High idle speed when warm...

[Northwestern]

Good morning. My S1 4.2 starts up fine, idles perfectly, when the choke is off, but when warmed up, say 10-15 minutes later, the idle creeps up to 1,500 and remains stuck there. Any ideas how to solve this? I've searched the literature and have also used foul and abusive language, both to no avail!

Paul

1962 S1 3.8 FHC
1967 S1 4.2 OTS

[caveman]

Hi Paul,
Did yo ever get to the bottom of this? I have similar issue with cold revs at 750 but approx 1200 when hot.

[mtnjag]

My 3.8 idles higher when fully warmed up. So I set my idle on a warmed up engine and use the fast idle/choke lever to keep the idle up when cold.

Beginning part of my lever is set up per manual to not enrichen the mixture, only to advance the throttle slightly.

Wondering if you have a linkage that may be jamming a little when hot?

[malcolm]

Caveman, is the 750 cold without choke? If so, it would run faster when hot; the cold rev setting is too fast. As said above, get the engine really hot and then set tickover to desired revs. Or are you saying that when it's hot you can't adjust it down enough? That's a different problem

[caveman]

From cold, I start with 3/4 choke. Full choke gives an idle of 2400rpm which I try to prevent before oil galleries are filled.
The carb choke levers begin to lift when dash lever is moved to halfway point. This seems correct by the manual and approx 1100rpm indicated for fast idle/mid point is ok.
As the engine water temperature moves towards Normal, I can ease the choke off and hence my original 750rpm. Once the car has been driven and is hot, the rpm sits around 1200. The 2 stage linkage works well from what I see and is free with full movement.
I’ve just ran the car up to normal temperature and managed to bring idle down via slow idle screws. She’s sitting nicely at 500-600rpm tonight so I will monitor on way to MOT on Friday.

[mtnjag]

The choke lever performs 2 functions.
The first section of movement should advance the throttle slightly without lifting the carb pots. This will slightly advance the rpm without enriching the mixture.

The choke lever doesn't choke anything and is not really a Choke but an enrichment lever.
So when starting cold on "choke", once started you leave the lever up slightly off enrichment but on Fast Idle section to speed the rpm while it warms up without it being too rich and fouling out.

This allows for a decent idle when cold and when warmed up it comes off the Fast Idle setting and will idle as prescribed at your idle setting. You may adjust it down a time or two as it warms if you are in a long idle period.

If it idling at the proper setting cold it will idle too high when fully warmed.

[caveman]

Understood and thank-you all for the replies, much appreciated.