Procedure for setting and tuning HD8s?

[SteveHall64Healey]

I'm looking for a detailed procedure for setting and tuning HD8s - has anybody got one?
thanks,
steve

 

[dougie]

This is the SU Bible, you need to own it: https://www.barnesandnoble.com/w/su...nual-des-hammill/1102585707?ean=9781845840730

 

[HealeyRick]

I'm looking for a detailed procedure for setting and tuning HD8s - has anybody got one?
thanks,
steve

Norman Nock had a good one in his "Tech Talk": https://www.britishcarspecialists.com/html/publications.html $49 is a bit pricey, but there's a ton of other good stuff in there.

 

[andrewss]

Steve,

Here is the link to the SU website and explains procedure and set up of HD8's..
https://sucarb.co.uk/technical-hd-type-carburetter-diaphragm-jet-and-auxiliary-enrichment

 

[SteveHall64Healey]

thanks everyone,
steve

 

[vette]

Steve, I wrote this a few years ago in the Forum. I you want to find the original thread just advance search for " HD8 Carbs" and my User Name: 'Vette'. I haven't proofed this this time, but I think it was accurate back then and my carbs are still idling at 400 rpms so it must be working.

Hello Bob, HD8 carbs were the standard model on the BJ8 Healey so that is what I believe you have. I have HD8 carbs on my BJ7. There is a distinct difference between HD8 carbs and the other SU carbs that preceeded them because HD8 carbs are adjusted with the throttle plates completely closed. You see the slow run speed screw is the same as an idle screw on an American carb in that it passes the full idle mixture around the throttle plates and at idle the engine runs on the mixture passing around the throttle plates via the passage past the tip of the slow run screw.
As it says in the book, close the throttle plates completely, loosen the interlink between the carb throttle shafts and allow the throttles to close all the way. Then retighten the interlink so the throttle shafts move in unison. Set the large slow run screws to 2-1/4 to 2-1/2 turns out. Set them both the same. now start the engine and let it warm to operating temp. It should idle alittle high. if too slow to idle turn the slow run screw each in alittle just to keep the engine idleing. If you can't keep it running on just the slow run screws then your jet adjustment which is your mixture is way out of the ball park or maybe your spark plugs are severly carboned from previous attempts to adjust carb. I don't remember what the initial setting is to the jet adjusting screw but hopfully the engine will run and idle till it reaches operating temp. If not, back out the jet adjusting screw till it clears it's contact on the jet adjusting arm. Then turn it down till contact and then another 1/2 turn. This should get the mixture in the ball park to idle the engine to operating temp.
Now with throttle plates closed and interconnection of the shafts tightened and the slow run screws at 2-1/2 turns, lift the piston lifting pin to see if the engine will stall, or increase speed or increase just momentarily. If when lifting the pin the engine stalls or slows down the jet on that carb is lean. you must then turn the jet adjusting screw on that carb in (clockwise) to richen the mixture for that carb. Obviously, if the when lifting the pin the engine speeds up and stays up then that carb is rich and you must back out the jet adjusting screw (counter clockwise) to lean that carb. If when lifting the pin the engine speeds up jus t momentarily then the jet on that carb is set just fine. Do the same technique to both carbs. Make sure your choke cable or anything else isn't hanging anything up and make sure you throttle plates stay closed when adjusting and testing mixture/jet.
On the model SU carbs before the the HD8s, idle speed is set by setting the position of the throttle plates to allow the fuel/air mixture to flow around the plates to get to the engine. That is why on the earlier models you had to balance the carbs to maintain near the same air flow. But with the HD8 carbs the throttles are kept completely closed to adjust. That's a significant difference and makes HD8 carb one of the easiest to set up. If I haven't gotten the explaination quite clearly enough, I hope that what I have said and another reread of the book will bring it all together for you. Good Luck. Dave C.

 

[steveg]

Dave,
The HD6s operate the same way as HD8s with the idle set with the throttle plates closed.

 

[BJ8Healeys]

I'm looking for a detailed procedure for setting and tuning HD8s - has anybody got one?
thanks,
steve

Yes, I have one that I put together a few years ago, illustrated with photographs. The available instructions from the SU manual and other sources were too confusing (they use different names for the same part, refer you to a non-applicable section for adjustment of dual carbs, etc.]. If you want it, please contact me directly at sbyers@ec.rr.com. I've shared this with many people and it seems to be what they are looking for.

 

[SteveHall64Healey]

Yes, I have one that I put together a few years ago, illustrated with photographs. The available instructions from the SU manual and other sources were too confusing (they use different names for the same part, refer you to a non-applicable section for adjustment of dual carbs, etc.]. If you want it, please contact me directly at sbyers@ec.rr.com. I've shared this with many people and it seems to be what they are looking for.

Thanks Steve - expect an email from me shortly.
steve

 

[steveg]

Just reviewed this document -- very thorough and well-illustrated! Thank you Steve Byers!

 

[DerekJ]

There are two reasons why people find the SU manual confusing. The first is that the diagrams are not very clear in identifying each of the adjusting screws and the second, and I think biggest reason is that the SU manual refers to Throttle Adjusting Screws. That is because SOME types of SU carbs including some HD8s have throttle adjusting screws BUT the HD8s that came on the Healeys do not have them. The fast idle screw is not the same thing as the throttle adjusting screw.