13 replies to this topic

[Jammy]

I need to adjust my screws (he he he) slightly as once my car is warm it idles at about 1500, which I think contributes to it running on, and I would like to take this down a few hundred revs, maybe to about 1200. Is there also an idle screw that sets the idle speed whilst the car is warming up. Like an idle and then a fast idle screws?! I have a HIFF44 carb. The other problem is, when its really cold it (as it has been lately), it idles about 1000 since it is never really warming up to quickly, epsecially with cold air always hitting the carb, although I am thinking of connecting up the intake manifold to the water supply, will this make the difference. Is it easy to change back again in a month or two?!

[Guess-Works.com]

There are two screws on the SU which control the idle, the first is the slow idle ( the one you want to alter ) which is next to the dashpot on the top, the other is the fast idle which is on the choke and engages on a cam device on the accelerator mechanism on the side...

I short a picture at the mo... but it's not diffcult to find them

[miniman5]

it mite not just be the carb, when did you last change the plugs and do the tappets? i did both of these and my car idles fine it didnt before

[Jammy]

So the slow idle is the one the controls the revs once the engine is upto temperature, and the fast idle is what controls the revs whilst its warming up!?

[Boab]

Heres one off your choices thread, can you use it to point out the screws you are on about. I would also like to know which is which.

Cheers

[Dan]

The idle speed screw controls the idle speed, the fast idle screw controls the idle speed when the choke is pulled out to the fast idle position. Both speeds should be set with the engine at full operating temperature, and the normal idle speed should be about 900 rpm, 1200 is much too high.

[CharlieBrown]

Mine idles at 1400

I was told its due to the carb being worn and it needed a refurb.

Will have to get round to sorting it.

[Jammy]

So does the fast idle come into play when the choke is fully out, or is there an adjustable position on the choke that sets when the fast idle jumps in, if you see what I mean?!

[Dan]

Which carb do yo have Jammy, the HIF or the HS?

[Jammy]

HIF44

[Dan]

The idle screws are the ones beside the dashpot. The throttle stop is the one closest to the dashpot and the fast idle is furhest out. When the car is fully warmed up back out the fast idle completely, then adjust the throttle stop until the engine idles nicely at just under 1000 on the tacho. Then make sure there is a little (1/16") free play in the choke cable, and pull the cable until the choke just strats to move the jet. Set the fast idle speed to about 1400 - 1600 rpm with the choke in this position. Well, that's what it says in the SU book, but I'm pretty sure it doesn't move the jet at all in a HIF so that should read until the choke control just starts to open the starter device.
When you first pull the choke out, the initial half inch or so of travel only increases the idle speed, it doesn't change the mixture at all. It's this fast idle at normal mixture strength that you are setting, so you need to find the point when the choke control has moved the throttle stop by it's maximum amount without changing the mixture. This is another great thing about SU carbs.

[998dave]

Mine idles about 800rpm, is nice and quiet.
Had problems with inlet manifold leaks making it impossible to get the mixture correct.

[Jammy]

I see, so since I only work a mile and a half away it should be ok to keep the choke out a tiny bit all the way til I get to work since my car never has a chance to warm up?!

[Guess-Works.com]

You live 1/2 mile from work and you drive lazy git ! :wink: