HD8 carb on Healey 3000

[OWD724]

I have been into garage and measures all my spare needles. They are all 48.5 to the middle of the groove from the tip and 60 in total length. When you say you have adjusted the screw one quarter of a turn, I assume you mean counter clockwise to lean out by bringing jet up very slightly. As a matter of interest, one half turn equals 0.015” of jet movement up or down. As I said before one quarter does make a big difference. All the needles are the same diameter at the top two stations at the idle end. But the variations can be quite large towards the tips. I have a set of UN, UO, UVO, UVR and UM.

 

[steveg]

AJ - it's important the springs have the same length and tension.

Hammill, p. 51 shows a technique with a diet scale and a cardboard tube of the compressed length spec. You put the spring on the diet scale and press down until the compressed length, then record how many ounces. Both springs should be very close. i bought 2 new springs because my old ones were very different.

 

[steveg]

...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....

This statement intrigues. Did a quick survey in the Burlen Catalogue of all the models using HD8 & HS8 carbs. They are about evenly divided between the AUC 2107 and 4826 (BJ8) springs. Assume from your experience the former is the weaker.

Some generalizations:
Jags use the 2107 on on manual trans cars from XK150S on; 4826 on auto trans cars; Rover uses both; Daimler uses 4826 extensively, with some 2107; Rolls/Bentley has their own 4818.

There are only the 2107 and 4826 springs listed for the HD8 & HS8 carbs on non-Rolls cars.

It's interesting the BJ8 even uses HD8 carbs, when the 3.4 Jags (up to 220 bhp) used HD6s. IMO it was done for marketing purposes (size matters). Hammill, IIRC, says Rover used a larger carb for marketing, but changed the linkage so it wouldn't open all the way.

 

[mgtf328]

Apologies again for hijacking the post but it's one of the most interesting posts I've read on the HD8.

Perhaps I might inject a couple more issues I've struggled with.
I read somewhere that it's best to fully close the large "slow running/volume?" valves and leave them that way. Mine are both screwed in fully clockwise. Is this correct? What effect does opening them up have. I haven't tried it but will when it stops raining.

I have had trouble balancing my carbs. I take the air filters off and get them nicely balanced on the "fast idle" adjusting screw to about 800rpm but when I re-fit the air filters (worst job on the car!) the idle jumps to 1500rpm and I have to resort to slowing it down with the fast idle screws which I'm sure upsets the balance again. I've done this 3 times over the last week with the same effect. Any advice would be appreciated.

What effect will changing the spring have not sure how to tell which ones they are mine just look black and oily!
Thanks
AJ

 

[OWD724]

AJ,

i think you are doing it wrong way round.

In theory the the HD8’s are meant to run with the butterfly fully closed and the idle air goes via a port from in front of the butterfly to behind it. The large volume screw controls the amount of air going through the port and thus the idle speed. The fast idle screw is only for the idle speed when the choke is pulled out, it does hold the butterfly open slightly.

As you know the H6 is simple as it just has the normal idle stop the hold the butterfly open slightly. Then a cam attached to the choke to further open the butterfly.

Steve,

i do have the lighter springs in my HD8’s in the XK120, I tried the heavier ones and to be honest could not tell the difference in driving. If you put the two springs on the bench they feel quite different and the thickness of the spring wire is noticeable. I am wondering if the heavier spring goes with vented damper and the lighter spring with the internal dome venting. Not actual checked this ??? But question is why does Healey 3000 have the Heavy spring and vented damper and not the lighter spring and internal vented Dome.

 

[mgtf328]

I'll give the volume screws a try but that's not what my Su Workshop Manual says.

AJ

 

[OWD724]

AJ, the fast idle screw 2 is not the same as the other idle screw 3 in the other picture. They tell you to pull the choke out that pulls the jet down and the fast idle screw 2 then contacts the plate and pulls the butterfly open. They say to do it when the engine is hot, so you can adjust it correctly to get 1000rpm with choke pulled. The fast idle screw should be just clear of the plate when the choke is pushed in. In the other diagram, they are talking about a slightly different set up, where the idle is set with a normal idle screw adjuster like an H6 carb. Then you do not use the large volume screw. Not sure what car that situation would be ?

 

[Lin]

Just want to give a big “Thank you” shout out to John for his help. While I am not completely finished with the carb tuning; for example, I want to make an interstate highway run at speed, and as Steve Gerow has suggested then cut off the ignition and coast into a rest area and pull the plugs to take a look.

But I can report that as John directed, once I adjusted my needles to get their proper length by seating them just so that the lower edge of the groove in the needle was hidden by the bottom of the piston (rather than having them pushed in until they stopped) I ended up with a tuneable situation. My car had been running rich because the needles never went down into the jets far enough resulting in an outcome that literally meant one could never sufficiently adjust the carbs to relieve the excessive richness.

