Holley 390 stumble

-
JR

JR

Pissed off senior member.
Joined
Oct 17, 2005
Messages
4,404
Reaction score
17
Location
East Renton,WA (Seattle)
The 390 on he slant has a nasty mid range stumble that I can't track down. When your accelerating it goes from 1st to 2nd fine (A-745 3 speed and 3.55 gears at the moment) but at the top of 2nd it will start to "cough" and stumble all over it self. It also does it when you floor it. I have been playing with different secondary springs, power valves and accelerator cams and the float level is right below the sight plug.
Have I just not found the right combo of secondary spring an accelerator cam yet? I am trying to track down the local carb guy so I can trade the POS Holley for a 500cfm Eddy that has been turned in to a 400cfm. I hate Holleys on daily driers! :angry7:
 
I feel the same way about Holley :angry7: But I must have been lucky on the one I have that my wife gave me for my /6. dual bump.
I wonder " sense it don't do it in first and the beginning of 2 gear " it's reading low vacuum in second and third gear and the dist is not advancing, do you get black smoke when it does this, could it be secondary opening to soon
 
sounds like you could be running out of fuel at the top end - you would notice that in 3rd gear, never 1-2

Hook up a fuel pressure gauge and see if it falls off when you have your issues.

beats buying another carb for nuthin.
 
The 390 Holley I had on my \6 ran flawlessly for 30k miles. As I recall I settled on the long yellow spring in the secondaries, the pump cam in the #2 position, went up 2 jet sizes on the main jets and used a #10.5 power valve.
 
I'm getting great vacuum at idle and I did just bump the power valve up to a 10.5 and it smoothed out the low end but I'm still getting the stumble mid range. I am with Memike on this and am going to hook up a vacuum gauge in the cab to see what it is doing when I drive it.

I still hate Holleys on daily drivers:angry7:
 
Yep, do the vacuum gauge thing, you maybe experiencing power valve closure.
 
Got it figured out! The diaphragm for the secondaries had a small rip in it right on the edge of where it sealed. I am still figuring out the right accelerator cam and secondary spring settings but the main stumble is gone and the secondaries actually work like they should now!
 
I knew all you needed was time to figure this out 8) I am glad to hear thing are moving forward and you are the tec I thought you are :read2:
So a big congrat's to you 360scamp :cheers:
 
You must log in or register to reply here.
-

Back
Top