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 Post subject: SU Carb help needed
PostPosted: Sat May 01, 2010 5:21 pm 
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Joined: Wed Sep 10, 2008 11:34 am
Posts: 124
Location: Trumbull, CT
These carbs are on a 1974 260z that I bought for parts. Previous owner swaped out he flat tops for these.

This is a parts car I bought. Got it running. Has good compression, fixed an ignition issue. If I can just figure out how to dial in these bad boys, I will have a nice spare motor on hand.

1 The choke when engaged move up toward the carb correct :?: :?:

2 Can any one tell what sub-modle, series etc. thse are. :?: :?:

3 Any links for tuning these. :?: :?:

I have a uni-sync tool I can bourrow.

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 Post subject: re:
PostPosted: Sat May 01, 2010 7:50 pm 
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Joined: Fri May 23, 2008 9:34 pm
Posts: 362
Location: Hamden, CT
They're not too hard to tune but you will definitely need a Unisyn or similar to set the air flow. Also, the round mixture nut on the bottom of the carb should be set down about 2.5 turns. These two settings are the most important, a complete teardown and replacement of needle/nozzles/gaskets is not a bad idea too...they're about 40 years old after all.

Check out Ztherapy at http://www.ztherapy.com/, they have everything you need. Google "tuning SU carbs" to find many secrets too.

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Bryan Little
Datsunzgarage.com

1970 240Z - enhanced F54 L28 w/P90, Weber DCOEs, 4:11 R200, Nissan T5 5-speed


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 Post subject:
PostPosted: Sat May 01, 2010 10:46 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 14779
Location: CT
I note those are the "3-screw Roundtops" which replaced the earlier '4-screw Roundtops'. Bryan, any internal differences btwn these and the ealier SUs? I'm pretty sure all dimensions are unchanged, but I would have to check the 1970-71-72 manuals before betting any money.

Frank


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 Post subject: re:
PostPosted: Tue May 04, 2010 3:07 pm 
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Joined: Fri May 23, 2008 9:34 pm
Posts: 362
Location: Hamden, CT
Three screw models were the "later" SU versions from the '72 240Z but are identical in terms of performance to the 4-screw.

The fuel needles/nozzles should be changed if the history of the carbs is unknown...Ztherapy .100 nozzles and Datsun SM or N58 needles will work fine, but the SMs will be a bit rich on a stock motor.

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Bryan Little
Datsunzgarage.com

1970 240Z - enhanced F54 L28 w/P90, Weber DCOEs, 4:11 R200, Nissan T5 5-speed


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 Post subject:
PostPosted: Wed Sep 29, 2010 5:58 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 14779
Location: CT
Here Jake ~ this is what I was telling you about:

http://forums.ctzcc.com/viewtopic.php?t=5275

Frank

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1970 240Z


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 Post subject:
PostPosted: Wed Sep 29, 2010 11:34 pm 
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Joined: Wed Mar 24, 2010 8:11 am
Posts: 596
Location: Finland
Here's a little something too http://www.teglerizer.com/sucarbs/techtip6.htm


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 Post subject:
PostPosted: Thu Sep 30, 2010 4:51 pm 
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Joined: Sun Feb 15, 2009 6:47 pm
Posts: 307
Location: Niagara falls, NY
those carbs and needles were designed to go with a 2.4 liter motor. SM needles work dandy with a 2.8 liter motor. If you are running a 2.6 motor then I can't say which would work out better for you. I would try carefully cleaning and reassembling those carbs before I spent the money on new parts like needles and floats. Properly aligned needles and jets don't wear out and if you get them clean as new then they are as good as new. The age and wear issues with these carbs lies in the rubber parts and the gaskets, and in the throttle shaft. Improper or stiff fuel lines can keep the chokes from working right, and wear around the throttle shaft can cause air leakage there which makes low speed tuning impossible.

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71 on a rotisserie, two more in pieces in my shed...and a 69 1600 waiting for me to get to it


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 Post subject:
PostPosted: Sat Jul 09, 2011 3:59 pm 
I do not quite understand the machine, I prefer the look. But the link from Mr. Frank T can help you about your problems.

http://forums.ctzcc.com/viewtopic.php?t=5275

thanks :) :D


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 Post subject:
PostPosted: Sat Jul 09, 2011 6:14 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 14779
Location: CT
Ummm, Pat? Looking at that lead (front) carb again, it appears you have a vacuum hose missing from the tap which sticks up from the carb spacer. Close that off and try running the car again ~ you'll probably zee some improvement.

Frank

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