle. You could have sticky valves and that is a cheap and easy try at a fix.

Ed

[P.S.]

Alternative- Use propane to look for vacuum leak. No worries about stripping the paint off the motor or other parts that way.

[BILL WILLIAMSON]

A cheap stethescope with the probe removed, just the open hose, will localize vacuum leaks, it'll "scream" like a Banshee! DON'T EVER stick the hose on a vacuum fitting, or it'll "suck" your earballs out!!! Good for finding exhaust leaks also good for localizing engine noises that seem to transmit throughout the engine. Bill W.

[Jordan]

Originally Posted by P.S.

First of all, a stock Model A with stock gears in the rear end isn't good much past 45-50 MPH. Most people run their A's around 45 MPH. Seldom would you even come close to 50 MPH.

I know a lot more people who drive at 50 or 55 mph than I do people who drive at 45. When my car was all stock, it would cruise at 55-60 easily. If they're put together right, they'll go as fast as you want.

[James Rogers]

What kind of a carb do you run?