Fuel vap canister overflowing?

[bd]

Remove both ends of the 3/8" hose connecting the carburetor fuel bowl to the vapor canister and nestle the low end of the hose in a clean rag.  Rinse the hose out with aerosol carburetor cleaner and inspect the rag for black carbon granules. 

Count the number of turns to lightly seat the idle mixture screws then remove the screws from the carburetor.  Were both screws adjusted the same number of turns?  Thoroughly blow out the idle mixture passages using carburetor spray and compressed air, alternately, then reinstall the screws and adjust them the same number of turns out from seated as originally counted.  Is there any improvement?

[Pearlmoto]

Update:

Running the fuel pump from a can did not change anything.  Motor fires like it should, and immediately dies.  It'll will only run if I make it using tons of throttle.

EDIT: I have checked spark, it is big and fat and yellow during cranking

BD - just saw your message will proceed that way next

[Pearlmoto]

Today I dug into the carb and found 2 hiccups....

I rebuilt this carb ab 1000 miles ago and it has run well up until the trouble I've recently run into.

I went ahead and pulled the carb down again and found a bit of sediment in the bowl, which I wasn't terribly surprised to see given the recent fuel tank service,  It was a super fine powder:



A thorough cleaning of all orifices is obviously in order.

Second, and I believe more critically, was that this brass tube next to the idle pickup tubes had fallen out the airhorn and was sitting in the carb body:



In fact, I hadn't even noticed until I flipped the body upside down to drop out the choke rod lever.  I carefully tapped it back into the airhorn.

I'll reassemble the carb when my rebuild kit arrives this week and see if this fixes the issues.

If problems persist, I think it could be safe to assume that tank sediment may have fouled the new fuel pump.

[Pearlmoto]

Reinstalled carb - truck has been sitting now about 2 weeks.  It wouldn't crank over at all.

Going to put in another fuel pump.  The pressure was not great enough to fill the bowl, and I'm concerned ab the color of the gas coming out of it.  It's as if the same gunk in the carb has fouled the pump.

I'm also going to add a second in line filter after the fuel selector valve to try and prevent this from happening in the meantime.

I suppose It's time to drop and flush the tanks.

[bd]

With that much silt in the tank(s) the fuel tank pickup sock(s) may be plugged.  Test the fuel pump before you replace it - there may not be anything wrong with it.  I would also look for a different fuel station - their storage tanks could be the source of all that silt.

[Pearlmoto]

I was worried about that, but since the truck behaved the same when I set the pump up on a remote tank, I figured I could eliminate all of the tank components as suspect for now.

I replaced the pump yesterday but need to get a filter before I start it. 

[Pearlmoto]

I went to start the truck today and lo and behold - SAME TROUBLE.  Starts up, runs a second, farts out.

I know these trucks are easy to work on, but dang if this one isn't stumping me.

I took a video of the behavior.  To me this sounds like a fuel issue.  I can get the truck to fire off after a few squirts of the accelerator pump, but it won't run:

https://www.youtube.com/watch?v=Z6xijtumkls


I may take the carb back off so I can take a close look at the idle screw circuits.  I was thorough with my cleaning using compressed air and solvent, but perhaps I missed something.

I'm running out of ideas here.

[VileZambonie]

Run the truck off of a fuel can directly to the pump. Prime the hose first so you have fuel in it before you drop the hose in the can and keep it somewhere safe where it won't spill or ignite fuel vapors.

Any chance someone poured something in your gas tank? Are you 100% positive the fuel lines are properly routed? I've seen the vent hose and return hose mixed up many times and would make sense with your overflowing canister.

You mentioned yellow spark, you should have a bright blue spark across a .060" gap. Don't spark test it with the fuel system open. How old is the pick up coil and module? are you sure you aren't losing spark? Is it consistent or intermittent spark? Have you pulled the distributor cap and inspected?

[Pearlmoto]

I have done a remote can test on the first fuel pump.  It did not change anything.  The fuel I was using was also from a different service station than the gas currently in the tanks.

I can set up a remote test for the pump I just replaced just to check for good measure.  The lines are correct - kind of a tough to mix them up given the hose size and routing, as well as the fact that the selector valve only takes feed and return lines.  I also had the truck running perfectly for a good while before it farted out.

