The 100-Six Forum

The cold weather starting on my BN6 is awful. The choke does seem to do something but obviously not enough. I've looked at two different SU books and still can't understand with the collection of levers and arms what is supposed to be going on. I'm pretty sure not enough fuel is getting to the engine for the cold start. As I'ved cranked for 3-4 times for several seconds and taken out the plugs and they are dry. It will after a while of trying to start, it will try to catch but not quite. Once warm it runs perfectly and will restart no problem. Which one of the many adjusting screws will richen the mixture when the choke is pulled out? Photo's of the current set-up, thank you for your help.
Regards,
Paul

Correct me if I’m wrong but your choke cable is missing ? There should be a cable to each carb from a single cable coming through the firewall .
Pulling the choke on HD 8 lowers the diaphram which gives it more fuel .

I’ve attached a pic of the choke cable set up you need for HD8s highlighted

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That’s not an oil leak , it’s my patent pending rust proofing system .



Edited 2 time(s). Last edit at 2025-11-11 04:45 PM by Healey Nut.

What you show is a completely different set-up Graham to what I have. Here is the photo of the choke cable, it links up with a mechanism that runs under the carbs. When the choke is pulled I can see movement at both carbs, just not sure what it is physically doing. These carbs do not have a diaphram, they have a needle and a jet. I think with normal throttle operation the piston and needle move off the bridge allowing the correct running portion of mixed gas and air. But when the choke is pulled the butterfly remains partially closed to give less air but I think the jet moves down to provide more gas. If this is the correct assumption, I need to identify the screw required to increase the downward movement of the jet to richen the choke mix.

Diaphragm …… jet , different terminology , Im from the UK so lots of different names for parts .
The jet get lowered so it allows more fuel to pass over the needle but you still have to have a cable to each carb to create the jet lowering unless some one cobbled together something on you car as it has BJ8 carbs on it and you have a BN6

See the blow apart drawing attached .

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That’s not an oil leak , it’s my patent pending rust proofing system .

No attachment Graham?

I’m not positive with HD8 like you have, but with my HD6 carbs, the choke cable, when pulled, will pull up a lever below the carb which will cause the jet to lower. The cable runs through a small pin with a set screw on the end. This pin is inserted in the hole in the end of the lever. If you loosen the set screw you can pull the cable further down on the lever causing the jet to move lower.
The first thing I would do is remove the screws holding the dash pot covers and then lift out the pistons. You can then see the top of the jets and determine if they actually drop when you pull the choke out. If they don’t drop or only a smidge, then adjust the cable so they activate correctly. Check that both jets drop about the same amount. If not, you may need to adjust the rod that connects the choke levers below the carb bodies. Make sure you keep the pistons and dash pot covers with the same carbs they came off of.

The HD8s each have a choke lever which is pulled up by a separate cable.

When I was running HD8s on my BN6, I built a choke setup which was superior to the BJ8 setup in that both ends of each cable housing were gripped by a set screw. This created a very positive push-pull on the choke wires. This was relatively easy given the BN6's under-steering-column choke handle position.

See:
https://pbase.com/stevegerow/healeychokes

Hi Rob, What you describe sounds correct for my set-up. Definately like the idea of removing the dashpots to access how much jet movement.
Thanks for your help,
Regards,
Paul

See pic . I’ve highlighted the choke levers . The each need a cable to them to pull them up lowering the jet . The jet has a flexible diaphram attached to it which allows it to move .
Originally a BN6 would have been a 2.6 litre engine with twin HD6s
I’ve attached a link to AH spares HD8 parts blow up .

It looks like in one of your pics that the choke lever arm is missing . 1st pic on your first post .

https://www.ahspares.co.uk/big-healey/carburettors-bj8-hd8/default.aspx

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That’s not an oil leak , it’s my patent pending rust proofing system .



Edited 2 time(s). Last edit at 2025-11-12 06:38 AM by Healey Nut.

There is only one cable required. On both my BT7 with HD6s and E-Type with 3 HD8s the arms, one of which you have circled, are linked by a rod with adjustable attachment points. When properly adjusted, all of the arms move as one. Paul described the mechanism in an earlier post.

H Paul, You have HD8 carbs and therefore you have diaphragms. Rob and Jack are correct - the HD6 carbs used one choke cable and linkages between the carbs. The HD8 evolution on BJ8s had individual cables and no linkage between the carbs. What you have is a hybrid - it is very easy to use the HD6 bottom pieces on HD8 carbs so your HD8 choke system is the same as the HD6. They both result in the jets being lowered, just a different way to get there. Attached pictures show HD6 carbs with the choke cable connection on the rear carb and the linkages going to the forward carbs (my non-stock HD6 tricarb).

I agree with Rob, pull the dashpots and pistons and look to see how much the jets drop - they should drop 3/16" or more, and they both need to be the same.



Edited 1 time(s). Last edit at 2025-11-12 10:04 AM by Red57.

Thanks Dave for your photos and confirmation of operation and especially the jet movement of 3/16" with the choke pulled that is such a great help.
Regards,
Paul

Hi Paul,
This is the arrangement I have on my 1960 BT7 that has been converted to HD8's.

1 - You may need the bracket that goes on the Firewall, two new cables and the little block;.
- The ones I use have lead balls on the end that fit into the little block with the set screw.
2 - You will also need the brackets that go on the backs of the flanges for the air filters.
They hold the ends of the outside housing of the cables.
3 - The screw or bolt with the cotter pin and two nuts (see photo) holds the inside cables to the choke lever.
These are the hardest things to connect.
4 - I use one Choke Knob from a BJ8 to operate the whole affair.

Hope this helps a little.

Buona fortuna,
Peter C.

Thanks Peter, your photos are great, I understand this is an alternate method of working the chokes. If I find my linkage does not work well then I may adopt this method.
Thanks, regards,
Paul

Paul,
You show a choke cable to the rear carb. Is there also one to the front carb? There should be.



Edited 1 time(s). Last edit at 2025-11-12 05:37 PM by steveg2.