Tiny Little Plastic Piece -Throttle Cable

[Dyn Blin]

I've been having a recent issue with my fast idle not catching and choke position at cold start-up.  'Not a big deal, she runs really well otherwise & it doesn't get too cold here, but it's a change and I wanted to fix it.

I've been chasing cause for a  couple of weeks, then tonight when I was driving home, I felt something drop onto my right foot.  When I parked, I noted  a green circular grommet on the cab floor that has obviously been deteriorating for some time.  

It appears it fit into the hole at the top of the gas pedal linkage where the cable slides through.  In any case there's about 1/2 inch of play between the linkage and the metal stops at the end of the cable and another about an inch "back".  The cable is swimming in the pedal linkage hole, and the metal stop crimped on the cable between the linkage and firewall slips through the hole too, sometimes catching and other times slipping through.

My presumption is the resulting cable slack has kept the throttle from its cold position and not tripping the fast idle cam.  While I shop for a new cable, I've cut  a slot in a thick nylon washer/spacer and slipped it over the cable, eliminating the slack from the linkage (the interior diameter of the washer is smaller than the crimped cable stop).

Although I doubt it would have stumped most of the sage bull-riders here, I'm posting in hopes it helps another tender-foot save some time eliminating a basic cause before diving into choke and fast idle adjustment.  Without that piece hitting my foot, I presumed it was something else, especially as my carb troubleshooting seemed to show the  sets were OK when I was manipulating the linkages by hand.

Next stop:  RockAuto.

[Gary Lewis]

Mark - I've not had that washer fall off, but I know exactly the one of which you speak.  And your temp fix is a good one to remember.

However, I haven't figured out how that keeps the choke or fast idle from working properly.  As long as you open the throttle enough to get the tension off the fast idle cam then both the choke and fast idle should work properly, regardless of how much slop you have in the cable.  But, maybe I'm missing something in this equation?

Anyway, I like the term "bull riders".  

[Dyn Blin]

You should put it on a t-shirt for your meet-up.  

I guess I have mis-thought it.  I figured if I had adjusted the sets while the cable was caught on the stop behind the pedal linkage (where it would normally be kept from slipping past the hole with the plastic piece in place), and the cable then slipped through, the resulting slack/slop with the "pedal to the floor & release" at cold start wouldn't have enough tension to set the fast idle cam at the appropriate step.

Help me point to the flaw in my my mental picture?

[Gary Lewis]

If you didn't take the slack completely out of the cable when you pressed the throttle to cold-start the truck then you are right - the choke wouldn't come on and, therefore, you wouldn't have the fast idle cam under the screw.  But, if you do put the "pedal to the floor & release" then the choke and fast idle should set.

The way most choke and fast idle combo's work is that the choke rotates the fast idle cam under the fast idle set screw.  But if the throttle isn't open enough to let the cam clear that screw then the weak tension of the choke's bi-metallic spring can't push the cam past the screw and the choke won't close and the fast idle won't be set.  However, by opening the throttle slightly the fast idle set screw lifts and the choke can push the cam under the screw so the choke is set and the fast idle will work.

It doesn't take much throttle to accomplish that, probably not more than 1/8th throttle.  So I'd be surprised if the slack caused by the loss of the plastic washer would be enough to do it.  If you can drive the truck then I'd think that you have enough throttle to let the choke set.  But you can test that - when the engine is "cold" pull the air cleaner and observe the position of the choke plate.  Then open the throttle slightly and the plate should close.

[PetesPonies]

Basically the extra slack will not allow you WOT . . possibly.

[Dyn Blin]

Thanks gentlemen,

Indeed, my cold start this morning didn't reflect any change in the fast idle performance, however, the choke did close as it should.  I'll be refreshing my carburetor overview this weekend.  

The to-do list lengthens, but truck "work" really isn't.  

[85lebaront2]

Mark, since you have the Motorcraft 2150, look behind the choke housing and check two things, there is a plastic lever that raises the fast idle cam and on WOT allows the throttle lever to push the choke partially open. FWIW (and I have seen people make this mistake) proper set procedure is push the pedal down and release it fully, then start the engine, it should com up to a reasonable higher idle depending on ambient temperature. If the plastic lever has broken, then you will never have a fast idle.

If you still have no fast idle, look at your emission label (hopefully still readable) and see what the specified fast idle is. It will be a hot setting and on a Motorcraft 2150, there is a small arrow on the cam, this is where the fast idle screw rests for this setting.

[Gary Lewis]

Mark - When Brandon was here the other day I took some pics of his carb's fast idle linkage to try to explain better what I've been saying.  Here's a pic with the choke completely closed, like when the engine is cold, and you can see the fast idle screw is against the fast idle cam in :




And here's what the linkage looks like with the choke fully open and no fast idle:




Here's what happens when the engine cools and the choke tries to set.  But the fast idle screw hits the fast idle cam and won't let the choke close fully:




And here's a close-up of the cam and screw.  The cam, which is trying to rotate counterclockwise due to the spring of the choke, has hit the screw and can't rotate any further until the throttle is opened and the screw lifts off the cam.  Then the choke will close fully and when you release the throttle the fast idle screw will come down on the cam and hold the throttle open slightly.

[Dyn Blin]

Much obliged, Gary.  "Dad" projects took a back seat to work and my son back from school for spring break.  I plan  on closing the loop on this trouble shoot this weekend and post a follow up.

Beteen these photos and my recent purchase of the 81/82 Ford training guide for carb adjustments they provided their techs, I should be in good shape  

Thanks for taking the time to post this.

[Gary Lewis]

Hey, I'm in time-debt to you.  I can't imagine how much time it took to get all those parts, pack them, and send them off.  So taking those pics was the least I could do.

And, "Dad" duties come before trucks - I fully understand.