Rough take off - The 1947 - Present Chevrolet & GMC Truck Message Board Network

iufan71 · 06-07-2003, 07:16 PM

Ok,just wondered if anyone out there has this same trouble. My Chevy 350 in my 78 GMC is a little hesitant when i give it some gas. Noticed this ever since i changed the air filter . Any thoughts to what i might have knocked loose?

gchemist · 06-08-2003, 12:10 AM

Are you using the stock air cleaner or an open air element?

iufan71 · 06-08-2003, 10:54 AM

Im using the stock air cleaner.

82 Silverado 4X · 06-08-2003, 12:02 PM

Might not have anything to do with your changing the air cleaner.
With the air cleaner removed and the truck "NOT RUNNING" look to see if you are getting good shots of fuel from the accelerator pump when you open the throttle.
If you are not getting two good squirts of fuel shooting into the primaries below the choke plate as you open the throttle it could mean that you have a bad accelerator pump.

iufan71 · 06-09-2003, 03:17 PM

Factory quadrajet has an accelerator pump? Thanks. Heath

rockman20 · 06-09-2003, 05:27 PM

Yup, it is that rod that sticks out the top of the air horn. On the front of the carb towards the throttle linkage.

Could also be your vacuum advance is bad. Check that also to see if it moves freely.

I would also readjust the mixture screws a bit. Get a vacuum gauge and start on one side. Turn in until engine idles rough and vacuum fluctuates. Start turning out until vacuum reading steadies. Readjust idle speed if need be. Then do the other side. Readjust idle if need be after that as well. I usually go back and forth like this about 4 or 5 times before I am finally happy that my mixture is set.

jimfulco · 06-09-2003, 09:57 PM

I've had light-throttle "tip-in" problems in late 70's Chevys several times. They hesitate on light acceleration from a dead stop, but do OK if you hit it kind of hard. I think it's just a slightly clogged transition slot (they are calibrated very lean to start with). I just run a jug of injector cleaner in the gas (I prefer Berryman's, smell it & you'll see why), or sometimes a tank of super Mobil will smooth it up.

06-07-2003, 07:16 PM	#1
iufan71 Registered User Join Date: Apr 2003 Location: Indianapolis,IN Posts: 138	Rough take off Ok,just wondered if anyone out there has this same trouble. My Chevy 350 in my 78 GMC is a little hesitant when i give it some gas. Noticed this ever since i changed the air filter . Any thoughts to what i might have knocked loose?

06-08-2003, 12:10 AM	#2
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	Are you using the stock air cleaner or an open air element? __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

06-08-2003, 10:54 AM	#3
iufan71 Registered User Join Date: Apr 2003 Location: Indianapolis,IN Posts: 138	Rough take off Im using the stock air cleaner.

06-08-2003, 12:02 PM	#4
82 Silverado 4X Genuine Chevrolet Join Date: Feb 2003 Location: South West Pennsylvania. Posts: 582	Might not have anything to do with your changing the air cleaner. With the air cleaner removed and the truck "NOT RUNNING" look to see if you are getting good shots of fuel from the accelerator pump when you open the throttle. If you are not getting two good squirts of fuel shooting into the primaries below the choke plate as you open the throttle it could mean that you have a bad accelerator pump. __________________ George 82 Silverado LWB 4x4 350 SM465 NP208 77 Chevrolet Blazer Chalet 400 TH350 NP203

06-09-2003, 03:17 PM	#5
iufan71 Registered User Join Date: Apr 2003 Location: Indianapolis,IN Posts: 138	Rough Take off cause Factory quadrajet has an accelerator pump? Thanks. Heath

06-09-2003, 05:27 PM	#6
rockman20 "The dude abides" Join Date: Apr 2003 Location: North Dakota Posts: 472	Yup, it is that rod that sticks out the top of the air horn. On the front of the carb towards the throttle linkage. Could also be your vacuum advance is bad. Check that also to see if it moves freely. I would also readjust the mixture screws a bit. Get a vacuum gauge and start on one side. Turn in until engine idles rough and vacuum fluctuates. Start turning out until vacuum reading steadies. Readjust idle speed if need be. Then do the other side. Readjust idle if need be after that as well. I usually go back and forth like this about 4 or 5 times before I am finally happy that my mixture is set. __________________ RockMan 1993 Chevy Silverado C3500 1 ton dually 1994 Honda Civic 1969 Oldsmobile Cutlass S 1953 IH Farmall Super M New to the fleet: 1992 Subaru Loyal

06-09-2003, 09:57 PM	#7
jimfulco Registered User Join Date: May 2003 Location: Shreveport LA Posts: 3,170	I've had light-throttle "tip-in" problems in late 70's Chevys several times. They hesitate on light acceleration from a dead stop, but do OK if you hit it kind of hard. I think it's just a slightly clogged transition slot (they are calibrated very lean to start with). I just run a jug of injector cleaner in the gas (I prefer Berryman's, smell it & you'll see why), or sometimes a tank of super Mobil will smooth it up.



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