Hi Ford-fans;

Its been a while since I've posted so please excuse the newb-ness. I hope we can find a solution to my problem.

1975 f250 4x4 360 4 speed.

About 3 months ago a friend and I did a full engine gasket set along with lots of other things (i.e. elec ign, new clutch, new fly, new igniton parts, headers, paint).

Amoung the additions, a brand spanky new Edelbrock 1406.

Everything seems to work well, (a lot more power!) but I do have one issue, especially now that it is cold (40 degrees)!

-when I first start the truck (morning or after work) after it has been sitting for a few hours, the throttle goes up instantly and continues to climb until it reaches about 3k, (idle is 800-900) the only solution so far is to tap the accelerator ,i get a pop! and down she goes to either 1.5k or idle (depending on if choke is engaged)

- once truck is warm (180-190) Idle will stay at 1500 unless i tap the accelerator above 3k and let it roll down to idle

- it will idle fine, but once i drive and bring accelerator up to 1500 or so it will not fall below unless i once again tap it...

Though it might be the choke (new to electric) but I disconnected it to rule out, and no dice. Any suggestions ford-fans?

 

The reason the idle speed is so high when you start the truck is because of the fast idle linkage. Pressing the pedal down once before starting a cold engine loads the choke (even if you've disconnected the electrical connector - all this will do is prevent the choke from opening). The idle speed needs to be increased to compensate for the rich combustion chemistry caused by the choke, and this is the job of the fast idle linkage. Yours simply needs to be adjusted down which is common for an out-of-the-box carburetor (I had to do the same thing).

The fast idle speed screw is on the driver side of the carburetor with the rest of the throttle linkage. The screw head points downward; you have to flip the fast idle linkage upside down to gain access. It is not to be confused with the horizontal curb idle speed screw.

The reason the idle goes down to normal once the truck is warm after you tap the accelerator is because the fast idle linkage will stay engaged until the throttle linkage is moved, even once the choke is open all the way. The fast idle cam cannot drop out with the throttle at rest because it is pinned in place. The throttle has to be pulled back for the fast idle cam to drop out and the idle speed to return to curb speed.

The third item in your list sounds like the choke may not be opening all the way, or the linkage is gummed up or binding. I would check the adustment on the choke and verify the fast idle speed is set correctly first.

The first two items you've described are completely normal (just need to be adusted). The third one does not sound normal; after the choke has opened all the way and the throttle has been pulled back past the fast idle speed, the idle should never rest past the curb speed setting. However, as I said before, verify that all the user-adjustable settings are dialed in. There should be no adjustments beyond fast idle speed and choke cap index for a brand new Edelbrock out of the box.

One last note, the pop you mention when you first drop the idle speed below 3,000 RPM is not expected and could be a sign of a lean condition. However, 3,000 RPM is way too high for fast idle (the engine will be screaming, and it's bad to start an engine dry that high) so it's not necessarily a valid use-case to diagnose. I'd see if that problem still exists after taking care of everything else I've mentioned.

 

Thanks a bunch, ill let you know! hopefully tomorrow!