Truck Starting Issues and the Red Herring

Several weeks ago when my dad and I picked up the truck it was a rough running truck with no brakes.  I was thrilled because brakes are easy to fix, eventually.  Engines are more complex and expensive.  From my earlier posts you can see some of the work I have put into fixing and cleaning her, specifically the fuel pump and lines to the carburetor.  After some initial issues we were able move the truck to another place on the property.  Then I replaced much of the ignition system.  This is where the trouble started.  We could get the truck to start and run for about 10 seconds with only a full choke on.  Then she would die.  No gasp or sputter or backfire, just a simple death.  This was repeatable and very frustrating.  

So here I was with a old truck that ran before I touched it and even if I finished the brakes anytime soon she would not have enough energy to go for a "drive".  I racked my brain, posted on the Old GMC forums, reviewed original operators brochure, asked friends and consulted with my dad.  These puzzles can be fun IF you are confident that the problem is easy to solve, however when the puzzle seems to have so many variables it can be daunting.  

Lets take it from the top.  Would changing plugs, wires and a distributor cap cause this condition?  No.  Could I have disrupted any other electrical components? Possible, but again the stalling was so repeatable that an erratic or permanent electrical problem was ruled out.  Next comes the fuel system.  Did we have a bad new fuel pump? Possible, but not probable.  Are the fuel filters clogged or leaking?  Again possible but I just cleaned them.  Is the carburetor clogged?  Possible but that means the filters are not working or I dislodged some gunk in the process.  I also touched the vacuum lines to the carb but that is an easy check and probably not the issue.  So far the problem points to the fuel system, which I touched.  Arrrg.  

The next thought was how to diagnose the problem the cheapest and quickest way possible.  Since we had visually seen fuel squirt out into the glass bowl fuel filter, a bad pump was ruled out, but it was possible that it was not high enough pressure.  I checked some specifications on the pump and discovered that the test involves installing a tee junction at the fuel filter and having a hose drain into a bucket while idling the truck.  The spec says that at idle 1 pint of fuel should be collected in 45-60 seconds.  This translates into 2 cups a minute or in 8 minutes 1 gallon of fuel, at idle!  This is a test only and real world driving does not reflect these numbers.  I assume that when the carburetor float shuts off the intake of fuel the system does not force more fuel into the carburetor.  Therefore you can't make an assumption of fuel consumption from this test.  We could not do this test cause we didn't have an idling truck.  Moving on to the carburetor,  we did not touch that part and it seemed to be working before so that is an option but could be a $30-$125 fix.  Moving on from there we considered the glass bowl filter.  This filter is actually a large ceramic or porcelain thimble.  A gasket on top seals it inside the glass bowl and all things seemed to be normal.  It could be that the ceramic is suddenly clogged or the gasket is blocking fuel.  The options to eliminate this filter would be to simply take it off and use a hose to bypass.  At this point there wasn't any smoking guns in the puzzle.The cheapest and quickest to look at were the vacuum line and glass bowl filter.

Now lets consider when the last time it worked and what did I do different. Well it seems that I moved the truck from one spot to another and that was all I did.  Though prior to the move I had removed, cleaned and reinstalled the fuel system.  We tried to start her and noticed a leaking fuel filter next to the pump.  That was easily fixed.  After that fix we could not still seem to get the truck started.  Our assumption was that the fuel line had air in the system and so we decided to "prime" it by removing the glass bowl and topping it off with more fuel.  That's when I also discovered that the steel line to the glass bowl filter was not installed correctly.  Sure enough it started up and we were able to move the truck to the new location. 

One of the puzzles inside the puzzle was how that glass bowl fuel filter worked.  It was always at half full except for the time we topped it off to "prime" the system. I even reviewed some early photos of the truck when it was sitting on my father-in-laws property and it was also half full.  So last night dad decided that the easiest and cheapest route would be to remove the ceramic filter.  Throwing my hands into some rubber gloves and a quick turn of the retaining screw I pulled off the glass bowl.  We pulled the ceramic filter and reinstalled the glass bowl without adding more fuel. 

As before, I pulled the choke stepped on the starter and prayed.  After three attempts, one being the starter not engaging, it started up.  The next few seconds would be critical.  Normally the truck would begin to die and not a single choke adjustment or throttle feathering could keep it alive.  This time it started to gasp and I slowly pushed in the choke and to my surprise and relief it smoothed out.  I sat dumbfounded as the engine purred with the choke completely off and was able to rev the engine as I wanted.  

Ever had that relief that is so overwhelming it makes you smile and feel light as a feather for hours afterward?  Well last night it started and I still feel great.  

So the red herring in all of this was that when we "primed" the glass bowl we unknowingly caused a full fuel condition and masked the gasket/filter problem. The timing of me turning the truck off after moving it was probably pretty close to it gasping for more fuel anyway.  So the fuel filter has a bad gasket.
 
The only other problem is a slight fuel leak between the carb and the filter and the gasket between the top and bottom half of the carb.  Easily fixed.

I will now replace the fuel filter gasket and or ceramic filter.  Napa has what I need for about $4.  It is a NAPA Gold Filter part number FIL 3943. Comes with the paper type filter and two gaskets. The gasket on the right is the one that should work.