Hesitation when I blip the throttle??

[rusty ol' 69']

When I gun my truck it hesitates then kicks in. I searched this site and got several conflicting ideas. Mostly about the accelerator pump, but when I look down the barrel and push the throttle gas squirts out both sides in a steady stream. So that's not my problem. Then I found the choke might not be opening so I held it open and fired it up, but it still hesitates. So the carb is good to go. I think my problem is ignition related. So besides the vacum advance what else could cause this. If this isn't enough info. to make an educated guess ask me what would help you to better understand my dilema. It's getting irritating and I want to narrow down the problem. Thanks for any help in advance.

Rusty

[bigjimzlll]

what kind of carb? Usally it is in the transition circuit of the carb..if you lean out the idle enrichment screws too much, you will have to lower the throttle idle adjustment screw..if you do that the transfer slot will be closed off..it will idle fine, but stumble off idle..try increasing your idle speed(with throttle adjustment) and turning out(rich) the idle enrichment screws to reach the idle you want..this is if its a holley..if its an edelbrock, try the next lighest springs in it..if its stock...dunno..also make sure your vacuum advance is working...if the carb is right try bumping up the timing a couple of degrees
Jim

[rusty ol' 69']

It's a stock 2 barrel rochester. It's running a little on the rich side, since I don't have a vaccum gauge I haven't messed with it too much. I guess I could try messing with the idle and mixture a little to see if that will help. It should unless it's an ignition problem. I like to try and pinpoint a problem before I mess with everything too much. Sometimes, playing with it too much can send everything out of whack. I guess I'll just have to dig in and see what I come up with. Thanks for your time and help. Any other suggestions.

[Gordo]

Point gap/dwell? Dist shaft/bushings worn? Does the dwell fluctuate with rpms? Timing? Vaccum advance diaphram is working? Mechanical advance plate/mechanisum inside dist worn/frozen? Vaccum supply checked with gauge?

[jays68yak]

other things to check
gas leak?
spring falling off in the distributor if it had them. Happened to me with my mallory unilite took me forever to figure it out.
Good luck

[rusty ol' 69']

ttt

[Blue Beard]

Keep us posted, I'm having the same problem.............

[Hooter]

Have you checked if there is any play in the distributor shaft?
if I were in your shoes I would convert to a 4 barrel, not to hard to do, and if you keep out of the 4 barrels you will get better fuel economy because of the smaller primaries

[bigjimzlll]

That is the exact argument I made to my dad 30 years ago..."Ill get better fuel economy dad" yea..thats why I wanted a four barrel...lol

[rusty ol' 69']

We all have the list of things we want to add to our truck. Seeing how I'm going to put another motor in later (the 307 just don't have the guts) either a 350 4 bolt with all the do dads or a 383 crate motor, I don't think I will be adding anything to this motor. Unless, I come across a really cheap manifold and quadrajet, I'm just going to work with what I got. Idealy, if I had the spread I would swap out the points and two barrel, but I'm poor for right now. I love quadrajets they do get better gas mileage that's for sure until you open up the secondaries!! I remember watching the fuel gauge move in my old 77' blazer when I'd gun it on the freeway!! Anyways, I'm taking the distributor off tomorrow and checking it all over. The one thing I neglected to mention is I put a new fuel line on when I rebuild the carb, and I used a crappy bender to bend the line. Needless to say I put two kinks in the line, and the final result was less then satisfactory. That could be the problem eventhough fuel seems to be coming out the pump without any problems. I might just switch over to a rubber line with some fittings and see if that's it, but it was doing this with the old line so it might now work.

Bluebeard: after searching all over the board I found a list of things under hesitation and bog when I did a search:

Timing chain might be stretch (grab harmonic/crank and see if it has any play)

Accelerator pump (look down the barrel and push the throttle and see if it pumps out a steady stream of gas)

vacuum advance (see if your diaphram is opening with suction, already mentioned on here)

And of course fouled plugs

I'll definitely let you know when I find the problem. According to other posts this is pretty common, although no one posted what they did that fixed it? So once I figure it out I'll give you an update. Thanks all for the ideas and thoughts.

[Blue Beard]

rusty ol' 69'

Thanks for the input. Have checked all of that with no results..........I just resently did a complete tuneup with all good parts.

I may have a leak issure around the intake....who ever put it on didn't do a very good job wiht the permatex.

Trying to hold off on that till warmer weather since I want to go to HEI at the same time (which should help).

[Long Knight]

I have an adjustable accelorator pump. When the carb was installed it was on the lowest setting. I could see a steady stream when I gave it a pump, but it wasn't enough. I adjusted to the highest setting and get instant response now. Came down to too much instantanious demand for fuel and withouth the adjustment the engine just has to wait. This is what the Edelbrock guy told me and it worked for me. That's it...$02

[rusty ol' 69']

I have a 2 barrel rochester though. I messed with the mixture adjustments and that doesn't seem to help any. I don't think the carb has an adjustable accel pump, it just has the two screws to set the mixture. Does anyone know if you can adjust the accel pump?

