Hesitation with My 305 in My 72

[Chance72]

Hey guys, when I drive my 72 I let it warm up and everything and it runs good, but yet when I punch it there's hesitation. After about 2 seconds it catches on and goes, it doesnt rev up when i do it just sits ther till it catches on like i said, this has been goin on since I've got it but I didn't think nothin of it. Now it's just annoying, can you guys help me diagnose this problem? Thanks
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[geezer#99]

It'd help if we knew what carb, what distributor?

[MSHax]

Originally Posted by geezer#99

It'd help if we knew what carb, what distributor?

Yeah, second that one. There's a 95% chance it's in either the fuel system (pump/carb/etc) or the distributor, if we knew what you're running we could help out.

[Chance72]

I know is it's a Holley carb. I havnt really got to check out everything with the engine. More body work for me. It's pourin down right now, but I'll have to go out and check the distributor...
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[cleszkie]

My guess is a bad accelerator pump diaphragm in the carb.

[buckskins4ever]

I actually would like more info before heading you to a carb issue.......You say when you punch it there is a hesitation to "GO".
First is it automatic?
Second, is the hesitation a gasping hesitation as if its trying to get fuel and almost die before coming back up to rpm and go, or is it something more like you accelerate as normal but seems like the truck doesnt move for a couple seconds?
If automatic trans, and the trucks remains running as normal but doesnt move, you most like have a vacuum leak on the tranny line, the vacuum is weak, or if the tranny vacuum line (if replaced with rubber) may be collapsing at first punch. this is caused sometime when people use thin wall rubber tubing such as wiper fluid type rubber hose.

[Chance72]

Originally Posted by buckskins4ever

I actually would like more info before heading you to a carb issue.......You say when you punch it there is a hesitation to "GO".
First is it automatic?
Second, is the hesitation a gasping hesitation as if its trying to get fuel and almost die before coming back up to rpm and go, or is it something more like you accelerate as normal but seems like the truck doesnt move for a couple seconds?
If automatic trans, and the trucks remains running as normal but doesnt move, you most like have a vacuum leak on the tranny line, the vacuum is weak, or if the tranny vacuum line (if replaced with rubber) may be collapsing at first punch. this is caused sometime when people use thin wall rubber tubing such as wiper fluid type rubber hose.

It is an auto and the hesitation is a gasping hesitation like you said, then jumps up and drives.

[CC69Rat]

Have you had the carb off the intake lately? I had a 307 in a 69 Camaro that was doing the same thing you describe. It was a 307 2brl when I bought it and it was in serious need of a rebuild .. I decided it needed an Edelbrock Performer and 4 brl and ditched the 2 brl setup.

Since I put the Eddy / Perf on it it had this same hesitation. I checked the Vacuum advance, replace the dist, worked for DAYS on the timing, fuel pump, voltage issues, accelerator pump, etc.

When you step on the pedal from a redelight, .. just pulling out normally it will cough for a second then all at once, take off. Cracking through the exhaust, etc. ..

I got so upset with this that I ordered a GMPP 350/290hp long block for it. Guess what, I used the same intake and carb on the 290 motor.

Take a wild guess what my problem ended up being? There was a small vacuum leak under the carb. The gasket has kinda blown through or in some kind of way it was leaking. You could see the 'pass thru' where it was not sealing well around one of the throats on the carb to the intake. I replaced this gasket, and it was FIXED. $3,000 later ..

This may or may not be the problem, but it's worth a shot.
Later.

[buckskins4ever]

Originally Posted by Chance72

It is an auto and the hesitation is a gasping hesitation like you said, then jumps up and drives.

If your timing is on, the next place to look is the diaphragm Springs can be made a little stronger on most carbs. If you have a old carb on that engine, and possible can afford a Ready to Run Carb like the Edelbrock Performer 600 or Holley Street Avenger 600, you would be going in the right direction. Those Carbs are flow jetted and 90% tune ready right out of the box.