Fuel delivery problem

T

thomas mike

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Dec 23, 2009
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Fuel delivery problem. Works fine on 5 gallon can but can't draw from the tank. So fuel pump, carb and filters are all good. It was drawing fuel from
the tanks only a few days ago. Questions: What PSI to blow the socks off in the tank? Also, can I bypass the fuel selector solenoid? I think one of
these two are my problem unless others have another proposed diagnosis. Thanks.
--
Mike Thomas
Troy, MI
77 ex Palm Beach, 77 Royale (rear bath)
 
I would disconnect the feed line at the fuel pump and start drawing a suction from the tanks to see if you can pull fuel or heat a leak. I would bet you have a cracked line somewhere and are sucking air.

-Dave
1978 Transmode near Pittsburgh (but written from somewhere near Bologna)

>
> Fuel delivery problem. Works fine on 5 gallon can but can't draw from the tank. So fuel pump, carb and filters are all good. It was drawing fuel from
> the tanks only a few days ago. Questions: What PSI to blow the socks off in the tank? Also, can I bypass the fuel selector solenoid? I think one of
> these two are my problem unless others have another proposed diagnosis. Thanks.
> --
> Mike Thomas
> Troy, MI
> 77 ex Palm Beach, 77 Royale (rear bath)
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Mike,
Any sustained pressure of more than 2 or 3 psig can cause the tanks to expand and it could come out badly. If you pop the fuel line with 30 psig for 3 to 5 seconds you should not have and problems in damaging the tanks.

JR Wright
Michigan

>
> Fuel delivery problem. Works fine on 5 gallon can but can't draw from the tank. So fuel pump, carb and filters are all good. It was drawing fuel from
> the tanks only a few days ago. Questions: What PSI to blow the socks off in the tank? Also, can I bypass the fuel selector solenoid? I think one of
> these two are my problem unless others have another proposed diagnosis. Thanks.
> --
> Mike Thomas
> Troy, MI
> 77 ex Palm Beach, 77 Royale (rear bath)
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
Make sure the cap is off of the tank when you do it. I assume that you are going to blow air in the lines and the air need to escape from the tank
somewhere. Do not have the tanks full when you do it. I really think that you have a leak some where. That is the suction side of the pump so you
may not actually seethe leak.

Also keep in mind that if you have had the lines disconnected all of the fuel in the lines drains back into the tank(s). then later When you try to
pump, you dry pump has to pump (suck) all of the air again. It is difficult for a dry pump to pull the air that distance. I have used shop air and a
rag in the filler to apply slight pressure to the system to get the fuel flowing again up to the mech fuel pump. It does not take much pressure. (a
couple of PSI) You are only trying to raise the fuel a foot or so vertically fromthe tank to the pump. DO NOT OVER PRESSURIZE AND BLOW A LINE OR THE
TANKS.

I use to have a barb fitting and an 3/8"? check valve that I stuck in the hose going to the pump. Apply air until fuel ran out of the end. Then
squeeze the line to prevent fuel from running back to the tank and reconnect the hose to the input side of the pump again.

There are lots of way to do it. It is easier with 2 people.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Mike,

Good to hear from you again.

If you have not replaced the fuel lines on top of the tanks, make the plan to do so. Those lines are probably rotted out by now and the selector
valve is also about gone. Getting the tanks down and back up is a pain, but it is easier if you do it with Hazard Fright straps and while you are at
it, split the fill vents so you can put fuel in the tanks faster.

I sent the note to mtt2961.

Matt

--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
As Matt pointed out, if you have not replaced the hose in last few years
with the new type, your wasting your time.
Also the tank selector switch wit New as there is a rubber in there that
has created trouble.

On Thu, Jul 25, 2019 at 1:54 PM Matt Colie via Gmclist <

> Mike,
>
> Good to hear from you again.
>
> If you have not replaced the fuel lines on top of the tanks, make the plan
> to do so. Those lines are probably rotted out by now and the selector
> valve is also about gone. Getting the tanks down and back up is a pain,
> but it is easier if you do it with Hazard Fright straps and while you are at
> it, split the fill vents so you can put fuel in the tanks faster.
>
> I sent the note to mtt2961.
>
> Matt
>
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
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