I recently bought this truck. It's a 1987 F250 extended cab with a carburated 460 engine. The carburator has a tag that says Motorcraft.

The problem I have is that when the engine is just started the choke sets in and it runs fine. As soon as the choke goes off the RPM's are really low until the truck reaches operating temperature. Once it reaches operating temperature I can hear a click near the carburator and all of a sudden the RPM's go up to normal. Now that the weather has turned colder I can't drive on the streets cause it stalls out on me until the temperature reaches normal. I've tried raising the idle adjustment so it won't stall out on me but then it races when at normal temperature.

Does anyone have any ideas what's going on and how to fix?

Thanks in advance.

 

You may need to rebuild your carburetor, ford carburetors are known for being not to good, you could get and aftermarket carb, and solve all your problems.

 

Hi,

If your set up is like mine, the carb is actually a Holley. When mine started acting up I bought a new one from Summit. I used the 600 cfm, vac secondary. I think it was around $225.00. Made a world of difference in performance and mileage. Good luck.

Rodger

 

I don't know if the 3/4 or 1 tons have the EGR Spacer Plate under the carb before the intake, but on a 1/2 ton w/ 5.8l and Holley carb they do have it, and, if the gasket between it and the intake is bad, it will cause a vacuum leak because of the thin area between the carb secondarys and the EGR passageway. In most cases you can't tell anything by spraying solvent around the plate, you must remove the plate to verify. This could be the source of your idle while hot problems because of a potential vacuum leak.
Phil

 

>I don't know if the 3/4 or 1 tons have the EGR Spacer Plate
>under the carb before the intake, but on a 1/2 ton w/ 5.8l
>and Holley carb they do have it, and, if the gasket between
>it and the intake is bad, it will cause a vacuum leak
>because of the thin area between the carb secondarys and the
>EGR passageway. In most cases you can't tell anything by
>spraying solvent around the plate, you must remove the plate
>to verify. This could be the source of your idle while hot
>problems because of a potential vacuum leak.
>Phil

You could be on to something. I do have that spacer plate. Also, I disconnected the vacuum hose to the distributor advance and it remains at low idle even when at normal temp. So I got my timing light out and it turns out that when the engine is cold the timing is at 8 BTDC. When hot and vacuum hose connected it advances to about 20 BTDC. When hot and no vacuum hose it remains at 8 BTDC. The hose routings are correct as shown on the decal under the hood.

Here is a picture of my vacuum diagram:

http://photos.yahoo.com/ibedgen

On the three prong port there is a restrictor that feeds the middle port that goes to the distributor. I suspect this is the feed when cold. When hot the feed comes from the bottom and there is no restrictor and hence now I got more vacuum pulling the distributor advance. I suspect something may not be working right and I should be getting lower vacuum than what I am getting.

I'll check the spacer plate and see what I find.

Thanks!

 

 

I have the same problem on my 86 250 only it doesn't sound quite as bad as yours does. I love my truck but the carb is a POS. Ford makes such a good truck, you would think they could put in a decent carb