Ideal idle RPM

sconnors

sconnors

Well-known member
Just installed a new Tillotson carburetor and am wondering if there is an “ideal” ideal speed the Model A she be at RPM wise when idling?
 
Slow enough that the idle circuit in the carb is fully activated, fast enough that it doesn't stall.
 
Guten Morgen.


I used to think it was something to be proud of, having a very low, smooth idle.
But the downside is that the oil pump delivers very little oil at this time.
I don't think that's good when the engine is hot and you're stopped at a red traffic light.
I can see from the transparent return line that only very little oil is being delivered at idle.
 

Attachments

  • 02_IMG_20260320_170514137.jpg
    02_IMG_20260320_170514137.jpg
    34.7 KB · Views: 80
The slower the better - you want that Model A sound for everyone to enjoy while sitting at a light.


A healthy Ford Model A at idle is characterized by a steady, rhythmic "chuff-chuff-chuff" or a deep, ticking hum. Because of its low-compression, four-cylinder engine, the idle is often described as slow and distinct enough that individual exhaust pulses can be heard.


https://www.youtube.com/watch?v=Cn_Sh9l_pms
 
Target 450 rpm

350 rpm is to low and engine can't recover when it dips down returning to idle.
550-600 rpm to fast and idle circuit is over come by the high speed circuit.

I never work on any early Ford without my EZ-TACH tachometer.
One wire hookup, internal battery.

It tells the story, no judgement, no guessing, no wasting time.

NO opinions, just numbers....

David Renner
 

Attachments

  • EZ TACH.jpg
    EZ TACH.jpg
    15.9 KB · Views: 42
Werner said:
Schoenen Nachmittag,


this is, where I would like to pose my question, as I do not know how much the oil pump still delivers at this halved low rotational speed.
Click to expand...

Werner,

Maybe you can use the 450 rpm suggested by David Renner and use the hand throttle to increase the idle to a point where you are satisfied that the oil pump is providing sufficient oil to the engine.

David Serrano
 
Werner said:
Guten Morgen.


I used to think it was something to be proud of, having a very low, smooth idle.
But the downside is that the oil pump delivers very little oil at this time.
I don't think that's good when the engine is hot and you're stopped at a red traffic light.
I can see from the transparent return line that only very little oil is being delivered at idle.
Click to expand...


I think you’ve made a logical error. The return line is an overflow line. It only passes oil if the pump is moving so much oil that the tubes feeding the bearings and the valve lifter bores can’t hold it all. I’m not at all surprised that you’re not seeing any oil in it when the engine is idling. You should not use this amount as a guide to how much oil is flowing overall.
 
Seems kind of odd to doubt the function and design of this engine after 98 years of proving itself ?

I like to investigate and learn, but I'm hesitant to challenge that Ford Motor Co. didn't know what they were doing and by now we would have discovered the flaws if any.
 
alexiskai said:
I think you’ve made a logical error. The return line is an overflow line. It only passes oil if the pump is moving so much oil that the tubes feeding the bearings and the valve lifter bores can’t hold it all. I’m not at all surprised that you’re not seeing any oil in it when the engine is idling. You should not use this amount as a guide to how much oil is flowing overall.
Click to expand...


That you wrote is correct, Alexis.

But only when I can see the oil flowing through the overflow, do I know that all three crankshaft bearings are receiving lubricating oil.
 
We had this figured out in high school in the 1950's. You closed the GAV, retarded the spark, took your foot off the gas and listened to it backfire! A classmate said his "popped 40 times" going down a hill. If it didn't backfire the idle was too fast, the carb was too rich or the timing was off!
 
You must log in or register to reply here.
Back
Top