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SU carb tuning guide L16, L18


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#1 hogboy52

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Posted 24 February 2011 - 10:14 AM

Complete guide here with other links at top.

http://www.teglerize...bs/techtip6.htm
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#2 MicroMachinery

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Posted 24 February 2011 - 10:19 AM

Very nice. Thank you.

#3 nismo dr

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Posted 24 February 2011 - 10:21 AM

vote for sticky

You shut up.  You're not helping

 

Not super hard.  You just gotta know the right people.  You now know the right people.  Welcome to Ratsun.

 

Fresco historia, hermano.

 

#4 Logical1

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Posted 24 February 2011 - 10:34 AM

Wow, Been scouring the net for some time on SU guides and this is the best one yet! Thanks :)
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#5 MicroMachinery

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Posted 24 February 2011 - 10:38 AM

True that. I spent a number of hours looking everywhere online, trying to get this info, and little to nothing came up.

I bookmarked this one, and am seconding the motion to sticky it.

#6 Skib

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Posted 24 February 2011 - 11:27 AM

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#7 erikcarter

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Posted 24 February 2011 - 03:08 PM

STICKY!!!
anything with a motor will give me trouble!

#8 nismo dr

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Posted 24 February 2011 - 03:11 PM

STICKY!!!


you are right, it is

You shut up.  You're not helping

 

Not super hard.  You just gotta know the right people.  You now know the right people.  Welcome to Ratsun.

 

Fresco historia, hermano.

 

#9 skunk

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Posted 26 February 2011 - 07:26 PM

STICKY!!!

thats what she said
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#10 Rotary510

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Posted 16 August 2011 - 08:22 AM

Grassy Ass!!! = spanish for Thank you!
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#11 Sealik

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Posted 12 January 2012 - 12:56 PM

More links....


http://www.datsunroadsterranch.com/

http://www.zparts.co...arb_111601b.htm

http://www.z-car.com/510/S_U.html

http://www.ozdat.com...2122ea&start=15

http://www.innovatem...hp?threadid=360

http://www.jetlink.n...leshooting.html

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

http://www.nicoclub....g-su-carbs.html

#12 screamer510

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Posted 12 January 2012 - 01:15 PM

I like this one.

Maybe more specific for those of us with British SUs?

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Who's got a Unisyn I can borrow?

I think mine are running OK right now, but I still need to do the valve adjustment first.

Thanks for the beneficial links!
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#13 Just Joel

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Posted 14 March 2012 - 11:14 PM

The gusset at the top of the rear dome should be pointing at the filters like your front one...

Thanks for the links!

Later
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#14 cimarronlibre75

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Posted 06 June 2013 - 11:43 AM

This is great! Thanks! But I have to admit I just took mine to Mike Z's out in Whittier. They are a great shop and great people.



#15 Ron1200

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Posted 12 November 2016 - 10:46 PM

Here's a bit of info on the Hitachi-SUs Flat-tops.  I've been told that these are the L18SSS carbs that came on Japanese crate motors. Though there is lots of info in this post, I could not find any help specific to the high-speed balancing of to these carbs. Note that there is no "service screw" to raise the engine RPM.

 

If you have these:

IMG_1485_zpsz1ncqnpb.jpg

 

Screws circled in red are the high speed balance screws, the screws circled in blue are the typical idle adjustments:

IMG_1487%20balance%20screws_zpsah7zwuns.



#16 wayno

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Posted 12 November 2016 - 11:28 PM

The blue circled screws are for balancing the carbs using an air flow meter, the red circled screws are to adjust the sync of both carbs so they move at the same time when you give it the pedal, BTW I have never seen two screws before, usually there is only one on one side, mine is on the back carb linkage, maybe one is to balance them and the other is for idle adjustment, I adjust my idle with the blue screws and a flow meter.

The fuel mixture is on the bottom of each carb center, if you don't know how to do any of this, buy a book or look it up on the internet and read the directions, it's not that hard to do.

Most SUs came to the USA on 30,000 mile used engines from Japan.

Flat top SUs are smog SU type carbs, you can alway tell because of the triangular pieces of metal next to the blue circled screws that delete the smog part of the cabs, other wise there are all these tubes hoses involved between the carbs. 


 

 


#17 Ron1200

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Posted 13 November 2016 - 10:10 AM

I used a uni-syn to adjust the idle balance using the blue screws.  I then raised the RPM to about 2000 and used the red screws.  I read, on one of the links above, about syncing at the higher speed being more important than idle as the engine doesn't spend as much time there.  However, I found that having both idle and 2000 RPM sync'd provides for a smooth transition when accelerating from a stop.  I adjusted the red screw pairs in the same manner as the blue screw pairs.  I tweaked each pair to get the same reading on the Uni-syn at idle or 2000 RPM. Your right, after reviewing all the linked articles on this thread, I could not find an example with a linkage like mine.



#18 MikeRL411

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Posted 13 November 2016 - 06:21 PM

The glove box Driver's Manual for Datsuns used to be very comprehensive.  My manual for my 1967 RL411 has the proceedure for regulating the front and back Hitachi "SU" carburettors.  Maybe scrounge up an original or reprint glove box Driver's Manual for your vehicle?



#19 Dolomite

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Posted 14 November 2016 - 02:42 PM

I use the old school mgb owners trick. Manually lift the rear piston and adjust the front carb to get the fastest, smoothest engine speed...repeat for the rear carb lifting the front piston and done. Its amazing how quick and accurate it is, I've checked with a tool and it's dead on.
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#20 wayno

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Posted 14 November 2016 - 04:06 PM

I use the old school mgb owners trick. Manually lift the rear piston and adjust the front carb to get the fastest, smoothest engine speed...repeat for the rear carb lifting the front piston and done. Its amazing how quick and accurate it is, I've checked with a tool and it's dead on.

 

That is how I do mine except I go for the steadiest low idle, I want them to chug exactly the same front and rear without dying, then I go by plug color after that.