beermanpete

This sounds right except that the cam towers also grow which increases the valve clearence. The gap actually gets wider as the engine heats up. The cold spec is 0.008"/0.010" cold and 0.010"/0.012" hot (in/ex). I have set the valves cold (using the factory specs for a cold engine) and then checked them hot and they are pretty close the the hot spec. I would set the valves with engine hot if I could do it with the engine running but that is not possilbe due to the design.

I imagine a lot of people have put on headers, do not "re-jet" and get decent results. My point is not that it is a necessity, simply that it should not a surprise. Since the round-top SU carbs have an adjustment for the jet height it seems a safe assumption that many of those same people simply adjust the mixture richer to get good drivability and live with a fat idle. I always check the valves cold. I think it is better because the engine temperature is not changing during the process.

With all due respect, your engine is not entirely stock. You reported in your first post of this thread that you have headers. This alone will have an affect on the air/fuel mixture. As a result an adjustment to the jetting is likely required to get the best performance from the new system. Changing the needles and/or springs in the SU carb is the equivalent to changing the main jets in a fixed venturi carb. Would you be surprised to need different main jets if you put headers on a car with a V8 and a 4-barrel carb? The ignition is likely performing properly and is simply unable to light the overly lean mixture. The valve adjustment, condition of the rings, valves, etc. would not cause the symptoms you report. With these types of problems you would have a rough idle and perhaps low power, not a part-throttle miss-fire. You report that your car idles well and runs good at full-throttle. Further, you get a positive response to pulling the choke while driving which enriches the mixture. This supports the hypothesis that you need to recalibrate the carbs.

Correct, no rev limiter on stock ignition.

Try here: http://www.sucarb.co.uk/ProductCategory.aspx?ParentId=261

What you say makes sense. The symptom is a lean miss-fire. It is is possible that making the mixture richer is treating the symptom rather than the cause. Weak spark will show up with a lean mixure because it is harder to light, as you said. The question now becomes; what is the air/fuel mixture of another Z during the same operating conditons that are causing the problem for Zedyone? I don't have a wideband O2 sensor in my car so I cannot provide any data here. Hopefully another reader here will be able to chime in on this.

Adding weight to the suction pistons should enrich the mixture. It may seem counter-intuitive, but it should enrich the because the velocity through the venturi will be higher, providing a stronger vacuum signal to pull more fuel despite have a slightly smaller opening between the jet and needle. SU offers different stiffness springs for the suction piston for this same purpose. The mixture will be affected at all throttle openings except idle when the pistons all the way down. It seems that this has become somewhat unnecessary now as Zedyone has accomplished the same thing by pulling the choke out while driving. I agree that the KD needle could solve the problem. The stock needles could be modified as an alternate. The trick will be determining the correct point on the needle to reduce the diameter, and by how much.

Yes, you can remove the lower control arm and strut assembly without removing the differential. The differential will be held by the mustache bar.

I thought of a way you can test the alternator to see if it is internally or externally regulated. The following assume your alternator works correctly regardless of which type it is. Disconnect the voltage regulator and the 2 pin connector from the alternator. Connect 2 light bulbs (12 volt, 23 watt, part number 1156), from the 2 pins on the back of the alternator (1 bulb each) to the positive battery terminal. If you have an internally regulated alternator: Engine stopped: The bulb connected to the L terminal will light, the other will not. Engine running: Both bulbs will not light, battery voltage will be normal (~ 13 at idle, 14.5 volts at increased RPM). If you have an externally regulated alternator: Engine stopped: The bulb connected to the F terminal will light, the other will not. Engine running: The bulb connected to the F terminal will light, the other will light but at about half brightness. The alternator will have some output but will not regulate (the battery voltage will rise with increasing RPM).

Your data from a month or so ago indicates a lean part-throttle condition. Why not try to richen the mixture at part-throttle while leaving the idle as it is. Add some mass to the vacuum pistons. This will richen the mixture at part without affecting the idle. Simply lay some wire solder or other weight to the top of the vacuum pistons (equal amounts for each carb). It is an easy test to see what affect it has to the air/fuel mixture and the miss-fire. If it does not help take it out and go on. If it does help it will give you a direction to go in.

The ignition is grounded through the distributor to the engine block.

