750 Holly problems

[LUCKY13]

I installed a new 750 Holly on my 396 last year. Til now, it's been perfect. Last week, the idle suddenly reduced by itself. Turning up the idle won't help, it won't idle til it gets over 1000 rpm while it normally idles fine at 750. I only have one vacuum line running to the passenger side valve cover, I checked it and it's connected solidly on both ends. There is no vacuum advance. I tried moving the idle jets but no positive effect. All fasteners are tight. I have no idea where to look next.........any suggestions?

 

[porch dog]

it may have blown a power valve which will load up at idle. has it suddenly gone rich ?

 

[gmjunkie]

750 Holly problems : When there is a Holly,There is always problems!! Power Valve, Sticking Floats,Vacuum leaks!!! Is it puffing any black smoke??upthumbs

 

[LUCKY13]

Holly carb problems

I bought the 6.5 Holly power valve from NAPA and my problem is solved.

 

[porch dog]

glad to hear it. remember if idle goes up , it's a vac leak. if it goes down it's too much fuel.

 

[LUCKY13]

NAPA sells two Holly powervalves, a 4.5 and a 6.5. The 4.5 is for more radical cams producing low engine vacuum. The 6.5 is for cams with less radical duration producing higher vacuum. My 396 cam is a:

139-011
Crane

Hyd.
Roller
.578I /.610E
.226I / .234E Cost$324.





I first purchased the 4.5 but when I installed it, I found it was way too rich. I took it back and exchanged it for a 6.5. The 6.5 worked perfectly.

(By the way, this cam is absolutely perfect for street use. It has a mean sounding idle, it has a ton of low end, stoplight to stoplight, and it does not foul my plugs.)