How perfect does an A idle?

MrTube

MrTube

Well-known member
I had our A running again today for a bit and had it idling pretty slow. Don't know exact rpm but it sounded pretty nice.

What i'm wondering is how perfect does a stock A idle? Should it be a consistent perfect idle where every cylinder firing sounds identical? Or do they idle kind of erratic with an occasional miss, but still run smooth?

Ours idles really smooth and slow, but no matter how hard I try I still get an occasional miss and its driving me nuts. If this is normal I can finally rest :)

The one in this link sounds like its running about identical.
http://www.youtube.com/watch?v=GnfJ0Pt3vgs
 
I get an occasional tiny miss or hiccup. Maybe about every 5-8 seconds at idle. Rebuilt engine, proper timing and modern zenith. My other 2 As are the same way. Could be a hot spot in the cylinder, a valve not sucking in as much air or gas in the rear cyl as opposed to the center ones, etc. I think you are fine.
 
Idle can be improved by opening up the plugs -Wide gap for nice idle (up to 38 thou or more ) Small gap for high end performance.

Correct timing is also important It's my observation that if I time the engine as Marco suggests I get a better idle and more responsive car than if I use the Les Andrews Method, One of mine doesn't miss but it does have a imbalance in it which means the engine sound flucuates slightly as it cycles smoothly - No big deal. I have finally got my rebuilt engine back in the other so we'll see what this one sounds like when I get it running over the next few days
 
Karl said:
Idle can be improved by opening up the plugs -Wide gap for nice idle (up to 38 thou or more ) Small gap for high end performance.

Correct timing is also important It's my observation that if I time the engine as Marco suggests I get a better idle and more responsive car than if I use the Les Andrews Method, One of mine doesn't miss but it does have a imbalance in it which means the engine sound flucuates slightly as it cycles smoothly - No big deal. I have finally got my rebuilt engine back in the other so we'll see what this one sounds like when I get it running over the next few days
Click to expand...


Yea, I noticed with the timing if I let it run more advanced idling it seems to run faster and easier but misses more. While if I run it more retarded it runs more labored sounding but also more consistent.

I understand these all behave slightly different i'm just curious whats "normal". Sounds like an occasional sputter and miss is considered typical at a slow idle.
 
An occasional, random "puh....puh..........puh..." is not unusual; even modern FI vehicles do it.

It's been suggested that getting an A ( or T) to idle down to where you can count the cylinders firing is more of a "neat party trick" than a practical tune-up spec.

I have found ( with a very tired 83,000 mile engine) that to get it to idle smoothly at such slow speeds, I have to set the carb idle mixture differently than I do for my "normal" idle.

I would go no lower than 350-400 RPM; you need to keep the engine turning fast enough to keep pumping oil up to the valve chamber.

Other factors that might contribute to slight irregularities in idle would be:

- incomplete atomization of fuel due to primitive carb / slow air-speed at low idle

-play in timing gears

-wear in cam bearings / block

-wear in distributor drive / distributor shaft bushings

- modern fuel

- the Ford's mood on a given day...

-any combination of the above.... ;)
 
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I'm a believer in your last statement " The Ford's mood on any given day".
If these things didn't have a personality would we love them as much?
 
I'll have to see if I can make an audio or video of my jalopy at idle and post it...

I was just thinking as I was driving home last night, that my A has almost never stalled at a light or stop-sign ( unless I was clumsy getting under way).

I live in work in a small city / large town, so I deal with a lot of traffic lights... stop & go driving...

One of the "issues" I had with a 1950 Chevy Fleetline was that it idled so nice and quiet that surrounding traffic noise drowned-out my own car at lights... the only way I'd know if it stalled was if the oil-pressure went to Zero...
 
MrTube said:
I had our A running again today for a bit and had it idling pretty slow. Don't know exact rpm but it sounded pretty nice.

What i'm wondering is how perfect does a stock A idle? Should it be a consistent perfect idle where every cylinder firing sounds identical? Or do they idle kind of erratic with an occasional miss, but still run smooth?

Ours idles really smooth and slow, but no matter how hard I try I still get an occasional miss and its driving me nuts. If this is normal I can finally rest :)

The one in this link sounds like its running about identical.
http://www.youtube.com/watch?v=GnfJ0Pt3vgs
Click to expand...

This is a great video - what I find particularly interesting when watching videos of Model A's (and it occurs on all engines with unshielded spark leads) is the static popping in the audio feed. Listen closely and you can hear it when the camera gets close to the engine.

It's the same sound you hear when lightning discharges close to a camera.

What a model in simplicity. Gotta love the "A"
 
A few things to ponder....

A worn-out engine generally idles slower than one that has more compression.

Idle speed is more closely related to the carburetor's throttle shaft & plate fit to the housing, than it is to ignition timing advance/retard. Engine speed is mostly controlled by shutting of the air, --not the fuel.

The condition of the distributor, ...more specifically the dist. cam has much to do with the idle quality. The reason is when the lobes are worn, the spark is delivered at different degrees of advance/retard causing unequal pulses. If all four spark plugs fired exactly at TDC, and the four cylinder's compression were all equal within 1 lb., and the throttle shaft fit was tight and the throttle blade can seat against the housing, it will idle slow enough that you can count the fan blades as they go by. I know this because I have seen it done.

Now the REAL kicker on all of this is that most people do not know what an original Model A engine is really supposed to sound like, ...because most Model A's have an aftermarket exhaust system or most have higher compression ratios than when they were originally delivered. Factor in any of this or the items listed above and it sounds different than when it was brand new.
 
MrTube said:
Yea, I noticed with the timing if I let it run more advanced idling it seems to run faster and easier but misses more. While if I run it more retarded it runs more labored sounding but also more consistent.
Click to expand...

Yep same with mine It's just a trade off . My 1910 Hupmobile has fixed magneto ignition . So the setting that will give peak performance at speed (relatively speaking in a 1910 car) is too advanced for a nice idle and hence it does "Fluff" a lot at idle . Some of this can be made slightly better by playing with the plug gaps and (richening) the carb settings but basically I just accept it as normal for the car - Since it doesn't have a water pump or effective fan => if I idle for to long it overheats anyway !!LOL - Karl
 
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