hopping timing on 81zx

[wa5ngp]

I've got a problem with my 81zx 275K miles with hopping timing. What happens is that everything runs fine but when I am about 2K rpm the tach shows a sudden jump to like 5K rpm and then jumps back and forth. Sometimes it will even stall. While this is happening I hear some pinging so I would assume that the ignition is doing a sudden advance. I've traded out the ignition module (I"ve got several) to no avail. When I look iniside the distributor and check for slop everything looks fine. I had an aha moment a while ago when I discovered that the magnet ring had broken into several pieces. I ordered a new one and I thought that fixed it but now its doing it again. I guess I'll take it appart and see if that magnet is broken again. Maybe theres enough slop in the shaft that the wobble breaks the ring. The rings do seem fragile. I thought I'd check here before launching into it again in case somehow I'm missing something obvious. If I can't sort it out I suppose I can just get a lifetime warranty rebuilt one from Autozone. I would be ahead by now if I'd done that to start with.

tks

Don

[mlc240z]

had this same problem with a '73 (ahem) Pinto.:tapemouth

yea, i know but fortunately it was a girlfriend's car.

it turned out to be distributor shaft bearings were worn out. at idle, timing would bounce all over the place and car would run crappier than usual.

if yours is severely worn, it might possibly cause some contact with the magnet, although that sounds a little too extreme. fractured magnet could have been a coincidence.

[boostedz]

I would say the same I had this happen on a 72 of mine, it would run great then go to $^!#, one day it just wouldnt start. For some reason as I knew everything was just new, I decided to look at the distributor.

It wasnt wobble but the top of the shaft itself broke.

Id just check into it to be sure. With issues like you ahve siad I would think shaft wobble myself or timing chain slip

[wa5ngp]

The timing chain crossed my mind. I wonder if there's some way to eliminate that possbility? That could be a biggie if that thing gives it up.

Don

[jmortensen]

I've got a problem with my 81zx 275K miles with hopping timing. What happens is that everything runs fine but when I am about 2K rpm the tach shows a sudden jump to like 5K rpm and then jumps back and forth. Sometimes it will even stall. While this is happening I hear some pinging so I would assume that the ignition is doing a sudden advance. I've traded out the ignition module (I"ve got several) to no avail. When I look iniside the distributor and check for slop everything looks fine. I had an aha moment a while ago when I discovered that the magnet ring had broken into several pieces. I ordered a new one and I thought that fixed it but now its doing it again. I guess I'll take it appart and see if that magnet is broken again. Maybe theres enough slop in the shaft that the wobble breaks the ring. The rings do seem fragile. I thought I'd check here before launching into it again in case somehow I'm missing something obvious. If I can't sort it out I suppose I can just get a lifetime warranty rebuilt one from Autozone. I would be ahead by now if I'd done that to start with.

tks

Don

Three problems are common to these distributors IME. The vacuum advance dashpot cracks creating a vacuum leak and the vacuum advance stops working. Also the vacuum advance mechanism comes apart, this is the usual culprit that I have seen. This can cause damage to the stator and irratic timing. Finally the bushings wear out, not as common but yours has 275K on it so could be a combination of any of the above. I've only seen one ZX distributor where the vacuum advance mechanism hadn't come apart. It was cracked, but hadn't broken into pieces yet.

I used this resource when I fixed mine (he sells bushings too):

http://www.jrdemers.com/280ZX/distributor/distributor.html

Later I came across this one which has a better tear down description but goes a little heavy on the grease IMO: http://www.atlanticz.ca/zclub/techtips/distributorrebuild/index.html

If you're going for performance I would completely eliminate the vacuum advance. It is so prone to breakage that I wouldn't put it in my car. What happens is that when the little plastic disk piece that holds the ball bearings breaks and then the bearings can fall out. When the bearings come out than the stator can tilt with respect to the trigger wheel (reluctor). When this happens the two can hit each other and this can do all sorts of funky things to your timing, not to mention wearing a groove on the stator and/or wearing the teeth on the reluctor.

The ZX distributor has a very good timing curve and only has 17 degrees of advance. This means that you can crank in a lot of initial advance; around 15 to 20 degrees BTDC works well and still does not go past the mid 30s at full advance. This works great for performance. Getting rid of the vacuum advance will hurt fuel mileage a bit if you run the stock advance settings, supposedly. With the timing cranked up I don't think there is a significant difference, though and performance is quite a bit better on the top end.

I removed the vacuum advance parts entirely, then JB welded the breaker plate to the piece that holds the stator. This locked them together permanently. I also cut off the arm on the vacuum dashpot, and plugged the vacuum line that goes to the distributor.