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Thread: HD8 carb on Healey 3000

Forum to discuss Austin Healey Sports Cars

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    HD8 carb on Healey 3000

    Hi, I normally post on here about my Healey 100. But this week I had a friend come round with his Healey 3000 for a tune up. Something does not make sense. In the SU book page 44 it quite clearly says the HD8 has to have a dustproof damper as internally vented. But on page 106/107 the details for the BJ8 clearly says UH needle and AUC8112 damper which has a vent. I.e. non dust proof. It also says a very heavy spring AUC4826 called the Red/Green 11.25oz. To get the car to idle properly with 15 BTDC the jets are very high almost on the bridge only about one to one and a half turns down, but plugs still look too rich !!!! This all seems very odd to me, as my other car is a Jaguar XK120 with two HD8ís. In that case I have the jets set at 0.07 down which is about two and a half turns. The needles are slightly richer UNís. The damper is the correct dust proof and the spring is the lighter Blue/black 4.5oz.

    What is the explanation for this strange combination, from an SU or tuning expert. I canít see why the BJ8 should not have the same normal combination as my XK120

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    Re: HD8 carb on Healey 3000

    You have described my situation almost exactly! I have checked ignition timing, and valve clearances. All good. My jets are virtually at the bridge after starting at .07. Red/green springs, but my HD8s are not internally vented and I use dampers with a hole in the cap. Very frustrating. Way too rich at idle and plugs sooty. I have not tried driving at speed, turning off the ignition and coasting to a stop to check the plugs yet. I can do that, but what I am objecting to is the smell of unburnt hydrocarbons and the burning eyes. I know these cars tend to like being rich but I am just not happy with where I am now. Perhaps I should try the lighter springs?
    Lin
    1959 AN5 Bugeye - now with my son 😀
    1960 BT7 3000 MKI
    1987 Alfa Romeo Spider Quadrifoglio
    https://valvechatter.com/

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    Re: HD8 carb on Healey 3000

    Are you quite sure your HD8’s are not internally vented ? If you take off the bells, turn upside down and look up at the thread. To one side you should see the small vent hole that goes from near thread to near a web casting.

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    Re: HD8 carb on Healey 3000

    Yes, positively sure. No internal venting on my HD8s.
    Lin


    1959 AN5 Bugeye - now with my son 😀
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    Re: HD8 carb on Healey 3000

    That is very interesting. Thank you very much for taking the time to photo these. So looking at the two webs on the top view there is no hole going through the threaded area to the inside of the bell.
    i note the number is AUC1040 which is the same number as on my HD8’s on the XK120, but I have vent holes. I now need to check my friends Healey 3000 to see what number is inside his.

    This has now added further confusion to my original questions and comments, as although your car symptoms are similar you have less venting. I believe this would cause your car to be richer ??? Let’s see what other comments we get to sort both of us out ?

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    Re: HD8 carb on Healey 3000

    I have a pair of UN needles that I had not yet tried. Might that help the situation?
    Lin
    1959 AN5 Bugeye - now with my son 😀
    1960 BT7 3000 MKI
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    Re: HD8 carb on Healey 3000

    According to the SU book the standard needle is UH. The UN is a thinner richer needle, so doubt it would help you. I am using the UN in my XK120 but that is a different story. All needles are the same diameter at the top or the idle end. The UL is the one that is specified as the lean needle for the HD8 on the BJ8.

    I am going to call both Southern Carburettors and Burlen Fuel services tomorrow, to ask their opinion on my original question about why the jets need to be so high and spring so heavy. See my original post comments.

    Your car with NO internal vent but a damper with hole maybe correct. My friends car with both maybe wrong ?? Either way I will check it out.

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    Re: HD8 carb on Healey 3000

    Forgot to ask what needles you are using. It is critical that they are seated in the piston at the correct height with the groove just out of sight.

    The standard needle in the E Type is UM, but that is very fat - lean.

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    Re: HD8 carb on Healey 3000

    Currently using UH needles. Each needle protrudes from the base of the piston 44.81mm.
    Lin
    1959 AN5 Bugeye - now with my son 😀
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    1987 Alfa Romeo Spider Quadrifoglio
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    Re: HD8 carb on Healey 3000

    Hi Lin, I think you mean UH. That is the correct standard needle. Near the top there is a ring groove. When you set the needle in the piston bottom the groove should just be covered. If you hold the two pistons horizontal to each other with the needles pointing at each other, then you can check that both needles touch the opposing pistons together. That is a further check that both needles are secured the same distance up into the piston and are the same length. Obviously the oil will pour out, so drain oil into bottle first !!

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    Re: HD8 carb on Healey 3000

    Hmmm, I pushed in the needles as far as they would go before tightening. That is actually a little beyond where the ring groove is. Perhaps I should pull out the needles until, as you describe, the ring grooves are just covered. It would only be a slight difference but if I did this it would push the needle down slightly into the jet thereby reducing fuel flow if I understand. I will adjust the needles to the ring groove and then measure the length and see what I get.
    Thanks for the help.
    Lin
    1959 AN5 Bugeye - now with my son 😀
    1960 BT7 3000 MKI
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    Re: HD8 carb on Healey 3000

    Interesting. If I only insert the needle until the ring groove is just hidden (rather than all the way in until it seats) there is a 3.4mm difference in length of the needle protruding from the bottom of the piston. That will make a big difference and I think is definitely the source of my problem. Page 44 of the SU Carburetters Tuning Tips & Techniques states, " The shoulder or lower edge of the groove must be level with the lower face of the piston rod." I am sure that I have read that a dozen times over the years. Why it did not sink in is beyond me.

