Jump to content

SU HS6 Jet Height Adjustment


Recommended Posts

Hi All,

I'm struggling to get the mixture correct on my 4A.

I can't seem to raise the jet high enough on the front carb, the adjusting nut bottoms out before the mixture is lean enough.

I did the basic starting setting at 1.25mm down from the bridge, but it was not possible to set it level with the bridge to start with. This setting is too rich.

Although I could with the rear carburettor and it is fine with plenty of adjustment up to the bridge and able to get the correct mixture.

It seems the front jet is too short! Is this possible?

Perhaps are AUD284 jets shorter? My carbs are AUD209's

Any ideas?

Thanks

Edited by DSJ666
Link to post
Share on other sites
13 hours ago, DSJ666 said:

Hi All,

I'm struggling to get the mixture correct on my 4A.

I can't seem to raise the jet high enough on the front carb, the adjusting nut bottoms out before the mixture is lean enough.

I did the basic starting setting at 1.25mm down from the bridge, but it was not possible to set it level with the bridge to start with. This setting is too rich.

Although I could with the rear carburettor and it is fine with plenty of adjustment up to the bridge and able to get the correct mixture.

It seems the front jet is too short! Is this possible?

Perhaps are AUD284 jets shorter? My carbs are AUD209's

Any ideas?

Thanks

Firstly, have the carbs been in bits? and have any parts been replaced?

On my own carbs (H6s) I found that I had 2 copper washers instead of 1 at the top of the jet holder as the original one had stuck into position and didn`t come out on dismantling.

Are the needles new? They do wear over time and should be replaced along with the jet tubes.

Having done all that I was still struggling to get the mixture lean enough and resorted to dropping the needles out of the pistons slightly. While on that subject the needle shoulders should be level with the bottom of the pistons to start with and not pushed fully in.

Make sure the float chambers are not flooding, and worthwhile fitting viton tipped float needles. It was the front carb on my car that was rich too and it was fuel passing the Grosse jets I had fitted, when I replaced it with a standard needle jet the problem was solved.

Hope some of the above helps.

Ralph

Final thought, make sure the choke mechanismn is not sticking and holding the jet tube down.

Edited by Ralph Whitaker
Link to post
Share on other sites

Thanks, some very useful points there.

Floats etc. seem OK and choke mechanism is good.

I did change the needles and jets many years ago (from the Northern TR centre....so that dates them somewhat!). But probably done less than 20K miles since than as the car was laid up many years due to family commitments!

I have not had the jet assemblies apart, so I think that's the next thing to look at and I'll also check the needle shoulders.

Link to post
Share on other sites

Sorted! 

Turned out the jet WAS too short! :o

Tried a cheeky fix which worked......I carefully removed the ferrule which then freed the jet from its plastic housing....reset the jet position and refitted the ferrule which secured the jet. (There is actually a small groove around the lower portion of the jet which seem to coincide with the correct length)

Don't know if it was always like this and I hadn't noticed or it had got pushed in sometime, although I can't think how as they are very tight in the plastic housing. I know they look old and are in age but not in usage!

Anyway a rather unusual situation sorted and all good now. :D

Thanks all for your comments.

20220517_194526.jpg

20220517_195440 (1).jpg

Edited by DSJ666
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.