260Z Carb Swap Issues. Please Help!

[fressssssh]

Okay, so I'm in the process of trying to get my friends 260Z running on early 240Z domed/round top carbs. We switched over the entire intake system(Manifold, Carbs, etc) from the 240Z. We also swapped the fuel rail from the 240Z over and removed the emission box(right before the fuel rail). We plugged all the unused ports on the intake and tried firing up the car... No dice. Added damper oil to the carbs... still no start. Finally we tried pulling the chokes up manually and the car fired up. The only issue now is that the car will only run with the chokes pulled and dies out as soon as they are released. Any advice would be appreciated.

[I'm BLUE]

Welcome to Ratsun (where creeper's dwell apparently ! haha jk)

 

For SU carbs ..Chokes are always needed as they do not have an accelerator pump to squirt* a shot of fuel in the throat of the carb for cold start.

 

* Is your fuel pump pumping fuel (volume test to check to see if faulty).

 

* Fuel Filter ... is it blocked or has it been changed (Typically needs to be changed often as the age of these cars).

 

* Do you have an electric fuel pump or mechanical ? If electric is it pumping when on ? (some electric pumps are too high of pressure for older carbs)

 

* Did you hook up the correct fuel line to the correct inlet ? (feed and return)

 

* If the carbs have been sitting a while ... they will get lots of sediment in the bowls and need to be cleaned ... sometimes they get stuck or cruded up really badly ... as well as repaired if needed. Check the needle/seat/float height. Make sure the piston domes are not stuck. Don't overfill the piston oil.

[datzenmike]

You're running 2.4L carbs on a 2.6 L motor. Likely you need to increase jet size decrease needle size. Simply pull the flattop needles and jets out and swap them.

 

The choke, on SUs, is simply a lever to raise the needle inside the jet. Because the needle it tapered the the opening between it and the jet increases, more gas can get by and the mixture is richer.

[Sealik]

Turn the screw(s) holding the jet(s)....lower them....which is what you're doing when you pull the choke cables

 

 

http://www.zcarz.us/TechnicalInformationPageCarburation.htm

[Skib]

You're running 2.4L carbs on a 2.6 L motor. Likely you need to increase jet size decrease needle size. Simply pull the flattop needles and jets out and swap them.

 

not needed at all actually.

 

 

turn the adjustment screws* out one half turn and see if it fires up and stays running then

if it doesnt go out to one complete turn and see if it stays, report back.

 

*(the big knobs on the bottom of the carbi, turn them clock wise if your looking at it from the top... so they are turning farther out from the carb)

[datzenmike]

Ah jet moves away from the needle. Doesn't this in effect lower the jet in relation to the fuel level in the bowls? I thought the fuel level is critical and has to be at the jet level?.

[fressssssh]

Thanks for all the tips. I'll check the fuel lines and then lower the jets with the screw tomorrow. I'll let you guys know how it goes. Thanks again, I really appreciate it.

[Sealik]

Ah jet moves away from the needle. Doesn't this in effect lower the jet in relation to the fuel level in the bowls?

 

Yes...if the fuel level in the bowl is at 23mm, the fuel should be 1mm lower than the bridge of the jet. Approximately 2 turns out on the adjustment screws

That should be the desired height when setting the carbs up....but.....when you drop the jets (from stock settings) to compensate for a larger engine and or, you change the needle stations.....relative to the jet.

I.E......engine will/could run lean or rich at part idle and WOT...etc...etc

At that point a thinner/re-shaped needle is necessary

 

Mine was pig rich at idle with RA needles....raised the jets...better.

But.....it changed everything else

 

This is where a A/F ratio gauge comes in handy

Might want to pull the needles out of the 260 SUs and try/compare them with the 240s after you get it running