Idles, bogs, dies ('71)

[KEINsm]

I've tried searching for an answer to my problem but came with no clear answer. It seems like FI cars have the same problem. My car is an early 1970 240Z with all stock components (except an alternator from a newer car, electric cooling fan, stereo, and alarm)

Almost a week ago, my car ran perfectly with no problems. Now, it is difficult to start and seems to misfire. The engine revs roughly up to 3000-4000rpm when cold then it hits a "rev limiter" and refuses to go any higher. I figured it would be driveable, but it lacks too much power and I must slip the clutch to get the car moved out of the way. (I need to do this at "full throttle" doing 3000rpm) When the engine warms up, the idle gets very unstable and stalls only after a few seconds. It also gets more difficult to rev past 2000rpm. What is wrong!?!?! When cold I can hear the timing belt slip with a high pitched screech. The car does not seem to be running rich. The exhaust is clear with a familiar gasoline scent.

Here is what I have done. I replaced the fuel filter under the hood because I figured it was clogged. This changed nothing. Next, I pulled the sparkplugs for an inspection. I found the plugs from cylinder 4, 5, 6 were in good condition with a nice amber color. However, the plugs from 1, 2, 3 had a dark brown/black color. The front carb may be running richer but it still didn't explain the bogging. Next, I pulled the oil filler cap while it was running. The engine hesitated and quickly stalled. From what I read on this forum, this indicated that there should be no vacuum leaks. Next, I tried pulling the sparkplug wires one at a time while the car was reving at 2000rpm to see if the cables and distributor were working. Funny thing is...there seemed to be no change in the rough revving with or without any single spark plug. This confirmed (to me at least) that it was a misfiring problem caused by a timing error. Before I spend money to check and reset the timing, would there be any other causes of this problem or anything else I should check out? I know my little diagnostic and theory may be completely wrong so please don't hesitate to poke fun and correct me!

[Bambikiller240]

One more thing for you to check before spending money is to see if the choke nozzles at the bottom of your carburetors are sticking open (pulled down) and not releasing (back to the closed "up" position) when you release the choke lever. You'll find it easier to check this if you remove the entire air cleaner including the base plate. It sounds like your front carb is running richer. It could be drowning the front 3 cylinders in fuel due to a stuck float or the choke nozzle stuck open. Just a few things to check. Good Luck.

[beandip]

check the vacume advance to see if it works or leaks vacume. If you dont know how , just disconnect the vacume hose from the manifold and suck on it and slip your tounge over the end and see if it holds vacume. Also remove dist. cap and look inside when you do it to see if the braker plate moves when you draw a vacume. If the vacume advance leaks repace it.

[Zedrally]

My guess it's electrical.

You don't exactly make it clear whether you did all these changes before the problem or whether the problem "just" appeared and you've started with the fuel filter [good idea].

My bet at this stage is points/capacitor.

HIH

[KEINsm]

Sorry about the confusion. I did those things after the problem showed up.

I'll check all the things you guys pointed out and update tomorrow.

[sjcurtis]

KEINsm,

have a close look at the breaker points in the distributor, sounds like you have a burnt set of contacts that may be catching or sticking in operation. The problem of hitting the rev limiter can also be the contact breaker points, if they are burnt out of phase or the return spring is weak.

My 2c

Steve

:classic:

[kyteler]

That sounds very similar to my problem which as it happens guys, seems to still be there somewhat and I still think it's electrical.

The first thing I thought was, condensor, changed that.. nothing.

Removed, cleaned, re-attached all earth and other wires in the engine bay, still no help.

Then it seemed to not do it after I moved the small plastic piece that holds the condensor and points wires bolt, so i figured a way around that, it stopped for a while, then came back.

New set of plugs, still not fixed.

I replaced the rotor arm, nothing, replaced the cap, and again it seemed to be fixed for a while, but now it's just nowhere near as bad as it was but still has weirdness going on.

I replaced the Fuel filter, nothing, did an oil filter and oil change, for no reason to do with the problem it just had to be done .

I'm still slowly elimating different things, although now the tach seems to be reading different than before. which is just bizarre so i might have to do some serious dismantling and check all the instrument wires.

Oh yeah, I've also tried Voltage regulators. Might have to try a new Alternator just to rule it out, even though it shouldn't really matter.

If you get it fixed before I do, let me know, if I do before you, I'll let you know.

[abas]

Apologies for the dimness of this reply but do the SU's on z's have rubber vaccum diaphrams inside the 'dome'. ??? I've never actually taken one apart.

I had a car that had stromberg carbs (which are like SU's) which had a rubber vacuum diaphram inside the dome. If this split or was replaced incorrectly it would give that same 'rev-limiter' at 3000 rpm feel that KEINsm is experiencing.

Hope it helps

Andrew

[Zedrally]

Originally posted by abas

Apologies for the dimness of this reply but do the SU's on z's have rubber vaccum diaphrams inside the 'dome'. ??? I've never actually taken one apart.

Andrew

No.

[KEINsm]

Earlier today, I bought a wire brush, some fine sandpaper, and electrical parts cleaner and did some cleaning under the hood.

As you guys recommended, I removed the distributor cap and sanded and sprayed all contact points. Next, I unbolted the ignition coil and all wires and removed all the rust and other crud from them.

I got a little impatient so I decided to give it a try to start the car.

To my suprise, it ran perfectly!!

I don't know if this is a temporary fix since I only did this a couple hours ago.

I drove it around town without a problem too.

I'll update anything that happens in the future regarding reoccurrences.

Again, I would like to thank each one of you for your invaluable input and for helping me out.

I am planning on meeting some local Z "doctors" and learning more about this car so I can start helping others as well.

[Bambikiller240]

Good to hear that your car is running as it should.

Seems like Zedrally and sjcurtis were the doctors who nailed the diagnosis.

Enjoy the Ride!