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Old 05-12-2019, 11:05 PM   #1
doobiebro
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bad fuel delivery 77 c20 dual tanks

Hello fellas I have another dreaded dual tanks/fuel tank selector valve question? Here's the story. I have a 77 C-20 that belonged to my father in law. From one day to the next the truck had no power/popping carburetor. After throwing lots of money and parts at it with no luck I realized I over looked the fuel pressure and low volume in the filter. I crawled under the truck and noticed the D/S fuel tank was by passed and the Passenger side tank was only hooked up. That explains why he would only fuel up on the passenger side. The fuel selector valve missing. I have read up on (hatzie) threads. I will need to replace the fuel sender and I noticed both tanks have the same 2 ports fuel sender. One port for fuel delivery and the other is just an open plastic nipple piece. Is this suppose to be a vent based on my pics? I don't believe this truck was designed to have return lines. I will replace all the rubber fuel lines while the bed is move back and get the truck running. Later down the road I hope to get the correct selector valve and get the fuel tanks operational. Any help is greatly appreciated. Thanx.
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Old 05-13-2019, 07:01 AM   #2
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Re: bad fuel delivery 77 c20 dual tanks

The plastic vent looks funny, maybe it's broken. I'm 99% sure my 76's have return lines. If your plastic vent is open I would replace it and leave everything as is. You should check either fuel pressure or do a fuel volume test. I don't know the specs for fuel volume. I would probably be tempted to splurge $20 on a new fuel pump anyway.
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Old 05-13-2019, 10:59 AM   #3
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Re: bad fuel delivery 77 c20 dual tanks

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The plastic vent looks funny, maybe it's broken. I'm 99% sure my 76's have return lines. If your plastic vent is open I would replace it and leave everything as is. You should check either fuel pressure or do a fuel volume test. I don't know the specs for fuel volume. I would probably be tempted to splurge $20 on a new fuel pump anyway.
Thanks for the reply. Yes I replace the fuel pump with an AC Delco. Also replaced the plugs, wires, Distributor, all rubber fuel lines/minus the lines on the fuel tanks. I rebuilt the carburetor and also had it double checked from a rebuild specialist. The truck had no power to move. I checked engine compression-Good, Engine Timing, and Camshaft to make sure no flat cams-Good. As soon as I installed a new fuel filter I can see the filter low in gas and fuel trickling. I found the problem! I ran fuel to the pump from a gas can and now the filter is full and engine revs high with more power. I will be replacing the fuel sender because I believe there is restriction in fuel flow. Maybe rust blocking the internals. I just want to verify both plastic nipples (on fuel tank senders) are vents because I can see through them before I put everything back together.
thanx.
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Old 05-13-2019, 02:04 PM   #4
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Re: bad fuel delivery 77 c20 dual tanks

The plastic thing is the vent. My 75 has the same setup. You use the 1 wire solenoid 3 pipe valve to switch between tanks. Probably want to replace the dash switch if your gas gauge has problems, especially the go to 3 o'clock issue.

The vent should have a hat like thing over the end. Looks like yours may have broke and settled. Orange ring in 1st pic.

Ask for a differential vent at the parts store. Should be the same thing.
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Old 05-13-2019, 03:40 PM   #5
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Re: bad fuel delivery 77 c20 dual tanks

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Originally Posted by Dead Parrot View Post
The plastic thing is the vent. My 75 has the same setup. You use the 1 wire solenoid 3 pipe valve to switch between tanks. Probably want to replace the dash switch if your gas gauge has problems, especially the go to 3 o'clock issue.

The vent should have a hat like thing over the end. Looks like yours may have broke and settled. Orange ring in 1st pic.

Ask for a differential vent at the parts store. Should be the same thing.
Dead Parrot you just answered all my questions! I just found a pic on the O'reillys Auto Parts page. How funny both fuel tank vents are missing the tops on my truck. I talked to a local guy who sells nothing but 1977-1989 Chevy truck parts where I live and he told me the fuel tank selector valve (3 port - 1 power wire) like you mentioned is an aftermarket on my truck. I don't know if he is correct. By any chance would you have part #s from your truck? While the bed is moved back I'm gonna replace both fuel senders, rubber fuel lines, vents, and get the truck running again. Hopefully I can locate the same selector valve without doing so much modification. Thanks again to all who responded
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Old 05-13-2019, 05:48 PM   #6
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Re: bad fuel delivery 77 c20 dual tanks

I am running a Pollak valve. Don't remember the part #. Here is a link to a similar one on Summit: https://www.summitracing.com/parts/smp-fv1/overview/

Don't know if the Pollak valve is still made. Found a NOS one on Ebay a couple years back as a spare.

Make sure both ends of the ground wires are clean as well.
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Old 05-14-2019, 07:07 PM   #7
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Re: bad fuel delivery 77 c20 dual tanks

Standard Motor Products makes the three port solenoid valve.

The early dual tank vent setup was just a differential type vent hooked to a Tee to both fuel tank vents. You can just run a short hose with a diff vent on each tank.
Whatever you do you'll want the vent to be several inches higher than the top of the sender to keep fuel from sloshing out the vent.

