l have a holley 600cfm on a chevy 350. l was adjusting the choke and when l open the choke a little it starts taking off good then starts to bog down and backfire, but when l close it a little it bogs when l start taking off then is fine when it gains some rpm. l need to know how to adjust the float, air/fuel mixture screws, and choke for best performance and mileage.

Boy u don`t want much,lol Get ready

Your choke has the following setting which u will have to go to Holley is web site for the actual spec`s as all r different.

On the choke You have to set the distance of the valve to the air horn when the throttle is closed.
You also have to adjust the unload-er, Thats when u have a closed choke & u open the throttle to WOT, in order to clear a flooded carburetor.
Next u have to set the choke pull off.
Those three tings will set the choke

Now on the float.
On the passenger side of the float bowl u will see a flat screw. This is a plug right at the fuel level in the float bowl. With ur car on level ground & ur engine cold & NOT running, remove that screw. If ur float level is correct u may get just atricklel of fuel out the hole or u will see the fuel right at the bottom of the screw hole. l like to see atricklel of fuel on myHolley'ss when the screw is removed. To adjust this level Look on top of ur float bowl, You will see a screw with a nut under it. You loosen this screw & screw the nut either up or down to raise or lower the fuel level. Take ur time & do ur adjustments in small increments as a slight turn of the nut will make a big difference on mostHolley'ss.

To set the air screws.

Start & warm up the engine. Make sure thechokee is wide open & if u can have ur air cleaner on the carburetor

You can start with either screw adjuster.
Turn the adjuster in till the engine starts to stumble, the instant it stumbles make note where it happened. Then turn the adjuster in the opposite direction again untill the engine stumbles. Then split that difference by turning the screw to mid way between the two points where it stumbled.

Now, back to the choke. In order for u to be able to adjust that choke properly u r going to need a shop manuel or directions out of a rebuild kit. Most all choke settins r different & spicific to ur vehicle. Also, if u have added on a lot of performance items u may need some one educated in the performance tuning field to dial in the choke for you. You may also have to pull the choke off the intake to make a couple of the settings as there r some tedious measuring that is needed when setting up a choke. One other thing, an electric choke settins r different than a linkage style.

You can get on ur computer & go to holley .com, search around in their site & u will find all the settings for ur carburetor. You will need the LIST # off the air horn of ur carb to match up with the numbers on holleys site. If all else fails u can mail it to me & for 150.00 plus parts l will make it perfect.

Hi Mike;

First do a simple compression test on all 8 cylinders.After that take an ohm meter check resistance on all plug wires.(resistance should be low)

Then be sure the (dwell is correct if it has points)then check the timing .Be sure the vaccum advance is operating.These r all a no cost job if u do it yourself.

If all the above r correct,then rebuild the carb. reset the floats to proper height & always change the carb. to manifold gasket when doing this. (In my experiences with Holly is l stopped using them in the late 80 is & switched to Eldlebrook manifold & Carb. l have been very happy with the performance of that product as opposed to Holly's.

Good-luck;

Frank

Maybe some smaller jets would help to if the carb was not straight outta the box. Most are tuned pretty good cfm to cid but if you got it used, you may not know what size is in there and are fighting yourself trying to adjust to much carb for what the motor can handle. just a thought. otherwise just do what them other guys said, Holley is are easy to work on.