SPICA T/A Question and Idle Adjustment Question

[montelatici]

74 Spider, Stock engine

T/A

Wes Ingram booklet indicates that when cold, gap to reference screw should be about 1/8 inch.

Should screw in pump that T/A pushes on be adjusted to achieve this gap?

I ask the question because to achieve this gap cold, my T/A must push against the adjustment screw when cold, i.e. no heat extension?

What exactly does one turn to adjust the idle? Both the Braden Bible and Ingram discuss it but maybe I am dense. Is it the tube that the hose to the air plenum goes to?

Thanks

Alfredo

[Farace]

Quote:

Originally posted by montelatici What exactly does one turn to adjust the idle? Both the Braden Bible and Ingram discuss it but maybe I am dense. Is it the tube that the hose to the air plenum goes to?

[Roadtrip]

The pump gap should be adjusted to .019" between the pump throttle lever and the reference screw using the screw down in the pump TA cavity. NEVER NEVER NEVER remove the plastic cap and safety wire from the reference screw and adjust that. The factory setting of the reference screw position is to a very precise point on the 3D cam. If you move the reference screw, I'll screw up the pumps overall calibration.

Setting the pump gap is correctly is very important. According to Alfa Romeo, to do this properly, you need a "dummy actuator" which is nothing more than a temp substitute for the TA that is set to a specific depth (either 27 or 29mm depending on the "T" number pump). Pop the long link off of the pump throttle lever and insert the dummy actuator and measure the gap. Remove the dummy and adjust the screw in the hole until the pump gap is .019" This sets the proper throttle lever angle baseline for the pump. Very simple. The other part of this is to make sure that the TA is good. I recommend if you're not sure, you remove it and check it in a pot of heating water. Older TAs had extensions of 27mm at 175F and the newer ones 29mm. Replacement TAs that you buy now are all 29mm ones, so if you have one of those on an older pump, you should shim where the TA mounts into the pump with a 2mm shim (a washer or two works good). The idea here is when the engine is cold, the TA isn't extended very much. This allows the throttle lever to go higher, thus creating a fast idle and richer mixture. As the engine heats up, the TA extends, driving the throttle lever back towards the .019" point, which is normal idle and mixture. There is no change in mixture at less than .019" reference gap.

You can make a dummy TA pretty easily out of brass and solder. Here's picture of one I made. The other way to set the gap is to use the TA itself, but you'll need to heat the engine up to about 175F, check for a 27 or 29mm extension, then insert it, check the gap, and adjust as necessary before the engine cools and the extension changes. Using a dummy presents less chance of damaging the TA tubing from repeated movement, plus you can set the exact extension and take you time in setting the gap.

Of course, setting the gap is just one part of tuning up the system. It should be remembered that many of the settings in the system (long/short rods, idle/WOT stop screws, etc.) are interrelated and adjustments must be done in precise order. The factory SPICA manual explains all this in detail.

[Roadtrip]

As to the second question about the idle air . . . .

The idle barrel screws into the idle air distributor on top of the manifold (where the five little hoses hook into). At idle, ALL the air to the engine should be going through those little hoses and NOT through the throttle butterflies. At idle, the throttle butterflies should be completely closed.

The amount of air available to the engine is regulated by the barrel and o-ring assembly that screws into the idle air distributor. As the barrel is screwed in, it compresses the o-ring against a concave surface in the distributor and the hole in the middle of the o-ring gets smaller (at least that's the theory). Often times you'll find that the rubber o-ring is old and the rubber has hardened, thus making it non-pliable.

From my personal experience, I've found that the o-ring system doesn't work very well and has a very limited range of control. Idle should be 600-900 rpm, I believe. Mine idles at about 750 rpm regardless of how tight I screw the barrel in.

A note of caution here. You'll see a pinch bolt on the top of the distributor that's suppose to keep the barrel from turning. There's a small washer in the middle of it. Keep that washer there. If you take it out and really honk down on it (technical term) it, you'll likely break a tang off. There's really no need to tighten it much anyway.

Here's a picture that may help.

[Farace]

John,
Thank you for the illustration.

I need to get my TA rebuilt. Instead of assuming the extension will be 27mm or 29mm or whatever, would it be prudent to heat the bulb to 175 degrees and measure the true extension and then adjust for the actual measurement, minus the measure of any shims? I think I read (maybe on this BB) that some rebuilt TAs are extending out to 31mm?

