I've been doing all sorts of reading on forums, articles, and my repair manual about how to adjust the carbs on my 240Z. I'm running into a problem, though- the mixture nuts that I see on all the articles and in the repair manual look totally different from mine. As far as I can tell I have the early dome-top SUs, but these mixture disc-things on mine don't even look like what's on the later flat-top SUs. I'm obviously confused.

Here are what I see everywhere:

And here are mine. As you can see, where the mixture nut would be is just a disc.

This is really halting my tuning process, as the standard mixture setting to start with is about 2.5 turns from bottomed out, while my disc-things only turn about a half turn before hitting a notched stop-point. I'd really like to know what's going on, especially if these turn out to be something other than 240Z carbs.

Looks like you have the 3 screw carb mixture nuts, which are from the later domed SU carbs. The piece that seems to be stopping your mixture nut can be removed or adjusted so it is not so much in the way. I believe it is just screwed in in the front of the carb.

Ah, thanks for that! I was afraid someone might've stuck the wrong carbs on this engine. So do the adjustments that apply to the earlier carbs still apply? Such as bottoming it out then turning 2.5 turns back out to start with?

Yes, just the same.

Patrick -

You have the same mixture nuts I have on my SU's (currently in storage). The lock downs can get a little tight and you may need to bend them or you fingers will have a hard time turning the nuts. Once my carbs were set I never had any free movement of the mixture nuts so bend the hold downs if needed. If you have not purchased the SU DVD from Z Therapy it is really a good purchase - great overview tutorial, and you know how us guys like to watch movies!

Be sure to read your plugs to confirm your settings.

I've had both styles and prefer the "knob" over the "disk". My current '72 has the disk and the locking tabs drove me nuts...right up until the moment I removed them.

yes, I've run into this issue right now out in the garage.... I need to turn the disk on the rear carb further than the bump stop will allow without me bending it to pass the "big" bump stop on the disk that ends the little notch fine tuning area (on the disk; half a turns worth)

but it sounds like I can disregard this bump stop and bend the lock tab out of the way

You may want to remove the locking tab - or - slightly bend it. Your carb may need that stop in place to keep things in the set position.

hmm...I bent the tab out of the way....but I'm not getting a pronounced response from my adjustments...it takes a full turn or more...on high altitude needles?

bogging on test drive at half throttle/ mid band