Hello everyone. I am ready to give up on this thing. Ok. 1986 F250 Lariat XLT. 7.5 L 460 Holley 4barrell. Just bought the carb factorry rebuild. In the past month, I have replaced Batter, alternator, solenoid, fuel pump(1), Gas lines, distributoir cap, and rewired practically the whole damn truck, And it runs worse then ever.

Starts right up, and idles at around 1500 rpm and then I kick down to around 800 rpm, after choke opens. Still running good, Then I commence to drive the ole Betty, Will run ok till I come to my first light or so. Then Idelss rough./ Have to keep one foot on gas and one on break, or shift to neutral. Then when I go it hesitates like she is starving for fuel. It has also started to shift hard, and takes alot more rpm till it automatically shifts. Then the brakes seep spongy at times.

Also put front pads and u joints in last week or two. also new ignition switch. could this be idel mix, or a vacuum. or where should I begitn to start...AGAIN? any help would be great., James

 

It sound like you definately have a vacuum leak in one of you vacuum lines. If your truck is like mine with a million hoses you will have a lot of lines to check.
Check the lines at carb first then the vacuum line to the modulator valve on trans. this could be the cause of the hard shift, Also the hard shft could be you are reving the engine to keep it running.
One other thing is you changed the carb and maybe the base plate is causing a vacuum leak. You may have to replace this if it still is the old cardboard plate. They do not cost that much to get a replacement. This can also be checked with a spray carb cleaner by spraying along the base on all sides and if the truck idle smoothens out or speeds up your base plate is vacuum leaking. Check the bolts to carb are all still tight, if loose can also cause a leak at the plate.

 

Could very well be some nasty vaccum lines. The funny thing is that it starts and runs ok at first. The problems seem to come after putting some load on the motor.

Another thing I might look at is the timing. Have you replaced the timing chain and gears lately? How is the distributor itself? A timing light might give you another point of view on the problem. If not for the age of some of the vaccum lines, I'd probably suspect timing issues first. This could also give you some of your seemingly vaccum related issues.

 

Also, check your throttle return. I didn't put the throttle return spring on my carb after I rebuilt it. Ran great in the driveway, but would race or sputter at stop lights. Putting the spring on fixed all that.

 

thanks guys but the timing I have at around 10 degrees (8 recommended) but I am in the mile high city. I have replaced many if the thousand I hoses I have, I just got a vacuum pump last night and I am going too check some of the crappy emmisions things they have. any other ideas would be great. Thanks James

 

Do you have a working hot air system on your air cleaner? It sounds like the carb is icing up. Mine will do it at anything under 55 degrees. The air bleeds in the carb ice up and then the carb runs really rich and will not idle and drives really bad.