[Roadtrip]

Bob - You really should not use the actual TA. Here's a quote from Alfa Romeo Distributor's of North America:

"Use of a real thermostatic actuator (or a dummy set to the length of the warm actuator) to adjust the cam centering screw to achieve the specific clearance (.5mm between the control lever and reference screw) will not correctly synchronize the internal pump linkage with the 3D cam."

Now, that said, if your TA is extended 27mm (the spec on a '71 1750) at 175F you can use it to set the gap. The pump doesn't know if its a real TA or a dummy. All it cares about is have the pump gap set at .019" (.5mm) with a 27mm extension on the actuator.

As to why that is, I'm not really clear. As long as the pump gap is .019" and the reference screw is undisturbed, it looks to me as if it should center the 3D cam. However, I can see that the schedule that the TA uses during warmup would be off. Regardless, I set my pump using a dummy as ARDONA recommends. I also make sure the TA operates within specs.

Chances are, when you get a replacement TA, it'll be from a later model (29-31mm extension). In that case you'll have to shim it 2mm or so to restore the cold length. This is important because the cold length regulates the cold mixture and idle speed. If you use a new TA with the longer length and no shims, you pump will think the engine is warmer than it really is. Washers that have been filed a little on either side to clear the screws, work fine.

[Farace]

Quote:

Originally posted by Roadtrip Bob - You really should not use the actual TA.

[montelatici]

After some tinkering I was able to get my daughter's 74 Spider starting with engine hot or cold (with cold start solenoid connected) and running quite well.

I figured out the idle adjustment. I replaced the O-Ring with a grommet that fit exactly into the orifice and the grommet, being thicker and more "squisshable" provides a far larger range of adjustment, idle wise. Prior to that, I did have to get the butterflies to close completely, which they didn't when starting the exercise.

I did what Mr. Farace suggested, I measured the real extension of my weak T/A at 175F and adjusted the gap, raising the screw in the pump using the fake T/A with exactly the same extension to achieve a .19 gap. Since this SPICA did not have the plastic on the reference screw, I was pretty sure that it would be off for starting and running. Sure enough it wasn't right. Engine popped and stumbled and had no power.

Until now I had to remove the cold-start solenoid connector for it to start when the engine was warm. I surmised that this meant that when warm the T/A was not leaning out the mixture enough. I raised the screw in the pump 1/2 turn at a time, installed clean plugs each time until the engine started easily when still warm with the solenoid active. It took about 4 half-turns of the screw until that happened. Then I took the car for a ride and while night and day from before it was still running a little rich (some popping on decel) after a plug chop, dark brown/black plugs. I then started leaning the mixture with the fuel cut-off solenoid, turning it one-half turn at a time. After two turns (4 runs), the plugs got brown (not quite a nice tan) and the exhaust passed the smell test. I then got the grommet idea and set the idle at about 700 rpm.

Final test was a cold start. We were at about 25 F today so after about 3 hours the engine was quite cold. Started immediately although it raced to about 2,000 rpm before settling down to a little higher than the previously set idle. After a few minutes the idle settled to the 700 rpm.

It runs strong but it is still a little rich (I'd like to get a nice light brown/tan color) and I am considering leaning it out a little more. But from an absolutely undrivable unstartable car, it was a good day. My daughter finally had a chance to drive her Christmas present around with a friend in the lae afternoon before going back to college.

Oh, my conclusion. 1. If you adjust the screw in the pump (with even a weak T/A as I have with 25mm extension) so that the engine starts easily when warm and solenoid connected, you are pretty close to having a decent runner. 2. Make sure the farfalle (butterflies) close all the way. This may be heresy, but it worked. I adjusted that short rod alone to achieve the complete closure.

Alfredo

[Roadtrip]

Bob - I'm sure lots of people have done what you suggest to compensate for a weak TA. It's going to throw off the cold start scheduling, I believe, but it will probably run acceptably . . . .but certainly not optimum. The real answer is to have an in-spec TA however.

Alfredo - Hopefully the cap just came off the reference screw and it hasn't been moved. It's possible to make a bunch of compensating errors in setting the system, and still run ok.

I would suggest that you both get the factory manual and go through and do a complete system tuneup, step by step. Hopefully you'll find that your tinkering has gotten you close. As for the weak TAs, you might as well get some rebuild ones. The seals are obviously leaking and will just get worse.

[Kipp]

I bought a new O ring at Alfa Parts in Berkley CA, pretty cheap. I was still missing the washer so Mike at APE in Tracy found one for me.
Don`t LOL but it did run better with the washer.