The early three hose evap cans are easy to plumb, don't cost you any performance, and they'll keep your garage from smelling like fuel on hot summer days.
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Old 05-15-2019, 02:59 PM   #8
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Re: bad fuel delivery 77 c20 dual tanks

Name:  selec.jpg
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Quote:
Originally Posted by hatzie View Post
Standard Motor Products makes the three port solenoid valve.

The early dual tank vent setup was just a differential type vent hooked to a Tee to both fuel tank vents. You can just run a short hose with a diff vent on each tank.
Whatever you do you'll want the vent to be several inches higher than the top of the sender to keep fuel from sloshing out the vent.

The early three hose evap cans are easy to plumb, don't cost you any performance, and they'll keep your garage from smelling like fuel on hot summer days.
HATZIE thanks for chiming in..I researched the Standard Motor Products and found part # FV1T. It states it comes with 3/8 inch hose barb fittings. It has Pollak marking on it too. Will this be close to what the truck came with? I appreciate your input. Thank you all..
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Old 05-15-2019, 05:51 PM   #9
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Re: bad fuel delivery 77 c20 dual tanks

Hatzie now that you mention the fuel sloshing out the vent. Years ago I over filled the fuel tank and saw a small puddle of gas under the tank. I never did it again. Vent piece without the (hat/cap) I can see that happening.
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Old 05-15-2019, 07:00 PM   #10
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Re: bad fuel delivery 77 c20 dual tanks

That should work on the stock single wire valve systems.
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Old 05-15-2019, 10:41 PM   #11
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Re: bad fuel delivery 77 c20 dual tanks

The OEM selector valve had short lifespans. 3 or 4 years if you were lucky. The Pollak valves usually last for decades. Uses the same wire and hoses.
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Old 05-16-2019, 10:28 AM   #12
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Re: bad fuel delivery 77 c20 dual tanks

Quote:
Originally Posted by hatzie View Post
That should work on the stock single wire valve systems.
Quote:
Originally Posted by Dead Parrot View Post
The OEM selector valve had short lifespans. 3 or 4 years if you were lucky. The Pollak valves usually last for decades. Uses the same wire and hoses.

Thank you Chevy Brothers for all your help! Much appreciated.
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Old 05-17-2019, 10:54 AM   #13
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Re: bad fuel delivery 77 c20 dual tanks

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Originally Posted by Dead Parrot View Post
The OEM selector valve had short lifespans. 3 or 4 years if you were lucky. The Pollak valves usually last for decades. Uses the same wire and hoses.
I bought a brand new 1973 with factory dual tanks, and the switch/valve worked fine right up until I traded it for a 1980.

Only reason I traded it was to go from an automatic to a manual transmission.
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Old 05-20-2019, 09:50 PM   #14
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Re: bad fuel delivery 77 c20 dual tanks

In 1980 A seperator valve ATE MY LUNCH!!! Over 100* for more than 30 straight days. I worked on it for all of those and more.
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Old 05-21-2019, 04:13 PM   #15
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Re: bad fuel delivery 77 c20 dual tanks

Got the Blue Goose running again! Thanks to all for the helpName:  fuel tank 2.jpg
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Name:  fuel tank.jpg
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Now if I can figure how to turn the pics..
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Old 05-21-2019, 05:58 PM   #16
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Re: bad fuel delivery 77 c20 dual tanks

My factory replacement duel tank valve was leaking from the extra nipple for drainage in case of failure. The valve wasnt very old maybe a couple years. And the connector was full of fuel.
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Old 05-24-2019, 11:02 PM   #17
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Re: bad fuel delivery 77 c20 dual tanks

I'll have to remember this. My new to me 78 has dual tanks and my driver sidejust kills the motor. Oddly enough it only has 16 gallon tanks so not being able to go far really really sucks lol
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Old Yesterday, 12:46 AM   #18
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Re: bad fuel delivery 77 c20 dual tanks

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I'll have to remember this. My new to me 78 has dual tanks and my driver sidejust kills the motor. Oddly enough it only has 16 gallon tanks so not being able to go far really really sucks lol

Mine has 16 gallon tanks also. Check your selector valve and see if it has the 3 fittings with 1 power wire also. Check for power with ignition on.
This valve I replaced is plumbed aux tank (left tank) and main tank (right tank). With ignition switch on Aux tank position/Left tank(valve energized). When you set switch to (right tank) Main tank the wire has no voltage/not energized. With some help from Hatzie I was able to figure out the installation instructions for the fuel selector valve.
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Old Yesterday, 11:13 AM   #19
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Re: bad fuel delivery 77 c20 dual tanks

Funny, my 1973 and my 1980 had 20-21 gallon factory tank(s).

The 1980 only had one factory tank (right side) but I had the dealer install a left side tank. It had a valve/switch but I can't remember if they put it in the middle of the dash just like the factory switch. I only had that pickup for about a year and a half.
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