SU carb/ running issues

[Blitzed]

Hi All,

90 days of preparing the 1973 240Z (L28 engine) to breath again, asleep for 17 years.  Read all the posts on 3 screw SU have the Ztherapy video as well. With all that said, the car has not cranked over in 17 years, little more complexed then a baseline tune up.

Completed the basic fuel mixture setting on the SU's, 2 1/2 turns down. Car backfires out of both carbs. With minor advancements to the setting (richer) the car will progressively start quicker but still backfires (more from the front carb then rear). After an hour of stop, restart, minor adjustments to the carbs the engine now backfires (carbs), stalls and then revs at high rate, repeats the process, until the revs get too high need to shut down. Carbs just rebuilt and I reset the floats to spec. Is this a needle, jet, timing, other issue or operator error?   

Car specs, 1973 240Z with a L28 with a bunch of transplanted L24 parts. Distributor, L24 single point with a vacuum advance, rebuilt and installed. N42 head, B cam. I believe the 3 screw SU carbs and manifold (N33) are from the L24 engine, not sure? 

Any advice would be wonderful . Thanks.

 

[jonbill]

I think you've got a few things need fixing. First up is a big air leak that's making the mixture lean and causing revs to rise. Either the throttles or chokes are open, or the carb to manifold or manifold to head gaskets aren't sealing.

[siteunseen]

I put my linkage back on wrong one time. Revved way too high right away. Check the stops on both sides, in the linkage between the carbs. Those flat things. 

[240260280]

Check timing too. It may be advanced. btw are you in Newfoundland?  We have club members there and I am in NS... and can ring to help you out.

[Blitzed]

All good stuff and a task for today. Need to deal with the high rev issues first, can't play with the timing or carbs adjustment before the need to shut down the engine. Will hunt for air leaks. Air cleaner / housing is not installed any issues with the vents on the carbs?

Tried to keep the engine mods to a minimum until running but did replace the 73 split balance tube with an earlier version (single tube) and removed all emission, ERG and PVC valves. I retained all should I reinstall?  New tube is fluid (old tube was fluid delete) and emission delete. California car. 

Thanks again for all the advice. 

[Mark Maras]

  The only way an engine will rev is more air. I agree with the air leak theory. The backfiring out of the carbs confirms a lean mix but I'm going to play Cap'n O here. Have you installed both throttle return springs? They hook onto the heat shield below the carbs. I forgot them one time. Your description jogged my memory.

[Blitzed]

Picture worth a thousand words.  Not sure on the linkage. I'm fully advanced on the distributor (only position the car will start), same position when purchased. Thanks again. 

[siteunseen]

Hard to tell but heres mine. there's a screw missing on the front carb stop on your first pic.

 

[Captain Obvious]

35 minutes ago, Mark Maras said:

I'm going to play Cap'n O here. Have you installed both throttle return springs?

LOL!  

[siteunseen]

The spacers in between the carbs and the manifold are a lot thinner than my '72.  Would that have an effect on the length of the rod with the plastic marbles?

Do the new spacers have the holes for water?

 

[Blitzed]

Hi All,

Yes, springs are attached. Not sure about the spacer and water response?. Spacer between carb to manifold? Not sure, I'll check.

There are zero threads to adjust the ball linkage, would need to bend to shorten the length. Purchased that linkage, not original to the engine. Had to reinstall the old throttle linkage rod off the split balance tube on the early single tube. The single tube linkage rod was too short would not reach the linkage rod coupler from the firewall. 

It was my understanding on the balance linkage between carbs, only one balance adjustment screw (lower screw) was needed.

Will disconnect the choke cables before cranking again. 

Thanks again for the info and advice. 

[siteunseen]

Here's a thread I found that talks about the water passages and the spacers.  I apologize if I've confused your problem.  I tend to think out loud a lot.