I recently replaced the Holley carb with the Edelbrock 1406. We changed out the metering rods and jets to help it pass emissions.

The truck runs really good except
1) It idles really high even after it is warmed up. If I mash the gas and let off fast it will idle slower.

2) Gas mileage is about 7 mpg
3) it diesels sometimes.

I have tuned it up when I put the carb on.

When I bought the truck it didn't have the part that returns fuel to the tank ( I forget the name) I have added this, but I am wondering if it might be plugged (checking that).

Any ideas on the idle, dieseling and mainly the mileage. I would like to get closer to 10 if possible.

Thanks for the great forum,
Randy

Truck is an 83 F250 4x4 460 Manual. flat bed regular cab.

 

i have the 1411 on my 460.

i had idle speed problems as well and it took a while to figure out. in my case it was the little plastic retainer on the gas pedal itself that would sometimes pop out and keep the idle high, ended up getting a new throttle cable. maybe you need to tweak the throttle cable bracket a bit toward the carb so the spring has enough tension to push the throttle fully back, however be sure you've still got full throttle. it could be a weak spring on the throttle cable which comes with a new one as well. it could also be a sticky fast idle cam in the carb. inspect closely these areas while it is idling high, see if you can see the fast idle cam drop down if you tap it.

i also had to play with the fast idle cam so that it would fully close when i tapped the pedal while engine was cold and still fully open once it got warmed up. i've got it now where it will fully open but takes a few taps to get it to shut fully and kick that fast idle on. been a minor annoyance for quite some time now.

 

the dieseling is a timing or build up of carbon problem. put another spring on to help the other spring. it will help your fast idle. i have a 1406

 

diesling is also from too high of an operating temp..for the high idle take the cable off the carb and check its actuation to see if there is a stiff spot..then check the carbs linkage for a bind or being stiff.. the fuel return being plugged shouldnt cause a fast idle.. fast idle means more air than gas.. also check carb mount gasket for a leak by spraying wd40 at the base.. it will fill that gap and change idle temporarily..

 

Randy,

Good comments on your sticking throttle. I have the same carb and had to tweak the throttle cable bracket to allow for the throttle to easily close. I simply used a small hammer and tapped the top edge of the bracket toward the front of the truck. I don’t think I needed to move it more than about 3/16”.

As suggested, when it is sticking, remove the air cleaner and carefully inspect everything on the drivers side. Is the high idle cam completely out of the way or is it sill against the high idle screw? If it is still against the high idle screw then it could use some lubrication or a tweak in the choke adjustment. If the cam is out of the way then it is probably either the cable or binding in the carb linkage. By snapping the cable off the carb you should be able to determine if it is the carb binding up by gently opening and closing the throttle by hand - without pushing it closed - to see if it will close on its own. I did have to lubricate my carb linkage to keep it operating smoothly.

Also, I had an air leak between the manifold and the spacer I used to replace the EGR plate. I had used an open plenum still gasket and had not realized that it did not cover and seal all areas, and thus, allowed a big vacuum leak. That and a high idle speed can contribute to dieseling. Once I fixed the air leak I was able to dial down the idle speed much lower. I have mine idle at about 725 rpm.

Air leaks and high idle will both lower your mileage. Find and fix those and then recheck your mileage.

Good luck,

Mark