[illavitar]

Hi all, I'm having trouble tuning the carb on my 1.3 sierra, I was wondering how I adjust the idle mixture screw? A search tells me set it 1.5-2.5 turns out, or to turn all the way in then start turning out until it runs at the best point.. then continue turning out until it runs crap again, then turn back 1/4 turn

I tried this and it gets good after 2 1/4 turns out.. then if i keep going (even 3-4 turns) there's no difference, idles a little higher again maybe, probably too high. And when the screw is fully turned in, it runs like crap as though it's about to die. I set it at 2 1/4 turns out which seems it's best point but it's still sort've sneezing and missing. I set the float height to around 7ml or 7.5.. from memory it was around 7mm or a touch more.

The most annoying thing is every time it's cold I have to turn in the warm idle screw around 3 full turns to get it to hold idle/rev high enough. Then once it gets warmer and the idle climbs too high (over 2k) I have to back the warm idle screw 4 turns out again to bring it back to 1000rpm. No idea why I have to do this everytime it's cold!!

[coily96]

You have two idle setting screws
None of them are a mixture screw, i wouldnt tamper with that.

Start with the cold idle screw, its located on the firewall side of the carby.
Start with a cold engine, you only have a few minutes to set this screw before the choke opens.

The screw is also the throttle stop screw on the throttle arm and can only be adjusted with the engine off. Lift up the throttle arm and adjust the screw, inwards will raise the RPM and outwards will lower the RPM, be careful not to wind it the whole way out as the spring will most likely fly out somewhere.

Start engine and check RPM, turn off engine and repeat the screw adjustment.

Once the cold mixture has been set you can only now adjust the hot idle, the screw is located on the rocker cover side of the carby, its the higher screw out if the two as the lower will be a tamper proof mixture screw.

You can adjust this setting with the engine hot and running.

The whole process can be out if the trottle cable is too tight, its possible to disconnect the cable for the adjustments then reconnect after and adjust the cable tension tight and just before it increases the idle.