Rough Idle (video)

[vling]

Hi everyone, I have a 1971 240z with an L28 (N42) block and E88 head. The PO said it had been sitting for two years and it had a valve lash pop off due to sticky oil that I fixed. I also just redid the fuel system (newish 280z tank, new hoses, pump, filter. Carburetor float needles were stuck closed, but I soaked them in carb cleaner and they move freely now, cleaned the banjo fitting mesh filter. Also adjusted float level as per FSM.

Here is a video of the car idling

Now to the problem. The car is idling very rough, engine is shaking, there is a loud clicking noise coming from somewhere and pulling spark plugs doesn't have much if any effect on a few cylinders (it was #1,2,3 that was not firing well on the old plugs, although swapping the #3 plug to #4 did have a bit of a positive effect on #3) I noticed that #1-3 were wet with fuel, while 4-6 were dry but still black.

So after swapping plugs and seeing a difference, I decided to try out all new plugs. I put them in, and #2-6 passed the plug test, while #1 failed. Pulled #1 plug and it looked like no fuel at all had gone near it, and there was a slow white smoke coming out of the plug hole (not steam).

Now after about 5 minutes of running, it seems the new plugs have started to foul again. Car is back to running like how it was with the old plugs.

Here is pictures of the old and new plugs (kind of erratic pattern of fouling on the new set)

Old

New

Also, I adjusted all the valves cold, a bit too tight (using measurements from atlanticz, which mustve been SAE, but i was using metric) but I'll be adjusting them again (correctly) right after I post here.

Any thoughts?

[Weasel73240Z]

This is a total shot in the dark, based only on the sounds of the motor from the clip, but what do you have the timing set at? The erratic idle could be from severely retarded timing, which could also cause some fouling issues with the plugs. Again, I'm guessing just based on the sound of the motor running in the clip.

It doesn't look like you've done all the cheap and easy stuff, like new plugs wires, rotor, distributor cap and points to go along with the new plugs. If not, that should all be done. It does look as if some of the plugs may not be firing consistently, which could point to a damaged plug wire.

[vling]

The timing is set at 10' based using the middle mark on the pulley (out of 5) and the 10' mark on the block. I'm not 100% sure if the mechanical timing is correct. It seems like the dimple on the cam gear lines up a tiny bit after TDC, but I don't know if this is compensation for belt stretch etc?. PO said it was running great before it was stored.

I'm going to order cap rotor, wires points etc. Where do you recommend to get this from (local parts store won't even order them for me)

Also, should I be getting parts for a 280z dizzy or 240z? Mine looks exactly like this:

Thanks weasel

[Unkle]

Sounds/looks like plug wires installed in the wrong firing order . Also, new gas used ? Was the distributor removed / installed correctly ? Hmm..... worn camshaft , bent valves ,, uh oh it's getting worse, I'll stop now. Distributor shot ?

Edited August 5, 2009 by Unkle
other bright ideas

[Weasel73240Z]

Thats a 280Z dizzy, I think between a 1975 and 1978. You should order parts (rotor, cap, wires) for the 280Z not for the 240.

The plug wires could cause a rough idle if you have 2 of them swapped.

Try Blackdragonauto.com, they have the parts you need.

[vling]

Checked the firing order multiple times, It's good.

Unkle - Don't know about the distributor installation, I just got the car and po didn't know much about the swap except "it ran really good". Yes new fuel (mid grade, been sitting for about 2 weeks now though, fuel additive in there too)

Weasel - thanks for the ID and link

[yetterben]

Those plugs look oil covered. There really shiny. Check firing order first. Run a compression test to. Buy the looks of the plugs its not good. the one looks like pepper not good.

[yetterben]

Also turn both carb adjustment nuts all the way in and back out to 2 1/2 turns. the nuts on the bottom. The base ring of the plug show jetting. I dont care what anyone says about porcelain the base ring where the ground strap is is where you check jetting. You want a light sooty ring 3/4 around that ring.

Look it up. But your plugs are oil fouled for sure.

[vling]

The wetness smells like fuel, I guess it may be both.

yetterben - did a compression test before I bought the car (cold, car had been sitting for 2 years and would not run) and got

1-179

2-166

3-166

4-170

5-166

6-200

Ill do another one warm in a minute.

[Weasel73240Z]

Thats a 280Z dizzy, I think between a 1975 and 1978. You should order parts (rotor, cap, wires) for the 280Z not for the 240.

The plug wires could cause a rough idle if you have 2 of them swapped.

Try Blackdragonauto.com, they have the parts you need.

I just re-read my post...just to clarify, that looks like a 280ZX (79 - 82???) dizzy, not a 280Z.

[vling]

I just re-read my post...just to clarify, that looks like a 280ZX (79 - 82???) dizzy, not a 280Z.

ackk my mistake, mine is different from the one in the picture posted above.

Here is a pic of my dizzy.

it looks pretty similar to the one in the 240z haynes manual, minus an e clip on the points knuckle...

[Weasel73240Z]

Thats a 240Z dizzy. You should replace the points when you do the rotor, cap and wires.