UPDATED - In Search of the Perfect Idle

[stu in wichita]

I’m sorting out a few minor issues on my ’61 Ranchero. It’s a 170/5-speed. The carb is a Holly 1908, with original Load-O-Matic distributor. Everything is new or rebuilt and I feel like it’s tuned pretty well. It has nearly 2000 miles on it, about half highway, half city stop-and-go. As I get each little quirk figured out, I’m impressed at how drivable this 50+ year old car is in today’s world.

My new quest is improving the quality of the idle.

• * Idle is set at about 650 rpm. In general, it’s quite smooth, but there's an intermittent miss every few seconds, like maybe it’s dropping a cylinder.
  
  * The miss isn’t even or consistent, and I don’t think it’s necessarily the same cylinder. If I pull the plug wires one by one, no particular cylinder is indicated. The intermittent miss is simply combined with the “regular” miss from the disconnected cylinder.
  
  * Just for fun, I’ve dialed the idle down to 400 and even lower. At those speeds, it is understandably rougher, but it still runs surprisingly well. Not sure that it matters, but it seems like that indicates that the overall set-up is working pretty well.
  
  * I’ve played with timing and idle mixture to no avail.

Any ideas what it could be, or how I can track it down? I suppose an oscilloscope might pinpoint it, but I don’t have easy access to one. I have this expectation of a super smooth idle like a newer car (WOW,it hurt to say that!).

As always, any help or suggestions will be greatly appreciated.
-Stu

 

[rbohm]

8) if you want the perfect idle, convert to port electronic fuel injection. it sounds like you have gotten your idle as good as it can get with a single barrel carb centrally located on a long restrictive log manifold.

 

[thesameguy]

IME, good but imperfect idle behavior is almost always ignition related. I'm sure a worn cam gear turning a worn distributor gear in a worn distributor housing firing an old coil powered by an old electrical system through a cheap cap & rotor (because that's all that's available these days) all contributes to an occasional miss. I *bet* it's fixable, but maybe not for reasonable money. Even newer Fords with gear-driven distributors (I'm looking at you Lima 2.3l) suffer from the occasional miss and they are much newer motors. It's just a bunch of imperfect accuracy all piling up.

Again to blast the EDIS horn, the idle on my '62 is flawless. It's better than on my '85 Saab or '86 XR4Ti with electronic ignitions, but unfortunately saddled by California emissions requirements. If I could get the choke on the Falcon to work properly it'd be perfect all the time, but alas it's only perfect when it's warmed up. But, once warm I'm pretty sure you could balance a cup of water on the rocker cover. Solid state ignition FTW.

I changed nothing on the carb after installing EDIS and idle improved *dramatically*. I have it set to about 725rpm, which is about 650rpm in Drive. I've tried moving it up or down 50rpm, but it seems happiest where it is because it allows some fudge room for temperature. If I threw fuel injection in the mix I'd have some more options, but at this point that seems like a lot of cost for little gain in an engine with a very narrow power band - the carb isn't letting down ~3000rpm of useful power.

 

[stu in wichita]

That's what I was afraid I'd hear. I knew my expectations might be unrealistic, but I wasn't sure why. I think rbohm nailed it with the carb/manifold issue, especially since it's an early engine with the restrictive log.

I'll continue to play with the ignition, but I'm stuck with the small shaft dizzy. That means I can only make it as good as a LOM can be. I may someday switch from points to Pertronix, but more to eliminate the maintenance, not to improve over properly working points. Also, thesameguy is right - there's lots of old parts in the mix. When I say everything is new/rebuilt, I'm kidding myself.

This is my first inline, but I also have a '68 AMX (390 with AFB). It's a pretty crude ol' ground-pounder, but it idles sooooooooooooo smoooooooooooooooth. I understand, though, it's a totally different set-up.

If that's the way it is, I'm okay with it. I love the way it runs overall, I just like the idea of tuning it to the best it can be. Maybe I'm there.

Thanks for the input.

-Stu

 

[chad]

"...but I'm stuck with the small shaft dizzy..."
I think some machine that wider to accept a later model?

 

[170-3tree]

If you wanted I have a small shaft D.U.I. I'd certainly suggest sending it to fsd for a recurve. It warned my 170 up greatly! I'm about two hours from you south of kc.

