hesitation on take off

car starts, idles, and runs down the road very well, the issue i am having is when i give the car gas from a dead stop there is a hesitation, or a bogg, car almost faintly sounds like its gonna stall, then it collects it self and drives fine untill i slow to a coast or a stop then apply the accelerator it only does it from a dead stop or a slow coast.

any ideas??


389 2brl

dwell 30
timing was at 6 moved it to 10 to try
new plugs, wires, condenser
carb been rebuilt,
nwe fuel pump, filters,

I feel as though its just a minor adjustment to carb??

Old Gold, If you have a Rochester carb, I'm told these are notorious for this. Mine was rebuilt also, but developed the same hesitation from the start as you describe. Brought it to a guy who knew these very well and replaced accelerator pump,adjusted points, and timing. Ran great for another couple months and now has a very, very slight hesitation. Not nearly as bad as it was. I'm told these Rochester carbs are prone to this if the car is not driven every day. Could also be the crappy fuel we run. Jim

Old Gold.....there are two probable causes of the hesitation. The most common one is, as Jim said, the accelerator pump in the carburator. The ethynol laced gas that we have forced upon us by the EPA, quickly destroys the rubber cup of the pump. Most of the rebuild kits that are available are almost as old as our cars and don't have a pump cup that will last very long.

The second most common problem, is sticking weights and springs in the mechanical advance. This is easy to diagnose by removing the distributor cap and rotor and examining them. Flick the weights with your finger to see if they move outward and snap back easily. If not, remove them and clean up any rust or gunk. Lightly coat them with a dab of oil and replace.

There is a solution to the accelerator pump problem. There are a couple companies that sell pumps that are impervious to the crap they call gas now. There are variations to the pumps though, depending on whether you have the small or large 2-BBL carb. Is your choke housing mounted on the carburator air horn or on the throttle plate?

TO ANYONE READING THIS.....this ethynol crap also eats away from the inside, at any rubber parts in the fuel system. From the factory, we have three hoses in the line from the tank to the carburator (more if there's been some modifications made.) Cheap insurance to go to your local auto parts store and get a foot or two of new 3/8" fuel line hose......John

I rebuilt the carb back in febuary, didnt drive or start car untill this june, maybe the accelerator pump cup has dryed up?? I live right on the coast so I can pull up to the pumps and buy what the call (marine gas) or leaded gas so that helps for about $4.50 gal

distributer has a new vac advance , new springs, condenser, rotar....


I am wanting to buy an after market 2brl carb does anyone know of a part number for a direct bolt on carb?? ....will I have to find an adapter to fit one to my stock 389 2brl manifold??

Old Gold.....there are two different 2-BBL intake manifolds depending on whether you have the large or small carburator. That's why I asked you where the choke housing was located in my previous post. The aftermarket doesn't fool around with 2-BBL carbs, except for Tri-Power setups. I've never seen an adapter for anything but 4-BBL carbs. Contrary to Jim's post there is nothing inherently wrong with the Rochester 2-BBL. AS a matter of fact, they are probably the most dependable and simplest carbs ever made, except for a lawn mower carb or a 1-BBL. Taking one of these carbs apart, cleaning it, and putting it back together with new parts is easy. The problem is that the available rebuild kits are old, and don't have parts made with modern materials. That's why you need to get kits from specialty suppliers. After reassembly, the external linkages must also be set to factory specs.

The vacuum advance has no effect on acceleration, only idle and part throttle cruise. It's the weights and springs of the centrifical advance that controls advance on acceleration. That's why they need to be free to move and be correct for your application.

Funny story. Back around 1962 or 1963, when I had my first 1959 Sports Coupe, I had the same hesitation problem. I, and the rest of the brain dead gang I hung around with, diagnosed the trouble as a bad accelerator pump. Yes they went bad then too, but then they wore out instead of disintegrating. Back then you could buy the pumps for almost any carb without getting a complete kit. After carefully removing the air horn so as not to ruin the gasket (the pump cost about $1.25-didn't want to blow another $0.30 for a gasket,) I managed to replace the pump, and get it all back together. I threw the old pump away without looking at it. Fortunately, nothing leaked, but the hesitation was worse then before. Oh well, I broke down and bought a complete carb kit. Took the carb off and opened it up. There inside the pump well was that little metal nose piece from the original pump, blocking the new pump from giving any meaningful squirt. Stupid is as stupid does......John

Have/had same problem.It seems that its got more power when you dont step pedal on the floor.
I tried lifting float level and drill idle emulsion tubes bit larger.
Still bad behavior.
Now i buy 56 cad 4gc for parts carburetor.It has slightly larger jets 68 vs ponchos 63.
well, i put those larger jets and adjust float lever bit lower and drill idle emulsion tubes again bit larger.
Oh jeah, i been struggling with accelerator pump many many times and it didnt work deasently even this time.Seems to be impossible to get it work.
Anyway, now i can adjust idle mixture reasonable level and it wil go rich if i turned screws too far open wich it didnt do earlier.
Just come back for test drive and it got lot better behavior and power.Yes, it wil bog if you step in gas but normal driving its ok.
gasoline here in finland is more than possible even worst than over there.

