having a problem with my 250

[the_legend_1981]

i'm gonna try and make it through the winter with my straight six and put an 8 in it next year but here is the issue...when i first start driving it it's fine, but towards the end of my trip its revving real high(about 4000rpm) and if i adjust the timing a little it will idle right down. what could this be?

[VileZambonie]

4,000 rpm idle? I would say you either have a serious vacuum leak or sticking throttle/linkage/carb adjustment. Is the fast idle cam sticking?

[the_legend_1981]

i'm not sure. i'm gonna check it out later... a vacuum leak could be it but why would it be fine when i'm first driving it?

[Lt.Del]

That's a lot of RPM's!  Have you tried to gas it abrubtly when it is doing that, to ensure, as Vile said, the unstick the fast idle or break loose a binding in it?

When it does that, I'd get out and look under the hood and see what is going on w/ the carb.

A possibly would be a vacuum leak, but not the standard run of the mill type. I don't know how far your trip is or time-wise when it starts to run up, but, if you have a crack in the intake (which may be the same has the head on a six) or the block, it doesn't get wide until the motor heats up good.  That would explain why it may not do it when the engine is cold.

With a crack, much may air get mixed w/ the fuel as if you had the throttle open. 

What year truck do you have.  Do you have an O2 sensor?

[Blazin]

Could be something sticking in your distributor like the weghts, vacume advance? First thing I would do is hose all the carb linkage down with PB Blaster.

[the_legend_1981]

if i rev it up when it's doing this its like the throttle sticks

[Fordeatinz71]

sounds like one of two things...a cracked intake (was a BIG problem on the 250s) and as mentioned, it's not opening up until it gets hot and things expand...or a sticking fast idle solenoid.  look under your hood, at your carb...there should be a small "can" with a wire going into it and what looks like a bolt sticking out of it...the "bolt" should be inline with your throttle linkage...that is your fast idle solenoid.  mine started sticking and was causing a high idle...i disconnected that dude and popped the "bolt" back in...no more issues.  unfortunately, that also compensates idle for the A/C so my idle doesn't increase when i have the A/C on, but it still runs fine with the A/C on...