Golly, I have only had this situation for about twelve years now! Some might say, “and, you are admitting this?” My answer is “sure.” Of course, I feel a little dumb for not reading more carefully, but perhaps this will help someone else. I have at least been persistent, if nothing else.

After getting the needles installed properly, I then adjusted the the carbs as recommended by John (Steve Byers’ white paper was helpful too) the car now starts and runs better than it has in years. Spark plugs look very good now, they were previously always black and sooty. As I said, I will do some more testing and plug checking before done. I am one happy camper!

John, I don’t know if the original question about your friend’s car has been resolved or not? I am guessing that the “double venting” is probably the issue and perhaps solved easily by adding non-vented dampers?

Again, thank you! I can actually drive my car without my eyes watering from unburnt fuel! Who knows, maybe my wife will go for a drive with me now.

Lin

 

[OWD724]

Hello Lin, I am very happy to hear that your car is going better now. What it probably needs is a good blast down the highway for 50 miles or so really clear it out. In the U.K. we would pour something like Redex in the fuel to help clear it out. I would also change your oil as all the excess fuel that you have been using has probably leeched into your oil sump.
i guess oil price per barrel in USA will now change !!! I will look at the stock market closely now that fuel usage in Florida will be less ha ha ��. Anyway, my friends car is still yesterday to be sorted, but hopefully soon ! Best wishes John

 

[Lin]

Hi John, Just to continue this subject a bit further....

1. You never mention even touching the fast idle screws other than to back them off when you start the adjustment process. Do you never have a need to adjust these screws?

2. Are the fast idle screws the same as "throttle adjusting screws?" If not, then what are "throttle adjusting screws on HD carbs? refer to the attachment below taken from Burlen's website under tuning HD carbs. The photo seems to show HD6 carbs from an early 3000 model or something similar.

This may be the source of confusion mentioned earlier about serving down the slow-running valves as this attachment states that they must remain closed. I found this nomenclature quite confusing. All of this is under the section on HD carbs!

Your thoughts?

Lin

 

[steveg]

Lin,
The Burlen SU Workshop Manual is like a salad bar. You gotta pick the right picture.

They call it the 'fast idle screw'. The Bentley manual mostly calls it the 'throttle stop adjusting screw', though on p110 on the previous drawing it's called the 'throttle adjusting screw'. It is only used for adjusting the fast idle with the choke pulled out.

Your pic above appears to have a throttle adjusting screw but not a fast idle screw.

Maybe this is from a Rolls or Rover - note it has both the fast idle (throttle stop) and throttle adjusting screws. I doubt it even has a slow running valve - what would be the point if it were to be kept closed:

This picture on another page shows the Healey setup: slow running valve with fast idle (throttle stop adjusting) screw:

When the shafts don't leak, the slow running valve works perfectly well to adjust the idle, per John above.

 

[steveg]

I'd argue the Burlen manual is generic and one should follow the specific instructions from the official Healey manual:

 

[OWD724]

Hello Lin, I agree with Steve. The Burlen pictures can be misleading. I can tell you when I visited their factory last year, even talking to them I got conflicting stories, because there are so many versions of the same carb. You have HD8’s.
On the previous page to the picture you sent is the way to tune a single carb. Yours is the same as that but just two tied together with a rod. So, the volume screw adjusts idle speed by letting air through the port around the totally closed butterfly. The other small “fast idle screw” only touches the plate to open the butterfly when you pull choke. So, what I have said is the same as Steve, but worded differently. If you still have trouble understanding, maybe organising a FaceTime call via iPad. When you are with your car ?

 

[Lin]

Thanks, Steve and John! I am fine with my car. It is running well now. I may try the 50 mile run tomorrow. I have not yet tried to start the car cold since I got it running well. Not anticipating a problem tomorrow, but that is why I was asking about the throttle stop adjusting screws (fast idle) - wondering if I might need to screw them down a bit to assist the choke on the cold start - just thinking too much I suppose.

When using a Uni-syn or a flow meter which screw do you adjust to balance the air flow? I assume the slow idle (large) screws?

I guess it has become an academic exercise with me and my wife has told me to let it go, since the car is running well now. I guess that I have had a hard time dealing with the inconsistencies in language which I find frustrating. I agree with Steve that the Worshop Manual is a much clearer source than the SU book. Thanks again to you both.
Lin

 

[steveg]

Thanks, Steve and John! I am fine with my car. It is running well now. I may try the 50 mile run tomorrow. I have not yet tried to start the car cold since I got it running well. Not anticipating a problem tomorrow, but that is why I was asking about the throttle stop adjusting screws (fast idle) - wondering if I might need to screw them down a bit to assist the choke on the cold start - just thinking too much I suppose.