Hi guys. The most common cause is the accellerator pump but you could have a bad rebuild too. There should be a check ball at the bottom of the pump well that's held in place by a spring in the pump well. Without that check ball you pump a lot of the gas back into the float bowl instead of into your engine.

Take the air cleaner off and look down into your carb from the top then pump the accellerator by hand. You should see a strong steady stream of gas through the entire movement of the accellerator. If you don't, check the accellerator pump and make sure that check ball is in there.

Do either of you have a vacuum gauge? Something else to think about is that if you don't have enough vacuum or you have unsteady vacuum when you tromp on the accellerator, you're car could spit and sputter until it builds up enough vacuum.

When you're cruising down the street holding the accelerator steady your car will run ok even if you don't have as much vacuum as you should.

Check for vacuum leaks. Especially check the lines to the canister under the driver's side fender and the brake booster.

With your car running, take some starter fluid and LIGHTLY spray it around the BASE of your carbs where it mounts to the intake and along your vacuum hoses. If your engine suddenly races you have a vacuum leak. Some people spray carb cleaner which bogs the engine down when you find a leak. Carb cleaner can damage your engine's paint and chrome but some people think its safer.

If you don't have any vacuum leaks, hook up a vacuum gauge inline to your vacuum advance on the distributor. If the needle on the vacuum gauge holds steady with no movement your intake valves are good. If the needle vibrates even a little you have at least one bad intake valve somewhere whioch will cause unsteady vacuum when you tromp on it.

John, master of the specs, can you tell us what the vacuum reading should be?

Another thing you can try is to buy one of those cheap vacuum brake bleeders, hook the pump up to the vacuum advance and pump it up to about 15. You should be able to hold it steady at 15. If the pressure drops your vacuum advance is leaking. You can use this pump to test your brake booster and that canister for leaks too.

Lot of struggle with carb this evening,again.
Well i just said to myself, you dont go home to sleep until accelerate pump works as it should, no less.
Lots of trial and error.Tweaking pump springs.i streching the piston seal round spring to get better sealing and add a thin copper washer under the cup spring to get all lash outta there.now it work 100% ok.
It didnt get any worse when i cleaned dist cap and add another point bridge ground wire and lubricate the advance mechanism.
Tomorrow morning i go to test drive.Now in here is night and my wife is asleep.She will wake up cause my motion detectors gonna warn if they heard odd noises (three guard dogs, maremmano-abruzzese,serra de estrela and white deutch shepherd)  
Im very hopefull...

Allright.Someone of you who has shop manual....
Please check at tune-up specs for ignition.
Is the vacuum advance in manifold vacuum or part throthle?
Whats the total advance, vacuum and base advance?In dist or crank degrees..
I´m pretty sure the other mark in damper is 6btc mark and other is tdc.Confirm this please.
My cat is taking full vacuum advance in idle and when i finally understand to adjust base advance with vacuum line disconnected it works much better.still all advance with vacuum in is somewhere 36 as i think it should be near 52.
As a total advance without vacuum the 36 is fine.So something in my dist is wrong i guess.
I did lubricated and adjust the dist but it do not make difference.
Next step is adjust kit for dist.Gonna try bigger weights and looser springs and in that point the factory specs would be good starting point.
Thanks allready.

Well well...seems like none off you dont have shop manual.
Dist should have 15 mechanical and 7 vac advance.
That on crank makes 30 mechanical + 6 base timing = 36 max advance at wot + 7 dist advance at crank makes 14. 36+14=50 degrees in steady cruise rpm.

Adjust base timing at first mark=6 with disconnect vacuum advance and measure that you have about 36 at 3000rpm and then connect vac and check that you have around 50 at 3000rpm.
No hesitation anymore.

Catalina Vista, sorry for the late response. There are 41 pages in the Shop Manual for Fuel system adjustments and Rochester 2 &4 barrel Carburetor. Not sure the best way to deliver them to you? I purchased the 1959 Shop Manual from the below web site in CD form. Hope this helps. Jim

http://www.faxonautoliterature.com/1959-Pontiac-Repair-Shop-Manual-Original-Catalina-Bonneville-Star-Chief-Safari-P15231.aspx

Did you read what i wrote?

I was telling you what degrees the ignition must have to working right.

now i just put stock 63 jets back and its lot lazier.
if you wanna have real muscle like these have when they where new, put 68 jets and make sure ignition is adjusted as i described.
With those minor modifications and little weaker centr advance springs my cat is accelerating so fast that i begin to fear how old hydramatic will stand in one piece.

Yeah, we all tried to interpret what you wrote, but your pig- Latin English made it a little difficult to understand your rant. I was just trying to help you out with the Shop Manual. Next time, don't bother asking for assistance.

Please, dont take my wrotes so personly.
And again if i dont tell it, i m from finland so my english isnt so good.
My type of writing may sound rude.Didnt mean it that way.
Really i dont want to, to...how you said, messing with you.

Read what i wrote carefully and understand the basic tuning trics what i try and learn good mods with these pontiacs.

Again, sorry.
Jussi from scandinavia.

Whoa...Whoa...Whoa...I thought we were ALL on this forum because of our appreciation for these cars. Let's have our disagreements civilized, and not descend into personal attacks......John