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1500 midget carb replacement
- Thread starter bcbug
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bthompson
Jedi Warrior
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+1...
Single HS4 is the way to go. Uses the same manifold and all. (The Brit-spec dual SUs for the 1500 need the hard-to-find manifold to match, and there are some minor clearance issues with the inner fender.)
If I hadn't've already chucked my Zenith for a Weber, I'd've gone the HS4 route. The Weber isn't <span style="font-style: italic">really</span> bad; but it's not British.
Single HS4 is the way to go. Uses the same manifold and all. (The Brit-spec dual SUs for the 1500 need the hard-to-find manifold to match, and there are some minor clearance issues with the inner fender.)
If I hadn't've already chucked my Zenith for a Weber, I'd've gone the HS4 route. The Weber isn't <span style="font-style: italic">really</span> bad; but it's not British.
SilentUnicorn
Yoda
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Twin hs4. available from quantum engineering with manifold. you do have to notch the inner fender a bit. not a real biggie. But i like the look of the twins.
https://www.quantumechanics.com/categories.php?op=newindex&catid=5
m
https://www.quantumechanics.com/categories.php?op=newindex&catid=5
m
dklawson
Yoda
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John-Peter, the HS4 is the 1-1/2" carb. The HIF44 (44mm) is a larger 1-3/4" carb. Did you mean HS4 and/or HIF38 (38mm)?
John-Peter and Bill... what needle are you running in the HS4 carb? Surely the standard MGB needle will be too lean when running a single carb on a 1500. An MGB running duals means each carb would have a needle sized to support about 900cc, not the 1500cc of a late Midget or Spitfire.
I've installed a single HS4 on my project '72 Spit but I know I'm going to be going to a richer needle than what I have... perhaps an AAA needle.
John-Peter and Bill... what needle are you running in the HS4 carb? Surely the standard MGB needle will be too lean when running a single carb on a 1500. An MGB running duals means each carb would have a needle sized to support about 900cc, not the 1500cc of a late Midget or Spitfire.
I've installed a single HS4 on my project '72 Spit but I know I'm going to be going to a richer needle than what I have... perhaps an AAA needle.
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dklawson said:
So, if you need to see the chart here it is https://tinyurl.com/y9vowwj
Basically an HS4 and a H144 are both usable. I only have experience with the HS4 and it works fine. The needle I have is size 5 - (I know but it's an old carb hence only one number) and somewhere Hap endorsed this size as usable. works fine for me. The book that I have borrowed on SU carbs suggests a needle size of ABT. I've also seen the AAA suggested but I don't know why. Don't know what else to add except to say so far so good with mine.
there are also computer programs you can use
winSu springs to mind
dklawson
Yoda
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Thanks John-Peter. I haven't seen that chart before and have been relying on books and verbal recommendations. Various people who claim experience and/or have the WinSU computer program have suggested the ABT and the AAA needles. That never made sense to me as I've seen the AAA needle recommended for single carb applications ranging from 998cc to 1500cc. I just don't understand how one needle and .090" jet HS4 can cover that much range.
I'll look up the profiles of the 5, ABT, and AAA and see which profile looks most promising compared to what I have now. I appreciate your suggestion and also your mentioning that Hap likes the "5".
Thanks again.
I'll look up the profiles of the 5, ABT, and AAA and see which profile looks most promising compared to what I have now. I appreciate your suggestion and also your mentioning that Hap likes the "5".
Thanks again.
SilentUnicorn
Yoda
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FYI
My twin carb set up came with ABT needles. seem to work just fine.
mark
My twin carb set up came with ABT needles. seem to work just fine.
mark
dklawson
Yoda
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SilentUnicorn said:
Well that's the sort of thing I find confusing. I know the 1500s sometimes are outfitted with the Euro-spec twin HS4s. If you have two HS4 carbs feeding a 1500, I don't see how the same needle can still be the appropriate choice when you have a single carb on the same engine. However, I guess it all depends on the piston lift for a given engine speed.
