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stevo_gj

Advice for an Amateur refitting SU carbs

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Hey Guys,

 

Well I have acquired a pair of the SU type (240z) carbs that I have been told were working when taken off a 240z about 3-4 years ago.

 

Since I currently have a working pair of Flat Top (260z) on my L26 I was going to turn the SUs into a project and clean and refit them. I figure I can learn a fair bit about carbys by doing so and will still have a car to drive in the mean time.

 

Basically I need to know where I can get my hands on a kit with gaskets and any other parts that would normally be replaced when refitting carbys. I have disassembled one and it all seems to be in fairly good condition, so I figure it won't need any major components replaced. I would also love to hear if anyone has a particularly good manual for this kind of work.

 

Cheers,

 

Steve

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Just give it till after Christmas Steve, the forums are dead atm cos people are away etc atm.

Merry Christmas mate

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well im having a coffee after getting the wakeup call at 6am lol Instead of reading the paper i read the forums :)

 

Now, personally i would pull them down, make sure your needles are nice and straight, springs are in good order and then buy some carby cleaner. Clean everything you can. Then reassemble and make sure the piston returns with a clunk in each carby. They should return at about the same rate aswell.

 

here a link for you to read it's all i could find.

http://www.jetlink.net/~okayfine/su/rebuild.html

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haha yeah your right of course sco.

 

Thanks for the tip Glen, that's pretty much what I've done but I figure I might as well get a gasket kit. That link is gold!

 

Quick question for when everyone gets back in the next few days: Do I need to replace the oil that dripped out the top of the piston/needle assembly? Can't find reference to doing so in the manual I purchased.

 

Merry Christmas

 

Steve

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Very important to replace the oil, i think you can use tranny oil iirc, Its about the same weight, but double check that first. You can use different needles aswell depending on what condition your motor is in. I have read that SM needles give a nice performance boost.

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hmm with my 240z i also got a old vhs tape that showed all about the Su carbs - rebuild tuning and all that stuff,

aswell as swapping door handles and fixing front fiberglass kits ill have watch it soon, - my vhs shuts down every minute or so, =L

 

Heres a few pics of the tape.

anyone seen it?

 

 

*Added pic of some wierd spider that jumped out First time ive seen one of these Bastards =L

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I can convert VHS to DVD if needed... That spider was just a friendly Huntsman. Painful bite is the worst you can expect!

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With the SU's replace all gaskets, replace the rubber fuel hoses and make sure the floats are not bent or broken etc..

 

They are fairly simple carb, so when putting them together the only problems I would imagine are the gaskets. The biggest problem is that the throttle shaft tends to wear out and cause a vacuum leak. Make sure the shaft is nice and firm and free from play.

 

If not sure, maybe ask a carby specialist to have a look. They may need to rebush the shaft.

 

The oil is important as it dampens throttle response and keeps the carbs in sync better. I think sewing machine oil is meant to work nicely, I can't recall the specific weight to use, but if you have a Haynes manual I think it has the recommendation in there.

 

Take your time, give them a good clean out and you should be alright. They are fairly easy to set up provided you have all the right parts with them.

 

You may as suggested consider some new needles since they are probably set up for 2.4 ltr engine and not 2.6ltr, not sure if SM needles will be too rich or not though. Which reminds me, at the end of the needle is a rubberish seat, make sure its not worn out or the car will run way too rich. So might be an idea to replace the seats and needles at the same time. I'm sure an SM needle kit will have this anyway - but just incase they don't I figured I'd mention it.

 

If you can, get them polished too with the manifold, they look the goods then. :).

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I can convert VHS to DVD if needed... That spider was just a friendly Huntsman. Painful bite is the worst you can expect!

 

That would be awesome, if you could stick it on Youtube too! :) But it might be copyright.

 

I think www.ztherapy.com sells DVD's now anyway.

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Nice, thats all very helpful guys thanks. I'm definitely going to replace the gaskets and see what I can do about getting them polished.

 

I'd never heard of SM needles before so I did a little research. I love the idea of an 'easy power upgrade'. After a little reading it seems to me that they are must when using twin SUs on an L28 but maybe not so much for an L26?

 

"SM's can work without backfiring in a stock 240 when the SU's and ignition are in good condition -- some autocrossers used them in the '70's. (The way to set SM's up is to minimize their mixture error by running low float levels and no or minimal manifold head, climate permitting, and be sure there's no wear as all in the nozzles. The normal idle adjustment procedure works with them, SM's just don't need quite as much nozzle drop as stock needles.)"

