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948 carb on 1275?

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Z

zimasprite

Jedi Hopeful
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Hey guys,

Would it work to put a carb from a 948 on a 1275? I have rebuilt carbs for a 948 and when I was tryig to hook up the choke cable on my "new" 1275, the dashpot things were really sticky. The ones for my 948 are nice and smooth.

Thanks for any help.

Also, I'm looking for some parts to finish off the dash. Need some of those spring retainers for switches(light switch and hazard switch), new heater control switch, flasher arrow, one of those U-shaped guage retainers and holding screw for fuel guage. If anyone has anthing, let me know. I'm going to head out to my local british car specialist and see what he has lying around.

- Drew
 
It would run but intake manifold would not match. When you got em hooked up you would find you have lost at least 10 and maybe as much as 20 HP. No way it would have any real RPM to speek of, they are much smaller.
 
Well, I have the intake from my 948 also, but I doubt using that would solve the HP loss. Guess I'll just try rebuilding the ones off of the 1275.

Thanks - Drew
 
I can rebuild those HS2 carbs to like new condiiton, give me a shout if interested.
 
The later 948s had 1 1/4" carbs, the same size as the 1275s. I think Jack is referring to the 1 1/8" carbs used on the Bugeye. I am using my 948 carbs with a 1275 with no problems. I was using the 948 intake until I realised I need the inlet for the PCV. At this time the jets seem OK, if anything it's running a bit rich. You will need to use the 1275 intake so you can connect the crankcase ventilation.
 
Did not know that 1 1/4 carbs were ever used on 948s.

Live and learn I guess.
 
Only the MkII Sprite and MKI Midget with the 948 had the 1 1/4" HS2s. They do not have the brass levers and caps like the BEs. There were not that many made since the 1098 was introduced in the later MKII Sprite.
 
sorry, I wasn't specific. My 948 is out of a 62 MK II Sprite. They aren't the bugeye carbs. They have the notation AUC990F I believe. The ones on my 1275 say AUD266F. They look identical to me. That doesn't mean the jets/needles are the same though. I'll give er a shot while I'm rebuilding the ones from the 1275 I guess. Can't hurt to have a spare. Who knows, maybe I'll get to rebuilding the 62 one day!

Thanks!!! - Drew
 
I cleaned up the 1275 carbs today. They were all gummed up. The jets don't seem to glide that well in their housing. I think the arm that directs it(for choking) isn't pushing it in a straight line. I added a small washer or two between the arm and jet and it seems to work better.

If I can't get them tuned well, I'll try the ones from my 62 MKII. They don't have that spring loaded thing on the butterfly throttle valve though...whatever that is.

I'll start it up tomorrow and try to tune it.

- Drew
 
If you decide to fit the 948 HS2(s) to the 1275, you should change the needles. If you don't have an SU needle selection table/book just post again and any number of us can make some starting suggestions.

EDIT: Or taking the obvious approach... clean and remove the needles from the 1275 carbs and fit them to the 948 carbs... since you already have them.
 
personaly I think the HS2s to be much more difficult to build than than the HS4 or HIF4 you see on the MGBs, the samller HS2s get alot of liitle problems you don't see with the bigger carbs, I build alot of carbs every year (50 sets or so) her'e some of the problems i see the HS2 give.

The HS2s h as no bushings in the carb body, they don't normally tend to wear the aluminim of the carb body but rather the throttle shaft itself wears badly over time, ever HS2 set I buld gets new standard shafts.

The butterflies get wear on the linkage side of the sahft, making the butterflies stick, i always replace butterflies on HS2s, you can change over any poppet valve butterfly SU carb to a solid butterfly, this is waht i do when building the later model HS2s

Because the throttle shaft diameter is so samll ina HS2, you have to be very careful when tightening up the butterfly on the shaft, taking baby steps tightening going frm one screw to the other, it's real easy to overtighten a butteffly screw and warp the shaft. Alway red locktite the butterfly screws, don't rely on the bottom split to keep them put.

The jet bearing can wear over time and get a little crooked on it upper face, if it does this no eedle alignment tool will save you, you have to re face the jet bearing on a lather or easier, just get a new jet bearing form Joe Curto. This is a much greater problem as for the solid needle carbs vs the spring needle carbs. If you just doing a clean up rebuild, leave the jet bearing in palce if everyhting line up now, disturbing it will only make you curse later /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

On the choke linkage arm, there should be a small bushing that goes the hole on the bottom arm, real easy to lose, alot of time if this is not put back on the arm, it will put a side load on the jet, making it stick.

There's alot of little trick like this to HS2s and of all the SU HS series carbs they are the most difficult to get right.
 
WEll, I checked the compression on all cylinders and they were all 145-165, so that checked out fine. Put the carbs back together and installed. Cranked up pretty quickly and after a few turnes of the idle screws and minor jet adjustments, the idle seemed to be pretty good. The springs don't seem to bring the throttle back to lowere RPM's very well, so I put a slightly stronger spring. Works better now.

So far, so good!!
 
Ahhhhh, progress.
 
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