Hello all

In my earlier thread I told how, when I pulled the choke out for a cold start, the idle wouldn't rise, in fact it started to gurgle and then the engine died. I received the advice to adjust the fast idle screws on the carbs (HS6), and this was my first foray into changing anything on my car.

So this morning I started from cold with the choke pulled out. Started well. Then I shot out to look at the engine. It started to die as normal, so I manually throttled it and at the same time screwed the fast idle screws clockwise (as if you were looking at them - 'tightened'). This did raise the idle sufficiently so that when I stopped throttling with my other hand, the idle was high enough not to let the engine die. So far so good. Then I did a test drive, with the result that the idle was far too high once the engine had warmed up, i.e. stopped in traffic. So I lowered the same screws to get the idle down.

So what result have I got. I have raised the screws to get one result when cold and lowered them again to solve the resulting high idle when warm. Surely I've cancelled it out!

I've probably not adjusted the correct screws. The ones I adjusted were labelled in the Haynes as 'fast idle' screws and are reached from below with the screwdriver pointing at an angle, upwards.

To me, at the moment, the fast idle is the same as the idle, but can you please tell me where I am going wrong. I've got the interest now, and don't want to lose it!

Thanks, as ever,

Tom
London

Just to answer the question of whether I touched the correct screws as detailed in Ron'e post earlier, please look at this picture; the negativised screw is the one I adjusted, which was called 'fast idle'.

[I hope the image comes out...]

Thanks

Tom

Yup... thats the right one. And that should have zero affect on the idle when the choke is off, so the next thing to check is if the choke is for sure disengaging fully.
--
-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

Tom;

Ditto to Matt's post.

I'll add to that, that disengaging fully is defined by the jets coming up to the rest position, AND the fast idle cams returning such that the FI screws are no longer in contact. Given sticky mechanical action which occurs without proper lubrication, choke may have trouble returning to the fully disengaged positions.

Cheers

Go back to zero and start over, or it will frustrate you for a long time. Get the motor good and warmed up first, then do this:

Remove the air filters.

Loosen the screws in the fittings that clamp the choke cables to the choke mechanisms so the cables slip, but do not remove.

Back off the fast idle screws so they are well clear of the choke mechanism cams.

Ensure the choke mechanisms are rotated fully off and the jets are seated upwards into their holders.

Back off the idle speed screws (vertical at outboard top corner of each carb) so the throttle butterflies are completely closed. If some slack is present in the linkage, you are now back to zero and can start adjusting properly.

Turn in the idle speed screws so they just barely touch, and go 1/2 turn further in so they are just barely opening the butterflies.

Start the motor, which will probably idle quite fast. Back off the idle speed screws so the intake roar from each carb throat is equal -- get your head down there so you can hear both at once -- and for a reasonable idle speed. Play with this until you are convinced the sound is balanced.

Operate the throttle linkage by hand while watching the pistons in both carbs. If they both begin to rise at the same instant as you open the throttle slightly, all is well. If not, you need to adjust the cranks on the shaft between the carbs so that they do operate exactly together (it's an 8mm wrench that fits the nuts on the cranks).

Shut off the motor.

Push the choke lever all the way in and tighten the clamps on the cables. Pull the choke all the way out and observe that both jets drop down 1/8 inch or so from their seats fairly evenly (it probably won't be exact). Push the choke all the way in and observe that the jets have retracted all the way.

Turn in the fast idle screws so they are just barely not touching the cams on the choke mechanisms. You can do this evenly by inserting a sliver of heavyish letter paper between the cam and screw on each side, and adjusting just to the point where you feel a slight drag pulling the paper out.

The carburetors and chokes are now synchronized and sensibly adjusted for airflow. Adjusting mixture is a different subject, but will not affect what you've already done.

Remount the air filters.

It sounds like you adjusted the choke adjustment screws. Haynes no doubt calls them something else but they should not be touching anything with the choke not in use. With the choke in use they should be hitting a semi round thing which opens the flap inside the carbs.
The screws your after face up and are at about 11 oclock on the carb closest to the cab and at about 2 oclock on the one towards the front of the car. When you turn them clockwise they speed up the idle, unless there's too much gas already getting through. In that case the idle will slow down and the engine will probably stall.
If you hear gurgling then it seems your getting too much gas. Perhaps try moving the jets up a couple of flats each.
It's important to adjust them both the same, but maybe you know that.

Pulling hte choke cable does two things... most importantly, it enriches the mixture by lowering the jets.

But it should also speed up the idle via a a sort of cam lobe thing when pushes *different* idle adjust screws. Those should not touch anything until the choke is engaged... I'm guessing you didn't adjust these ones, and thats what needs to be done. I can't really describe where they are, but if you watch carefully as an assistant operates the chokes, you'll see what's going on...
--
-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC