I've got an 86 trans am, 305. I recently took the old quadrajet off and replaced it with a holley 4150. I checked for vaccum leaks and used my service manual to make sure all the lines are in the right place. I noticed after everything was done the car hesitates and almost jolts when you accelerate. Another funny thing is the idle, it is set to 700 rpm. But sometimes and not always it idles at like 1200 rpms. Anyone have any thoughts?

what size 4150?
the high idle could be choke adjustment or a vacuum leak.
the hesitation is probably the accelerator pump arm adjustment. to set this it helps a lot if you have another pair of hands. have a friend hold the throttle wide open (engine off!) and press down hard on the end of the accelerator pump arm with a flat blade screwdriver. adjust the nut/spring/bolt assembly until you have .015" clearance betwen the bolt head and the pivoting arm that actuates the pump arm.
this might be more clearly explained in holley's setup instructions on their website.
Eric B

It's a 670 street avenger, I've put a vaccum gauge on it everywhere and there isn't any leaks. It does idle fine sometimes though. Do I have to change my distributor with the carb or can I use the stock one?

Unless your car was built for the export market without computer control, you need to change the distributor.

u need a vacuum advance distributor

Alright I put in an accel distributor, and the car runs better. In neutral it revs up fine but still bogs out when in gear under load, but only when you step on it like trying to spin the tires. Does anyone have a recommendation for the vaccum advance setting? I have it at 12" now, the setting the instructions recommend.

did you set up your mechanical advance with a spring kit? one blue and one silver spring worked well in the 305 i had. your mechanical advance should be all in by 3000 rpm. also your initial advance (set with the vacuum advance plugged) will probably be around 10-12*. it's pretty cold to set initial and vacuum advance for all season driving, but i would start with 10* advanced. then advance 2* at a time til you get detonation at full throttle over 3000 rpm. when you get detonation, back off til it just goes away, then another 2*.
once mechanical and initial advance are dialed in, dial the vacuum advance to minimum (all the way clockwise), hook up the vacuum advance, find a good steep hill and cruise up it at fairly low rpm. if you don't hear detonation turn the allen head screw inside the vac. canister counterclockwise 2 turns at a time until you do. then dial it back until detonation just goes away. then add 2 more turns (clockwise). all timing adjustments should be made with the engine fully warmed up. take your time, make several runs until you're sure you have it right.
that should get you in the ballpark. your engine's advance needs will change with fuel quality, ambient temperature, humidity, and elevation. easy to see how valuable a tool the adjustable unit really is.
this is from memory, so if i messed up somewhere i'm sure the guys here will be delighted to correct me!
Eric B

When I took the car out this morning it did the same thing. Even in neutral. Is it just too much carb for the motor? How do I change the mechanical springs?

remove the cap and rotor, there they are. use needle nose pliers, don't lose one in the distributor body or down the carb! jegs has a G.M. hei kit for $5.99 with springs, bushings and weights included part # 555-40004. if the weights aren't siezed up i would just use the springs and bushings. different kits use different weights and that can change your curve. also, if the weights are sticking that can cause a bunch of wierd problems, after you clean the weights and add new bushings a dab of di-electric grease can help prevent that
excellent bang for the buck!

Well that should all be fine its a brand new distributor. It seems like the problem is too much fuel.
Is 670 cfm too big?

No, it's not too big, you just need to adjust the carb. When I had a 305 I ran the same 670 carb, never was happy with it though. While I was gathering parts for my current 350, I put a 750 on the 305 and it drove around just fine, even had better throttle response. Could be a number of things for you, pump cam, squirter size, float level, pump arm play (should be zero play), vacuum secondary spring, idle mix screws and the list goes on. Can't always expect a carb to run properly right out of the box. Check out the Holley tuning sticky on top of the forum.

Is the engine bone stock ? If so the jets are to rich for a stock 305. You will have to jet it down some on both primary and secondary. Have you set the idle mixture to best lean condition ? This will affect idle and stumble issues.
To set best lean.
Hook up a tach that reads in 20rpm increments.
Adjust pass. side mixture screw out untill rpm stops rising.
Turn in until rpm drops by 20.
Repeat on drivers side.
Adjust idle to desired rpm.
This should help with the stumble and some of the idle problems.
You will need to redo this when you change the jets.

try 68 jets on the primary side too. i forget what i was running on the secondary side, but 2 to 4 sizes smaller than what holley puts in there should be real close.