Author Topic: Truck stalls upon heavy acceleration  (Read 3446 times)

Offline Riptor98

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Truck stalls upon heavy acceleration
« on: August 22, 2017, 01:14:26 PM »
1974 Chevy C10, Rochester 2 barrel.

Offline Henry

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Re: Truck stalls upon heavy acceleration
« Reply #1 on: August 23, 2017, 10:19:53 AM »
Hi Riptor 98:
Sounds like the carb to me...probably the accelerator pump seal cup is shot...time for a carb rebuild. I would go around and look at all your vacuum connections/hoses first just to make sure you dont have a vacuum leak that could be causing it.
Regards,
Henry

Offline Irish_Alley

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Re: Truck stalls upon heavy acceleration
« Reply #2 on: August 23, 2017, 11:15:20 AM »
does it do it all the time?
is your choke working properly?
like stated, have you checked for vacuum leaks?
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Riptor98

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Re: Truck stalls upon heavy acceleration
« Reply #3 on: August 23, 2017, 11:38:33 AM »
Well the funny thing is it will drive ok as long as I don't fully open the choke (converted it to a manual a few months ago.) it started doing this a few days ago after I changed the spark plugs. They came pre-gapped at .035.

Offline Irish_Alley

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Re: Truck stalls upon heavy acceleration
« Reply #4 on: August 23, 2017, 02:12:10 PM »
does it idle ok? did you re adjust the idle after the manual swap? did you triple check your firing order?
If you can’t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

Offline Riptor98

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Re: Truck stalls upon heavy acceleration
« Reply #5 on: August 23, 2017, 02:39:12 PM »
It idles fine. Revs fine in park and in neutral. Stutters only in drive. I didn't adjust the idle screws

Offline Riptor98

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Re: Truck stalls upon heavy acceleration
« Reply #6 on: August 23, 2017, 02:42:16 PM »
And when I pulled the old plugs I did it one at a time so there is no way I mismatched wires

Offline Riptor98

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Re: Truck stalls upon heavy acceleration
« Reply #7 on: August 23, 2017, 06:31:15 PM »
How do I test accelerator pump

Offline Henry

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Re: Truck stalls upon heavy acceleration
« Reply #8 on: August 24, 2017, 01:11:55 PM »
Hi Riptor98:
I think your carb is a Rochester 2G, 2GC, or 2GV model...I do not know of any way to test the accelerator pump mechanism other than to remove it and inspect it. This carb has a removeable air horn (top plate or choke plate) that when removed will also allow the pump plunger assembly to be removed. It can be done on the engine but is a back-breaker if you are an old git like me. To open up the carb to service the pump plunger assy, it is just as well to just remove the carb and rebuild it or disassemble it to give it a cleaning and install a rebuild kit. Usually the rebuild kit has the seal cup, but another failure item could be the garter spring that holds the seal cup against the bore of the float bowl housing. There is a company called Quadrajetparts.com that should be able to sell you just the acc pump parts or the entire rebuild kit...or just gaskets. What happens with the seal cup is that it is a rubber that will eventually dry out and get brittle and not seal anymore. Sometimes the garter spring will eventually rust away and not apply uniform pressure to the seal cup to effect the seal. Essentially the accelerator pump assembly keeps a charge of fuel ready to dump into the carb primaries when you mash the throttle so the engine doesnt lean out and stall.
Regards,
Henry 

Online bd

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Re: Truck stalls upon heavy acceleration
« Reply #9 on: August 24, 2017, 01:35:00 PM »
How do I test accelerator pump

With the engine off and choke plate wide open, using a bright flashlight, look down the throat of the carburetor and open the throttle by hand.  You should observe two well defined streams of fuel squirting into the center of the throttle bores that are proportionate in volume to the rate of throttle opening.  The quicker you open the throttle, the stronger the streams.  You should observe three to four full throttle squirts before the fuel supply is exhausted.  If you need to replace the accelerator pump, look for a Viton rubber replacement.


Please clarify the exact symptoms.  First, is it a hesitation or does the engine actually die?  Is the symptom instantaneous with throttle opening, or does it begin to accelerate okay for about 1/2 second before stumbling/stalling?  Or, does it "stall" only after accelerating for several seconds at wide open throttle?
« Last Edit: August 24, 2017, 01:49:01 PM by bd »
Rich
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Offline Riptor98

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Re: Truck stalls upon heavy acceleration
« Reply #10 on: August 24, 2017, 05:26:44 PM »
Thanks for the help! I looked up a Rochester 2 barrel online and it costs about 200. Is it worth the effort to rebuild or should I just put in a brand new carb? And yes the engine will completely stall if I mash the gas too quickly. It only does this while in drive. I've inspected the flow of gas. It is not impeded.

Offline Riptor98

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Re: Truck stalls upon heavy acceleration
« Reply #11 on: August 24, 2017, 05:28:20 PM »
And yes it is instantaneous with the throttle.

Offline Henry

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Re: Truck stalls upon heavy acceleration
« Reply #12 on: August 25, 2017, 12:00:33 PM »
Hi Riptor 98:
bd is correct that you can check the function of the accelerator pump by manually tweaking the throttle and seeing if fuel squirts out of the pump shooters into the venturi. I think you could still have a accelerator pump bleed-down problem while the engine is running and under load and you can still pass this static test. If your carb is a 4GC, the pump rod is adjustable and another quick and easy thing to check is the adjustment of the pump rod...see attached image. For manual transmission the dimension should be 1-9/32 inch...for automatic trans the dimension should be 1-3/16 inch. Other possible problems are associated with the accelerator pump assy: discharge ball could be sticking or dirty or discharge ball passage leaking.

A rebuild of the carb by yourself (if you feel you are up to it and have time) would be much more economical than buying a rebuilt one...but if you dont have the time or skill to do it, a rebuild by a specialty carb shop or buying a rebuild is a way to go. If you were to buy a rebuild kit, be sure it has the new viton material acc pump cup...sometimes these rebuild kits dont have the acc pump parts.

When you said you converted the choke to manual, what exactly did you do?...(just wondering if you accidentally disconnected a linkage or connection that was necessary for proper function other than choke).

Regards,
Henry


Offline Henry

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Re: Truck stalls upon heavy acceleration
« Reply #13 on: August 25, 2017, 12:11:56 PM »
Hi:
In my previous comments I referred to a "4GC" carb...I really meant "4GV".
Sorry bout that,
Henry

Offline Riptor98

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Re: Truck stalls upon heavy acceleration
« Reply #14 on: September 01, 2017, 11:05:00 PM »
You were right about the accelerator pump thanks so much! I pulled it off and wha days know the rubber cup on it was bad! Changed it out and it runs like a champ thanks man!