The overflowing canister was a result of the selector valve stuck in a half open position - I believe it caused the tanks to bleed over and overfill, thus backing out the vent.  This problem was solved with the new selector valve.

The pick up coil is the only part of the distributor that has not been replaced.  The module is new.  I am not sure I'm not losing spark - I did the test visually by holding a spark plug to ground and cranking, but it seems to be consistent.  I pulled the distributor cap to replace the module, the cap and rotor are only a few hundred miles old.

The gas tanks have locking gas caps, so unlikely someone has sabotaged anything.

[bd]

Do this:  start the engine and run it until it quits.  Shut the ignition off and without moving the throttle, remove the fuel bowl cover and check the fuel level.  If the bowl is dry or nearly so, there's a fuel delivery issue.  If fuel is at the normal operating level, the problem is caused by something else.  While the bowl cover is off, verify the float setting @ 13/32" (10 mm). 




Referring to the image above, lay a straightedge across the "flat" underside of the cover from side-to-side across the main air bleeds and measure the net amount of arch.  Some arch is normal, caused from tightening the forward two carburetor mounting bolts.  Excessive arch will cause late tip-in of the main circuit.  Post your findings.

[blazer74]

Any chance you have the little filter in the inlet of the carb with the rubber check valve backwards. Some have it.
Don't recall if you checked or replaced that filter.

Did you try to keep it running by carefully pouring a small amount of fuel in the primary bowls after it starts to eliminate the ignition system?

You can also slightly crack the secondary's open by hand at the lower linkage. This will add a little fuel from the secondary system to see if it will run.
May sound unorthodox but...

If it does run better, fuel supply or primary carb circuit problem.

Have you plumbed in a pressure gauge between the pump and carb?

Also there should be residual pressure in the fuel line to the carb after it quits. Take a straw or similar and through the vent  towards the center of the carb above the float bowl and push gently down on the float a bit and it should flood if the bowl is full of fuel.

As far as spark, an inline spark tester works nice also for checking that.

Best of luck, sure can be frustrating.

[blazer74]

The tube that fell out is for the POE (pull over enrichment) in the secondary system. Comes in to play when the upper secondary flaps first start to open adding fuel as the secondary's begin deliver fuel preventing a hesitation.

They are not a primary or idle circuit function.

[Pearlmoto]

Thanks for the replies fellas.

I'm about to go outside and do the suggested steps.

blazer74 - the filter is new and oriented correctly, with the opening towards fuel flow.

I have not tried to keep it running by pouring gas in - I can try that when I have a second hand.

I have not put a pressure gauge between the pump and carb since I replaced the unit altogether anyway. 

My neighbor is experienced with these old trucks - he sauntered over and told me my condition sounds like timing, and that it could have jumped time.  I was skeptical of this as it is a completely out of left field suggestion.  I went ahead and pegged the distributor in either direction to see if it offered an improvement.  All it did was make the truck sound really advanced or really retarded.  I don't think this is a timing issue.

[Pearlmoto]

Here's a few pics of what I found when I pulled the air horn:





Fuel pump is working as it should.  I'll measure the airhorn deflection when I check the float.

I have the carb on my bench now.  My top gasket tore when I pulled the lid so I may have to wait and order another one.

[bd]

If that image was taken immediately after it died out, unless there is fuel contamination, the symptoms are not fuel related.  Are you certain the tanks are not contaminated with diesel?

Your neighbor hinted at "timing," referring to valve timing.  Valve timing problems can produce various symptoms, but generally cause decreased engine vacuum and power output.  To check for a valve timing issue, read through Re: 86 C10 Loping.  Then to verify correct harmonic balancer registration, which can impact the relative position of the ignition timing marks on the balancer, read through Re: Not 100% what's wrong here.  Replacing a timing chain and sprockets, if you determine they are the cause, involves removing the water pump, the crankshaft harmonic balancer and the timing cover.  Some people also remove the engine oil pan.  You can anticipate that a timing chain replacement will consume an entire weekend the first time you perform the repair.

Once valve and ignition timing are verified, move on to ignition system diagnosis.