    Thanks your guidance. I will make the changes and give the car a try tomorrow. I will first need to lower the jets since I had them up near the bridge. Fine tuning from there!
    1959 AN5 Bugeye - now with my son 😀
    1960 BT7 3000 MKI
    1987 Alfa Romeo Spider Quadrifoglio
    https://valvechatter.com/

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    Re: HD8 carb on Healey 3000

    Hi Lin, that is great that you have found your mistake. It must have been running incredibly rich !! So, now try the mixture screw down two half turns or about 0.07”. Please be aware that a quarter of a turn either way makes a Big difference to mixture and idle. Put the large volume screws to about 4 turns up counter clockwise. Make sure the butterflies are closed at throttle stop and the fast idle from the choke is not holding butterflies open. Start the car and adjust both mixture screws together up and down a quarter of a turn at a time to get the highest idle. Then you have right mixture. Then adjust larger volume screws to get about 600-700 rpm.

    So, now I have sorted by default your problem, still not sorted my friends problem. But at least it shows the benefit of these posts on the forum.

    Come back to me when you have adjusted and tell me how it is going.

    regards

    john UK time 10.30pm

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    Re: HD8 carb on Healey 3000

    John,
    Surprised your 120 has HD8s - that's a later carb. Most I've seen have H6s.
    FWIW, my HD8 domes have no vent holes per above. We discussed the vent situation not too long ago in another thread. IMO SU found it to be cheaper to just drill the caps.:

    http://www.britishcarforum.com/bcf/showthread.php?119717-SU-damper-cap-vented-vs-non-vented

    Last edited by steveg; 07-26-2020 at 04:52 PM.
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    Re: HD8 carb on Healey 3000

    Hello Steve, yes you are quite right the standard carb on an XK120 is the H6 same as my Healey100. But my XK120 has been modified with higher compression pistons, bigger valves, Rob Beere cams, 123 Bluetooth with E type ignition curve setting. So, nearer 200bhp than standard 160bhp.

    Most HD8 domes on other cars have internal vents and sealed dampers. This is what I see in the SU book, so the
    Healey 3000 is the odd one out. I also notice that most Healey 3000’s I have seen with HD8’s seem to have a dull texture surface to the dome, rather than shiny like as E Type.

    Thanks for your confirmation your domes have no vents. I think this is the problem with my friends 3000 that initiated this whole post. He has vented dampers, domes with vents. So, he is find that with snap acceleration the car miss’s. Where as slow throttle pedal push down is ok.

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    Re: HD8 carb on Healey 3000

    Sorry to intrude on your post but I too have a BJ8 and I find that the rear 3 cylinders always seem to run richer than the front. I can tell by the soot on the plugs which I check routinely.

    So I just took my bell and pistons off. I have UH needles and they are both vented thru a hole in the damper cap.

    Both needles were set so that the groove just disappears into the piston. I measured the rear needle as 48.38mm long and the front as 48.01mm. I've set them both to 48mm now. The rear jet was set at .08" and the front as .074". This seems a little odd really as you would expect the rear to be leaner than the front rather than the other way round with this set up But perhaps the extra depth of the jet on the rear carb compensates for the longer needle.

    AJ

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    Re: HD8 carb on Healey 3000

    AJ hello, the needles should both be set with the groove just not showing. Not by the length that the needles stick out. The needles are both the same length anyway. Hold the two pistons horizontal on their sides opposite each other with the needles installed and pointing at each other. Both needles if correctly installed will just touch the opposite piston together.
    that is a final check they both the same. I would say that 0.08” is quite far down. I would try 0.06” ?
    If you run the car, you will find that only one quarter turn on the small mixture screw makes a lot of difference to the idle.
    The object is to get the fastest idle with those two small screws by going up and down, then adjusting the final idle speed with the large volume screw to about 700rpm.

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    Re: HD8 carb on Healey 3000

    Quote Originally Posted by OWD724 View Post
    ...with snap acceleration the car miss’s. Where as slow throttle pedal push down is ok.
    He should try thicker oil in the dampers. That'll retard the pistons, causing more richess on snap acceleration. Some have even used gear oil.
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    Re: HD8 carb on Healey 3000

    Hi Steve, yes that is a thought, but what is quite odd is that the spec for the Healey with HD8’s is a very heavy spring, much heavier than other HD8’s in other cars. So, in fact the piston is far less likely to go up easily. Look at one of my early posts where I mention the spring weights and spring spec colours.

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    Re: HD8 carb on Healey 3000

    Yes I set the needles just as you describe, with the groove just inside the damper so it doesn't show. I did match the pistons against each other as stated to ensure they are the same length. I then measured the length of each as a check that they were the same, I got 48mm not the 44mm dimension given by Lin above. Not sure why there's s difference and I'm not sure that it matters a great deal.

    I use engine oil, Mobil 1, in the dampers.

    By the way the car runs very well it's just that the rear 3 cylinders always seem to run richer that the front cylinders. I've adjusted the rear jet a 1/4 turn now to see what happens.

    I also have a colourtune plug and I usually set the carbs just on the positive side of the flame going from blue to yellow, i.e. just a little on the rich side as I was told that Healey's like to run a little rich.

    AJ

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