high idle in neutral, low when in drive in 1976 automatic

[rufurt]

I have a 1976 automatic. Weber 38's. Electric choke.

 

Mainjet: 145

Idlejet: 50

Air: 75

Needle: 250

Emulsion: f66

Float: 40

 

I've set valves, timing, and dwell (60 degrees, new points). Timing the BB (25 BTC) at 2400RPM (according to '76mintgrün'02 's sticker

)

 

It runs well. Starts alright. A month ago it started easier, but it is getting colder up here in Massachusetts so it needs a little more time to warm up. Have to apply a little pressure to throttle for a minute to keep it from stalling. Might need to adjust fast idle screw, not sure.

 

I had set the idle to about 1000-1100 rpm while warm, but when in gear the engine would stall when coming to a stop. I upped the idle so while in drive but parked/stopped the idle was near 900rpm. That means the neutral idle sits at about 2000rpm.

Just rebuilt the engine and transmission, new oil/fluid in both. I didn't do the transmission myself, had a shop do it. Trustworthy place, but I didn't do it myself so I can't attest to it being perfect.

 

I would like the neutral idle to be lower, but don't want to stall at stopsigns, what do you think?

['76mintgrün'02]

I don't have much to offer here, unfortunately, but will say that the sticker I'd shared with you regarding timing came from a posting that Conserv made.  That sticker was all chewed up on my car, so I rubbed what was left of it off. 

 

I think the timing setting should be applicable to  your situation, but did not realize you had the 38-38 and an automatic.  I believe the automatic cars had different distributors than the manual cars had.  Not sure though; nor do I know what the difference between them would be. 

 

IIRC, you have the distributor with a model number ending in #164, which the sticker would be referring to.

 

Here is the sticker photo.

[rufurt]

Sorry, I thought the sticker was yours. Didn't mean to mis-attribute it.

 

You are correct distributor is a 164. Man, I hated doing the dwell. I wish I had a set of your improved points so I didn't have to trial and error the gap. I am envious.

 

I appreciate the help. The automatic is a persnickety beast i guess.

[Schnellvintage]

When I worked on these cars I would keep the neutral idle at around 1100 and the drive or trans engaged idle at around 950. It was a fine balance between operating temperature, timing and mixtures. Should never try to tune a car while on the cold/choke circuit. The colder temperatures will through a wrench into the mix. I know it can be done with patience. Pertronix helps more than points.
Matt


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[rufurt]

The engine was warm and off choke when I set the timing and dwell. Ugh, it's like herding cats. Fix one think and another problem surfaces that is intertwined with the first. 

 

 

[Arizona02]

idle mixture screw might be set to lean, or small vacuum leak causing lean idle.

[rufurt]

I followed the Weber instructions on best lean idle. It was running lean. After I changed some of the jetting it seems to be running well (originallly idle jets were 45's and main's 135). 

 

If I had a vacuum leak, it would allow in extra air, which to compenstate I would have had to richen the mixture via jetting (idle jet I suppose). It would then make the carb appear to be running at best lean idle. 

 

I set the idle under load, (in drive with chocks in front of the wheels), but that leads to high idle when not under load (neutral). How would the vacuum leak cause it to run so much higher ( at 2000rpm )under no load? I am befuddled. 

 

I'll search for a leak, just to be safe.

[Conserv]

3 hours ago, '76mintgrün'02 said:

I don't have much to offer here, unfortunately, but will say that the sticker I'd shared with you regarding timing came from a posting that Conserv made.  That sticker was all chewed up on my car, so I rubbed what was left of it off. 

 

I think the timing setting should be applicable to  your situation, but did not realize you had the 38-38 and an automatic.  I believe the automatic cars had different distributors than the manual cars had.  Not sure though; nor do I know what the difference between them would be. 

 

IIRC, you have the distributor with a model number ending in #164, which the sticker would be referring to.

 

Here is the sticker photo.

 

The underhood sticker shown here is mine. It’s a reproduction of the original sticker that came on my ‘76, a 1976 49-state version with manual transmission.

 

I don’t believe the following comments will address your idle issue, but I can’t keep my mouth quiet any longer.... ?

 

1. Has someone compared their car’s EPA-mandated tuning sticker to a “higher source,” e.g., the factory service manual? I’ve seen a tii with an original non-tii tuning sticker: clearly some bad tuning advice! And we’ve found so many typos and errors in underhood stickers, in general, that I’ve never thought to use the tuning sticker as actual guidance. I’ll be pleasantly surprised if the sticker is accurate. 

 

2. I am slightly surprised to find the manual and automatic 49-state versions share the same distributor, the part number ending in 164. But they share a single “emissions schematic,” so perhaps the manual and automatic are closer than I thought.

 

3. The factory tuning instructions were intended for Solex carburetors. My understanding of the stock Solex on my ‘76, for instance, is that it has a choke actuated by water temperature and electrically, depending on circumstances. My understanding of the Webers is that they have manual, water, or electric chokes, but never a combination of water and electric.

 

4. Lastly, the factory tuning instructions were premised not only on a stock Solex carburetor, but also full emissions controls, the actual tuning being a sacrifice to ensure the car met the U.S. (or California) standards. Few 2002’s retain today their full emissions controls. Should we be tuning these “de-smogged” versions on the basis of the original instructions?

 

It just seems to me that actual tuning experience with these cars, developed over time, as Solexes were replaced by Webers, and as emissions controls were replaced with....nothing, would result in a much better operating car than relying on the original instructions. My two cents.

 

Heck....I’m already using Pertronix, but I’m ready to try a 123 distributor (or 123 guts in a 164 housing, so Tom, a.k.a., ‘76mintgrun’02, won’t know) ! ?

