Hey Gang,

Just got install 1.12 4V on my 66. I'm running slightly rich on the primaries at idle. I cannot back out the air screw much more. If I warm up the engine, let it rest for 1.5-2 hours, the start is immediate and the idle is silky smooth. Once the engine totally warms again, the idle is rough but otherwise does not stall or smoke black (presumably needing a less rich mixture). It is drivable, but I dont like it. I know its rich and not lean because I used a towel to test...

Does the approach of lowering the fuel level by re-adjusting the floats seem to be the next move? Or do people think I should tackle the jets and change the 48's down to 47's or 46's (I will need to find a supplier...please recommend)?

Fred

 

Try http://www.ponycarbs.com

 

Try lowering the float level a bit.. That tends to take more throttle position to get fuel flowing through the boosters. Dont go so far as to create a lean stumble after the accelerator pump does its thing, just drop it a bit and see how it does.

The jets dont have anything to do with idle mix. They are more about part throttle and full throttle, after the fuel is flowing through the main circuits and boosters. Jetting it down wont make it idle and not burn your eyes.

 

Maybe I'm not reading this correctly but it sounds like you are backing out the screws in an attempt to lean out your idle. Do some of the Autolite 4100's have reversed mixture screws like a few of the old Holley's out there? I've never seen an Autolite/Motorcraft 2100 or 4100 that LEANED by BACKING out the mixture screws.

 

You are not at all clear as to which carb you are using. In 1967 for began using the 4300 series carb which had a large screw on the back which was the idle speed control and also the normal idle mixture screws on the front.

Almost every carburator ever built will idle reasonably well if you turn the idle MIXTURE screws in until they touch bottom and then back them out 1 1/2 to 2 turns.

From there you adjust the idle speed by whatever method your carburator uses. Then turn each mixture screw in slowly intil the engine gets rough. Back it out until smooth. If emission a consideration leave it there for test. If not back out an additional 1/4 turn.

Go back and forth 2-3 times until idle speed and mix are good.

 

Hey everyone,

I just wanted to followup on this post. I'm sorry I was not specific enough. I just assumed most people would know that 66's have 4100 autolites on them!

Basically, my carb needed leaner jetting so that it would idle properly. I worked with a guy that rebuilds them for a living. His first suggestion was to lower the fuel level by altering the floats. I kept doing so but then a small flat spot was introduced. He then told me to lean untill I could set the mixture screws 1-2 turns from fully seated. I progressively worked down from 48's and wound up with 46's. I still have some float work to do but have gotten a feel for fuel level and its affects on idle etc.

The car now idles as smooth as silk when warm (its too lean when warming up but the choke adjustment is for another day or maybe not at all since it rarely gets below 40 here). I also changed the secondary jets from 54's to 48's (it was blowing black smoke previously). Like I said earlier, I still have some float work to do. Things are not silky smooth at all throttle angles...there is a position where (probably around 1/5 throttle) where its either lean or rich (the engine kinda labors...I am guessing lean). At this point, I have put several 100 miles and the car is very responsive although for some reason, hot starts result in a rough idle for a few minutes (even though I have a phenolic spacer).

Now guess what? The car now has delivered 19 mpg on the highway with less than 10% city driving on 2 separate occasions! Not bad for a v8 convertible. My timing is set to 6 degrees which I know is low but I am pretty happy with my results so far. The temp guage has not been affected by of this (I was expecting warmer operating temps).

I checked on of the previously black spark plug and the insulator appeared dusty white this time (no oil residue either!!! This car is a recent acquisition for me and now it looks like the rings are good to go for a while at least). I think at this point, I am going to do some more tweaking on the floats. Anyway, just thought I'd share. Hopefully this will help someone out.

As for the idle screws, my findings are that they do lean out the idle if you back them out or at least have a strong relationship to fuel mixture at idle. When I had the 47 jets, I had the screws out to around 4 turns and the engine was CLOST to idling well but not quite. When I went to the 46's I was able to set them around 1-2 turns which is closer. I'd like to hear other peoples experience here.

Fred