Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties S U Carb

S U Carb

Moderators: Curt!, Pa

Post Mon Jan 13, 2014 3:06 am

Posts: 19
Another little snippet. I've run an 1 1/4" SU carb on my 45" for many years, and I'm very pleased with it, it does however run somewhat rich, anyone else run an SU?, if so, what needle do you use?.

Post Tue Jan 14, 2014 5:58 am

Posts: 1608
More details please? I've had an SU on the shelf for years and don't know how to set it up...
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Tue Jan 14, 2014 1:41 pm

Posts: 19
Seems it's not such a common conversion then.?.
It's a NOS SU 1 1/4" as I remember, but I'll check, with a separate float chamber, made up an adaptor to mount it on the stock Linkert manifold. Throttle was no problem, I used the little bracket that clips on to the brake rod to in effect give you a handbrake, OK, not clear, it has a wing nut, you move it up the brake rod and clamp it in position on the brake rod so it's kind of like a handbrake, to hold the throttle cable on the manifold bolt, used the original throttle cable with a made up lever on the end of the carb throttle shaft. Choke is a shortened BMC mini choke cable. It comes through the cylinders and is between them on the other side from the carb. Mounted it on the head steady bolt. Fuel pipe was a cut back repro stock one with the end cut off close to the float chamber then a bit of rubber fuel pipe clipped on. Air filter was a repro round Harley one just re drilled to bolt onto the SU, when it's fitted you can hardly see the carb.From the word go it was a huge improvement on the Linkert, which at the time was also NOS. Much more responsive, and even though it's running rich (plug is black) was still doing over 70MPG on a run. Starting was also a breeze. I highly recommend one. I have a new Mikuni I bought from the 45 resto company but haven't fitted it because the bike was running so nicely. My only problem was the idle was a little high, I think I had an air leak. Oh yes, I blocked off the vacuum take off which is used for an advance retard . Hope thats clear?, please ask specific questions and I'll try to answer.
I like SU carbs, they are simple, I even fitted one to my old Renault 4TL, worked a treat.
I'll go out and find it tomorrow and take a few snaps if you want.


Post Tue Jan 14, 2014 9:18 pm

Posts: 1608
I've seen them occasionally ( there was a much-photographed yellow 45 that Ray Leon built in the 70s so fitted ) but I've never had experience of one. Amals were always preferred over here, I suppose because they were freely available and everyone understood them.

Are there no internal changes or adjustments? Or is it just a bolt-and-go set-up?
Shoot, a man could have a good weekend in Dallas with all that stuff...

Post Wed Jan 15, 2014 2:31 am

Posts: 19
Yep, I just bolted it on and away you go!. I've done a lot of miles on it, about 45K on this carb, been to Holland, Germany, France, all over, most miles done up in the North of Scotland and commuting, my 45" was my only transport for many years all year round, that explains why it was so rusty!. A good bike in the snow though, nice and low, wide bars.
Last edited by Bison on Thu Jan 16, 2014 9:45 am, edited 1 time in total.

Post Thu Jan 16, 2014 3:59 am

Posts: 19
Hopefully a photo of the carb and manifold here.
The first SU I had fitted was a left hand carb, IE, the flange was mirror image, so rather than making a new manifold I just made the square adaptor plate. ... 151205.jpg


Post Sun Jan 26, 2014 1:45 pm

Posts: 367
Location: Bergen, Norway

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