 

"SM needles run rich at idle & low end. Especially on stock engines."

 

 

To recap I'm running a stock L26 and was just looking for a slight performance/reliability upgrade from the infamous flat tops.

 

Has anyone got any good links/info/experience with the SM needles? Are they difficult to setup? Am I gonna lose much driveability swapping over to these needles?

 

Man I am so full of christmas cake.  ;D

 

Steve

 

Edit: Guy on HybridZ suggested using Flat Top needles in the SUs. I didn't even realise they were interchangeable.

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I think sewing machine oil is meant to work nicely, I can't recall the specific weight to use, but if you have a Haynes manual I think it has the recommendation in there.

 

According to Haynes we are supposed to top it up with 'engine oil'.  ???

 

 

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Hey Steve, I'm stretching back to MGB days here but if I remember correctly, the heavier oil will give a more stable but slower responding throttle.  A lighter oil can speed up responsiveness but can become unstable resulting in the mixture fluctuating/oscillating wildly.  I would suggest starting at the heavier end till you've got it running well and then moving to lighter oils.

If I recall, play in the butterfly shaft bushes is the major maintenance item and results in air leakage and poor mixture control.  Needles and seats as mentioned, and also the float chamber needle valves may need a good clean or replacement.  Gaskets on the float chamber bowls are said to leak if they become soaked in fuel, not sure about that one.  Cleaned up a pair for a '66 Mini a several years ago like you're doing.  Classic British car sites (ie MGB, Mini) are a great source of info for SUs.

Mike

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After receiving this reply to the same question on Hybridz I decided to forgo SM needles and stick with the current ones.

 

The SM needles are widely regarded as too rich by many on this forum, for even a stock L28. The original N54 needles are fine for the L26, and even good for the L28 too, as long as the carbs are set up right. Start with the N54 needles, and if you need more fuel (use a good wideband to determine this) then look into the british SU needles for something between the N54 and the SM.

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Ok, I have heard that instead of using the orange intake box the Carbys are able to breathe better if I get some kind of 'socks'. What do I need to change to fit socks onto my carbs?

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Steve

I fitted these to my HS6 SU's..

they are ramflo SUH6-HD6...1 3/4"  PART NO RF404S..

Im 75% sure theyll fit your Hitachis.

cost me around $45-ish  each including filters. work well.

post-632-144023507933_thumb.jpg

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I think Redline make trumpets that fit onto the 240 carbs then you need some Unifilters (they come in packs of two and in low profile if you need it and cost about $40)

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I just gave SU Midel in NSW a call (SU specialists) and they said that the Authentic SU gasket kits will not fit onto the 240z Hitachi SUs, and more over he had no idea where to find hitachi SU gasket kits. Then he tried to talk me into upgrading to authentic SUs.  >:(

 

 

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Ive heard this before...rebuild & gaskets kits for hitachis are as rare as rocking horse crap..I believe most guys get them from the U.S.

Yeah the ramflos do help the carbs to breath better, which is probably a good thing if your driving in muggy-hot Brisbane weather.

The ramflos can be a bugger when your trying to warm-up the engine on a freezing canberra winters morning though..

 

Ive seen pics of the ram-"tubes" comming off the Hitachis / or SU's, Im sure they work very well, its just that ....well , it kinda looks ugly..elephant man or something.

or maybe were just used to seeing tubes-trumpets on webers & dellortos & mikunis all the time, (they just look so classy)  ;D

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I vaguely recall a company by the name of Fuel Miser as having gasket kits for the Hitachi's, but after a quick google search I can't confirm this. Dose Fuel Miser sound familiar to anyone?

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Hmm interesting. Thanks for the input Chris.

 

I think I'll wait until I've got it fitted, and if necessary upgrade the air filters afterwards.

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I vaguely recall a company by the name of Fuel Miser as having gasket kits for the Hitachi's, but after a quick google search I can't confirm this. Dose Fuel Miser sound familiar to anyone?

 

Yes it does! When I bought my first 260 with the flat tops and upgraded to the 240 carbs I bought 2 of those Fuel Miser kits from a carby shop in Oakleigh (Perfection Carburetors) and rebuilt them. This was in the late 90's though and I'm not sure if they are still available.

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I remember reading somewhere (maybe hybridz) that trumpets, or at least well formed inlet rings are essential when putting aftermarket filters on.  The mouth of the SU's causes a lot of turbulence which reduces airflow, whereas the stock airfilter box has well shaped inlets.  I can't remember any more detail than that, it might have only related to the very high performance end but could be worth doing some searching on...

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