Holley spring loaded needles and seats

[Oregonite]

Has anyone installed spring loaded needles and seats in a 390 Holley 4-bbl? I have a '74 CJ5 AMC 258 i6 / 4.2l with HEI, header, Offenhauser intake, K&N air filter. Is that the way to go if you're running a carb

 

[LongHorn]

I’ve run a Holley 4 barrel on my Jeep for over to 30 years. I did some of these mods by trial & error as I had problems off road that couldn’t be fixed with just a float level adjustment. Keep in mind I’m not into the extreme stuff, but I have had my Jeep in some crazy situations so these mods should work for everyone. My early mods were taken out of an off road magazine with some minor differences in materials used. I did the “Holley Off Road Avenger” vent tube design, and years before Holley decided to do it. My first mods were on a standard Holley 600 cfm model 4160 vacuum secondary P/N 1850. It’s essentially the same carb as the 390. The 390 is just smaller. This carb has the side hung floats, which are more desirable for off road use than the center hung floats, but the mods will work on either carb. My early mods were basically just to extend the vent tubes. I used straight 1/4″ copper tubing because it fit perfectly into the stock Holley vent tubes. I extended the vent tubes to within 1/2″ of the top of the air cleaner. Any closer than that and you may draw fuel vapor out of the vent tube thereby richening your mixture. Next I played around with spring loaded needle seats. To me they made a difference coming off big rocks, going down staircases or waterfalls. My next mod was to install a vent whistle, While they are not recommended for side hung float bowls (model 4160’s) I modified it to fit. This is for the primary side only as the secondary side has a metering plate and the whistle won’t fit on the 4160 model carbs. I have had one in for close to 20 years with no problems. Basically you just cut the whistle down to about 1 1/2″-1 9/16″ then install in the metering block. Instead of using the rivet supplied with the whistle I staked the bottom of the metering block. Now it’s tight enough to hold the whistle in place and I can still remove it You can run a vent screen instead of the vent whistle if you like Holley P/N HLY-26-39 but I have never tried this. later on I bent the tubes in a arc & used fuel line to connect the tubes, but cut holes at the top of the curve. Like I was saying, like the "Off Road Avenger" I have to shake my Jeep pretty hard to get fuel to slosh out. I used to set my floats at a lower setting to help prevent slosh, although with this new style vent tube the standard setting seems be good to go.

Now, that Holley started making a carb you can run out of the box.
I just run the “Holley Off Road Avenger” it’s pricey, but It’s been a great carb with very little adjustment has run great .

 

[Oregonite]

Thanks for the information Longhorn!

 

[LongHorn]

Just glad to be able help if I can.
Good Luck with it.