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SU on a 1500 - anyone done this?

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JPSmit

JPSmit

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While my Zenith Stromberg is being checked out, I'm looking to the future. I know the most common is the weber - but it's $360+ on ebay. If I put an SU on, I presume it would be cheaper. It would certainly be easier. I've had an offer to make an adapter but, I'm not sure what would be involved. thoughts anyone?
 
SUs and make it sing.
 
Stay far, far away from those lousy weber downdraft carbs.

Several people on this forum have fitted a single HS6 I believe. And you could always go for a euro-spec setup with twin HS4's, but that will most likely cost you much more than $360... and you have to cut some metal on your car to make it fit.
 
I considered twin SU's - there was even a pair on ebay when we went to Scotland - then I looked at Ms Triss's freshly painted frock and though - nah!

I know nothing about SU's - is there any range of models? Are they all the same? Interchangeable with MGB? Inquiring minds need to know
 
Check with Scott (blkcorvair), he managed to do this. You'll have to see how he did it, but I saw some pictures of his install. I had bought a set of SU HS4s to try it on mine, but found they didn't quite line up with the studs, so I sold them to Scott and he managed to do a single HS4 installation. My guess is he had to enlarge the mounting holes on the SU to make it fit. A dual HS4 setup can be done if you can find the manifold, but the body has to be doctored to make room for the rear carb.
 
While I was in England for the 50th, I took this picture of the factory modifications necessary for the double SU on the 1500 engine
https://i183.photobucket.com/albums/x288/frogeye61/Spridget-50/P1010763.jpg
Otherwise a single should go onto a Stromberg manifold fairly easily. Just have to get one with the right flange, and maybe a spacer. The general flange shapes are 4 bolt, two bolt diagonal (both left and right) and two bolt vertical. Different carbs have different bore diameters and different bolt spacings. I think the 1500 had a 1 1/4 inch carb (you might want to check this), measured at the throttle side, as the inlet side is slightly larger. A 1 1/4" SU would have a last digit of 2, denoting 2/8 inch. ie HS2
 
The stock carb on my '79 1500 is 1 1/2" on the throttle side and 1 3/8" (roughly) on the air filter side. Weird, huh?

You would definitely want to go with at minimum an HIF4 or HS4.

However, the problem with any carb swap is jetting. Jetting (or needling as the case may be with side draft carbs) is a dark art and there are few practitioners left thanks to the ubiquity of fuel injection in modern cars. In other words, swapping carbs can lead to endless tweaking, changing and adjusting. And there is a distinct possibility that you will never get your car running right.

There are quite a few drawbacks to the stock carb. The main complaints being that it is difficult to adjust, and that it tends to run very rich (a symptom of the water choke design). But with a stock carb, you at least have a clearly defined basis to start out with. In other words, you can go back to the factory settings and expect the car to at least work, even though you may be haunted with the feeling that your car COULD be better.

By swapping carbs, you COULD improve the performance and economy of your car, but you could also open a Pandora's box of adjustments and configurations that you may never be able to close again.

Just my 2¢.
 
I had an HS4 (like on an older MGB, but mine came from an old Volvo) on my 1500 Spridget when it was a street car.
It was fine....no problems.
Easy starting, good fuel economy, etc.
The bolt pattern for the HS4 is slightly different so I had to "slot" the holes with a rat-tail file. It was easy.

I didn't even have to rejet or change the piston needle. I just messed around turning the jet-nut until it ran good (normally on an HS4, the main jet-nut is turned all the way "up" and then turned down two full turns or "12 flats".....that will get you close and you can play with it from there).

Depending on what car you get it from, the float bowl may sit at an angle. It will run with the float bowl as-is, but it's easy to re-angle if you want.

The HS6 or HIF4 will work too...I've seen them fitted but do not know the details on those.
 
It's probably not actually lousy. I just have a big problem with downdraft carbs on English cars.

Since participating on this forum, I have noticed quite a few posts about troubles with the weber downdraft. So it seems to me that contrary to the marketing, the weber is not the bolt-on solution to all your carburation woes.
 
Ive been down that weber road. Always needed constant finetuning and adjustmnet to keep it running smooth. Finally tossed it for a single 1 1/2" HS4. Never would bolt up anything else. You do have to Enlongate the holes abit to make it fit but definatally nothing major, I even fabbed a thin heat sheild out of some spare aluminum sheet I had. Im using this for racing and it works amazing. Even on a worked up 1500 the HS4 supplies plenty of power and I tuned it simply by spinning the needle down on a drill press. I went the extra step of fine tunig it with a wide band sensor. Sent the carb to Jeff Payalpa of Micro Polishing and for $110 I got a better than new HS4.

IMG_2215.jpg


DSCN0349.jpg
 
I'm planning to convert my Spit 1500 to dual SUs. I bought a used intake/HS4 set and brought them back from London a couple of weeks ago. Also found a brand new manifold on eBay.

Just need to send the whole deal off to Paltech for rebuilding/polishing. The extra (used) manifold will go to eBay, probably this weekend. I do not have the throttle linkage, but that's easy/small enough to source from the UK.
 
There is a single carb intake for the 1500 that has larger runners and is better for the single carb SU conversion ona Spitfire of Midget. It think it came on the Triumph Toledo. You are likely going to have to try getting one from the mother country. I've been checking around a very little bit, but no luck so far. I have a twin carb set up that I need to get to work on. I'm still needing help with the exhaust manifold.
 
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