Help setting mixture on SU's please

[V8 50]

Afternoon

I'm looking for advice on setting the mixture on my SU carbs, I've tried searching but can't use the terms V8 or SU as they're less than 3 characters.

My 3.5 is running very rich, i.e. it'll start in cold weather with no choke and you can see black smoke out of the exhaust which can't be good at idle!

I've found the two mixture screws but have no idea which way enriches and which leans out the mixture

Any help would be greatly appreciated

Thanks

Charles

[101nut]

Afternoon

I'm looking for advice on setting the mixture on my SU carbs, I've tried searching but can't use the terms V8 or SU as they're less than 3 characters.

Try google and search on 'tuning su', there are several guides.

AndyG

[istruggle2gate11]

Try google and search on 'tuning su', there are several guides.

AndyG

If I remember right, turn the screw "In to Richen".

The key to tuning SU,s is to being the "jet" flush with the bridge, then turn the screws ½ a turn at a time.

They are a very easy carb to strip down and clean, also gives you chance to re-set the float level if required.

A simple tuning tool to use is the Gunsons colour tune, its gets reasonably close, available from Halfords, they also sell a cheap (read pretty carp) carb balancer.

Also, remember to dissconect the connecting bar, and that on a typical inlet manifold, the left carb feed more of the right bank and vice/versa.

[missingsid]

The mamual says to use a gas anyliser, I bought one, the range doesn't help set it so I now watch for the smoke.

I keep a small srew driver in the motor so I can change it.

Put a dot or line of paint on the screwheads so you can turn them equally. With out this I could not work out how much I had turned them.

[landmannnn]

Check your timing and plug gaps before you start.

First job is balance the airflow between the carbs.

The cheapest tool to use is the gunsons carb balancer. Disconnect the link between the the carbs and with the air filter off adjust the idle stop screw on each carb to get the same air flow through each carb.

Now set the mixture - with the engine idling and the dashpots unscrewed lift the first piston about 1mm with a screwdriver. The revs should drop slightly then stablise. If the revs go up or down you will adjust the mixture screw in or out.

Now do the other carb.

Now go back and balance again, reconnect the link and you are done.

[Andy]

on my MG - twin SUs i set the mixture before i balance them. cause if the mixture is different between the carbs they'll need rebalancing after tuning anyway. oh & make sure the dashpots are full of oil before you start or it'll never work right.

screwing adjuster right in is lean, out for rich. a base setting to start from is 2 turns (12 flats is easier to count i find) out. shouldnt need to go far from there to get it running nicely.

i balance them with a bit of pipe. hold one end in your ear & the other right at the carb intake, adjust the idle on each carb till they sound the same then do the clamps back up on the balance bar.

i find that the needle seat (the bit the mixture adjuster moves) can stick partly 'on-choke' worth checking the choke moves & returns correctly before starting as well.

[V8 50]

Thanks for all the help

I've learnt to keep an eye on the oil level in the dash pots already cheers

I'll have a go at them later and see what havoc I can cause.....

[Andy]

i find i have to re-adjust the MG every 500miles or so. on the later (for its day) SUs that uses the only 'locking' mech is a spring. so the front carb always goes rich while the rear one goes lean.

[V8 50]

Thanks for all the helpful advice, I think that I've managed to get them to a reasonable state of tune, well there's no black smoke out of the exhaust and the fumes don't make your eyes water and your throat hurt any more!

Cheers

Charles

[101nut]

Thanks for all the helpful advice, I think that I've managed to get them to a reasonable state of tune, well there's no black smoke out of the exhaust and the fumes don't make your eyes water and your throat hurt any more!

Obviously not on a 101 then ...

AndyG