Idle RPM

[Junior64]

I have a '64 Falcon with a 170. The problem I have been trying to tackle is that I can't seem to set the idle to factory specs of 500 RPM. The lowest I can go is 750. Below is a list of all the recent work done.

- Rebuilt top end, great compression.
- New timing set/harmonic balancer
- Rebuilt Load O Matic with new points, condenser, rotor, cap, wires and plugs.
- Rebuilt Autolite 1100 with SCV
- New fuel pump

I am using the ported vacuum line to the distributor and can't get it to idle right below 750. I don't know if it's because of a difference in today's fuels or what. I have tweaked timing, mixture screw, gaps and everything else. When I do set the RPM at 750, I have a constant vacuum going to the diaphram at idle which gives me no vacuum advance at increased RPM. I think it may be because the throttle plate is past the orifice in the carb at this higher setting. Any suggestions to fix this or is the higher RPM setting normal?

 

[oldgrezmonke]

I run my Falcon on the cheapest regular and probably could get it down to 400 . I presume that rpm is in neutral ? If that is an automatic in drive , it's really high . You basically have a stock engine so you should be be able to get the idle speed lower than that . You have checked for vacuum leaks ? Your diagnosis is good , at 750 rpm the carb is in or close to the off idle/cruise circuit . It sounds like the idle circuit is faulty in some way . Was the rebuilt carb from a parts house ? Rebuilt carbs have long been a dice roll and quality has gotten worse the last few years .

 

[Junior64]

I am setting the idle with my automatic in drive. I rebuilt the carb myself and it is in great condition. There are no vacuum leaks either. How is yours set up? Do you pull the vacuum line and plug, then set 12 BTDC?

 

[MPGmustang]

choke linkage... as the hot air tube plugs into the exhaust manifold it's possible your exhaust manifold CAN be bad...

with a GLOVED hand, plug the hole on the OPPSITE side of that hole on the exhaust manifold while running (it will be VERY hot). then take your ungloved hand and see if you can FEEL EXHAUST gas escaping out the top hole. if so your carb has probably melted and your choke will never work unless you replace the whole carb.

but for idle rpm range... I found before my engine mod my stock engine like 750 out of gear and 650 in gear... but I also had a bad C4 at that time...

My tip would be to check to see if your exhaust has a hole in it.
then set the rpm accordingling..

Try tunning without a timing light...

1- Unplug LOM vacuum line, and plug that hose from breathing
2- set throttle idle high, (1000-1100rpm)
3- play with idle mixture to get the MOST RPM you can get,
4- set timing to get the MOST VACUUM (you really do want 20-21 vacuum)
5- play with idle mixture to get the MOST RPM you can get,
6- reset your throttle idle range to lower and repeat steps 3-5
7- plug in your LOM vacuum line
8- set your idle rpm to 700* out of gear, and check in gear - aim for 550 to 600 and then slowly tune it down with
*- If you have A/C I highly recomend that you keep it 750-800 out of gear and aim for 650 in gear with the A/C on

IF you ping, decrease timing by 2* then play with the idle mixture to get your vauum high again and readjust your throttle idle

Hope it helps

 

[bubba22349]

Have you read this great tech article about the LOD’s, it might help you?
http://classicinlines.com/Loadomatic.asp

 

[Junior64]

Thanks for the great tips MPGmustang. I forgot to mention that I have a manual choke though. I will buy a vacuum gauge when I get back from this business trip I'm on and try tuning it the way you suggested. I did read the LOM article, very good info. Maybe when I hook a vacuum gauge up, I'll have a better idea of what's going on.

 

[Junior64]

If I set the timing 12 BTDC with the vacuum line disconnected and plugged, what will it read with it's connected? Will increasing RPM then advance or retard the timing?

 

[bubba22349]

Will increasing RPM then advance or retard the timing?

If the line is disconnected and plugged than the answer is No! An LOD works very different than other distrib's in that there is no centrifugal advance. Make sure that “SCV” is good and that the “vacuum. Can” on distributor is working (it will hold a vac,). Otherwise the timing (advance) is essentially locked out.

