Height main jet HD8

[norman m. macleod]

Hi all,
Setting up the 3 x HD8's on my Series 1, I duly noted in the Jaguar Workshop Manual an instruction to set the top of the jet flush (level...) with the bridge, then screw down the mixture adjusting screws two and a half turns, as a starting point. This gives a dimension of jet below bridge of approximately 1/16" (0.062" or so....). So far so good......Reading an article in the Technical Section of the Forum (private company author...) there is a dimension of 0.125" given ( 1/8".......) Mmmmm I suppose I'd prefer to use the former dimension (from the Jaguar Workshop Manual...) but thought I'd ask the Forum members .......I've tried to use the "Search" Facility to find other wisdom, but nothing comes up ( no doubt my IT failings, no fault of the Facility..... ....!)
All input appreciated,
Kind regards,
Norman

[mgcjag]

Hi Norman....use the manusl settings.....i followed the entire set up section.....my cay fired up straight away and ran really well.....just needed slight tweeking after

[christopher storey]

Norman : I think the confusion has arisen because the jet diameter is 0.125" . For setting up , I use a depth measured with a depth gauge of .065" as a starting point. The 2.5 turns on the screws is a very approximate measure , because the thread pitch is very coarse and, therefore, liable to very considerable inaccuracy as between individual screws . I set up, obtain the best idle I can on the indiviual carbs, and then re-measure the jet depths and reset them to the average of the 3 depths, so e.g. if after adjusting I have depths of 58 thou, 75 thou and 47 thou I set all 3 to 180/3 = 60 thou .

[Mich7920]

Hi Norman,

As Steve said, follow the jaguar book.
Be sure to follow each steps !
A thing really important is to disconnect them, they must to be independant

I do not like the idea of making an average setup. You will not get a perfect setting.
Your 3 carbs aren't not exactly the same, so if you have not the same set up it's normal.

The 2 1/2 mixture adjusting screw don't need to be precise, it's just to allow you to start the engine.
After you'll setup the weak/rich for each carb you'll forget your 2 1/2 turn... But your carbs will have the real good setup for each one.

Mich

[cactusman]

Follow the book....Do what Chris says....she will purr like a jag should

[norman m. macleod]

Hi All,
Many thanks for the comments, much appreciated. Went for the general consensus (and the Jaguar Manual......), so two and a half turns down on the mixture screws, oil in the dashpots, fuel in the tank, and lots of choke.....Two to three seconds on the starter and Vrooooooom!..... with a passably regular idle....bit of fine adjustment will fix that.
(No confusion at all with the jet diameter, Christopher, the dimension is given (with photograph..) in an extract article from CMC held in the Forum Knowledge Base (Tech. Info and Doc. Section), and titled "Tuning Carburettors".) No doubt a typo on their part......?)
Only trim to finish, and it'll be another "E" back on the road (albeit an 'umble 2+2.......) Main thing, though, is that my 7-year-old grand-daughter approves, space in the back for her.......
Best regards,
Norman
(in Antipodean exile.......)

[abowie]

Rather than using the 2 1/2 turns from the book I start out with the jet set 60 thou below the bridge as measured with a vernier mic.
I have found that if you use the screw turn method you can end up with differing heights on the 3 carbs, presumably due to wear and other variables causing inaccuracies with the initial setting. This way you start out with all 3 jet heights exactly the same.
I tune the car, and then remeasure the jet heights on each carb and set all 3 to the average height. I then recheck the tune. This usually gives me a pretty good result.

[christopher storey]

As Andrew says . The reason for averaging the heights is that on all Es there is a great deal of inter-dependence between the carbs because of the large connecting passages in the manifolds, so that an adjustment to one carb in fact affects mixture strength to all 6 cylinders