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Replacing carburator on Midget

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bcbug

bcbug

Freshman Member
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I am replacing the stock carburator on my 76 Midget with a SU HS4. What would be a good needle to use? I am going to remove the smog equipment at the same time. Any suggestions?
 
You might check with blkcorvair, he did such a conversion. I had planned on it, but I wasn't up to doctoring the mounting holes and throttle linkage and ended up selling him the carbs. He said it wasn't too hard, but you do have to cut the sides out of the mounting holes (think of a "U" slot) to fit the studs. I believe he said he didn't change the needles, and it worked pretty decently. They were AUD465 if I remember right, which would fit a '71 MGB.

Welcome! :cheers:
 
I have an HS4 on mine - still has the original needle and works OK - the needle is getting old so has a few nicks and will need to be changed. AAA or ADT is what has been suggested - the comparison is below but I have nio idea what it means. The HS4 is a little big for a 1500 so my mechanic needed to put a plate partially covering the air intake to get it to run right. Mine is from the back of an MGB pair and it took 10 minutes to open the holes enough to fit.
 
When I put my first Midget on the road around 1987 it was built up from the remains of a Sprite, two Midgets and an Austin America. I used the head and single HS-4 off the America but it used a one piece intake/exhaust maniford. I cut the exhaust part off to clear the standard Midget manifold...as I recall the car ran really well at low end. I still have that manifold/carb too...I should try it again :smile:
 
JPSmit said:
I have an HS4 on mine - still has the original needle and works OK - the needle is getting old so has a few nicks and will need to be changed. AAA or ADT is what has been suggested - the comparison is below but I have nio idea what it means. The HS4 is a little big for a 1500 so my mechanic needed to put a plate partially covering the air intake to get it to run right. Mine is from the back of an MGB pair and it took 10 minutes to open the holes enough to fit.
Click to expand...

JP, can you put an ABT needle on that chart? those are what come with the euro spec twin carb setup for a 1500. I have a pair of hs4's on my 1500 and they work very well. I find it hard to believe that a single is too big for a 1500...


mark
 
Try some of these sites for needle comparison:

https://www.mintylamb.co.uk/suneedle/ -free web based

https://www.winsu.co.uk/ -software you download. One version is free and the other cost 10 pounds

https://www.teglerizer.com/suneedledb/index.html

Good luck. Also below is recommendation for dual HS-4 setup. Don't know if that might be helpful.

Needle Suggestion ID No. Part No.
Standard Early ABT CUD1041
Standard Late ADT NZX4013
With K&N Filter & Sports Exhaust AAQ CUD1014
With K&N & Sports Exhaust Lean AAT CUD1017
As Above + Modified Head AAM CUD1011
As Above + Modified Head Lean AAB CUD1001
AS Above + Camshaft
With Road 83 Camshaft AAB CUD1001
With Fast Road 83 Camshaft AAL CUD1010
 
Mark, I added the ABT - Let me emphatically add that I still have no idea how to actually read this chart. Therefore I have no idea what it means. If someone could let me know what these numbers actually mean and therefore help me choose a needle, I would be insanely happy.
 
JP,
i will give it shot. needles have 16 stations. These are defined points on the needle with defined diameters. larger diameters will be leaner and smaller are richer- at any given point(station). Numbers on the graph bottom are the stations. The numbers on the vertical side of the graph are diameters. The leading zero is missing (836 is really .0836 inches)

Here is a page with a visual. Also here is a Link to a excel based needle selector. I just found this myself and have not had a chance to dissect it yet but you may find it helpful in trying to pick a needle.

HTH

m
 
SilentUnicorn said:
JP,
i will give it shot. needles have 16 stations. These are defined points on the needle with defined diameters. larger diameters will be leaner and smaller are richer- at any given point(station). Numbers on the graph bottom are the stations. The numbers on the vertical side of the graph are diameters. The leading zero is missing (836 is really .0836 inches)


m
Click to expand...

that I sort of get. what I don't get is how the station numbers relate to actual performance. which is to say, do I want a needle profile that runs up the middle of the chart? lower than 45%? higher?

that's what I don't understand?
 
JPSmit said:
that I sort of get. what I don't get is how the station numbers relate to actual performance.
Click to expand...

depends on whether you want to run rich or leaner. My ABT needles are richer than the other two you have charted. Higher on the chart = richer. ANd i am running two hs4's, header, HD muffler and a road cam. It all depends on how your engine breathes and how you would like to drive it.

Are you having troubles?

m
 
SilentUnicorn said:
JPSmit said:
that I sort of get. what I don't get is how the station numbers relate to actual performance.
Click to expand...

depends on whether you want to run rich or leaner. My ABT needles are richer than the other two you have charted. Higher on the chart = richer. ANd i am running two hs4's, header, HD muffler and a road cam. It all depends on how your engine breathes and how you would like to drive it.

Are you having troubles?

m
Click to expand...

always having troubles - Oh you mean with the car. I need to replace the needle just cause mine is old and not as smooth as it once was - so, would an AAA (from the chart) make the most sense? as it goes tight up the middle - average as it were
 
Just bought new needles for my HS2's. Keep it simple! Call Joe Curto, tell him what you have done to the motor and drive train and he will recommend a needle for you. Went from ABC's to AAL's. I have not installed them yet.
 
Dadandson said:
Just bought new needles for my HS2's. Keep it simple! Call Joe Curto, tell him what you have done to the motor and drive train and he will recommend a needle for you. Went from ABC's to AAL's. I have not installed them yet.
Click to expand...

Excellent Advice


m
 
As you try this conversion please, please post your results.

My Spitfire is a 1300 and has the same single Stromberg ZS carb that should be on your Midget. I picked up a dual HS4 carb/manifold setup for it but I really am not ready to put that on the car as I'm preparing it for my son so I want to stay with an easier to adjust single carb.

I think any SU is simpler than a smog era Stromberg so I bought a used Spitfire manifold and a late model single HS4 (originally from a Mini). The carb is so late that it's got the WaxStat jet and spring loaded needles.

I found that a few 1300 TR engines in Europe were fitted with single HS4s. I am fortunate that I have in my collection of parts a couple of needles "close" to the profiles used for stock tuning of those European TRs. I also believe I have a needle comparable to what would have run in an Austin America. That gives me perhaps 3 needles to try. Hopefully one will work well enough but as you make this conversion to your Midget I would be VERY interested to know what works for you.

EDIT: I have never talked with Joe Curto. I know he's the SU/Stromberg guy and by all accounts knows his stuff. However, what we're talking about here is fitting a non-standard carb to an engine. Joe Curto may be able to make some educated guesses but this may also be too non-standard for him to offer advice.
Regarding the needle charts, as mentioned above, the needles have "stages" and each point is 1/8" down from the one before it (that's the X-axis). The charts usually go all the way to zero and start there by specifying the diameter of the needle right at the shoulder. The diameter of the needle (in thousandths of an inch) is the Y-axis. Keep in mind that an HS4 will have a throat diameter of 1.5" (12/8") so, any diameter information on the charts after position #12 (or #13) will have no importance as higher stages of the needle never become even with the entrance to the jet.
 
Also keep in k9nd with the HS4 there were solid needles in the earlier HS4s, a #5 was stock for a MGB, that wouldn't be a bad pale to start with a single on a Midget 1500, and then later the HS4 used the biases, or spring neelde, and the number earlier quoted here were for the biased needle, which you may or many not have depending on what SU HS4 you have.
 
I almost certain mine is a #5 - Hap you're the first person who has acknowledged that there is such a thing (as opposed to the 3 letter code) - should I just stick with it? can I buy a replacement?
 
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