Main Jet height

[PaulB]

I have a problem with setting the carbs.
The carbs have been overhauled, cleaned and new needles. I cannot get the idle emissions below about 6% with the needle screwed all the way down.
I have checked the float height and it is within the 16 - 18mm range.
The needle is new and is has the correct taper measurements.
So the only other thing which can effect the idle mixture is the jet.
I have measured the jet height and its about 100 thou below the base of the carb body. This measurement was to the outer part of the jet, not the lower centre part..
I have another set of carbs which were the originals on the car, in poor condition which is why I changed them. But the jet height on these is 75 thou.
I have searched the forum and cannot find what the jet height measurement should be.

Please can anyone help?

[MikeParker]

Paul,
100 thou is about right I believe. You say you have changed the needle but did that include the jet itself? The jet is brass and prone to wear. Wear of the jet will richen the mixture more at idle than under normal running so that could be your problem. Don't know if anyone knows of a good way to measure jet wear?
Mike

[NeilR]

I thought 100thou was to the lower / inner part of the jet. When I last did mine my max CO was about 3.5%.

Gone back to a Weber now though.

[MikeParker]

I think the 100 thou is to the raised outer rim of the jet. From memory the jet is pressed in. I think I just set them to the same height as the old jets. I don't think they had a shoulder to set the height. Perhaps someone has done this more recently?

[trunt]

I have 4 or 5 carbs in my attic, I’ll measure them.. but you will have to wait till tomorrow, it’s 92 degrees here so my attic is probably 150 degrees!

I’ll fish them out later!!

meanwhile. Which needles did you get? There are 2 types usually used on the stag

Terry

[MikeParker]

Found this from 2015

https://socforum.com/forum/forum/stag-owners-club/soc-forum/28708-needle-valve-base-height

General view is 100 thou - 2mm to the raised part of the jet. Really odd that there is no definitive reference.

[richardthestag]

zenith / burlen instruction is to press the jet in to the same depth as the old one.

100thou iirc

[Sheepdip]

Unfortunately never know what previous owners have done so need to setup from scratch, I had several carbs with different heights!

Coincidentally overhauled mine few months back. I set it with outer edge to 80 thou which is about 100 to inner and take no credit for the idea Flying Farmer had:

Ground away an old 80thou tappet shim to JUST fit on top of the jet and then knocked it down till flush with the bridge (of course if lower then jet will need knocking up first).

Great way of getting both same hight and of course can use whatever shim you decide

Paul