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Thread: 84 Chevy carbureted - dual tank fuel delivery problem.

  1. #1
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    84 Chevy carbureted - dual tank fuel delivery problem.

    Ok. I'm new around here, but not to forums in general. I tried the search, but got limited results. So I'll try here. I'll try to give a back story & describe my problem as short as I can, but it will be lengthy.I have recently purchased an 84 chevy pickup, long bed fleetside, 305--dual fuel tanks. This truck has spent the last 12 years parked at the edge of a cow pasture. The previous owner said they parked it due to a carburetor problem that could not be remedied. It originally came with NO carburetor on it. So, I put a different carburetor on it (Quadrajet) that I had from a previous pickup. Sooo, here's the problem I found. Truck will sit & idle in the driveway all day & purr like a kitten. Get it out on the road, it runs good- until you step into it to pull a hill or anything requiring moderate to heavy throttle. It starts out good, but quickly starts to sputter & will die if you stay in it. It will recover if you back out of it. If you let it die, pull it over, pop the hood, the fuel filter is dry. Let it sit a few mins, crank it a bit, it will fire & there will be fuel in the filter, & it will run & drive as long as you don't get heavy on the gas pedal. So, now what I have done already to try to remedy the problem. I aquired the original carb from the previous owner, tried it- same problem. So, I believe it is not a carb issue like they thought. Next thought- fuel filters. Replaced the small one in the carb body, also replaced the screens in the glass aftermarket one mounted just before the carb. Same problem. There are no other in line filters. Next up- mechanical fuel pump. 12 years in a field can't be good for a $20 fuel pump, right? So I replaced it. Same problem. Next thought- sending unit socks clogged. Pulled both tanks- tanks have no rust, socks flow as they should. While pulling tanks, replaced all rubber fuel lines between fuel tanks & selector valve to fix any cracking, collapsing, or dry rotting possibilities. Also blew air through all metal fuel lines both with a compressor and by mouth to determine any restrictions. No restrictions found in any of them. Feeds, returns, or vapor lines. The only thing I found that restricted at all was the selector valve itsself. Now, this valve does work, it switches tanks, the gauge switches accordingly. But the same problem still persists. So, the only thing left at this point is the tank selector switch, & the selector valve. They are the only 2 pieces left original at this point. But before I dump another $100 chasing this elusive gas ghost, I wanted to ask opinions here to see if anybody has traveled this road before me, & could offer some advice. Thanks in advance for any help offered!!

  2. #2
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    has it ever sputtered on you while just cruising if so i had a problem once that every now and then truck would just sputter on me untill one day it just died on me and i did everything you have done untill i pulled out the pushrod behind the mechanical fuel pump and found it to be bent so try that

  3. #3
    Forum Moderator Boudin's Avatar
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    My current daily driver is an 84 C20 with the dual tank option as well. I dealt with fuel problems soon after aquiring this truck a few years ago. I have dealt with every part of the system and maybe can suggest something that might help you.

    It seems as though you have approached this problem in a similar manner that I did. Based on what you wrote, it seems like there is the simple matter of adequate fuel volume not being delivered. You mentioned that it only does this when the truck is under load. This is what leads me to think this.

    You have eliminated a few possibilities....fuel tank socks, fuel filters being clogged, etc. One thing that I'm thinking here is that the fuel restriction is on the line from the mechanical fuel pump to the carb. Originally, there was only the fuel filter located in the base of the carb. Obviously, someone must have added the inline filter. I'm assuming that the steel OEM line was replaced with a rubber one. If they used the incorrect inside diameter fuel line for this, it would be highly suspect as to the culprit of your problem. Check your line and see if it is the proper 3/8" line.

    If either you replace that line with the correct diameter.....or you check and see that it is the proper diameter and you still have the problem....I would next consider getting rid of one of the filters. There is no need to filter the fuel twice. Personally, I took out the filter located out of the base of the carb and instead used an inline filter placed about 6" from the carb. I did this because I had read somewhere that the paper fuel filters in the base of the carb can tend to be a little restrictive even if they aren't dirty at all. Try this next and see if it solves your problem.

    If it isn't solved after trying these two things, I would try putting a fuel pressure gauge on the line from the pump to the carb. I added one to my setup to help me diagnose any fuel related problems. You should see between 5.5-7.0 psi at idle. I would definitely try these things first before I spent the money for a new tank solenoid.

    Let me know how it goes.

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    You know, I never thought of a bent pushrod. I'll check that out! Yeah, the inline filter was my add on, I wanted to see what was coming from the tanks, since this thing spent a very long time in a field. Turns out, the tanks didn't even have any rust in them. That gas was rather nasty, though. I think I will pull the paper filter out, like you suggested. And I will check out that line from the pump to the fuel filter. Its mostly still metal, but I never did check it for kinks.
    Thanks guys!!

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    Ok. Solved this problem.....It was the selector valve. The fuel pump pushrod was straight, the steel line from the pump to the carb was not kinked, & had the correct sized rubber line to the carb. I could blow air through all the fuel lines with no problems, but When I removed and tried to blow through the selector valve, the harder I blew, the more restrictive it became. So I replaced it. When I got the new valve, it passes air with no restrictions. Truck runs fine now. (Well, as good as one can expect from still using the factory exhaust system complete with factory cat)
    One thing I have found, & will recommend is shopping around if possible when looking for parts. I priced the AC Delco brand (Made by Pollak) selector valve for my truck (u7001) at all the local part stores, all the prices were $130 and up, plus tax. I found the valve on Amazon for $65 & free shipping- no tax.

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    Forum Moderator Boudin's Avatar
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    I'm really glad to hear that you solved it. I should have read your initial post closer. I took what you wrote concerning your evaluation of the selector valve too literally. I took it to mean that you had definitely eliminated it as the cause. I just assumed you either had already replaced it with a new one or had been able to definitely determine that it was functioning properly. They do go out a lot and cause exactly what you are describing. Sorry for not pushing it and instead just thinking of other slim possibilities that may be the cause.

    Thanks for the tip on the source of Amazon. I think the cheapest I have ever found them is 79.99 (one time).....and usually they are over $100.

  7. #7
    Senior Member chevyguy's Avatar
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    Glad you got it right. Might want to run some seafoam thru the fuel system to remove any built up varnish that acquired from sitting.
    The only good thing that came from cash for clunkers is that it got most of the OBAMA bumper stickers off the streets.

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