SU Carb needle and jets

[roughground]

I have a carb 1970 TR6 that I have fitted HS6 SU Carbs to. The donar car was an Automatic 2.5 saloon. My car has a 150 bhp cam shaft and the compression ration is 9:1. Has anyone any suggestions for the type of Needle it should have?

I want it to go well but run smoothly throught the range.

[rpurchon]

I have a carb 1970 TR6 that I have fitted HS6 SU Carbs to. The donar car was an Automatic 2.5 saloon. My car has a 150 bhp cam shaft and the compression ration is 9:1. Has anyone any suggestions for the type of Needle it should have?

I want it to go well but run smoothly throught the range.

 

yellow springs and BAE needles.

richard

[dingle]

I have found that the recommended needles BAE and BAG are too lean. The plugs stay quite white, but the engine doesn't mis-fire. I am also using the early PI cam with a CR increase to 9.1+.

Berry

[AndyGT6]

I run a 2.5L GT6 with the Chris Witor higher lift Vitesse/PI Saloon cam, and also found the BAG needles too lean. I currently have BCH needles fitted with green springs. I have used yellow springs, but find the Air/Fuel ratio to be much more stable with the green springs, I have an Innovate LC-1 wide band kit fitted. I didn't notice any change in performance by going to a heavier spring. Other similar needles are BDA & BAM. Hope this helps.

 

Andy

[dingle]

Andy-Thanks for the needle suggestions. I am going to try SM (fixed needle used on TR-4). They appear to be quite close to BCH and are very common. I have a narrow band sensor that is better than nothing, but not much. All of the leds are out above about 2k rpm with the BAG needles and yellow springs.

Berry

[BlueTR3A-5EKT]

SM are fixed type needles

BAG etc are bias type

 

Unless you have unearthed a stock of the special SM needles Cox and Buckles had sourced in the 70's to fit bias pistons you will not be able to fit them unless you change your piston and housings to TR4 type.

 

Cheers

Peter W

[dingle]

Peter-The cap on bias needles can be easily removed to allow them to be used in fixed needle pistons. I have SU HS6 carbs from an elderly Volvo that uses fixed needles. When the caps are removed from the bias needles, the shank dia. is the same as the fixed ones. There is a light knurl on the shank that sometimes requires light filing to remove, but other than that, there is no problem in fitting the needles.

Berry

[BlueTR3A-5EKT]

Sorry Berry,

I read it that rough ground was using carbs with bias needles and was considering using fixed type needles in them.

Cheers

Peter W

[dingle]

Peter-I have never tried to use a fixed needle in a bias piston, but wouldn't

it be possible by fitting the "top hat" from a bias needle?

In re-reading rough ground's post, I noticed he mentioned using carbs from a 2.5 saloon. This rang a bell as I remember some posts on other lists of people who used these carbs on a TR6 and had problems with flooding. Joe Curto, the stateside SU guru, recommends using float chamber from a Spitfire (AUD 2140) that allows a lower fuel level in the jet.

Also, I think the Saloon carbs use "waxstat" jets, which can be troublesome.

Berry

[roughground]

Thanks for all the info and replies. The carb has fixed jets and are standard not waxstats. The CR is 9.5:1 ( I skimmed 40thou off the haed to get it). The donar was a 2.5 Auto saloon.