Su carbs 1 1/8 to 1 1/4

[sim]

Hi
Is is it possible with out modifying too much to get 1 1/4 su carbs to fit where the 1 1/8 were.
I am also thinking of switching to Weber Downdraft Carburetor Kits from moss part number 222-275
Any reviews on this carb?
thanks
sim

 

[AN5Sprite]

Easy to go up to 1.25". You need the HS2 intake mani/heat shield also to go with the carbs.

 

[Rut]

Rod,
just as Steve says, very easy swap. You can find carbs/manifold on eBay for very little if you are willing to rebuild them. I also have a Weber on a Pierce manifold that will be sold in the next month or so. It has the PCV port fitted to the manifold boss and works ok...in like new condition.
Rut

 

[sim]

Rod,
just as Steve says, very easy swap. You can find carbs/manifold on eBay for very little if you are willing to rebuild them. I also have a Weber on a Pierce manifold that will be sold in the next month or so. It has the PCV port fitted to the manifold boss and works ok...in like new condition.
Rut

Is this the down draft? Not sure what a Pierce manifold looks like but there is the net. how much do you want for it?

 

[Jim_Gruber]

Rod,
i'd you to a classic Motorsports article from several years back that compared SU vs Weber performance on a 1275. For a flat all out race engibe that spends most of it's time above 6000 rpm the Weber had a slight performance difference. For street use difference was negligible. And if you think the problems you've had getting your SU's dialed in have been bad, just wait until you've got to deal with a Weber. There is no magic bullet other than turning to the more expensive page in the catalog to forced induction. HP costs $. IMHO of course. Ask Trevor about Ugly Bug.

 

[Rut]

Rod,
Scroll down to the 1275 listing for genuine Weber with manifold. New is $339.95 and I'll let mine go for $175. As noted it has the port for the PCV valve that theirs don't. Personally I would buy a set if used HS2s with manifold and rebuild them.
This particular set up worked well on a 1275 that was bored .060 over, 276 cam, with a little head work and 12:1 CR, but didn't like street gas...go figure!
Rut
https://www.piercemanifolds.com/category_s/85.htm

 

[nomad]

I know of no one that has been happy with the Weber downdraft on a street motor. Some folks like them on MGB's and some don't. I had one that came on a car I turned and it would run great but the car came with a bucket full of Weber jet's and venturi's that the previous owner had used to get it to run. Gas literally ran through it and MPG was below 20.

Kurt.

 

[sim]

Rod,
Scroll down to the 1275 listing for genuine Weber with manifold. New is $339.95 and I'll let mine go for $175. As noted it has the port for the PCV valve that theirs don't. Personally I would buy a set if used HS2s with manifold and rebuild them.
This particular set up worked well on a 1275 that was bored .060 over, 276 cam, with a little head work and 12:1 CR, but didn't like street gas...go figure!
Rut
https://www.piercemanifolds.com/category_s/85.htm

HI
Thanks for the advise would this one on ebay be a good choice? https://www.ebay.com/itm/390720913881?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

 

[sim]

I know of no one that has been happy with the Weber downdraft on a street motor. Some folks like them on MGB's and some don't. I had one that came on a car I turned and it would run great but the car came with a bucket full of Weber jet's and venturi's that the previous owner had used to get it to run. Gas literally ran through it and MPG was below 20.

Kurt.

Thanks this puts the Weber idea in the trash. sure looks like a good carb from the outside

 

[AN5Sprite]

HI
Thanks for the advise would this one on ebay be a good choice? https://www.ebay.com/itm/390720913881?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT

Personally, I'd say no and pass on these.

 

[sim]

Personally, I'd say no and pass on these.

A little more help. what do you see that will cause problems?
Thanks
sim

 

[glemon]

I am not the guy who said pass on these, but I agree with him, if they were used on a race car they may have been modified in some way (and you probably won't know what it is) such as very rich needle or some modifications that may increase flow, but not do anything for having a steady idle for instance. I think you would be better off buying some much cheaper used carbs off a stock set up, although the velocity stacks are kind of cool.

 

[AN5Sprite]

Rod,
Look for a PM in a few minutes.

 

[sim]

I am not the guy who said pass on these, but I agree with him, if they were used on a race car they may have been modified in some way (and you probably won't know what it is) such as very rich needle or some modifications that may increase flow, but not do anything for having a steady idle for instance. I think you would be better off buying some much cheaper used carbs off a stock set up, although the velocity stacks are kind of cool.