When using a Uni-syn or a flow meter which screw do you adjust to balance the air flow? I assume the slow idle (large) screws?

I guess it has become an academic exercise with me and my wife has told me to let it go, since the car is running well now. I guess that I have had a hard time dealing with the inconsistencies in language which I find frustrating. I agree with Steve that the Worshop Manual is a much clearer source than the SU book. Thanks again to you both.
Lin

Lin,
Bentley, p129, sec DDD.11 tells how to pull the choke out a certain amount then adjust the fast idle screws to obtain 1000 rpm - do this after the sync.

For the sync, you need to undo one of the pin couplings so the carbs are independent of each other. I've used the fast idle screws to get the carbs up to around 1500 rpm then use them to change each one until the Uni-syn reads the same for both. Then you tighten the pin coupling screw, then back off the fast idle screws till you have clearance.

I installed vacuum ports and a Weber balancer on mine so I could balance the carbs with the air cleaners in place. (cue smug smile )

 

[mgtf328]

Guys, I want to thank y'all for setting me straight.

Like Lin I thought the note on para 1 of the SU Workshop Manual shown above was clear. You'd expect the SU Workshop Manual to be the definitive word on the subject right!

Browsing thru the archives I found a copy of Steve Beyers instructions (thanks Steve) and followed his excellent advice along with the guidance you give above.

I think I got it sorted now but I suspect the guy that fitted the new throttle shaft for me didn't get it quite right as I've had to close the rear volume valve down a lot more than the front valve to get a balance. I suspect the rear throttle isn't completely closing. I too use the Unisync tool.

I set the mixture with colourtune plugs. The colourtune showed the rear carb to still be a little on the rich side (yellow flame) I turned the mixture screw anticlockwise but it didn't seem to make a lot of difference until I found that adjusting the front as well as the rear mixture settings seemed to work.

Much improved. I took it for a drive then took the plugs out. The rear is still a little on the rich side compared to the front but this is the first time I've managed to get it relatively soot free. I'm still fine tuning but I think I finally got the message.

Thanks for your help a great post and sorry to but in.

AJ

 

[steveg]

....sorry to but in.

AJ

Not butting in. A good contribution, AJ!

 

[AUSMHLY]

Two more questions about the HD8 that came on BJ8 cars.

I rebuilt 2 HD8s that came on BJ8 cars, 1964 and 1966.
One set had a chamber/piston assembly with AUD 1040 printed on the inside of the chamber (Lin's AUD 1040 shows the imprint.) The chamber tube extended to about 1/2" from the bottom of the chamber. The pistons with those had printed AUC 2053.
One set had a chamber/piston assembly with AUD 3202 printed on the inside and it's tube extended to the bottom of the chamber. The piston with those had printed AUC 2053 (same piston as the other set)
Both chambers are the same height, the internal tubes are different lengths.



I believe the HD8 carbs on the BJ8 came with the cap & damper made with black plastic. Some people have brass caps on them which I think they swapped out?
Looking into it farther I found out the brass set up is a different size then the plastic. Brass is 2" 15/16 the plastic is 3" 3/16. Both caps have the air hole.



Does it matter if the AUD 1040 with the shorter tube uses either the longer or shorter cap/damper? Or AUD 3202 with the longer tube uses the longer/shorter cap/damper.

What did the BJ8 cars come with AUD 1040 or AUD 3202?

Did all the HD8 have the AUC 2053 pistons?

 

[OWD724]

This hard to answer, as I do not have my friend here with his 3000. But from memory the domes were 1040. Not sure about the pistons. My XK120 also has 1040. There are two different dome heights. The tall one I have with the slightly longer neck. The shorter neck version, was on the E Type to clear the closing hood. I have several dampers and don’t think it makes any difference as long as the piston can go fully up without bottoming out on the damper, which I don’t think any do. But the most strange point that I have never got to the bottom of, is that the SU book says all HD8 domes are internally vented with blank non hole damper. But the 3000 seems to be listed as the opposite, why I don’t know ? No one seems to come up with a plausible explanation. To further answer your questions about numbers, try putting those numbers into the Burlen fuel systems website, with a gap between letters and numbers. Not all are recognised.

 

[John Turney]

The Burlen website doesn't list either of those parts. They do list the parts for BJ8 SUs at http://sucarb.co.uk/carbspec/carburettor/spares/id/400/.

Clicking on "VIEW" for part #19, "Suction Chamber & Piston Assembly", indicates that you must contact Burlen because the parts varied during production.