idle rpm

[mmindling]

Hi, worked on a tune up on the 28 today.
Does anyone have the spec for idle rpm? I have all of the data on adjusting the Zenith and other tune up info, but don't find the spec data
on idle rpm.

Have a laser tachometer working off the crank pulley. Right now, it's idling at about 700 rpm. which seems a bit fast but not sure about reducing the idle. Engine is totally stock with no hc head, running a Zenith double venturi carb, stock distributor, coil.

Any advice appreciated.

Regards,

Martin Mindling *A 11739* mmindling@aol.com

 

[TreeTopFlier]

Lord have mercy on your soul! I kid, I kid but I asked a similar question and many an ol' timers scolded me for trying to put numbers with a "seat of your pants" adjustment.

My engine currently idles cold at 450 and warm at 550 rpm and I was never able to locate any specs. Yours seems a little high to me.

 

[BILL WILLIAMSON]

Yo, Martin,
Buster T. says, set it like you want it to sound, IT'S YOUR CAR!! Bill W. & Dog

 

[mmindling]

Thanks, guys. I suspect there would be two idle specifications, one with the spark fully retarded and one with the spark advanced for normal operation, both with the engine warm.

Realize that this question violates the traditional method. However, I'm a data driven A owner and believe there must be a range for proper rpm.
I'm pretty sure the correct idle will "feel right" once obtained.

Agree that 700 seems high (spark advanced). I'll turn it down a little and see how 550 to 600 rpm sounds. On other matters, the engine starts immediately, runs smooth and no weird noises. Not much in the way of leaks either, except at the back end of the transmission box.

Look forward to hearing from you,

Regards,

mmindling@aol.com

 

[marc hildebrant]

I too tried in vain for a specific idle number in the past. For all the experts on the Forum, nobody would give a number.....

I use about 700 RPM at full retard, although it will idle so slow that you can hear each cylinder fire...at least on my car.

Marc

 

[Walt Dupont--Me.]

I like to hear it at 475-500 at full retard. You can hear the engine count, 1234 1234 1234 but it's not good to idel an engine real slow for a long time, it won't through oil up on the cam lobes. Walt

 

[BILL WILLIAMSON]

Thanks, guys. I suspect there would be two idle specifications, one with the spark fully retarded and one with the spark advanced for normal operation, both with the engine warm.

Realize that this question violates the traditional method. However, I'm a data driven A owner and believe there must be a range for proper rpm.
I'm pretty sure the correct idle will "feel right" once obtained.

Agree that 700 seems high (spark advanced). I'll turn it down a little and see how 550 to 600 rpm sounds. On other matters, the engine starts immediately, runs smooth and no weird noises. Not much in the way of leaks either, except at the back end of the transmission box.

Look forward to hearing from you,

Regards,

mmindling@aol.com

Martin,
DATA, that's a good word to describe the low, retarded idle sound, like, DATA-DATA-DATA-DATA! Some come up with unusual descriptive words. I use TADA-TADA-TADA-TADA. That was Minerva's sound! When Vermin, my avatar car fires, He may have a sound of his own! No! I'm not KRAZY, just havin' FUN! Chief, my long gone Model A mentor, calld that sound, "Countin'em off!"
It should do that perfectly at retarded idle, at half spark it should have a faster, smooth idle, then at full advance, it should be an even faster, but a "rolling" idle. If you have all these, then the timing is "DEAD ON."
Great lookin' engine room! Be proud! Do you like your air filter & does it have a bracket/brace to the engine? Bill W.

 

[Tom Wesenberg]

Engine warm and spark half down, mine is about 500 RPM.

 

[mmindling]

Bill, thanks for the advice. Your question: Air Maze Filter. No, it has no bracket to the engine. It hangs on the carb with a single set screw. However, seems to be attached to stay. I painted the pot metal part black with engine enamel. Keeps out the 4 pound June bugs around here from getting sucked into the carb.

Martin

 

[lookin-backtexas]

With the spark fully retarded the engine should say "TA-PUCKTA PUCKTA PUCKTA PUCKTA PUCKTA". Say that out loud and see how long you can repeat it; you'll sound like a well-timed Model A.

Fred

 

[mmindling]

Gentlemen,

First, thanks for all the replies and the laughs. Good to see humor post-election.

Here's what I did today:
*Set point gap at .020
*Timed from #1 Cyl. TDC, so that points are just about to open
with spark fully retarded.
*Verified coil polarity (slant pole)
*Rewired dash panel, including ampmeter (original non script)
*Set Zenith air control to open 1.5 turns
*Set GAV at 1/4 open with warm engine
*Checked distributor slotted cap to be sure upper plate has full
movement from end to end.

Now have RPM at 475 with spark fully retarded and at 550 with spark advanced 3/4. Getting that nice Model A bubbling teakettle sound.

Two things noticed:
*The idle,especially in the spark retarded position, has a little roll.
Not completely perfect count off.

*The distributor main shaft has no lateral movement, but does have
some lash which allows the rotor to have about 1/8 to 3/16 lash.

Let me know any thoughts on the above.
Your suggestions are very helpful.

Regards,

Martin Mindling mmindling@aol.com *A 11739*

 

[700rpm]

Sounds like you did it correctly: Not too fast. Not too slow. But j-u-u-s-st right.