Typically the ignition voltage is measured with an oscilloscope and an inductive probe. This is one of the capabilities of the engine analyzer that was common in repair shops years ago. I don't know if they are common these days. You will need to ask about this at your local mechanic to see if anyone still has one. The Pertronix Flame-Thower coil is advertised to put out 40kV so it should be enough.

The engine won't turn during the leak down test as long as you get it at true TDC for each cylinder. It is not as difficult as it might seem. Start on #1 since it is easy to find TDC. Then proceed in the firing order and turn the engine 120 degrees each time. If you need to, use a probe through the spark plug hole while turning the engine (by hand) to find TDC for each cylinder. Regarding the mystery miss-fire, I know you have check every part 20 times, but have you tried to measure the high voltage at the spark plugs, or more importantly, the voltage capability of the ignition system? Your symptoms suggest inadequate spark that is not capable of reliably lighting the lean mixture at part throttle.

The factory service manual specifies the maximum cylinder taper at 0.0006" (0.015 mm) taper. Your taper is well beyond the max allowed and is also equal to the maximum specified piston-to-cylinder clearance. Boring the cylinders seems to be required.

Your post from last night suggests no output from the alternator. 11.6 is the battery voltage with a load from the ignition, fuel pump, etc. without any charging from the alternator. It is steady and therefor seems regulated because the load is steady. When the charging system is working correctly the battery voltage will be about 13.5 with the engine at idle and rise to about 14.5 when you increase the engine RPM. It will regulate to 14.5 at all engine RPM above idle.

This seems to confirm that you have the correct alternator (externally regulated). Get a new regulator. If you are still wary about your (our?) diagnosis take the car to a mechanic and let them fix it.

Try this to determine which alternator you have: With everything connected normally, start the engine, turn on the headlights (to load the alternator) and verify the output voltage is 14 or higher. Now unplug the 2-pin connector on the back of the alternator. If the battery voltage stays at 14 or higher you have the internal regulator. If the voltage falls to 12 or so then you do not.

Yes, having both regulators will cause your symptoms (as Steve has already said). The only thing I can suggest to look for on the alternator is the terminal markings (if there are any) near the 2-pin connector. The externally regulated alternator has "F" and "N" terminals. The internally regulated alternator has "S" and "L" terminals.

A fusible link is a short piece of wire used as a fuse. Typically this wire is smaller that the wire it protects and has flame retardent insulation. If there is a short or other over-current event the fusible link melts and opens the curcuit just like a conventional fuse. The fusible links are located on the relay bracket just in front of the battery. They are the short wire loops that are attached to plastic connectors. There is also one that is part of the wiring that attaches to the positive battery terminal. In your case this is not the problem. If a fusible link was bad your car would not run, the headlights would not work, or some other accessory would not work.

Good. This means the alternator output stops when you unplug the regulator. Your regulator is bad. Try another new regulator. If the wiring has a problem the alternator would still over-charge when you unplug the regulator. Yes. The alternator is capable of putting out 60 amperes. This will easily raise the battery voltage to 18 volts or more if it gets the chance.

Try running the car without the voltage regulator (unplug it). If the battery voltage is now 12 volts the regulator is bad. If the voltage is still too high unplug the 2-pin connector on the back of the alternator. If the battery voltage is now 12 volts there is a wiring fault. If the voltage is still too high you have a bad alternator.

How far off center is the new hole you drilled from the true center of the original thread? If it is not too far off just drill it out with the correct tap drill and re-thread the hole. If this is 1 of the 4 screws that hold the cross-member in you should be ok with just the 1 off center a little bit.

We plugged most of the vacuum ports on ours and I recall using some 3/8 NPT plugs.

It sounds like the fuel delivery to the carbs is ok to me. I doubt that 1/8 pint per minute low would cause a problem. The only thing left would be to attach a fuel pressrue gauge to the car in such a manner that you can watch the fuel pressrue while driving to see if ti drops when the car is running poorly. If you try this DON"T run fuel into the car, mount the gauge outside the cabin. Have you check the fuel lines that connect the float bowls to the jet nozzle? Perhps they are kinked or restricted for some reason.

The engine speed will affect the output volume. Did you have the engine speed at 1,000 RPM per the manual's instructions? If you race the engine does the pressure increase or does it stay as 3 PSI? I am wondering if you have an air leak in the fuel line. When you measured the flow rate did the fuel look foamy of bubbly? Another thought is perhaps the return line is returning too much fuel. There is a restrictor orifice in the end of the hard line. Perhaps it is too big.