 

[Junior64]

I understand that there is no mechanical advance. I was just wondering if I set the initial timing at 12 BTDC with the line disconnected and plugged if it will advance when I hook it back up. Is there any vacuum advance at idle or only when the throttle plate is opened past idle?

 

[ludwig]

Typically, you set the idle with the advance hose disconnected. The advance kicks in as you accelerate. You need to plug all the vacuum ports to set the idle.

 

[Junior64]

So there should be no vacuum advance at all at idle??

 

[ludwig]

No

 

[MPGmustang]

okay lets back up here cause I'm thinking manifold vacuum and i'm sure others are confusing it with scv vacuum being zero... at least that's what it sounds like to me...

so, for vacuum what you want is the max intake manifold vacuum and no SCV* vacuum
your vacuum gage is to be hooked up at the intak manifold somewhere after the carb but before the intake valves... and should read 20-21

mechanical = centrifical.. you don't have...
only advance you get is from the SCV vacuum going to that little can on the LOM, it won't advance any other way unless you move it (would be funny to see @ 65 mph )

*you don't have vacuum on this because it's plugged while tuning, granted I remember after I finshed tunning my stock engine that there was vacuum going to my vac-can thru the scv, IDK if it's correct but my vac-can was good and I still had great response under load...

 

[ludwig]

I have a three-way brass block right under the [non-LOM] carb, on the the side of the intake manifold. That is where I hook up the vacuum gauge. I forget where the dist advance vac line goes. Probably from the base of the carb. Pull everything off, plug the holes and set your idle.

 

[Junior64]

I bought a vacuum gauge and here's where I'm at now.

I tuned the engine using the vacuum gauge. It pulls 19". It still doesn't like to run at the 500 RPM idle. When I do set it that low, the GEN light flickers. It's happy at 750 RPM. Even when I had it set to 500, it was still pulling a vacuum enough to give the distributor full advance. I am content on leaving it the way I have it since it seems to be working fine, but it still bothers me that I can't figure out why the vacuum advance isn't working right. The service manual I have for it says you can adjust the posts in the distributor, but I have no idea how to do that. I have verified the timing mark on my new balancer when I changed the timing set. With the timing light on it, the mark is well past 14 deg BTDC while in drive. The mark is right underneath the fan pulley when looking at it from the driver side fender. It remains there throughout the RPM range and does fine on the highway without any pinging. That's another strange thing. It doesn't ping at all, just runs rough when I advance it too much. Anyone have any ideas what's going on with this setup? I shouldn't complain since it almost does 90 MPH (GPS) with the 2 speed Ford O Matic! Thanks again for the replies.

 

[bubba22349]

It still doesn't like to run at the 500 RPM idle. When I do set it that low, the GEN light flickers. It's happy at 750 RPM.

It is normal for a Gen light to flicker at idel. A gen dose'nt charge at low speeds (RPM) like an Alternator.

The service manual I have for it says you can adjust the posts in the distributor, but I have no idea how to do that.

You would need to pull the top plate out of distribitor to see them you can also adjust the vacuum can on some. Edit (Okay I stand corrected see below post a few pictures sure helps jog the cobwebs out)

Anyone have any ideas what's going on with this setup?

The advance is based on engine load controlled by the carbs SCV (spark control valve) totally different in operation than a vacuum advance type distributor. Having the engine idle higher than the factory specs and your are by passing the idle circuit of the carb. Assuming that you have the right carb for your LOD distributor there should be no advance at idle. So if you want it to work like it was designed too you should in this order set the point gap correctly (or better still is to use a dwell meter) than set the initial timing to mark, tune carb to best idle RPM or Vacuum. Last set the idle RPM to the factory specs (in drive with emergency brake set for an Auto). When you get that set and working properly drive it to see how it dose if you like it you’re now all done. Than you could maybe try about 2 more degrees initial timing bear in mind that the more you start changing the initial timing than carb idle speed is going to also change at a certain point it’s not going to idle down and be smooth. I think by your description that you are all ready there with too much initial timing.

 

[Frankenstang]

The service manual I have for it says you can adjust the posts in the distributor, but I have no idea how to do that.

