Hot Rods Big Block Chevy & Holley gurus . need help please.

Hey fellas . Chasing a problem and not finding it so im looking for some ideas.

Engine is a 1969 chevy 427 . Compression is in the 10.5 area , solid lift cam " not sure on specs , trying to track down the builder"

th400 , 4:56 gears . The problem is i am getting a lean condition on top end . Normal driving through the primary side is great , no hesitation and a good burn on the plugs.

When i stab it and bring the secondaries in , it develops a lean pop and stumble.

Carb is a holley hp 4150 series 830 . Pump is a holley blue pump with a small holley regulator.

I did a wide open / shut it off at top end plug reading and it shows lean . I pulled the carb down and it had 76 jets on all 4 corners and a 28 shooter in the front with a 29 out back.

I went with 84's in the primaries and 86's in the secondaries , along with 31 shooters on both ends and a 50cc accelorator pump on the back . Still a lean pop persists and shows it on the plugs . I went ahead and replaced intake gaskets to rule out a vacume leak there also ...

Im wondering if the blue pump and regulator are my problems , wondering if those items are up to the task and if i would be better off going with a stout mechanical pump .Im not sure on a horsepower rating on the engine . Im going to say its going well past the 500 mark . this thing spins up like a tight winding small block . itll walk right past the 6k mark before you realise your there.

Now the lean condition actually seems like it leaves if i bring the secondaries in on a stationary burnout , but it comes back under a load.

Heads are 063's oval ports . 1.7 rollers.

I

 

Have you tried jet extensions on the secondary jets?

 

No sir , i have not . I knocked the power valves back to 3.5's due to the low vacume from the big cam . Not getting any better.

 

try the jet extensions as recommended , sounds like its getting air on the hit .

 

Dont rule out a ignition problem.... when you open the secondaries you are stressing the ignition and a barley adequate spark might not be up to the task... seen this happen a time or two in my time.

 

What intake you ruing?

With 4.56s that things got to be accelerating pretty hard the gas is going to be in the back of the carb.

 

Intake is a Team G single plane. I was told the heads had 2.18 intakes on them . Just had one fella get ahold of me and he said he ran a very similiar set up on a 427 and his would not run with any jets in the 80's . Said he had to get to mid 90's and in the spring and fall he would bump them to 101 and 102 . The ignition is a crane fireball box and an accel super coil on a gm hei.

 

2800-3000 on the convertor

 

Thanks for the help everyone ... My main goal at the moment is to get this lean popping situation to leave . I DO NOT want to burn up a piston . Ill start jumping jets and look for some extensions andsee where i end up then ill start on the shooters.

 

I am dealing with a similar problem, my car won't rev past 4500 under load but happily will if spinning the tyres, i'm going to mount a fuel pressure gauge somewhere where i can see it while driving to make sure there is no fuel pressure drop. Also make sure that the float level is set right.

 

fuel pressure gauge is a good idea. Although I ran a holley blue pump and regulators on my 55 for years with the blown 454, ran low 11s, same pistons over 100k miles.

 

If you try the jet extensions be sure that they allow the float to drop enough for adequate fuel flow. They make floats with notches to clear the extensions. They also make a high flow needle & seat assy.which may help if your not already using them.
I ran a Holley blue pump & regulator for years on similar 427 with no problems. I set the fuel pressure at 7lbs with the engine running.