Guest bastaad525 Posted October 25, 2002 Share Posted October 25, 2002 Okay... again from what I understand the four screw SU's, which came on the first 240z's, are more rare, at the least. These ones also did not come with the drain on the float bowl. The reason I thought that the four screws would be worth more is because anyone doing a true full restoration of an early 240 would need those carbs (I think they were only on '70 or maaaaybe '71), and if you're going to Z shows/contests or what-not you're gonna be judged on that. As far as Ztherapy goes, they actually sent me some of the four screws when the cores I sent them were three screws, so I guess they don't care much either way anymore. The other weird thing is that my four screws actually do have the drains on the bowls, which makes me think they probably put the new float bowls on there after redoing them. Another difference is my three screws had a place for coolant to flow in them from the intake manifold and the ones they sent back don't, so I had to block that off. Also, about the thick thumbscrew being able to be adjusted all the way down, this isn't always the case. My carbs have the thicker thumscrew, but they can only be unscrewed so much as there are these little mushroom shaped bolts kinda behind them and below them that block them from coming all the way out. I also actually kinda like that they sent me the ones with the adjustment for the nozzle... sure beats having to get nozzles custom made if things somehow get out of alignment! Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted October 25, 2002 Share Posted October 25, 2002 My 3 screw ones run much better then my 4 screw ones. I am seriously thinking about sending the 4 screw ones to ZT for the throttle shaft replacement. I think that is the real issue with the set I have, the shafts are worn. I have also noticed when I run the SM needles, my car will turn more rpms then with stock needles. It also rev's better in neutral, but the idle is a pain to get right, and it is much richer at idle, so I don't like the fumes. Burns my eyes. I may take the car to the strip and see what happens tonight, and I will take both sets of needles and see what happens. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted October 26, 2002 Share Posted October 26, 2002 Yeah other than a few little differences 3 screws and 4 screws are identical so if your 3 screws run much better then yeah maybe the throttle shafts are fudged on the 4 screw. About the SM needles this is the problem I have run into also. It seems the stock needles are great but will limit the top end, where as the SM's have plenty of top end but idle too rich and I'm finding out seem to be harder to tune right. Someone suggested getting the stock 240 needles then regrinding them with sand paper from the middle to the tip, leaving the low end mixture the same, but regrinding the high end thickness to match that of the SM's. If I had any kind of tools I'd probably give that a shot... seems it would be the best of both worlds. Anyways, I don't really mind the SM's even for street driving they fine I just dont like how rich they run at idle and that they black up the plugs so easy. Quote Link to comment Share on other sites More sharing options...
DAW Posted October 26, 2002 Share Posted October 26, 2002 SMs are not the only performance needles for SUs. SMs are from Citreon (or some other older European car) SU carbs originally. There are other choices and what's best is to modify a needle so it's custom-tailored to your engine. There are factors other than the needles which you'll want to modify also e.g., damper spring selection, damper oil type (use ATF and don't overfill as this adds wt to the piston), choke linkage if it's hanging up at all (affects needle ht), and ignition timing (affects throttle response). If you really want to get results, read the SU book I told you about in one of your parallel posts on this subject (I'm not being critical, just trying to focus your search), and a good source of SU parts is APT (Advanced Performance Technology, 595 Iowa Ave, Suite C, Riverside, CA 92507, 800-278-3278). Their roots are in English sports car racing and what better place to look for SU tuning experience? DAW Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted October 29, 2002 Share Posted October 29, 2002 I have that SU book and have read thru the tuning/needle making section. I'm looking at getting a dremel and/or some other tools and maybe giving this a shot. I also have the How to build/modify datsun engines book but it's section on SU's is pretty limited and really only tells how to do basic tuning on them. The SM's were found on some Volvo's or at least one of the places that I know carries them is a Volvo restoration place. Quote Link to comment Share on other sites More sharing options...
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