 

[Mike Peters]

Thanks for the engine comartment photos! You've got a Jan. 1928 number. I can see the early starter switch with the dog leg rod which attaches with a cotter pin, early powerhouse generator with side mounted cut out and belt tensioner, what appears to be a banana cut out, and fan shroud. Also the cad plated oil filler cap. I just bought a late 28 business coupe as a project and feel very fortunate to have most of the early stuff as well. Again, thanks for the great photos!! mike

 

[modela@aol.com]

It takes some trial and error sometimes to get that perfect idle or cotton picker, cotton picker sound.
Some people will compensate for the disti lash in a worn disti gear by slightly pulling the retard lever down by ~ 1/2 inch before timing. Once your car is timed you can check it with a timing light. Once your car is timed to TDC and running OK then you should not have to worry about any disti back lash again.

The rolling of the car can be tweaked out by adjusting your Zenith on a warm engine. Lots of discussions on on past FB posts on how to do this. What works for me is to retard the spark first. Basically make sure you do not have any air leaks in the throttle shaft openings or around the carb mounting flange. Any air leaks will affect the adjustments.... Put the GAV around 1/4 turn open. Disconnect the throttle rod and get it to idle as slow as you can with the throttle adjustment screw. Adjust the idle adjustment screw to it's sweet spot between too rich and too lean. Then set your idle speed and reinstall the throttle rod. This works for most Zenith's if they are functioning properly.
Then run the engine at a faster rpm and then advance your spark lever down until you get the best smoothest rpms. Remember where this spot is if it is not full advance and then use this advance lever spot for your cruising speed. The spark lever and the GAV is adjusted for power during operation depending on your driving conditions and octane / quality of the gasoline.

 

[mmindling]

Thanks Mike, other details you might not see in the photo - slant pole coil, early small hole water pump held on with cap bolts, oil return pipe high on valve plate, smooth oil pan with no ribs, solid front motor mount, square hole distributor, script cap, first generation accelerator linkage, smooth clutch and brake pedals, multi-disc clutch., zenith double venturi with no number, early intake manifold with bulge, left hand single brake system, fan shroud with three clips at bottom, early radiator..
Not a perfect car by any means, but a nice driver with a lot of early details.

Thanks for your comments.

Thanks for the engine comartment photos! You've got a Jan. 1928 number. I can see the early starter switch with the dog leg rod which attaches with a cotter pin, early powerhouse generator with side mounted cut out and belt tensioner, what appears to be a banana cut out, and fan shroud. Also the cad plated oil filler cap. I just bought a late 28 business coupe as a project and feel very fortunate to have most of the early stuff as well. Again, thanks for the great photos!! mike

 

[mmindling]

Thanks for the advice. I'll try your method this week. Will be looking for leaks around the throttle shaft first. Any thoughts on how to detect the leaks? Drop of oil? If I can get the rolling out of the idle, I'll be happy again.

Best Regards,

It takes some trial and error sometimes to get that perfect idle or cotton picker, cotton picker sound.
Some people will compensate for the disti lash in a worn disti gear by slightly pulling the retard lever down by ~ 1/2 inch before timing. Once your car is timed you can check it with a timing light. Once your car is timed to TDC and running OK then you should not have to worry about any disti back lash again.

The rolling of the car can be tweaked out by adjusting your Zenith on a warm engine. Lots of discussions on on past FB posts on how to do this. What works for me is to retard the spark first. Basically make sure you do not have any air leaks in the throttle shaft openings or around the carb mounting flange. Any air leaks will affect the adjustments.... Put the GAV around 1/4 turn open. Disconnect the throttle rod and get it to idle as slow as you can with the throttle adjustment screw. Adjust the idle adjustment screw to it's sweet spot between too rich and too lean. Then set your idle speed and reinstall the throttle rod. This works for most Zenith's if they are functioning properly.
Then run the engine at a faster rpm and then advance your spark lever down until you get the best smoothest rpms. Remember where this spot is if it is not full advance and then use this advance lever spot for your cruising speed. The spark lever and the GAV is adjusted for power during operation depending on your driving conditions and octane / quality of the gasoline.

 

[BILL WILLIAMSON]

Martin,
I gotta' get a rubber stamp for this one as I type SLOW!
A CHEAP stethescope with probe removed, just the open hose, is great for finding vacuum leaks, it'll SCREAM like a Banshee! Also helps find miniscule exhaust leaks around ports, etc, you know, the ones that sound almost like a valve tick. Also helps localize engine noises that transmit through the engine when using the probe. To do this, run the hose close, but not touching engine areas.
DANGER--- NEVER stick the hose on an open vacuum fitting to see what it would sound like----IT'LL SUCK YOUR EARBALLS OUT!!!!!! Bill W.

 

[700rpm]

Also, if you have a newly rebuilt engine, it will take a while to get broken in before it will idle real smoothly.

 

[40 Deluxe]

Here's some "data" straight from the Model A Instruction Book, dated 1931: "With the engine warmed up; fully retard spark and throttle levers. Unhook throttle rod at carburetor. Adjust throttle adjusting screw so the the engine will run sufficiently fast to keep from stalling. Next turn idling screw in or out until engine runs evenly without rolling or skipping. Then slowly screw in throttle plate adjusting screw until engine picks up slight additional speed. Connect throttle rod to carburetor."
Note that no specific RPM number is given; the amount of "slight additional speed" is determined by the gray computer between one's ears!