Prolonged fast idle on warm-up. Why so many idle screws? SAS1, SAS2, SAS3? 1987 2.6
With the cold setting in my 1987 2.6 liter baby has developed some choke quirks. It cold starts just fine - idle just a little low but stable. As it starts to warm up the idle speed climbs to maybe 1500-1800 and won't drop until fully warm. Linkages and coke plate are clean.
I've read up in the forum and examined the carb diagrams. Why so many idle screws?? Warnings about not touching SAS2 and SAS3 have me worried, and I don't understand what the 'throttle opener' does. Carbs don't frighten me - my hobby car runs dual Weber DCOE side-draughts an I do fine by them.
What exactly can I adjust to get the fast idle to drop back faster?
The Mikuni is a complicated bit of gear and not fun to pull down and rebuild. The fast idle adjustment screw is on the underside of the throttle linkage right next to the cable end (an adjusting screw with a captive spring in it) Try winding the screw out while the engine's running cold to drop your fast idle RPM. This screw and the throttle stop screw affect each other so if they've both been tampered with before you got it you'll have to try to wind them both out, reset the throttle stop and then readjust the fast idle screw until your cold idle is about the right rpm. As the auto choke on these gets tired it gradually messes with cold idle rpm as well (as well as the actual choke function) and adjusting the choke requires taking the actuator apart to reset the tension on the small nylon gear that forces the choke butterfly open gradually during warm up. Most guys end up replacing the Mikuni for a Weber 32/36 due to the Webers' simplicity and the HP and performance gain that comes with it.
I'm guessing that the actuator spring you mention is the culprit here. The cold idle is fine, it just stays on too long as the engine warms. I'll look for posts on how that is done.
Nobody has messed with the carb -- I bought my baby new in '87 and I've been the only wrench on her.
Whoa, it is definitely a family member! You can get a bit of adjustment off the bracket that the small tensioner spring gear is mounted to. But if it takes more than that be warned - taking apart the whole mechanism takes some muscle as the main loading spring is really strong. It'll bite off a finger if you're not careful...normally it only takes bumping the small tensioner gear a tooth to set it right. Good luck!
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