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Old 11-26-2005, 11:49 AM
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No fuel to carb?

My son has a 85 GMC short bed PU with a 350, and I am having an issue getting fuel to the front bowl of the carb. I have the same symptoms since the issue started, even after doing all of the below:
1. Dropped both tanks, no debris, clean as a whistle as the day it left the factory, no blockage on all 3 tubes (send, return, vent), blew compressed air through all of them in both directions.
2. replaced rubber fuel lines at tank, at change over valve, fuel pump, and at carb to chrome line with new rubber "fuel" lines.
3. replaced crossover valve
4. replaced mechanical fuel pump 3 times (stock O’Reilly, had a catch spot in pump arm movement, 2 Carters one bad, not suction, finally a good one)
5. rebuilt carb, changed out needle and seat, float moves freely, etc. for extra measure
6. I verified no vacuum pressure in tank.
7. I pulled mechanical pump, put finger on push rod, and had son turn over engine, can feel 1-1.5” of movement of fuel pump rod.

You can blow compressed air through all three lines, no blockage, regardless of side. I will pull the line before or after fuel pump, and after I blowing through lines, I can momentarily receive gas, but it stops, and does not matter which tank is selected. I have my son turn the motor over, and with the line removed after the pump, gas will shoot out initially, then stop. You can not even feel pressure. But to get it to start pumping fuel again, I have to blow through the lines. I have checked it with a gauge, and you can see it start at 6 psi, then drop to 0. Any suggestions? This is driving me crazy!!!

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Old 11-26-2005, 12:00 PM
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gas problem

loosen the gas cap first
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Old 11-26-2005, 12:01 PM
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Done that as well. No vacuum pressure to tanks with clear vent tube that should go to charcoal cannister.
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Old 11-26-2005, 12:32 PM
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Just a thought, if you could get an electric fuel pump (borrow one or get a really cheap one) and attach it to the inlet line at the mechanical pump and prove you can draw fuel through the lines. If that works, then I think the mechanical pump would be bad or the line between the pump and carb is blocked or pinched. you could also use a bucket for a tank and put a line from the bucket to the inlet and then it goes to the carb from the pump. That would also prove the same thing.
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Old 11-26-2005, 12:59 PM
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it is a rochester carb? when you rebuilt it, did you check the inlet filter? right behind where the fuel line goes into the carb is a paper filter, although some have a brass filter as well. when they get very dirty, old, or water in them, they will collapse and cause the same problem. just need a big cresent wrench or a 1" wrench to take off that big fitting. i had one fail on me during a cross country road trip.....never knew about it before then, but two fuel pumps and several hours lost, some guy pulled over and told me about it..........took it out, and it was black and all mashed up........took it out, truck started right up and ran great after that.................
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Old 11-26-2005, 01:50 PM
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I had the same problem with a truck a while back. Turned out that a hole was rusted in the fuel line at the top of the tank, just where ut comes out of the tank. It was sucking air. Since it was on top, no gas was leaking on the ground.

I can't see it happening with 2 tanks though.....would be a real coincedence. There may be a hole in the line after the fuel line switch......While you are at it, check out the fuel line switch.
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Old 11-26-2005, 06:10 PM
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I did some other things to it today, to clear my mind on the issue, and went back to it. I was able to pull fuel from the tank at the end of the hose before it connects to the chrome fuel line with only 2 -3 pumps of a hand pump. I pulled the line off the Holley 670 Street Avenger, and checked AGAIN if there were any obstruction on the inlet, none. Checked the brass filter, clean as a whistle. I used my mirror to check the needle to see if it was open, yep it is. I could not try to fire it up do to running the battery down last night. I have it on the charger now, and will try it in the am. Craziest thing.

Poncho - The fuel switch/valve is new, and using the switch, it moves between tanks with no problem, and I can verify that by blowing compressed air through the lines from up front, and my son under the truck checking the air on the outlets. Fuel gauge reads correctly on both tanks. This is crazy. I just may have it whipped, but due to dead battery I will not find out till tomorrow.
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Old 11-27-2005, 08:52 PM
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Camshaft Fuel Pump Lobe Flat?

I went back to it today, after letting the battery charge, and I am able to pull fuel from either tank, at the end of the line before it attaches to the chrome fuel line to the carb, with 2-3 pumps of a MightyVac hand pump. The guage also reads a little over 1 psi when pumping it.

I pulled the pump again, and put my finger on the pump rod while myh son turned over the engine, and I was mistaken earlier when I said it moved 1-1.5 inches. I only moves 1/2" or less. I looked up the pump rod hole with a mirror, and the cam lobe looks smooth, no gouges, etc. all the way around.

Is it possible the cam lobe for the fuel pump has gone almost flat? The problem has progressively gotten worse to where it will not pull fuel at all anymore, and that is the only thing left. The pump rod measures exactly 5.75", no wear on it at all.

Again, is it possible the cam lobe for the fuel pump has gone almost flat?
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