Is every PO an idiot --

[Wade Nelson]

Is every previous owner an idiot?

My 1980 ZX runs well, accelerates very rapidly, gets nearly 30mpg highway. It would be very hard to complain, performance-wise, for a car with 207,000 miles.

Still, I had this nagging suspicion some power was being left on the table. I had a local guy who has owned numerous Z's drive it and he told me the same thing, he felt like it was missing a little power, might need a valve job, compression down a tad perhaps.

Today's earlier discussion about octane and pinging, and advancing the timing made me think...why am I NOT getting any pinging under heavy load? NEVER! NONE! Timing incorrectly set? Timing advance mechanism not working properly?

So I pop the hood, hook up a piece of long hose to the distributor advance, and suck on it. The plate rotates, begrudgingly. Like it hasn't been getting worked. Clearly it deserves to be taken apart and greased, re-assembled. Even so, it's providing SOME advance.

Next I decide I'll inspect the little piece of hose on the other side of the 1-way vacuum valve feeding the advance mechanism. I decide to suck/blow through it, and guess what.

The idiot (previous owner, or his mechanic) had installed the valve backwards. I was getting NO vacuum to the distributor mechanism.

I'll report later in the day after I've had a chance to drive what sort of difference it made. My guess is it will provide this motor with an additional 10-20 horsepower WHERE IT COUNTS, and at LEAST an additional 3mpgs.

Maybe you want to check yours.

[Zed Head]

Under heavy load, with the throttle open, the vacuum advance goes away. Vacuum advance comes in to play at partial throttle openings when the intake vacuum is high enough to pull on the diaphragm. You'll feel more "pep" at a partial throttle but probably not much when climbing hills or accelerating quickly.

Check your mechanical/centrifugal advance mechanism. Easiest is with a timing light and the vacuum advance hose disconnected.

[5thhorsemann]

Even at WOT, as the RPM climbs so shall the manifold vac and the advance comes back into play, Wade is correct that it SHOULD make some positive difference. I would assume the mechanical section is working since the car runs as he reports.

[Zed Head]

You're right, it's not completely gone. It starts kicking in at about 3-6 inches of vacuum and gets full at about 11 or 12 depending on the distributor, by FSM numbers.

Back to WN, it's funny that someone who hasn't checked that their timing works right is calling someone else an idiot for putting an inline valve in backward. Just sayin', maybe the frustration is misdirected.

:devious: I like to pick on people who call names...

p.s. Interesting side-note - my 76 280Z didn't even use the vacuum advance unless the car was in 4th gear. It actually has a solenoid valve on the vacuum line, activated by a switch in the transmission. Weird.

Edited July 6, 2012 by Zed Head

[LeonV]

No, there will not be a 20hp gain, nor does it affect WOT operation. Vacuum does not "climb" at higher rpm. At WOT, there is no manifold vacuum, it's completely open to the atmosphere (besides intake pressure drops). I agree with Zed Head's sentiments, you'll notice some gain in part-throttle conditions but that's about it. Fuel economy should slightly increase.

Put a timing light on it and test, it's not that hard.

[grantf]

Is every previous owner an idiot?

Yes, They sold there Z for one. Anyhow you have no idea how many stupids I found with my car. Upsidedown thermostat and hacked wireing to start.

I just hope that after changing out my head gasket I do not become the dreaded P.O.

Edited July 6, 2012 by grantf