What idle speed are you folks with 4v carbs seeing?

I was fiddling around with a tach and timing light and got the Bronco idling between 575-600 on ported vacuum. Around 650-675 on manifold vacuum with the idle screw backed off the throttle. Base timing 8° and on <strike>ported</strike> manifold vacuum 22° at idle.

Derp, edited - meant to say the timing jumps to 22° with the v. advance on the manifold vacuum side of the carb.

 

I have an automatic and set the idle at 750 with ported v. With your manual trans you should, iirc, set the idle 100 rpm lower, at 650 rpm.

 

600-650 works for me.

 

Put one of the smaller Autolite 4100 carbs on today and it will not idle below 800 rpm. Reckon I need to yank it and look it over again. Secondaries are fully closed - double checked before installing the carb and no drop in idle speed with the idle screw backed loose off the throttle lever. Other than that it runs nice. Will have to see how the AFR looks.

 

I quite often have probs with the 4100 having v. leaks after an install. Try using a 4 hole spacer with double gaskets on carb side. I know you're not supposed to do that, but it has worked often for me in the past. The slightest nick in the mix screws will screw your idle. (couldn't resist the word play.)

Did the throttle butterflies go in with the bevel to the correct side? Did you remember the check ball, and use old one to redo the 'seat'? On the choke side there is a plastic pin that the linkage hits. Sometimes it will prevent throttle from dropping to normal level. Did you replace the plastic seal and gasket between the choke housing and carb body?

Good luck. k

 

The plastic pin that rides the secondary linkage and fast idle cam is a maybe. I didn't reach back and see if I could push the secondaries closed at all while it was running. That damned pin doesn't come with the kit and I couldn't find one aftermarket so I replaced it with a nylon screw from Lowe's. It worked fine on the stand but need to check now that it's been up to operating temps.

Throttle plates is another maybe. Gonna give them a look-see as well.