a 460 i just built has a terrible ruff idle and surge when the brakes are applied right before a stop. ive checkd and recheckd vacum lines and vacum run items on the motor, un hookin to listen for the motor to strugle even more to stay runnin, but they dont really seem to make a difference. is there some piece of gunk stuck in a idle air screw sum where? i was told to turn the air screws in all the way the back them out till it runs smooth or ruffly 2.5 turns. does it just need to be drove? do i have the timing 1 tooth out? WOT the truck runs awsome no pingin or sputterin. i took it for a mild 6-8mile drive on and off the throttle many times ( gotta love straight pipe...).

another thing that was noted tonite was the engine temp, at first it was right level with the L on "normal" but as we neared home it was over the A, did i have a stuck air bubble? i plan on gettin a good mechanical guage to rule out a crap stock guage. the Tstat is new , water pump is new, the fan is a stock 351M flexfan, which i want to switch out soon with the 460 clutch fan. the ran is clean.

-D1VE block bored 30 over, stock heads, edelbrock performer plus cam with lifters, stock exaust manifolds, and stock intake/carb
-Timing set to 14*, vacum advance is workin.
-it holds 15-18psi vacum at 1000rpm.
-the stock motocraft 4bbl and intake are from a 78 lincon (whole motor was taken from car for this build)
any adivce welcomed. thanks

 

first thing i would do is get rid of the motocraft carb find a good carb carb eather a new one or get one rebuilt a holley 750 should do the trick on mine i run 36deg advanced but i also run a welded disturbutor one thing you could try is blocking all of your vacum lines and than see if it dose it your brakes will be harder to stop but that should tell you if it is a vacum issue and as far as the temp gose well i wouldnt even run it till ya get a good set of manual guages for your oil and temp

 

It may not be a vacumn hose, you said it does it when you apply the brakes, which means your power brake booster could be going bad and have a slight vacumn leak when applied, this is usually the first sign of them going bad. And running lean can cause a motor to run hot.

 

the brakes do feel poor, but it could be im just used to a 04 6.0L diesel brakin system. we did unhook the vacum line to the booster, engine struggled a little bit, we plugged the line but i never really made a huge difference. i thought about a new holley till i figured out what they were worth, i was quoted 600 bucks. thanks for the info