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Hesitation on heavy acceleration
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white
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Sep 2, 2009, 12:48 AM
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Hesitation on heavy acceleration
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 1976,Chevy,Montecarlo,305,rebuilt.approx:55k,auto tranny,wheather warm or cold Hesitates on heavy acceleration at any speeds,also has slight inclination to backfire,runs smooth at Idle and at speeds. carb is single barrel. I can second guess myself all day,so why not go to the pros and get it done the first time,Thanks alot for your time and help with this matter. Hope I gave you enough info.
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Hammer Time
Ultimate Carjunky
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Sep 2, 2009, 1:18 AM
Post #2 of 14
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Re: Hesitation on heavy acceleration
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You don't have a single barrel on a V8. It's either a 2 or a 4.
It sounds like the carb has a bad accelerator pump. The best way to fix it is to just replace the carb with a remanufactured unit.
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white
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Sep 2, 2009, 2:01 AM
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Re: Hesitation on heavy acceleration
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Thanks for the quick responce to my problem and DUH it's a two barell carb,Im going on 15 hours with no sleep, cant I just replace the accelerator pump?. While I got your attention and I'm still fairly alert,lol, I just replaced the fuel pump and they had a fuel filter between the tank and the pump,should I go ahead and put a new one back on?. I learned from one of the posts that my window motor is going bad,because as the weather is cooling down it has been working but when the weather heats back up it doesn't want to work as well if at all,Thanks. Hammer Time! 'I know I'll be recomending your site to all my friends and then some. Believe it or not I used to be a "Shade tree Mechanic" but I've forgotten alot more than I learned apparently.But I still like to bust a knuckle once in a while.
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Hammer Time
Ultimate Carjunky
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Sep 2, 2009, 2:08 AM
Post #4 of 14
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Re: Hesitation on heavy acceleration
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It's usually futile to just replace an accelerator pump because the rest of the carb is going to be just as bad and taking one of those apart can be real risky if you've never done it before. The carb is over 30 years old. It's going to be pretty dirty and messed up inside.
As for the fuel filter, yes, it's always good to have good filtering for the fuel.
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white
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Sep 2, 2009, 2:24 AM
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Re: Hesitation on heavy acceleration
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Man you guys are quick,Thanks again HammerTime. I know what you mean by the risky part,I've rebuilt a 4 barell Rochester before and found that the accelerator pump was the problem. I just didnt know if the accelerator pump on the 2 barell carbs were some how built into the caseing,If that makes any sense?. Funny thing happened though on that Rochester after I rebuilt it and remounted it,I had another problem that I didn't have.Long story short,LOL I found a small pebble in one of the small ports,I'm sure you know how much fun I had doing it a second time in just one day.Thanks once again for all your help you've been a big help.[cool]
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Hammer Time
Ultimate Carjunky
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Sep 2, 2009, 2:30 AM
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Re: Hesitation on heavy acceleration
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That's my point, with the tiny ball bearings falling out of who knows where. To do it right, you also need some special chemicals to soak it in so all the tiny passages get cleaned out. You will also have a big problem if there is excessive wear in any of the housing parts like the throttle shafts. The factory rebuilders have ways to take care of all that stuff.
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Guest
Anonymous Poster
Sep 2, 2009, 2:49 AM
Post #7 of 14
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Re: Hesitation on heavy acceleration
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I'd try some carb cleaner before replacing the carb.
The accelerator has its own tiny jet that can get clogged. Run a tank full of gas with fuel system/carb cleaner at a high recomended concentration and use a can of spray carb cleaner. You'll either need to be creative and bend the plastic spray tube back/up so you can get it in the jet or remove the carb.
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white
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Sep 2, 2009, 3:04 AM
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Re: Hesitation on heavy acceleration
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Thanks,Anonymous.
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Hammer Time
Ultimate Carjunky
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Sep 2, 2009, 3:16 AM
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Re: Hesitation on heavy acceleration
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GUEST,,,,,
You need to register and log in to give advice. The poster needs to know who is giving out this bad advice.
The problem is not a clogged nozzle. It's deteriorated rubber plunger along with a lot of loose rust in the bowl.
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Guest
Anonymous Poster
Sep 2, 2009, 3:26 AM
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Re: Hesitation on heavy acceleration
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That's purely speculation, as is mine, however, mine is the most inexpensive attempt at a fix. I prefer to start with inexpensive first.
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white
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Sep 2, 2009, 3:27 AM
Post #11 of 14
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Re: Hesitation on heavy acceleration
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Thanks once again Hammer Time,You wouldn't happen to know what a carb like that might cost me?.With money tight right now,I'm gonna atleast take a look at the carb,then go from there,atleast I know what I'm getting myself in to now. I have a friend who can probably soak the carb for me so I can see what kind of shape it's really in.No pun intended but I'll keep you posted,Thanks again. Not a threat but I shall return.
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Hammer Time
Ultimate Carjunky
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Sep 2, 2009, 3:45 AM
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Re: Hesitation on heavy acceleration
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If you do a Google search on carburetors, you will see a number of sites. Most of the parts stores don't carry them any more
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Loren Champlain Sr
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Sep 2, 2009, 11:43 AM
Post #13 of 14
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Re: Hesitation on heavy acceleration
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white; Pardon my jumping in; First, the accelerator pump isn't that tough to replace. You should be able to buy one from NAPA....But, have you checked the distributor? These years used a vacuum operated advance as well as a centrifugal advance that would seize. If the centrifugal advance isn't working, and the timing has been adjusted to 'compensate', you'll get the hesitation you describe. Remove the rotor and make sure that the centrifugal advance is free and not binding in either direction. You can buy a repair kit with replacement bushings and springs, or just bite the bullet and replace the distributor if that's the case. I've even seen rotors mis-installed that would keep the advance weights from moving. You can check the centrifugal advance curve with a timing light. Disconnect the vacuum advance. Watch the timing mark as you bring the engine speed from idle to about 2500 rpm. It should advance about 25 degrees. When you attach the vacuum advance, you should see about 35 degrees. I'd check this before going into the carburetor. You can also, with the engine off, look down the throat of the carb while pumping the throttle. You should see a spray of fuel. If not, then the accelerator pump may be to blame. btw, there is a fuel filter in the carburetor, just behind the 1" nut where the fuel line connects.
Loren
SW Washington
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white
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Sep 2, 2009, 4:56 PM
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Loren,the more the more confusing,lol, not I appreciate all the input I can get.I've allready replaced the carb fuel filter and as I stated earlier I had to replace the fuel pump which is why I was origionally having problems. I was having to prime the carb to get the fuel to the carb.Now the plugs are fouled and I know they need replaced,but the problem on the hessitation could very well be ignition related,but I'm hopeing not that's where I really get lost even though it's pretty rudementry on older vehicles like mine.Also The hesitation was happening before and after the fuel pump failure.
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