Which needle for SU HS6 1 3/4" ?

[nospark]

I've got a standard 240z with 1 3/4" SU's (HS6). Also K&N filters and bigger header/exhaust. Jets are 0.100"

Could you please recommend a standard needle for these carbs

I bought the car with TW needles which might also have been filed by specialist tuner. I've got running issues but want a standard needle to get back to basics . I,ve seen SM needles bandied about but not sure these are for a mild tune set up. I want standard

Thanks for any advice

 

[jonbills]

I'm afraid I can't answer your question, but what sort of running issues do you have? running rich?

 

[nospark]

Yeah, over the year increasingly rich very sooty plugs. Stripped and refurbed carbs and got much sweeter consistent tickover with flowmeter. BUT with Gunsons colourtune got good blue burn at 1500RPM + but could never get good blue burn under 1500rpm (yellow,too rich). Suggests needle/jets worn. Might also be float setting too high. The SU trick of raising the piston slightly to monitor a change in revs and hence guage correct mixture works on rear carb but has absoluetely no rev change on front carb.

Took it for a spin. Got quarter mile and everything immediately just cut out. Would not start and pushed it home. Fuel high in float bowls. Plugs black. Hopefully just needs readjusted lower float levels and to clean plugs.

However, last year when travelling about 70mph the engine cut out in the same way. After 5 mins it restarted and never occurred again.! Going to get a new coil just in case. Oh and I find my static timing is 22 degrees advance at 650RPM !!(with vacuum advance plugged). So that needs redoing once I get it started.

Will fiddle when in the mood but in the meantime I want to get "standard" needles and a new coil

 

[jonbills]

I'm certainly no expert on these SU/Hitachi carbs, but I would be surprised to learn that you can get so much wear on needle or jet that you can't adjust mixture for good idle.
It does sound much more likely to be a float level problem - I do believe they're very sensitive to high float level - looks like as little as 10mm too high will have fuel level above the jet level.

The page I got that from looks like it has other useful info, inc reference to those SM needles.
http://www.zcarz.us/technicalinformationpagecarburation.htm

 

[nospark]

Thanks Jon. I've come across that info and I've got the Haynes SU manual. Yes, the general consensus is that the SM needles are "for performance". I think the N54 is a Hitachi Reference number so what is the equivalent SU number, I wonder. As you know the 1 3/4 SU is roughly the same as the 240z Hitachi carb.

The way to measure the float hight on SU's is to invert the lid and then measure the gap between the float edge and the lid rim

I read in a previous post that Mike Feeney was sent comprehensive needle data info from a previous member who went into this in great depth and posted his results in the club magazine. This was some time ago.

 

[SacCyclone]

I would check to make sure that your choke lever is all the way off. Check it manually as well by pressing up on the main jet at the bottom of the carbs. SU's have a tendency to have the main jet "hang up" causing a fat burn at lower RPM's. If you are able to push up on the main jet at all or hear a click etc, the main jet is not seated correctly with the choke off. I have had this problem on several Zeds with older SU's.
Regarding SM needles, i have heard very good things about them even with stock engines, better running and harding acceleration etc.

 

[toopy]

I have SM needles in my Hitachi's and she runs really nice, engine is a standard 2.8 with K&N's and a performance manifold and exhaust.

With regards the cutting out and not always restarting, i had this exact same thing last year, turned out to be the coil

 

[nospark]

thanks guys.
Yes, I,ve checked that the jets sit properly when the choke is pushed off. But I will double check.
I've done more reading on SM needles and get the feeling that they a bit on the rich side for my taste but something to look at if you are going for performance and/or are running a 2.8 litre engine.
The breakdown engine cutout happened on the cars first run out this year and after I had been faffing about with the carbs so carbs likely to be the issue. But the engine cutout was so instantaneous that might be an electrical issue. Will get a pertronix flamethrower 3ohm coil to cover that base and a new dizzy cap. (From old receipts its 10 yrs old)

I asked Burlen (the UK SU people) what was the equivalent SU needle/code for the Hitachi N54 needle. They said they had no cross reference information and that with aftermarket air filters and exhaust its really suck it and see. Anyone got a view on what a "standard" SU needle could be as a starting point???

 

[toopy]

Early last year i had 2" SU's on my car and i also could find no real info on what needles to use. The ones in the carbs when i got them were for a 3litre car, make i cant remeber now, but they were unsurprisingly too rich and a pig to tune properly.
I renewed the jets, same as yours i believe, and in the end i just chose some needles out of the Burlen catalogue that were good for a 2.8 jag!
They worked better, but i wasnt happy and switched back to 240 Hitachi's and fitted the SM needles