Twin Su On 3K Help

[nickyboy]

hey all.

 

just out on twin SUs on my warm 3k.

 

now i'm having issues getting the thing to idle

 

at first i had it running but i had fuel pouring out the reservoirs so i was told to put a fuel pressure regulator in the line. i did so between the fuel pump and carbs. now... i then had it running again and now the fuel issue from the reserviors was fixed, but now it wouldn't idle and i had flames coming out the trumpets. after letting it sit for maybe 2 hours i came back to it and now i believe its getting bugger all fuel to them as it just constantly sounds like its starving of fuel, i disconnected the regulator on the side of the carbs to see if fuel was coming through, from 1 through to 4 psi i was getting nothing but at 5 it was kinda dribbling through. so... is my new regulator stuffed? and why can't i get it to hold idle?

 

i'm newish to the SU carb scene, so if anyone can shine some light on the situation, or possibly lend a hand (i'm in SA) it would be greatly appreciated

 

cheers nick

[altezzaclub]

OK- do you know how to set the mixture at idle using the jet and the little lifting pin??

[parrot]

I don't know the answer, but when you fix it, make sure you change your oil, as it is probably has quite a bit of petrol in it.

[snot35]

How does it sound like it's not getting fuel?

 

Did you also do your timing before changing over?

 

When you say you disconnected stuff, are you getting fuel out after the regulator? What condition are the carbs in?

[altezzaclub]

SUs run on low fuel pressure, so you could assume your new regulator is working. If it was more than a dribble think of your fuel consumption over an hour's drive!

 

It sounds like it might be running lean, and air leaks would be likely if you've just fitted them. All you need is a mis-match between the exhaust and inlet manifold flange heights to make sure one or the other doesn't bolt up tight.

 

The other option would be the jet set too lean at idle. You can see the top of the jet if you take the top of the carb off and take the piston out. The brass tube in the bottom of the throat is the top of the jet, and that should be within a few mm of the throat base. The fuel should be a couple of mm below the jet top. If you wind the jet down it makes the mixture richer. A rough start is to wind them right up, then down 2 and a half turns.

 

The idle mixture test is done by the idle lift pins underneath each carb, and they will either speed the idle up if rich, or it will die if lean. Change the jets a hex turn at a time, they are quite accurate, screw down for riher, up for leaner.