You would need to pull the top plate out of distribitor to see them you can also adjust the vacuum can on some.

Not on a load-o...your dizzy should look like this
http://www.mustangmonthly.com/howto/mum ... to_17.html

The springs and posts are visible with the cap off. Both springs must be in place and correct type.

Even when I had it set to 500, it was still pulling a vacuum enough to give the distributor full advance.

There should be no advance signal at idle from the vacuum port on carb with an scv/load-o combo. Also the vacuum canister is very specific to the load-o and it's not uncommon that the correct one(rare) was replaced with the wrong type(common) by PO or other. It has to be that larger, circular, flatter canister made for the load-o.
http://www.mustangmonthly.com/howto/mum ... to_14.html
You should be able to advance the dizzy by hand (pic) with cap off and not running and see it return. If it does not return via springs there is mechanical failure, wrong hardware, etc in the dizzy. The springs and post adjustment govern total advance.

I'd first check the breaker plate action then the vac can...if both are okay then I would guess your scv circuit is fouled up. SCV alternates between manifold and venturi vacuum signals (both from the carb) to provide continuous advance under load. Could be fouled up in such a way that it's sending the dizzy constant manifold vacuum or some such.
Good luck!

 

[Junior64]

It's the original Autolite 1100 carb (manual choke) and a rebuilt distributor. The can is the correct type, matches the picture above. I can see the eccentric posts and how turning them may affect the spring tension. I may try tweaking them a bit. Is there any special way to turn them or can I just put a pair of pliers on it?

 

[Frankenstang]

It's the original Autolite 1100 carb (manual choke) and a rebuilt distributor. The can is the correct type, matches the picture above. I can see the eccentric posts and how turning them may affect the spring tension. I may try tweaking them a bit. Is there any special way to turn them or can I just put a pair of pliers on it?

I'd check a couple more things before I started adjusting the posts inside the load-o IIWIYS, because that will change the advance curve on a load-o.
1. Can you measure the vacuum at the port on the side of the carb (the one going from the carb to dizzy, measure vacuum at that port)? If you have more than a minimal amount of vacuum, let's say more than 2-4hg, at idle, there is something wrong with the SCV signal coming from the carb(does not have to be a defective scv itself could be a passage obstruction). I assumed the 19* you measured was at the vacuum port on the "log", is this correct?
EDIT: 2. Then check vacuum at that port while increasing rpm's if vacuum does not increase then again there is a problem with scv signal.
3. Check the mechanical action of the breaker plate by hand, by rotating the plate counter clockwise and visually watching it to see if it returns (you can see them using a screwdrive to do this in the pic above). Not uncommon for rebuilds to be defective (wrong springs, defective breaker plate hrdware/construction).

However, yes a small pair of vice grips should work to adjust the posts, there is a special too but can't put my hand on a picture of one just yet. If you decide to adjust the post(s) I would mark there current position (fine point sharpie) in case you need to return them to that position in case you find the problem lies some where else. The posts are off-center/eccentric, so there is a limit to spring tension can be added (Note in the pic, that the spring & post closest to you is almost at the limits of it's eccentric...as far away as it can be from the fixed post).

I still think the issue may not be as simple as a spring adjustment. I'd measure vacuum at the port on the carb and check breaker plate movement & return first...my $.02
Let us know what you find and good luck

 

[Junior64]

I pulled the SCV out and put some .020 safety wire through the orifice and blew some carb cleaner through it. There seemed to be no obstructions. I also cleaned out the distributor vacuum orifice. When I measured 19" vacuum, it was from the intake manifold. I hooked it up to the tranny vacuum line fitting. Today I hooked my gauge up to the distributor vacuum line on the carb and it did increase when I hit the gas. The breaker plate moves freely and the posts are maxed out already. I couldn't get a good read on how much vacuum was actually coming from the distributor vacuum line since I removed the brakes a few days ago. I couldn't put it in drive to drop the RPM without getting run over . With the RPM well over a 750, it was reading about 11". I think since I had a nice increase in vacuum that that it would be working as advertised. Who knows, maybe the previous owner put in an aftermarket cam. I'm out of ideas, but am comfortable with the way it's set up since it runs great.