Hey all-
I am having trouble with my 1969 F-250. I really need this truck to be running as soon as possible. The engine is a rebuilt 360, with the basic mods (aluminum intake, 4-barrel, headers). The truck starts up and does drive if I keep a light foot on the gas pedal. If I start it up, and just let it run- when warm- it will slowly idle down, then run very rough, and die out. When it slowly dies down, it almost sounds like it is misfiring. I can drive it around just fine, it runs pretty solid although I think I still need to dial in the carb a little? When I come to a stop sign though, I have to hit the brakes and the gas to keep it alive. I have checked everything I know how to check. I might switch out the fuel pump- does this sound like a fuel problem? Please give me some help! Thank you!

-Tristin

 

What kinda 4bbl on the engine?

 

I think you've got to do some basic troubleshooting and eliminate possible things. What is the condition of the firing system? I'd check your points, condenser, rotary button, distributor cap, wires. I'm thinking the problem is probably not there but I'd just be sure there's nothing wrong with the firing system. Also be sure the timing is set properly. One thing that does come to mind is that aluminum intake. These things are tricky to seal on the FE's. One thing is that you've got to use shorter bolts as the factory bolts, and even some aftermarket ones, are too long and will bottom before the intake is sealed properly. You can spray some carb cleaner around and check for a vacuum leak. I'd check around the intake to head gasket and also check around the carb. You could also just put a vacuum gauge on a manifold vacuum connection and see what you've got.

Good Luck!

Tracy

 

I have checked all my ignition/firing many times. The timing is set, firing order correct, new cap and rotor, new points, new wires, new plugs. I know the manifold is sealed correctly, and all the bolts are torqued down to the appropriate pounds.
What do you mean by "spray some carb cleaner around and check for a vacuum leak"?
Also, the carb I have on there is a Carter AFB Competition 650-cfm, mounted on a spacer, then bolted to an edelbrock manifold.

-Tristin

 

Well, the bolts could be torqued to the appropriate pounds but are bottomed in the hole. If that is so then the intake manifold might not be sealed properly. You can find a vacuum leak by running the engine and spraying carb cleaner around the intake manifold gaskets, outside the carb, between the carb and intake, vacuum hose connections, etc. What happens is, if you find a vacuum leak you'll know it because the carb cleaner will get sucked into the engine and you'll notice the engine rpm change. I'm not positive you have a vacuum leak but it is one thing that is a possibility. This method works well and is easy to do. It won't take but a few minutes and you'll either find a problem or rule one out.

Good Luck!

Tracy

 

Is the choke opening up when warm?

 

It sounds to me that you may have a plugged idle circuit on the carb if it runs fine off idle or just some fine adjustments needed on the carb.

Have you tried to adjust the mixture screws on the carb to see if there is any difference in idle?
First thing while the engine is not running screw both mixture screws in all the way(don't tighten them) back them out 1 1/2 turns.
While the engine is running at as low an idle as you can, adjust 1 screw at a time in to see if there is any change in the way the engine is running.
If you can adjust either of the 2 screws in all of the way without any change in how the engine runs then you have either something plugged in that circuit or you have a vacuum leak on that side.
It would be best if you have a vacuum gauge to work with while working on the carb and intake side of the engine.
You should be pulling atleast 15 inches of vacuum at a constant vacuum port on the carb. closer to 20 inches with a pretty mild cam is better
Once you find and repair the issue then use the vacuum gauge to dial in the mixture screws on the carb by adjusting each one until you get the highest steady vacuum at the gauge.
also adjust the timing with the advance hose disconnected from the carb. as low an idle as you can (between 700 and 850 rpm would be best) set the initial timing between 8 and 12 degree's
Good luck with your engine and I hope what I said helps some.
Ken

 

2x on the adjustments. You never really said if this has been going on since the engine was put in service, or the engine was set up and this is a new problem.

Sounds like you need to start with the curb idle. It seems like a paradox that the engine must be at specified curb idle, at operating temp (!?! that's the problem...right?), with the choke fully open. My old Chilton's also says to set the parking brake, put the automatic tranny in Drive, turn on the headlights (high beam) before adjusting throttle stop screw to achieve 500 rpm curb idle.

Since adjusting the carb and initial timing require the curb idle to be in spec, you really have to start there. After you start making those other adjustments, you'll have to re-adjust curb idle.

Hope this helps, Mike

 

Thanks for the ideas guys. I plan on going out right now and attempting them in order, and hopefully the solution turns out to be simple, rather than having to reseal/reinstall the intake manifold.
Also, in responce to one question, I have a manual choke on my carb.

-Tristin