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Triumph TR6 - SU HS6 Needle Taper

For the SU owners: what needle designation are you using?
Rick Orthen

Rick,
I've been using BAG needles in my HS-6 conversion but they may be a touch too lean. Another outstanding guy on this board has been using BAX needles and he used an onboard fuel/air meter to determine the best profile. I'm going to order them a soon as I get the chance but the BAG does okay for now. Best of luck and let us know what you decide, Robert
Robert Rutschman

Rick- Install a O2 sensor and run the needles you need.
alot depends on your driving and and engine set up.
Don K.
DON KELLY

Thanks folks. I'm new to SU's and rebuilding a pair now to replace the ZS's. I was intimidated by the SU needle selection. I wasn't planning to go the oxygen sensor route; is that a must-have? What is the jet size (0.900?)? I'll have to find that gentleman with the BAX needles and get his station profile. I bet he even runs different stations in the front and rear carbs.
Rick Orthen

Rick,
The HS-6 uses a 0.100" jet while the HS-4 uses a 0.090" jet. The profile for the BAX is:
0.099 0.0958 0.0926 0.0896 0.0861 0.0814 0.0774 0.0742 0.0718 0.0694 0.0673 0.0652 0.063 0.061 0.059 0.057 I would strongly recommend using the same needle for both front and rear carbs. Best of luck, Robert
Robert Rutschman

Rick-The jet size for HS6 SU is always .100" and the same needle is used for both carbs. An air fuel monitor is very useful for showing the mixture strength at all speeds.
Berry

Robert--Thanks for the BAX station profile. I'll update after I get these babies rebuilt, installed, and tuned.
Rick Orthen

Sorry guys, I didn't have a computer for a couple of days. I am running the BAX's on both the front and rear carbs - something I was relagated to doing since I only installed one O2 sensor in a part of the exhaust system where front and rear exhaust flow joined. If you installed an O2 sensor in the part of the header where flows were still separate, I suppose it would be feasible to use different needles on the front and rear carbs. If you didn't know, there is a program available on the net where if you were getting lean running at certain rpms with a certain type of needle, you can indicate that you want a needle with a richer profile only at a certain needle position (or a range of positions) and it will recommend the closest needle suitable for your requirements. Quite nifty. The info provided to you so far has been well sourced and I wish you the best of luck. Your efforts will be so worth it...
Geoff P

Thanks Geoff. So what does your O2 sensor tell you about the BAX vs. BAG for WOT and in-between?
Rick Orthen

Just out of curiosity, is there anyone out there running triple HS6s or HIF6/44s on one of Richard Goode's manifolds and if so what needles are being used? If HS6s, would also be interested in knowing how they are set up float bowl wise. I ask as we were talking about 6 cylinder TRs the other night over at the shop and one of the guys with another TR250 mentioned the Good Parts manifolds while eyeing the two sets of HS6s off of a 4A sitting in my "inventory" of spares.

For Geoff P, any chance of posting the URL for the jet needle calculator? Long ago and far away I had a book of nothing but SU jet needle charts and selection guides published by SU. Then one night, someone broke into the MGB that I had at the time and took it out of the cubby box along with the shift knob and some other odds and ends. I haven't been able to get my hands on another one of those books since.
SteveP

Steve-The URL for the SU needle base is: http://www.teglerizer.com/suneedleb/index.html. If the HS6's wont't fit the goodpart triple manifold, you might try the z-s 175 cd's that were used on the TR4. They have an adjustable jet, lack the emission do-dads of the later carbs, and SU needles can be easily adapted.
Berry

Rick,
my O2 gauge shows little difference in needle profiles with subtle differences (such as the BAX's and BAG's)when using the accelerator indifferently. Where you could visably see a difference was at wide open throttle, where with the BAG's the LED's on the gauge would meander in the middle to upper range, with the BAX's the LED's would remain solidly in the upper range. It was also a difference you could clearly feel. Also, it was possible to adjust this leanness out by lowering the jet, but this would artificially richen the mixture throughout the whole range, even when it was not needed such as at idle - the O2 gauge also picked this right up. Cheers Beery for getting that URL out - way too busy these days!
Geoff P

Thanks Geoff. I'll see how the BAG's work when I get the throttle bodies back from Joe Curto. How are the fuel supply hoses run on your setup? Do I need to put a Y-connection in the feed to split front and rear? My bowl tops have two nipples apiece and I presume one is strictly a vent that I can put a hose on and drop to the chassis area. Thanks.
Rick Orthen

Rick,
I emulated the original line routing as much as I could. I used steel fuel pipe and compression fittings as we are talking about low fuel pressures. I took my time with the bender and got some very good looking results. You are correct: the fittings on the bowl lid are for fuel intake and bowl venting. I still had my charcoal cannisters and routed the bowl vents to that.
Geoff P

Geoff--Got the carbs reassembled and can't wait for the install. Regarding the cold start mechanisms, do you have relay linkage between the rear and front mechanisms? Or simply have your choke cable attached to the rear mechansim and don't do a cold start on the front carb?

Thanks.
Rick Orthen

Rick,
I can't wait for your maiden voyage with those SU's. With the K&N's - that air intake sound when you stab the accelerator - pure magic... In regards to the cold start, I thought about going the route of a cable to the rear carb and then linkage to the other, but in the end I went the route of twin cables. At first I tried fabricating my own - big waste of time. In order to circumvent the length issue, I ordered a choke cable for a PI TR6 from Rimmer Bros and had it here in a week. Lots of length, looks like stock.
Regards
Geoff
Geoff P

The SU's are installed now and I'm tweaking them. The idle is rock steady, but I may have them too lean (used a starting point of two complete CW turns on the jets from full up). I know every engine is different, but about how many turns or flats rich are you running? I want to be in the ballpark before I read plugs or Colortune.

Also, the two holes in the top part of the air filter housing flange: what purpose do they serve? I reused my stock filter housing and those holes are now covered up.

Thanks.

Rick O.
Rick Orthen

This thread was discussed between 27/08/2002 and 07/10/2002

Triumph TR6 index

This thread is from the archive. The Live Triumph TR6 BBS is active now.