Engine running rich

[markleigh]

Newbie here who doesn’t know how to adjust the mixture - or identify the type of carb… but photo attached!
Thanks all!

[Andyhereford]

I am certainly no expert but how to adjust the mixture is very clearly explained in the Haynes Manual. Even I managed to follow it.

[svenedin]

It looks like a standard HS2 carburettor.

Adjusting the mixture is easy and covered in numerous web articles or on the SU website. Getting the mixture just right is not quite so straightforward and may take some trial and error.

Do not fiddle with jet centring unless there is a problem that actually needs to be corrected.

https://www.howacarworks.com/fuel-syste ... e%20richer.


Stephen.

[markleigh]

Thanks Both.
Just ordered the manual

[svenedin]

Thanks Both.
Just ordered the manual

The Haynes manual is quite useful but the BMC workshop manual is much better and clearer.

If you think you will be rebuilding an SU carburettor or fuel pump then the SU Workshop Manual is definitely worth having.

Stephen

[philthehill]

Save yourself the cost of a manual - all the information you require for maintenance and adjustment of HS2 carbs is available on line from Burlen Fuels:-
https://sucarb.co.uk/technical-hs-type- ... djustments

Details for the repair and adjustment of SU fuel pumps are also available through the Burlen Fuels web site:-
https://sucarb.co.uk/technical-electrical-fuel-pumps

[svenedin]

Just make sure you adjust the mixture nut and not the jet centring nut above it.

Get your mixture reasonable with a hot engine. Do not adjust the mixture when the choke is engaged. Then ideally go for a decent drive. 10 miles would do but not in town traffic. When you get back take out the spark plugs and examine their colour. Black and sooty the mixture is still too rich. A biscuit brown (or like weak coffee) that's perfect. White and pale looking the mixture is too weak. Be aware that the mixture can be affected by such things as a clogged air filter (this restricts the air so the mixture goes too rich).

My personal preference is for the Gunson Colortune (sic). This is a special spark plug with a glass window in it. It enables you to see the colour of the combustion gases inside the cylinder. I have used this method for 34 years and it always works. You adjust the mixture to get a Bunsen blue flame in the cylinder (yellow like a sooty candle is too rich; pale blue is too weak). Many will rightly say you don't need a Colortune but it's very handy and easy. I am told that the Colortune has a close agreement with an exhaust gas analyser in terms of accuracy of setting the mixture. It's also fun to use and satisfying to know that the mixture is definitely correct.

[kevin s]

Have a watch of this, at around 14 minutes in Ivan goes through setting up su's.


https://youtu.be/rCsaN7U1VNg

[philthehill]

Do not make things too difficult!!!
If you have the right needle and jet - lifting the piston using the lifting pin under the carb body and the engine revs rise slightly and then drop you will have the mixture about right.
What ever method you use to set the mixture a good road test will confirm if you have the mixture right or not.

[markleigh]

Thanks all. Have taken all advice and mixture now as it should be... Run to Goodwood in Sept validated it!