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Weasel73240Z

ZX Dizzy and Timing....

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I took the car out for another shake down run, and found that the grinding noise I was hearing in the rear end has been solved. It was the brake drums rubbing against the backer plates....:stupid:.

Now, I have a problem that feels like timing to me, but I've searched alot and can't find what I'm looking. I'm hoping for some direction before I start messing around too much.

Heres the deal...bone stock L24 with 28K miles, new ZTherapy SU's and a 1979 E12-80 ZX dizzy (installed last Fall) with a MSD Blaster 2 coil. The dizzy was not rebuilt, but it came out of a 79 280ZX (5Speed) with only 60K on it. It seemed to be an improvement when I installed it last year over the original points set-up.

I have tuned and balanced the SU's, and they seem to be dialed in right. It idles steady at 800 RM's. I'm about 3 turns out on the needles, and the car revs right up past 5,000 RPM's (if its in the garage in neutral). When I drive it, the powerband seems to run out at about 3,800 - 4,000 RPM's.

Initial timing is set at 7 degrees (without the vaccuum attached). The dizzy is stamped 8.5, so I believe it should give about 17 degrees total advance. When I hit it with my timing light, it jumps from about 7 degrees to about 25 degrees, its tough to say exactly because my crank pulley only has 5 marks (TDC through 25 degrees BTDC, I believe). I get the exact same amount of advance with or without the vaccuum source attached.

The dizzy has a new breaker plate, and new vaccuum unit. I'm pulling my vaccuum from the ported source behind the front carb. The only other change that I made was changing from the Longflo filter to the stock air cleaner box (with a K & N filter). It should be getting plenty of air, right?

My question is...shouldn't I be getting more than 17 degrees total advance if the dizzy is stamped 8.5 and I'm using the vaccuum advance? I'm thinking I'll trying moving initial timing up to about 10 or 12, and see what happens. At least then I would get up to about 29 degrees total with just the mechanical advance. This is so frustrating, because the car seems like it ran better with the old points set-up than it does now.:mad:

Could it be that I'm missing something really obvious? Could the carbs be running lean? I left the carbs right about where they were dialed in to when they arrived from ZTherapy, and they seemed great last year, so I don't think they're a problem now. I turned them out to about 4 turns to richen the mixture, and felt no difference. It feels like timing, but not initial timing...just when accelerating.

Edited by Weasel73240Z

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I have a similar set up.How high are you reving the engine to check total timing? The zero mark is the bottom mark (of the 5) on the crank pulley. I had to rev mine to 4k to be certain all of the advance was in. My problem was to much advance. Also I believe that the number stamped on the advance tab is distributor advance, which is half of crankshaft measured advance. So 8.5 would actually be 17 measured at the crank. Confirmation???

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Paul, your vacuum advance isn't working. Don't know much about how to fix, because I always take the vacuum advance apart and lock them down so they can't move as a matter of course. Just for laughs, try keeping the vacuum advance disconnected and setting the timing at ~18 degrees BTDC and see how that feels. That's the way I ran mine. I think you'll see a nice improvement.

8.5 is 17 at the crank. The mechanical advance should be in by 2800 rpm. Vacuum advance can work at any rpm, so long as there is vacuum. If you want to measure total advance at x rpm, you should be measuring without the vacuum advance connected. If your mechanical advance is still working up to 4000 rpm, I'd say you probably need to clean up the mechanism and relube it.

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Just for laughs, try keeping the vacuum advance disconnected and setting the timing at ~18 degrees BTDC and see how that feels. That's the way I ran mine. I think you'll see a nice improvement.

Thats what I was thinking...but why does everyone seem to agree that 7 degrees BTDC is correct?

And why the vac advance isn't working is a mystery to me, since the vacuum unit and the breaker plate are both brand new. With the suck test (yes..me sucking on the tube) it moves easily. I'm gonna bring home a manometer from work so I can measure the actual amount of vacuum I'm getting at the ported tap, as well as at the balance tube. Maybe I'm just not getting enough "suck" to make the advance work. I'll report the results.

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Thats what I was thinking...but why does everyone seem to agree that 7 degrees BTDC is correct?

Because when the vacuum advance works, that's what you want. You'll have high vacuum just off idle where the port vacuum works, so you'll be probably somewhere near 20 degrees, and you'll have quite a bit of advance while driving in town. You'll have buttloads of advance when you're cruising on the freeway where you have high vacuum and you're over 2800 rpm; might be well into the 40s. And that's the point. That should be OK since the load is relatively low, and when the load increases the vacuum decreases so you get less total advance. Vacuum advance is all about trying to absolutely maximize advance to get a little better mileage.

There are two reasons I don't like it.

1. They usually don't work right or are outright broken.

2. If you're on the freeway and need to pass someone so you downshift and punch it, you've now just eliminated (or nearly eliminated) vacuum advance, so your back to your base timing of 7 degrees plus the 17 from the distributor, so you have 24 total, which is NOT ENOUGH FOR PEAK HP. If you set the distributor to get 35 total without it, then the vacuum advance will add way too much advance at low load cruise. It might be possible to tweak it so that it only adds 5 degrees of advance or something, but that's a lot of work for very little gain in my opinion.

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So I went home and played with the Z for a couple hours yesterday. After getting the car warm, I brought the initial timing up to about 15 BDTC. Vacuum advance is working. Much better....although there is still a little lag at around 3,800 or so, but its much better than before, and with some more fine tuning/tweaking, I'm sure I'll have it running like a Z again. If my new neighbor didn't come over with a 6 pack, I would've gotten more done.:laugh:

But like so much good news, there was some bad. The car ran well enough that I took it to the highway, so I could check out my new 5 speed/4.11 combo at highway speed. Got it up through the gears, until 5th....it wouldn't go into 5th.:mad: The car is also a little tough to get into reverse sometimes, but it always goes.

Reminder..it's 1979 280ZX 5-speed with my original L24, same clutch/pressure plate/throwout bearing/master cylinder/slave cylinder as I used with the 4 speed (under 2,000 miles on all). Flywheel re-surfaced in Jan. 2008. The 4 speed always shifted fine into all gears and reverse. The only old part, is the clutch fork (its from the 4 speed).

I'm pretty handy around the garage, but other than taking them out, and putting them back in, I have no idea how tranny's work. I though I had bled the slave cylinder properly, but I'm going to try again. I did have the whole system disconnected for the tranny swap (I never took the clutch cylinder off the firewall - adjustment is the same as it was w/ the 4 speed), and I did bleed it once. But I don't remember any air coming out (which I though was weird), and I only had the wife pump the pedal a couple times. I'm not sure whats the best way to bleed it, because theres no "pressure point" like when you bleed brakes. Any tips would be great.

I'm going to re-check the pedal adjustments, but I though that since I didn't remove the master cylinder, and it worked well before, it should be good. Maybe that was my problem.

Now I'm wondering if, even though its a bolt-up swap, do I need to do some toying with adjustments to get it working because theres a mix of 4 speed (clutch assembly and non-adjustable slave cylinder) and 5 speed parts, or does it sound like the 5 speed I bought needs to be re-built?

If I have to get the 5 speed rebuilt, I can throw the original 4 speed back in for now. But the car will be almost un-driveable on the highway with a 4 speed and 4.11's. :tapemouth

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