Kind of my set up since I have 6-2 to duals. It's nice to be able to swap from front carbs to rear. Of course you have the odd man out with the center carb. When my idle was so funky, I found after switching the sensor back to front that I had a lean conditions. On #1 carb. When I richened it up mixture the idle got perfect. It's nice to be able to split your troubleshooting ability like that.

But then you spiral into the consuming obsession of perfect running carbs as you try to achieve 14.7

Sometimes I wish I just pulled the spark plugs and called it a day-

On 5/26/2015 at 1:05 AM, rossiz said:

managed to have a productive long weekend in spite of the temptations (beer & brats, etc.) 

turned back the z technology clock a little: ripped out the efi and associated spaghetti/plumbing and installed the su's.

 

the worst part of the whole process was installing the choke lever... i picked up one of those tunnel-mount plates in order to avoid breaking the underside of the console (the choke lever set came with the telltale chunk of broken plastic mounting post still attached to the mounting screw) and it was a bit of a pain to set the layout on the tunnel so the choke lever would line up in the console slot. every time i have to do work on the interior (especially under the dash) i wish to god i had a chevy van instead... contortions upside down, holding a flashlight in my teeth, having my glasses fog and dropping the fastener on my forehead for the 5th time... but eventually it worked out just fine. i had purchased a 240z choke cable fire wall grommet but it turns out i didn't need it. what i had assumed was a metal blank-off plate next to the throttle linkage turned out to be a dual-opening rubber blank. so i just drilled two holes in it and the choke cables go through with a nice airtight seal.

 

getting the manifold off was cake thanks to the multiple head swaps i've done and i went ahead and pulled the afm, charcoal cannister and associated mounting brackets as well. i left the wire harness in for now, coiled up and tucked out of the way by the windshield washer bottle.

 

i'm using the stock fuel filter & lines for now, but will revise when some parts come in. 

 

next was swapping out the efi fuel pump with a cute little airtex unit. mounted it up near the moustache bar and looped the fuel line over to the existing hardline. i left all the efi wiring/relays/etc. in place, so it all works exactly as previous - just a lot less pressure. the airtex pump is so quiet, i had to put my hand on it to make sure it was working - nice.

 

i then got the carbs mounted up and checked the float levels. interesting side note: i had done this previously in my basement using water, with the fuel pump wired to a power supply and a juice glass as a see-thru bowl. even though i had both set dead-on to 23mm they were quite off when i put them on the car. not sure if it has to do with the density difference between gas and water, the tilt on the car or what, but i eventually got them both to 23mm (again). i used some clear vinyl tubing as a temporary sight glass which was quite helpful these first times around.

 

she fired up quickly and after warm-up i synched them at idle and high-speed w/the old unisync that i've had for decades in my tool box. worked a treat.

 

took her out for a test drive and was sorely disappointed... no power, burbled and popped horribly on decel, wouldn't rev, no fun. it sounded like the mixtures were way out of sync, and i couldn't get them to match up. decided to do another float level adjust, but this time i figured i'd go for the fuel in the jet nozzle rather than the height of the float bowl. read on one of the blogs out there that the recommended fuel level corresponds exactly to 1cm (10mm) below the bridge, which you can check by turning down the jet adjusters 10 full turns (1mm each) and fuel should be right at the top of the jet nozzle. turns out that i needed the rear bowl to be set about 5mm higher (18mm down, vs. the 23) in order for the nozzle to get its fuel at 1cm down. not sure why... 

 

she ran much better and is now quite driveable, although still not perfect - i ran out of daylight so will need to do more testing/tuning. next step will be setting up the dual-sensor afm so i can get a better idea of what's going on vs. just reading plugs. 

 

stay tuned...

 

carbs on - ready to run

 

 

temp sight glass setup

 

 

 

 

I want to save this and the newest stuff you put up today.  Thanks rossiz!  Fantastic work I hope to follow someday soon.

 

aww, shucks...

This is a awesome write up and I will definitely be using it to help me out with my swap. Just a couple questions for you, what did you do with the line that went into the charcoal canister? Did you just cap it off? Also as far as the gas smell goes from removing the canister, is it as bad as people are making it seem?

 

 

yes, i capped off the old vent line w/a bolt in a piece of fuel line. i've never had any gas smell - neither inside the cabin nor in the engine bay.

Do you not get any pressure build up in the tank?

I’m late to the game. How did you plum the carbon canister to the SU carbs?

 

my current situation.

Use a 74 fuel rail. It has a line to go to the carbon canister. 

23 minutes ago, SteveJ said:

Use a 74 fuel rail. It has a line to go to the carbon canister. 

Ok, but there is no way to jerry rig a 73 fuel rail?

13 minutes ago, MM569457 said:

Ok, but there is no way to jerry rig a 73 fuel rail?

The 74 has the vent line. Of course, you could come up with something else.

Download the 74 FSM and start reading at page EF-31 on the carbon canister.

Yea before the halftime I show I had just downloaded it!