TR6 SU HS6 carb needle questions

I have dual HS6 SU's on my 6. Question I have is the needles to use. These came off a TR4. I have not changed the needles and since the 4 is a smaller motor, I may not be getting enough gas to my 6 with the needles in them. I did push the needles all the way up in the hole, that effectively riches them up, but they have the same profile. What needles have others used for this conversion?

Perry

I bet he'd know:
https://joecurto.com/contact

Joe Curto is definitely a guy to ask.

Just taking a bit of a stab at it, I looked at the Burlen site and they use a spring loaded BAG as the standard needle with their HS6 conversion for the TR6. That's not to say that the BAG profile is the best for your application. Engine set up/modifications and altitude could come into play as well. Make sure that you give all that information when you talk with Joe Curto. I'm not aware of any TR4 or 4A cars fitted with spring loaded needles so you would probably need the old style fixed .100" needles.

Just to give you a jumping off point before you talk with him. Here is a link to SU jet needle charts that I found:

https://www.rrocncr.net/technical/SUChart/SUChart.html

here is a link to the table with the BAG needle dimensions:

https://www.rrocncr.net/technical/SUChart/34.gif

And here is where it gets murky. Digging back into the far recesses of my brain, my guess right off hand is that you would need a fixed needle that is somewhere in the "K" family and more specifically in the "KK through "KS" range (EDIT to more closely match the BAG profile compared to the TW {standard} and SW {rich} needles listed for the TR4). You can compare the profile of the BAG needle to the profiles of the needles there and see if you find a match. If nothing else, profiles can be matched by gently removing metal from the diameter of the joint at selected profile points to get you what you want. If memory is failing on the "K" family of needles, you can go through all six pages of the .100" fixed needles, it's not hard, it will just get tedious after a while.

Depending on the engine mods, I have found that the commonly recommended needles (BAG or BAE) were too lean in the upper range. The stock needle usually found in the TR4A carbs (TW) is pretty close to BAG. One person on the 6 pack forum suggested KN. He used a wide band AF meter to verify the mixture. An AF meter when combined with a device to measure piston lift takes a lot of frustration out of profiling a needle.
Once the cap is pressed off the spring loaded needles, they can easily be fitted to the fixed needle type pistons. There is a light knurl on the needle shank that may need some minor filing.
Berry

Thanks for the help. I have found this site that has profiles of SU needles. https://www.teglerizer.com/cgi-bin/needle100db.cgi If you input the code, it gives the needle diameters at various stations. I was hoping to find a 2500 CC car with dual HS6's that I could crib the needle number from. I have the fixed .100 needles. Now, when I settle on a needle, where do I get them?

Perry

gbtr6 said:

Thanks for the help. I have found this site that has profiles of SU needles. https://www.teglerizer.com/cgi-bin/needle100db.cgi If you input the code, it gives the needle diameters at various stations. I was hoping to find a 2500 CC car with dual HS6's that I could crib the needle number from. I have the fixed .100 needles. Now, when I settle on a needle, where do I get them?

Perry

Click to expand...

First where to get needles, three sources right off hand:

Joe Curto https://joecurto.com/metering-needles-

Advanced Performance Technologies https://www.aptfast.com/ListItems/MainCategory/SU Carburetors.aspx (look to menu at left for the needles categories, this is the general SU page

Burlen Fuel Systems (UK) https://burlen.co.uk/ ( the "official" source of anything new for SU now)

I tried going to the Teglerizer link you posted, just got a blank page with the Teglerizer logo. This was with Firefox, tried IE and same thing. When I tried Chrome, it looked like the briefest flash of something, then it was just like Firefoz and IE, just the Teglerizer logo with the balance being a blank page. Could I trouble you to tell me what browser and version you used to get the the Teglerizer needle information?

You would think that the needle (BDU) used on the 2500 sedan would be close, but it is way too lean.
The Haynes SU manual has a complete list of needle profiles.
Joe Curto should be the best choice for a large stock of needles and advice.
Berry

Here's a pretty neat needle comparison program. It'll chart your original needle size with up to four others at a time along with a graph.

https://www.mintylamb.co.uk/suneedle/

Here's another one where you can input a bunch of car, engine and drive train parameters and come up with appropriate profiles, but to get full use it has to be registered and costs a few bucks.

https://www.winsu.co.uk/index.html

FWIW, I have used BAE needles in my TR6/SU carbs for years, and it runs fine over the whole rpm range.
Of course, altitude, and the state of tune of the engine plays an important role here. I run mine on a slightly higher compression ratio, and sport exhaust system,

Mine is being rebuilt, but what I have is higher compression, @9.5 or 10:1, stock exhaust, dual, an S2 cam, and stock intake.

With that information, I'd say you yourself are going to have to do some experimenting.
Get Joe Curto to send you a few needles with some profile variations and then you give each one a chance to exhibit it's ability in your specific engine.

The TR4 engine is not smaller, it is bigger! Well, each cylinder is bigger, and since only one cylinder at a time is drawing mixture through a carb I think you have to consider the displacement per cylinder.
At least, that would be my assumption...maybe someone could tell me if and why I am wrong.

Tybalt said:

I tried going to the Teglerizer link you posted, just got a blank page with the Teglerizer logo. This was with Firefox, tried IE and same thing. When I tried Chrome, it looked like the briefest flash of something, then it was just like Firefoz and IE, just the Teglerizer logo with the balance being a blank page. Could I trouble you to tell me what browser and version you used to get the the Teglerizer needle information?

Click to expand...

I got the same results with IE11 on Windows 8.1. You might see if you can get the information you need from these two links at the site.

https://www.teglerizer.com/sucarbs/index.html

https://www.teglerizer.com/suneedledb/index.html

Scott

I took a needle out of the front carb and it has a W on it for sure, can't make out the first letter. I sent that to Joe. Waiting to see what he says. Need to make progress and get this lump out and to the shop quick or the summer will be gone.

Perry

Perry-If your carbs came from a TR4A, TW would have been fitted as the standard needle. Way too lean if you have fitted a S2 cam and higher CR. SM or KN would be a good starting point.
Also, having the dist. to match the mods. will be necessary.
Berry

It is a TW needle. I have a stock distributor but run Pertronix. What distributor should I use, or what mods should I do to mine?

Perry

Perry-I think the total advance would need to be reduced because of the 10.0 CR. If you look at at the adv. curve for the PI cars that had 9.5 CR (shown in Haynes or Bentley manuals), it is maxs at 12-16 deg at 2600 rpm. Where as the dist. used on the 74 carb cars continues to adv. up to 24-28 deg. at 5600 rpm.
I would recommend sending the dist. to Advanced Dist. to be recurved for the cam&CR you are using. The cost is about $150 for a total rebuild and recurve.
Keep us posted on Joe Curto's recommendations.
Berry

Sent pictures of my carbs and the tag on the rear one to Joe. Waiting for response. A friend brought the engine hoist last night so I will remove the engine this weekend. Want to get the head off so I can see in #1.

Perry