I forgot that I had the link below bookmarked. It may be of interest to some of you. It's a program where you key in your SU needle number after selecting the carb type. You can enter up to 5 different needles and it will graphically show you their profile relative to one another. It gives you an idea how rich or lean needles are relative to each other. For example, the #5 and the AAA needles are actually identical for the first 5/8" of their profile after which the #5 needle will run a bit leaner. Of course... the #5 is a fixed mount needle while the AAA is a spring loaded needle. But you can still compare them.
https://www.mintylamb.co.uk/suneedle/
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bthompson said:Considering it's replacing a Zenith, you could run with a paper clip and it would still be an improvement.
now now, paper clips are notoriously difficult to tune, in part because they are very difficult to mount tightly and correctly unless you attach the proper paper gasket, and, they run very lean - too much air getting through.
dklawson
Yoda
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This '72 Spit is my first exposure to the "late" style ZS carbs... there IS another style.
On my '67 GT6 there are a pair of EARLY ZS carbs. They do NOT adjust the needle from above and they do NOT have a bunch of emissions air bleed things on the side. The early ZS CD carbs (CD2 ?) are VERY much like a melding of the SU HS and HIF series. They have fixed needles, jets that adjust from below, and an integrated float bowl.
When I heard people complaining about Strombergs I didn't understand it since the GT6 carbs were SO much like the HS2s and HS4s I'd worked with. Then... I bought the Spitfire and it was all clear to me.
The links below are not to my carbs but to someone else's early GT6. Note that the brass adjusting nuts for the jets are visible below the integrated float bowls. Those are GREAT carbs. I've been very pleased with them on our GT6 and I wish the design had been retained by ZS.
https://www.sportssix.info/images/blog/manifolds/orig.jpg
and the link below is a bottom view of a 175 CD2 carb
https://www.naimy.net/forsale/images/175%20CD-2%20STROMBERG%20SIDE%20DRAFT%20CARB.%20002.jpg
In short, not all ZS carbs are the same... or bad.
On my '67 GT6 there are a pair of EARLY ZS carbs. They do NOT adjust the needle from above and they do NOT have a bunch of emissions air bleed things on the side. The early ZS CD carbs (CD2 ?) are VERY much like a melding of the SU HS and HIF series. They have fixed needles, jets that adjust from below, and an integrated float bowl.
When I heard people complaining about Strombergs I didn't understand it since the GT6 carbs were SO much like the HS2s and HS4s I'd worked with. Then... I bought the Spitfire and it was all clear to me.
The links below are not to my carbs but to someone else's early GT6. Note that the brass adjusting nuts for the jets are visible below the integrated float bowls. Those are GREAT carbs. I've been very pleased with them on our GT6 and I wish the design had been retained by ZS.
https://www.sportssix.info/images/blog/manifolds/orig.jpg
and the link below is a bottom view of a 175 CD2 carb
https://www.naimy.net/forsale/images/175%20CD-2%20STROMBERG%20SIDE%20DRAFT%20CARB.%20002.jpg
In short, not all ZS carbs are the same... or bad.
dklawson
Yoda
Offline
I don't think the Strombergs are really that much shorter Doc. The dashpot knob of the Stromberg ends up being almost as tall as that on the SU in the end. I think when you throw the air cleaner/filter housing into the equation the Strombergs end up being a bit shorter though.
Regarding the diaphragms, I have yet to have one fail but everyone has told me that the new ones aren't made the same as they used to be. If the new ones are coming from China I certainly can understand the problems people are having with them. A buddy of mine prefers the Strombergs because in his eyes, when the diaphragm fails you know what's wrong and can easily fix it yourself (his words, not mine).
Regarding the diaphragms, I have yet to have one fail but everyone has told me that the new ones aren't made the same as they used to be. If the new ones are coming from China I certainly can understand the problems people are having with them. A buddy of mine prefers the Strombergs because in his eyes, when the diaphragm fails you know what's wrong and can easily fix it yourself (his words, not mine).
tweety
Jedi Trainee
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Now I really want rid of my Zenith.....
I have a '79, CA car. I don't think the Governator allows any changes like this.....
So every two years I would have to put the Zenith on, get it to pass smog and then put the SU back on?
There was a single SU on Ebay earlier this week, I think it went to $50. I was too cheap to bid any higher. I'll probably regret it.
I have a '79, CA car. I don't think the Governator allows any changes like this.....
So every two years I would have to put the Zenith on, get it to pass smog and then put the SU back on?
There was a single SU on Ebay earlier this week, I think it went to $50. I was too cheap to bid any higher. I'll probably regret it.