I just braved a non running blackwidow infested 59 sprite that I have had for some time.
Think I bought it in 1974. I have been saving it and using a part now and then. Today I just removed the intake manifold with carbs. I think a little cleaning and adding some missing screws will bring these back to very good usable condition. The throttle shafts are nice firm. May change out the float bowl seals.

 

[Rut]

Rod,
the H1s in your picture won't do much for your engine and the ones posted on eBay are ridiculously high. You should be able to find a set of decent HS2s with manifold and heat shield for under $100, but they will need a rebuild. You don't say what your budget is, but figure $100 for the carbs and $120-$150 for the parts to put them right. These are easy to rebuild if you take good pictures, do one at a time, have the SU rebuild instructions, and a genuine SU master rebuild kit. No special tools are needed, but I would buy a gallon can of carb cleaner(kind you soak in, like Berrymans) and soak them until they look new.
Rut

 

[sim]

Rod,
the H1s in your picture won't do much for your engine and the ones posted on eBay are ridiculously high. You should be able to find a set of decent HS2s with manifold and heat shield for under $100, but they will need a rebuild. You don't say what your budget is, but figure $100 for the carbs and $120-$150 for the parts to put them right. These are easy to rebuild if you take good pictures, do one at a time, have the SU rebuild instructions, and a genuine SU master rebuild kit. No special tools are needed, but I would buy a gallon can of carb cleaner(kind you soak in, like Berrymans) and soak them until they look new.
Rut

About how much performance boost will the HS2 give?

 

[Rut]

Rod,
I've forgotten what the book states, but it was enough that they went with the HS2 after the Bugeye. To me the HS2 is easier to rebuild and get right. I really like the HS2s with the PCV ports/Y connection and floating needles.
Rut

 

[Gerard]

I know of no one that has been happy with the Weber downdraft on a street motor. Some folks like them on MGB's and some don't. I had one that came on a car I turned and it would run great but the car came with a bucket full of Weber jet's and venturi's that the previous owner had used to get it to run. Gas literally ran through it and MPG was below 20.

Kurt.

There's absolutely nothing wrong with the downdraft Weber if it's jetted correctly. I always use one on the Datsun 210 conversion in Morris Minors and they are simple to keep in tune and operate flawlessly. The problem with putting one on an A-serties engines is that they are never jetted right out of the box, even for a 1275. I had one on my '72 Midget with a mildly tuned 1275 and it had the typical flat spot everyone complains about. I changed to one size smaller needle than whatever was in there and it ran perfectly after that. I think the lack of the same "sex appeal" of twin carbs is more a factor in people objections. There's nothing wrong with the SU's of course, and once you know what you're doing as far as keeping them balanced and in tune, they are just fine. The problem is, most people don't know how to do that correctly or are just too intimidated by the whole process and avoid it.

The best option I have found, especially for a street car however, is to use a 1-3/4" single carb. I've done this swap many times and it is a big improvement in every way over HS2's, again, except perhaps on visual appeal. It's the way to go if you want simplicity and improved performance, but it does of course require different manifold and heat shield. Adding a header if you don't already have one is a good thing too.

 

[sim]

There's absolutely nothing wrong with the downdraft Weber if it's jetted correctly. I always use one on the Datsun 210 conversion in Morris Minors and they are simple to keep in tune and operate flawlessly. The problem with putting one on an A-serties engines is that they are never jetted right out of the box, even for a 1275. I had one on my '72 Midget with a mildly tuned 1275 and it had the typical flat spot everyone complains about. I changed to one size smaller needle than whatever was in there and it ran perfectly after that. I think the lack of the same "sex appeal" of twin carbs is more a factor in people objections. There's nothing wrong with the SU's of course, and once you know what you're doing as far as keeping them balanced and in tune, they are just fine. The problem is, most people don't know how to do that correctly or are just too intimidated by the whole process and avoid it.

The best option I have found, especially for a street car however, is to use a 1-3/4" single carb. I've done this swap many times and it is a big improvement in every way over HS2's, again, except perhaps on visual appeal. It's the way to go if you want simplicity and improved performance, but it does of course require different manifold and heat shield. Adding a header if you don't already have one is a good thing too.


View attachment 33888

That set up looks nice. thanks for the info of rejetting. I do have headers on it. I guess the best solution on getting the correct jet would be to add a Co2 sensor at the end of the header. With that it is easy to see what to do

 

[nomad]

Well, Gerard, you have far more expertise in the spridget area and I agree with you 100%. The Weber I'm sure will work if jetted right but not very well out of the box. As to the 1 3/4 SU, that is what I'm running on my Datsun engined Midget. BMC used them on 80hp 1800 engines so it work's well and is so easy to tune and keep in tune.

Kurt.