New ping
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
what carburetor are you using? if a Holley what is the list # such as 4779-8. many of the newer generation Holley's and their clones have a lean at part throttle problem due to the location of the idle jet and the size of the idle well, Holley used a idle jet that was at the bottom of the idle well but it costs less to produce a metering block with the idle jet near the top of the metering block along with a idle well that is too small thus a lean at part throttle issue. Henry @ olescarb
Thread Starter
Melting Slicks
Joined: Dec 2009
Posts: 3,232
Likes: 656
From: Thunder Bay
Interesting. Thanks for the input.
The carb is a Holley Street Avenger 770. The numbers on the air horn are 80770 3230. Does not say 'LIST' like most of the other Holleys I have worked with over the years, and when I look up 3230 it comes back as a '66-67 GM small block, so I'm not quite sure what to tell you.
I bought it new many years ago. It was scary fat out of the box. It is currently jetted 67/69 and I have increased the accelerator pump squirter when I built the 427 although I neglected to record the size of the one I installed. Other than that it is box stock.
This thing has performed flawlessly since I got it. It was on a 383 for many years before I put it on the 427 in 2017. I've only had the preignition/detonation/pinging problem since late last summer.
The carb is a Holley Street Avenger 770. The numbers on the air horn are 80770 3230. Does not say 'LIST' like most of the other Holleys I have worked with over the years, and when I look up 3230 it comes back as a '66-67 GM small block, so I'm not quite sure what to tell you.
I bought it new many years ago. It was scary fat out of the box. It is currently jetted 67/69 and I have increased the accelerator pump squirter when I built the 427 although I neglected to record the size of the one I installed. Other than that it is box stock.
This thing has performed flawlessly since I got it. It was on a 383 for many years before I put it on the 427 in 2017. I've only had the preignition/detonation/pinging problem since late last summer.
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
oem jetting is 72 primary and 75 secondary in most cases the street avengers are too lean. If you used a a/f meter or exhaust gas analyzer to jet your current jetting then I would take a look to see what the a/f mixtures are at when you have the ping problem. In most cases I would start with 72 primary and 78 secondary along with enlarging the idle well to 0.106" (oem sizing of most performance holleys from the 1960s) we also use the Barry Grant trick of using a stronger pump duration spring to make the pump duration spring mimic the strength of the duration spring they used in the 1960s with a 0.031 squirter and I like the pink cam. the idle mixture screw is often only open about 1/2 of a turn from seated to get the correct idle a/f mixture.
Thread Starter
Melting Slicks
Joined: Dec 2009
Posts: 3,232
Likes: 656
From: Thunder Bay
oem jetting is 72 primary and 75 secondary in most cases the street avengers are too lean. If you used a a/f meter or exhaust gas analyzer to jet your current jetting then I would take a look to see what the a/f mixtures are at when you have the ping problem. In most cases I would start with 72 primary and 78 secondary along with enlarging the idle well to 0.106" (oem sizing of most performance holleys from the 1960s) we also use the Barry Grant trick of using a stronger pump duration spring to make the pump duration spring mimic the strength of the duration spring they used in the 1960s with a 0.031 squirter and I like the pink cam. the idle mixture screw is often only open about 1/2 of a turn from seated to get the correct idle a/f mixture.
Everyone here has given me something to think about. It always helps to bounce some ideas around.
I bought an 8.5 power valve so I'm going to try it, if only for my own education. It also won't do any harm to try and decarbonize (why do I hate that term now?) the engine. After that I'll try monitoring vacuum and mixture more closely while it's detonating.
Thanks for the help.