 

[chad]

"...warned my 170..."
thinkin that's not it, it's got all the pep/power he wants (w/o 'performance prts') - is
something pretty basic here...

 

[170-3tree]

He also mentioned doing an ignition upgrade. And having a proper ignition can enhance idle quality as well.
The log head engines are not the best for idle quality and when I put my D.U.I. in it helped more than expected.

 

[stu in wichita]

I'll be installing 170-3tree's old DUI in a couple of weeks. I'm definitely hoping the ignition upgrade will help.

I'm not looking to optimize power but I'm finally convinced the LOM is not much good. My fascination with the odd technology has completely subsided. :rolflmao:

-Stu

 

[chad]

"...My fascination... has completely subsided..."
Shucks, oh well...
On ward & up ward!
I thought you'd hafta machine the opening larger...nice
to have friends w/parts! Let's hear back when THAT's installed.

BTW: very nice rig U got there. My imagination went to early '60s
'chero destruction when hearing about the cash for clunkers thing
a few yrs ago (had to replace that vision with early '80s GM diesel
'experiements'). Very glad this 1 didn't go!

 

[stu in wichita]

I finally got my DUI distributor installed this weekend and I'm impressed with the difference it made. The car runs noticeably smoother and stronger and I'm extremely pleased with it.

The idle is still not perfect, but it's waaaay better. At normal 500-600 rpm idle, it's real nice. At the tailpipes, I can hear an occasional spit (like a dropped cylinder), but much better than before. Just for grins, I turned the idle down real low and it still ran pretty smooth.

For now, it's set up to DUI specs (manifold vacuum, 14 degrees advance0. I only opened the plug gaps to .045, but I might try the .050 to .055 they recommend. Eventually I'll send the DUI to FalconSedanDelivery for a recurve.

Thanks to all for the help and suggestions.
-Stu

 

[ludwig]

NOW is the time to check your A/F mix at idle with a vacuum gauge. Should be about 18* with a stock cam.

 

[Gene Fiore]

I finally got my DUI distributor installed this weekend and I'm impressed with the difference it made. The car runs noticeably smoother and stronger and I'm extremely pleased with it.

The idle is still not perfect, but it's waaaay better. At normal 500-600 rpm idle, it's real nice. At the tailpipes, I can hear an occasional spit (like a dropped cylinder), but much better than before. Just for grins, I turned the idle down real low and it still ran pretty smooth.

For now, it's set up to DUI specs (manifold vacuum, 14 degrees advance0. I only opened the plug gaps to .045, but I might try the .050 to .055 they recommend. Eventually I'll send the DUI to FalconSedanDelivery for a recurve.

Thanks to all for the help and suggestions.
-Stu

FYI, I am running .052 gap and runs great.

 

[64Comet404]

IME, good but imperfect idle behavior is almost always ignition related. I'm sure a worn cam gear turning a worn distributor gear in a worn distributor housing firing an old coil powered by an old electrical system through a cheap cap & rotor (because that's all that's available these days) all contributes to an occasional miss.

I was wondering about the same as posted by the author of this post... so I'm glad to read this post... I think you hit the nail on the head, regarding the general cause of "misses". I've read nothing but positive about converting to an electronic ignition. I'll be upgrading mine shortly to a Crane Cams XR700 simply because I got an awesome 1/2 price deal on it.

 

[JackFish]

I think the funny idle we get is related to poor atomization of the fuel, and it's subsequent delivery system, ie. the log.

 

[thesameguy]

My experience says otherwise, as I've got a 1bbl on a small log 200 with EDIS and my idle at 650rpm is flawless.

 

[stu in wichita]

My experience says otherwise, as I've got a 1bbl on a small log 200 with EDIS and my idle at 650rpm is flawless.

I'm inclined to agree. I opened the plug gap to .052 and it smoothed out even more. I'm about to call it good and just enjoy it.

I have a 200 on the stand that I'll eventually swap, and I'm considering something like your EDIS installation. I read your detailed thread again and I'm thoroughly impressed how you figured it all out, as well as how good it works. Thanks for sharing.

-Stu

 

[powerband]

consistent idle at varied seasonal temps and conditions seemed futile on the '71` Mav 170 until a swapped 5200 series (Weber type) progressive 2bbl carb. Smooth consistent idle and strong off idle-cruise on primary bbl - secondary bbl punch at WOT (with OEM points ignition).

have fun