Hi everybody! Ive been scanning the forums and trying to solve my problem, but to no avail. First, a little about the truck. 1976 F-150 4X4. 3 speed with a granny gear. Engine is a 428 bored .030 over out of a '68 T-Bird. Holley 4160 750CFM, vacuum secondaries. New brake booster and master cylinder. New battery. New fuel lines and filter. New vacuum lines. OK, the problem I'm having is the truck starts fine when I adjust the choke(which I seem to have to do every time I go to start it). She runs at high idle, and when she warms up she begins to sputter and stumble whenever the brakes are pressed. Ive gone around the intake manifold, bottom of carb, and vacuum line to brake booster with WD40 to check for leaks, but no luck. She also doesnt have the power she once had. Number 4 cylinder has oil on plug, but thats the only one. Not sure if thats related to the current issue or a separate one. She will drive all day long so long as I dont let off the gas. I havent hooked up a tach, but she doesnt sound as though the idle is too low. Actually sounds a little high. Like 9hundred to 1k RPM at idle when warm. Definitely not the old glub glub I grew up with(was my dads truck). Any help would be greatly appreciated.

 

68 T-Birds came with either a 390 or 429.

Does the booster check valve hold vacuum?

 

Check valve is brand new. Came with the booster. Any way to check it without removing the valve? Removing it voids the warranty.

 

And as for the engine size, 428 was also used, but wasn't as common. Once I find the book I made on it while I was overseas I will post links. I went through this same argument with my dad when he told me it was a 428 from a 68 T-Bird. LOL.

 

Yeah, put a vacuum pump on it. New parts can be bad.

10-4... So long as you know the difference between an FE and a 385.

 

So, I haven't had the opportunity to check the check valve, but I did notice something else. Fuel lines are running awfully close to the engine. Grabbed the steel line, and it was hot. Not burn my hand hot yet, but still hot. Could this be a contributing factor? Fuel filter had bubbles and a lot of what I originally thought was air, but am beginning to think is vaporized fuel. Thats why I replaced the lines and filter. This would explain the need to give her gas when hot to keep her running at lights and what not. Would also be affecting my fuel/air mix. Could this be robbing my truck of just enough power so that applying the brakes is the straw that breaks the camels back?

 

I tell people all the time "new" does NOT mean "good" anymore. Plug the brake booster altogether and see how it runs. ....and yes, vapor lock could be an issue. Cut a rubber hose length-wise and put it around the steel line for insulation. See if that makes a difference.

These are not permanent fixes, just diagnostic tools to narrow the field a little.