adj. ZS carb needle

[rdssdi]

I have installed adjustable mixture needles into my Zenith Stromberg carbs. I read that you need a special tool to adjust. I see that a long allen/hex will fit into the adjuster. Why a special tool?

Bob

[enskr]

Bob
The problem is this: If you use an allen key and turn it, rather than raising or lowering the needle on its thread, instead you will just twist the whole rubber diaphragm (because this has less resistance than rotating the needle on its mounting thread). This will obviously not change the needle height at all, and will probably tear the diaphragm if you twist too hard.
The solution is the "special tool" which has the hex key, with a concentric tube around the outside which keys into the slot in the air valve. By holding this tube still, the hex key can be turned to raise and lower the needle, without putting any torque on the diaphragm.

This makes a lot more sense if you have a stromberg carb diagram to look at!

I think I paid about ?12 for my tool, off some sportscar place on the dreaded eBay.

Kevin

[Frank Howard]

Bob,

Guess I should have read your original post more carefully.

[collins_dan]

Bob, Where did you get the adjustable needles and pistons? I was on the phone with Burlens today. I found the needle I want (B1BT), but they weren't sure which piston I would need for it, other than it was not the one I currently have (B1G). You would think their system would indicate which piston goes with which needle. Thanks. Dan

[oldelanman]

Here's what the tool looks like. This one was home made.

[Frank Howard]

It's actually better if the allen wrench is "L" shaped rather than "T" shaped because it makes it easier to keep track of the turns while adjusting. As I recall, there are threads for no more than 3-1/4 revolutions.

[rdssdi]

I dont believe when I use a hex wrench that it twists the diaphragm.

I purchased the air pistons with the adjustable feature and new needles so I was able to convert my fixed needle carbs.

Where can I purchase this tool in the U.S.?

I would like an electronic air/fuel mixture analyzer to adjust the mixture. Is this available at a reasonable cost? One with a probe which can be placed into the exhaust tip.

Bob

[collins_dan]

I am trying to make the same switch. Where did you purchase the adjustable pistons and needles? Thanks. Dan

[oldelanman]

I am trying to make the same switch. Where did you purchase the adjustable pistons and needles? Thanks. Dan

If you have no luck with Burlen you could try these people in the UK. They also list the adjuster tool on their website.

http://www.gowerlee.dircon.co.uk/index.html

Regards,

[69S4]

Are you aware that there are two versions of the tool. The hex head / allen key type referred to is one of them but there is a second type where the end is a cylinder (about 6mm/1/4" diameter) with a slot cut into it. Which type you need depends on what type of adjuster is screwed into the top of the needle. If you can get a regular allen key to lock in, then fine but if you can't find the hole with it then you may have the slot type.

How do I know - My carbs have one of each!

As I understand it mixture adjustment on the ZS carbs is by changing the needles for another profile rather than screwing them up and down. If you've set the (correct) needles and the jets to the datum position/ hight the mixture should be right. The adjustable function is to allow for slight differences in manufacturing and isn't something you adjust in the way you would raise the needle on a motorcycle carb to richen the mid range. Mid range / full throttle etc mixture is designed into the profile of the needle. Half a turn either way from the start position to fine tune the idle mixture (mainly to allow for differences in jet hight) and that should be it - or have I got it totally wrong?

[oldelanman]

Hi Stuart,
On the Gower and Lee website they show both versions of the needle adjuster tool and say the slot type is 1977 onwards. I guess that means that one of your carbs has come from a later vehicle and not an Elan.

As to adjustment I think you are spot-on. It's only provided to obtain the correct relationship between the needle and jet and thereby set the idle mixture, the profile of the needle then takes care of the mixture throughout the range. Of course if you get this initial needle/jet relationship wrong you will affect the mixture throughout the whole range - too rich at idle and it will be too rich throughout the range etc.

Regards,

[69S4]

To the best of my knowledge the carbs are the matched pair that were on the car from new but the needle adjusting screw was replaced on one of them back in the 80's with what was available at the time - the slot type. That's how I've currently got one of each. That may be a situation others are in as the adjusting screw is easy to damage when you're trying to replace the o ring.

I'm in the middle of setting up the idle mixture at the moment after a complete carb rebuild and it's proving to be a little more tricky than I thought. The carbs are fine but air leaks from elsewhere are throwing the settings out. The rear carb seems to have an o ring air leak that, despite a couple of changes of ring is still there and the front carb seems to be getting extra air bleeding in from either the brake servo or the headlamp system. Chief suspect at the moment seems to be the headlamp pull switch.

[collins_dan]

Stuart, I am having a similar problem with apparent air leaks after a rebuild. Check the throttle bypass valve. I read a previous post that suggested that could be a possible source of air getting through. elan-archive-f16/too-fast-t11270.html

Dan

[oldelanman]

Dan, I think the throttle bypass valve is only on the federal emission set up so Stuart won't have that on his, just the temperature compensator. Have you checked the balance pipe O rings are sealing properly ? If they came with your overhaul kit they should be OK but if they are the wrong thickness material they won't seal properly. Also did you renew the throttle spindle seals ?
Apologies if all this is obvious and you've been over it already - just trying to help.

Regards,

[Frank Howard]

The adjustable function is to allow for slight differences in manufacturing...Half a turn either way from the start position to fine tune the idle mixture (mainly to allow for differences in jet hight) and that should be it

That would explain why there are threads for no more than 3-1/4 turns.