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Identify My carbs, i think HS6 SUs not Hitachi. Good, Bad, Indifferent?

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Ok so my new Z came with what looks like to be HS6 not the early hitachies.

 

Can someone tell me what the main differences are and are these worth keeping or going to Z therapy 240z carbies with SM needles etc.

 

Current;y, ca pulls hard, however i have lowered the jet down another one turn as it was lean, now seams ok still a bit flat above 5600rpm and will not rev to anything over 7K not even at idle,that could be more the dizzy.

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Leave them on it!

Seem to be working fine, a bit of a adjust here and there has helped!

 

As per your other thread, better to be looking at your dizzy for your issues.

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They look like HS6 SUs to me. Can tell by the nozzles. Why are you trying to rev past 7k anyway?

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SUs are fine, plenty of parts available for fine tuning them, why spend money to change for Hitachis which are so very similar?

And I really don't think you'd be wanting, or needing, to rev past 7.....why? Asking for trouble. Better to sort the car's gearing out to suit your needs.

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Sorry should clarify, im not trying to drive to rev to 7k, its more the engine simply will not rev to that high, I was trying to say that in neutral just sitting there, jt won't get to that rpm it seams to break down at say 6.5k like it missfires.

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They're genuine british SU's (HS6).

 

Very similar performance between these and Hitachi's, nowadays how well they run depends on the condition of the carbs rather than what type they are.

 

Real SU's are easier / cheaper to get parts for, both standard bits and "tuning" bits. I rebuilt a pair a year or two back for a cost of under $200, including having the carb bodies re-bushed, new jets / needles / gaskets / special non-sink adjustable floats and high-flow ball valves for the float chamber. All the bits (except the fancy floats and needle / seat) were available from Carburettor Service Co in Sydney, who also did the rebushing. Fancy bits came from Burlen in Pomgolia.

 

Only thing I don't like is the method of adjusting float level on the British SU's - most of the 1 3/4" ones I have need to be adjusted by adding / removing shims / washers from underneath the valve (which is a little fiddly to get spot on). Hitachi's can be adjusted by bending the float lever. You can get (as I did) special adjustable floats for the SU's.

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Also, had a look in one of my SU books, according to the little tag on the float chamber in one of your pics that says "AUD661R" that carb is the rear carb off a '74 onwards Triumph Dolomite sprint with a 2l engine.

 

Perhaps you may need to look at re-jetting them if they are still jetted for the smaller Dolomite engine.

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Out of curiosity, what size engine in your zed ?

 

"SM" needles are listed as British SU needles, I assume Z-therapy use these in their Hitachi carbs. You should be able to get a pair of these needles and bolt them into your carbs quite easily and cheaply.

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Just a quick question, whats the difference between HS6 and what I have which are HU6 ? Does the middle letter, mean year of manufacturer ? The Hu6 I purchased new around 7-8 yrs ago..

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they are in my 260Z running an L28 motor with an early E88 head i think. If they are still jetted to be from a dolomite, i might have an issue. Looks like i should check the jet size and the needle but i don't want to fiddle with it as it runs nice.

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Just a quick question, whats the difference between HS6 and what I have which are HU6 ? Does the middle letter, mean year of manufacturer ? The Hu6 I purchased new around 7-8 yrs ago..

 

Dunno, only types I know of are H, HD, HS and HIF. H & HD are quite old, HS is the most common type from the 60's / 70's, and the later HIF which are completely different with the float chamber built into the carb rather than bolted on the side.

 

Could be something newer I guess, I've only fiddled with older carbs.

 

The "6", incidentally, is the size - 1 3/4"

 

 

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Ok so i took the HS6 carb jest out, stamped BCM. I also took a set of jets out of the spare set of 4 screw dome tops.

 

The HS6 needle is much longer and fatter then the hitachi one. The hitachi one will not fit into the HS6 carb as this has a spring loaded needle seat. SO i think SM needels are in order.

 

Thoughts>

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another problem, SM needles are not available in swing cab sets, so looks like i need to find something similar to an SM needle in a swing type

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Ok so if SM is to rich, SH appears to be just right going by numbers. The closest to this is a BFN needle, so looks like i am getting a set to try, might be worth while.

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BCM is the standard Triumph Dolomite needle.

 

Also be aware that if the "SM" is recommended for an L24 (I'm not sure exactly what it is recomnmended for), it may still not be ideal for an L28 due to the larger capacity of the L28. Probably a good starting point though I guess.

 

I've already mentioned CSC in Burwood, Sydney, but SUMidel in Sydney also stock a large range of needles for $12 - $15 each - http://www.sumidel.com/shop/category/su-needles Don't be put off if they answer the phone as "Fabre" - once you start talking SU carbs, they put you onto someone else who seems to specialise in them, not sure what the business relationship is between SUMidel and Fabre ??

 

And just for completenes, if you get really carried away with a rebuild, here are the newer style floats that are adjustable, unsinkable and ethanol resistant - http://sucarb.co.uk/float-chambers-spares/floats/hs-floats/su-hs-type-stayup-float.html. Not needed, but make float level setting a little easier.

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pulled my other set of carbs out, turns out they have a BAX needle in them, which is ritcher then the SM profile. HUMM, time for a test drive and see what it does.

 

fun and games

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BAX needels = wholy shittttt what a difference. Need to lean out idle a bit but so far blood great. car now revs freely all the way to 8k if needed.

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Good to hear. You can see the difference between the needes in the graph below - BCM are much thicker, especially at the "fast" side of the scale (right hand side), meaning less "space" between the needle and the jet for fuel to get through.

 

Interestingly, I run (I think, should check again one day) BAX needles converted to suit "fixed" needle carbs on my overbored L18 (so around 1.9litre). But it is quite modified and I don't care for fuel consumption or low speed running (because race car).  These were chosen by a very good dyno guy with lots of MGB / SU carb experience, after I rebuilt them initially with BAZ needles from a recommendation by another guru with SU's on Datsuns.

 

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Does this needle swapping work for the Hitachi SU's also? I need to find out what needles are in mine, but I suspect my L28 is running out of fuel higher up in the rev range due to the L24 size needles in it and hence feeling flat.

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Most certainly does, although U need needles with two precedes like sm or sh. Mine is a l28 with an early N88 head. Most people say that sm needles are to rich but you can lean them out just your idle will be a bit off. I have two seta of needels of a 260z but they are not stamped.

 

New needles are 14 each.

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Looks like I have a pair of "SR stamped needles" in my glove box. I think they came with the car many years ago. They seem to be unused and a quick Google search it looks like they might be the profile for a Jaguar XK140. Which is a 3.4 ltr motor. Probably would run too rich I'd assume.

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