[gman]

You might try this....pertains to Q-jets but might help......sorry for the long post.

How can you tell if an off-idle stumble is caused by a lean or a rich condition?
A carb running rich, as well as a carb running lean, can cause an off-idle stumble or hesitation upon acceleration. To narrow it down, tap the roll pin out of the accelerator pump lever by using a small pin punch or a small finish nail. I actually use a small, broken drill bit that’s just the right size. Using a hammer, gently tap the roll pin in towards the choke air horn wall. Don’t jam the pin right up against the wall: Leave just a little bit of a gap so you can get a screwdriver blade in between the wall and the pin to pry it back again. With the pin tapped out, remove the accelerator pump lever. I like to do this with the engine running so I won’t have any trouble starting the engine without the accelerator pump. Now, rev the engine a little with the throttle. Notice if the engine seems quicker and more responsive, or if the hesitation & stumble is worse. If the engine actually feels more responsive with the accelerator pump disconnected, you have a rich condition. If the hesitation is worse than before, you have a lean condition. If there is no change whatsoever, you have a non-functional accelerator pump.

To verify a suspected lean condition after this test, simply hold your cupped hand lightly over the choke air horn area with the engine running at idle, restricting the air flow. If the idle speed and idle quality momentarily increases, you have a verified lean condition. You need to select a jet/rod combination that will give you a little more Cruise Metering Area. Make these changes in less than 10% increments.

Wisdom provided by a gentlemen named Lars Grimsrud somewhere off the 'net. Its helped me.

[rusty ol' 69']

Alright I tried that little trick and it makes a lot of sense. You take off the gas supply and if it acts like it's starving it's too lean, and if it acts like ahh thanks for not drowning me in fuel then it's rich. Nice trick there. It goes worse once I cut out the gas, so I've been messing with the mixture trying to get it right. I don't have a vacuum gauge so this is kinda tough. I'll have to go old school and check the plugs and just listen to the motor. Now, here comes the really dumb part. Do I turn the screw in to make it rich and out to lean or is it the other way around. Thanks for the input btw hopefully this will fix it.

[EdB]

Rusty,

I had the same problem a few years ago and It was
driving me up the wall. I checked and set everything.

I was running, what I call, the new style Holly 600.
I had replaced the old style a couple of years prior.
I still had the old carb. that had been in my attic
since the change. A friend got me to swap back
to see if it would help. It cured the problem and
it never came back. It was just something in the
carb. I bought it new. I rebuilt it in trying to solve
the problem but it did not cure the problem.

EdB

[rusty ol' 69']

Ed I did the same thing once. I had a crappy running holley and I just changed it out for a quadrajet and it ran like a champ. Too bad it's not a four barrel or I'd just switch out the carb, but I don't have any two barrels lying around so I have to mess with what I got till it's fixed. I tried out what gman said and it got worse when I cut out the gas, so I turned in the mixture screws till it almost died and backed it off about 1 and a 1/2 turns and that seemed to help a little. But now it's kinda popping a little under a hard load when I test drove it. I wish I had a vacuum gauge that would help to take out the guess work. My Dad has so many frick'in tools from being an engineer (and a packrat) that it just makes me sick when I have to go buy a new too. Their his tools though so I don't feel right asking him to borrow one. If I lived around the corner rather than 4 hours away I would. Oh well I guess I'll have to keep messing with it for now.

[gman]

Turn in to lean it up and out to richen it.

[Tynee]

If you get black sooty residue at the end of the tail pipe, its running rich, right? Why did this gunk go away when I back out the mixture screws? Also, one screw is for fast idle, the other slow idle, right? If so, which is which?

[bigjimzlll]

if the screws were too far in, it could of hurt your vacuum...by doing this your vacuum advance would of been decreased, and also the spring for the rods would have been affected allowing the carb to flood.

that is id its an edelbrock were talking about..if its a holley, it could effect the power valve

[Tynee]

Actually its not a holley OR and edelbrock. Its the factory rochester 2bbl like Rusty is dealing with.

BTW, Rusty, sorry if I hi-jacked your post. Wasn't my intention.

Tynee

[rusty ol' 69']

Well I finally broke down and bought a vacuum gauge so I would know for sure if my mixture was messed up. I found out my vacuum advance wasn't connected to the right source first off. Now it doesn't sound like it has a mean cam in it anymore That seemed to fix it pretty good, but the problem is still their now every so slightly. If I give it a quick blip it will do it slightly, but If I raise the rpm slightly and blip it there's no hesitation. BTW does anyone have a schematic for the vacuum hoses on a 2 barrel rochester? Thanks again for all the help!! It's not totally solved yet but getting closer

Tynee- Start your own damn post!! Just kidding man. No worries mate!!