 

Regards,

 

Steve

 

 

 

 

 

 

 

[Simeon]

My old W108 Mercedes Benz used to have a vacuum dashpot arrangement on the throttle that would crack the throttle slightly as the load went up with the transmission in drive and the car at idle. Pretty sure I have seen similar installed on auto 02s bolted into the manifold but obviously interfacing with the dual choke Solex carb. 

 

Could you reinstate one of these?

 

http://jaimekop.com/CarbManual/Page26-27/index.html

 

Edited November 14, 2018 by Simeon

[Conserv]

Actually, all the later ‘02’s had dashpots. I’m embarrassed to admit I don’t know precisely when it is activated on my manual transmission 1976! ?

 

Regards,

 

Steve

 

[Simeon]

6 minutes ago, Conserv said:

Actually, all the later ‘02’s had dashpots. I’m embarrassed to admit I don’t know precisely when it is activated on my manual transmission 1976! ?

 

Regards,

 

Steve

 

 

From the link in my post above. This explains when the dashpot is used (dependent upon engine vacuum). No 3 is less relevant in a manual car, with no A/C but 1 and 2 would still be useful (for emissions purposes). 

 

CONTROL OR VACUUM DASHPOT

The function of the vacuum throttle control or vacuum dashpot is: 

1. To prevent stalling, when the throttle is suddenly closed. It insures a gradual or slow closing which permits the continuing air supply to lean out the rich mixture of fuel that occurs on sudden throttle closing.

2. It works with emission control. During coasting it holds the throttle plate open slightly.

3. It acts as an idle speed stabilizer when the engine is under load at idle. The plunger extends as the vacuum falls due to the load. This causes the throttles to be opened slightly.

[rufurt]

Interesting points. My old Clymer manual recommends 2800 rpm for a 1976 atuomatic at 25 degrees BTC. I have de-smogged the engine. I have Ireland's shorty headers and a 292 cam. With all the variables I guess I should just try different settings and see what seems to run best. I am willing to try lower rpms for 25 BTC. It might help. 

 

From what I can tell the 164 distrubutor is mechanical advance and vacuum retard. I have the vacuum line to the distro coming off the manifold, some people like the line coming off the carb, which i believe they call "ported". I will give that a try to see if it makes a difference.

 

I could always go Pertronix. 

 

Beautiful engine Conserv.

['76mintgrün'02]

25 minutes ago, rufurt said:

From what I can tell the 164 distrubutor is mechanical advance and vacuum retard.

 

No, it is a vacuum advance pod on the #164; since the points plate is being rotated counter clockwise, causing the points to open sooner.

 

I am a believer in using a ported vacuum signal for the pod, since manifold vacuum will bring in all of the advance at idle; whereas the ported signal will not add any.  The same is true during deceleration situations, when your foot is not on the gas.  Both vacuum signals cut out completely when you mash the gas pedal to the floor.  The pod should be adding around twelve degrees of advance.  (Six degrees at the distributor).

 

Setting the timing using the BB will tell you that you have 25 degrees of advance at that rpm, but that is all.

 

If you want to know whether your distributor is 'healthy', I suggest you to buy a timing light with variable advance.  The Innova 5568 is the one I bought and have been very happy with.

 

This is not directed at you, rufurt, but it drives me nutz that so many people jump to spend money on bling, but will not pay $100 for such an empowering tool.  Likewise, an AFR gauge takes the guesswork out of jetting.  (Or, perhaps I should say, it allows one to see the consequences of the guesses/changes they are making).

Tom

[rufurt]

Thanks for the correction on the 164. So vacuum advance. Does it have mechanical advance at all? Would seem redundant.

 

I'll try ported and see what I get for idle.

 

I have a 5568. Was pondering using it to plot an advance curve. When measuring the advance, you achieve desired rpm, set the advance on the 5568 till you see OTC mark?

I ssume this is done with vacuun line attached to see if is functioning corrctly?

 

Haven't given much thought to an AFR gauge.

 

thanks for the advice.

 

['76mintgrün'02]

Just now, rufurt said:

Does it have mechanical advance at all? Would seem redundant.

Yes it does.  Not redundant, because the mechanical advance is a response to changes in rpm, whereas the vacuum signal is meant to interpret/respond to fueling situations.

 

At any given rpm you can bump up the advance on the gun and watch for the OT line to appear.  The reading is taken referencing the driver's side of the oval hole.

 

Timing is set with the advance pod disconnected.  If you set the timing by the BB with the pod connected to manifold vacuum, it will be way off.

 

The pod should provide its six degrees of advance (twelve at the crank) between around 5-11 inches of mercury.  You could see how much the pod is adding by measuring the advance at idle (by advancing the light until the OT mark lines up) and then connect the pod to manifold vacuum.  That should bring in another 12 degrees, or so.  

The diaphragm inside the pod could have a hole, or the points plates could be sticking... either of which will not allow the advance to happen.  Distributors require maintenance, such as cleaning and lubrication, in order to function properly.  The most common wear I've seen has to do with axial play due to worn or missing fiber washers on the shaft.  There were two of them, one inside the case, under the advance mechanism and another on top of the gear.  The one on the inside often goes away and that slop causes a bouncing BB, which indicates erratic timing.  Pulling up on the center post will not indicate that play, because there is also play between that post and the shaft.  You will need to remove the distributor and use a feeler gauge between the gear/washers and the body.  If you are seeing over .030" of slop the inner fiber washer is probably gone.

 

If you do decide to plot the curve, I'd suggest setting the light to the advance you want to plot and then raising the rpm to find where that happens.  Repeat the procedure up through the curve.  Or down.  If you set the rpm and then hunt for the marks it is much noisier.