Author Topic: Ongoing Mystery Stall Problem  (Read 333 times)

Offline docsuess84

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Re: Ongoing Mystery Stall Problem
« Reply #15 on: September 12, 2018, 10:45:16 PM »
So I havenít had a chance to test the fuel pump draw but I did decide to do an experiment on our street. I backed it up instead of driving up and lo and behold, she kept right on going. Iím not sure what that means. Bad float angle In the carb when going uphill?

Offline Henry

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Re: Ongoing Mystery Stall Problem
« Reply #16 on: September 13, 2018, 11:56:06 AM »
Hi Docsuess84:
Keep going through the checks already suggested even though your backing up a hill did not stall out. Yes, the Q-jet carb float is front-to-rear hinged which makes it somewhat susceptible to excess movement on front to rear tilting but if it was the float angle adjustment alone, you would have the same problem if the rear of the truck was tilted at an upward angle the same as if the front of the truck was tilted up at the same angle. It could be a carb problem...just not float adjustment...it could be a gunked up carb where there is sediment and varnish in the bowl that is causing flow problems with the jets and float based on the vehicle's angle. Is the carb pretty dirty on the outside?...how does it look down the air horn bores?...if it is all brown and varnishy looking it may be time to open up the carb for a cleaning. When was the last time the carb was serviced?
Regards,
Henry

Offline JohnnyPopper

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Re: Ongoing Mystery Stall Problem
« Reply #17 on: September 14, 2018, 12:59:04 PM »
Hey Doc,

It means that your carb isn't getting enough fuel and here's why: When you backed up the hill, you forced the gas in the float bowl to the front of the bowl, Exactly where the jets are. When you are going up normally, the gas goes to the rear of the bowl, starving out the jets.

Where the fuel line enters the carb, there is what looks like a big nut, it's actually 1". The 5/8th fitting on the fuel line ties into it. Inside there should be a paper filter. I suspect that it's clogged and is the culprit.

Offline 75gmck25

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  • 1975 GMC K25 Camper Special, 350/TH350/NP203
Re: Ongoing Mystery Stall Problem
« Reply #18 on: October 11, 2018, 12:24:02 PM »
Another item to check:  If your fuel pump has a fuel return line (there should be one on an '86), make sure someone did not remove it and just plug it. 

When you have a 3 port fuel pump it will have 1). fuel in from gas tank, 2). fuel out to carburetor and 3). return back to gas tank.   In hot weather, when the float closes off fuel flow, you want that return line to allow the pump to send hot fuel back to the tank and pull cooler fuel back to feed the carburetor.  If there is no return, the fuel just dead-heads against the carburetor float input and the pump continues to try to pump the fuel.  Allowing it to return helps prevent vapor lock and improves the fuel flow to the carburetor.

When you remove the Quadrajet filter on the carburetor, make sure you get a wrench that fits it properly (the nut is 1", I believe), and when you thread it back in you want to do it by hand until you are sure its lined up.  Many of them have been cross-threaded.    The filter will also have a spring, similar to this diagram. http://www.carburetor-blog.com/rochester-fuel-filter-installation/

Bruce