Hope your week is going well.

I have a Series 1 240z with an L28 and dual SU carbs.. I have had this car since 1979 and it was my daily driver for many years. Now it barely gets used, sad but true.

Recently it has been cutting out really bad under load, back fire out the exhaust ( kinda think I see black smoke) and is real annoying. I was thinking it just had built up carbon from moving it around the shop with the choke on. I have had some nice dives with it, but it keeps going back to this sad running condition.

Things that have been done in the last 1000 miles:

Valve Adjust

Sync Carbs

New Plugs,

Rebuilt Distributor ( tried my spare too)

Just running out of ideas, so I thought I would ask for advice.... I was thinking old ethanol free gas..... so I might test the fuel........ Any suggestions is appreciated

Try running it without the air filter.

Be sure the carb nozzles are returning to the up position when the choke is off. The nozzle linkage (small flat bar with bent ends) that pulls and pushes the nozzles down and up gets warped over time and needs a bit of twist with pliers to align both ends to their attachment points.

I would think lean mixture...

Air leaks, varnished up carbs, poor fuel supply, bad fuel

Thanks for the responses.
Went through the basics today, compression test, carb balance, mixture settings. I went through all the timing marks and alignment. I did end up putting the car on a lift and dropping the oil pump and rechecking the alignment marks. Last time I worked on this part of the car, I didn't have a lift and crawled under and had the sway bar in the way. I might have been adjusting distributor to compensate for a distributor drive being in the wrong place..........I kinda looks like it was off by one "tooth". I think the the distributor rotor looks like it's in a better spot. I will test drive it tomorrow .........

On 8/17/2026 at 9:25 PM, 70z4fun said:

Recently it has been cutting out really bad under load, back fire out the exhaust

That's really a broad description of a problem and could probably use a little scope narrowing... So when you say it cuts out under load, does that mean:

A) You're cruising around no problem at light throttle, but when you punch it it backfires and cuts out for a brief instant and then maybe pulls OK?

B) You're cruising around no problem at light throttle, but when you go WOT, it pulls great for a little bit and then it starts to backfire after maybe five seconds or so?

C) You're cruising around no problem at light throttle, but when you go WOT, it pulls but not well, blowing black smoke out the exhaust the whole time?

Just trying to narrow scope some.

Well. it seems to run better, need to check a few things, as it feels flat after 5K RPM. Wondering if I went too far on "one tooth"?

No back fire, no hesitation, much happier........

IF the distributor drive is off by on tooth, will it drive this well? The rotor seems to be at the right position on the cap, but the "11:25" looking into the hole in the distributor mounts looks more like 11:30........

I am happier, but not sure it's perfect. Was able to set timing at 10degrees before TDC, but could not advance it much further with the 10mm lock down bolt.

What is the total timing advance at 2500-3000 rpm?

not sure I checked that. Are you asking what the advance is with the vacuum disconnected at 2500 - 3000 rpm?

I can hook up the timing light and rev it up.......

That's what they call "all in " timing. What the engine would see at open throttle (low intake vaccum), accelerating. It is commonly set at 34 degrees. Do it with the vacuum advance disconnected and watch it as you rev. It should smoothly rise to that number then sit there. If your weights are gummed up or a spring broken you'll be able to tell.

If you can't get there then you might be right about the drive gear being off a tooth.

Ok, will check how the vacuum advance works as it revs up.

How much change is there in the look of the 11:25 if the distributor drive is off by one tooth? I was thinking of dropping the oil pump and hold the distributor drive from above with some hemostats and try moving it back on tooth, the install the oil pump, but then the oil pump markings won't match the drive gear.......Is there a "trick" to turning the oil pump as you insert it into the front cover?

I assume that the car will run when you are off by one or two gear teeth?

Edited August 21Aug 21 by 70z4fun

Yes there is a trick in Tom Monroe's book that has worked for me. I posted pictures that I took of the text in the book. They're in this thread. Hope it helps.