Dualjet cruising lean hesitation

[Shifty]

Or the rubber at the tank end is split, and sucking air, or soft and sucking shut.  The amount of ethanol in todays gas is high, and not very rubber friendly.

I actually replaced all the hoses when I replaced the tank.

I used the stuff rated for alcohol

BUT I actually found a gas station here that sells ethanol free, so that's all the truck and my other old cars get

It's a dollar more per gallon but worth it not to be tearing into the carbs all the time

I'm jealous! 

[Scaryfastatx]

I was shocked to find it to be honest. But all the Quick Trip gas stations here have it now. So I get ethanol free for my truck and the lawn mower haha

I'm jealous! 

[Scaryfastatx]

So today worked on the truck more still haven't found the problem, getting really frustrated

I'm thinking maybe it's the vacuum lines

So I pulled everything and wanted to rerun them with new lines

My big question is, where does the vacuum advance hook up? The ports aren't labeled on my diagram

I had it originally hooked up to the port on the base plate, but read on another form for G vans where the guy had a dualjet and his distributor was connected to port B



Thanks

[JohnnyPopper]

So obvious question: Is smog compliance still part of your truck's existence?

If yes, then keep digging.

If no, then apply direct manifold vacuum.

[Scaryfastatx]

So obvious question: Is smog compliance still part of your truck's existence?

If yes, then keep digging.

If no, then apply direct manifold vacuum.

It's not smog compliant, it's older than 25 years so they don't make us test them anymore for inspection

So is the port I need to connect to the lower passenger side one?

[JohnnyPopper]

My understanding is that all ports on a carb are metered except the EGR.

Direct manifold vacuum bypasses that.

Look for, or create a port that goes directly into the intake manifold.

If you have an automatic transmission that has a vacuum operated modulator, that would be a good source to tap into.

[Scaryfastatx]

Well I got some time today, and put my vacuum gauge on the ports

Port B is full manifold vacuum and port on the bottom passenger side is ported

Fingers crossed that does the trick

[Scaryfastatx]

Well, I don't know what else to check

On vacuum port B it felt a lot better with the full manifold vacuum

But got it out on a more open road that I could get some speed and it's still cutting out

Usually at higher speed

If I downshift and get to the rpm where it's stumbling it seems fine

Also if I go really light on the throttle up to speed sometimes it will go faster and maintain the speed

But it's intermittent and will also stumble sometimes

But if I go heavier on the acceleration it stumbles quicker

Other times it stumbles at really low speed

I'm really confused and frustrated

[bd]

Have you inspected the spark plug electrodes and checked the ceramics for cracks or carbon tracks?  Check the spark plug wires for hard spots especially where they route near metal edges and the exhaust manifolds.  Use a bright flashlight to look up inside the spark plug boots and the distributor boots for black soot or green discoloration.  Inspect the cap & rotor for black carbon tracks and cracks.

[Scaryfastatx]

Have you inspected the spark plug electrodes and checked the ceramics for cracks or carbon tracks?  Check the spark plug wires for hard spots especially where they route near metal edges and the exhaust manifolds.  Use a bright flashlight to look up inside the spark plug boots and the distributor boots for black soot or green discoloration.  Inspect the cap & rotor for black carbon tracks and cracks.

I'll check it out

The plugs and wires are basically brand new

I thought for sure it was either fuel or timing but seems like those are fine

[Scaryfastatx]

I think I may have cracked the case!

I was reading through the service manual about engine cut out at higher speed and it had a procedure to do pump down on the fuel lines to see if it is sucking air

So I have a fuel filter in line where the lines cross the bed and go onto the frame rail

I pulled it and did a pump down and it read ~14in Hg


I then was going to lower the tank to tie my vacuum gage in when I saw this (fairly new yikes)


Once I dropped the tank completely looks like there was some minor leakage on the fuel feed line, so definitely was sucking air




So I put my lines back on and pumped down and it's looking great

Think I may have cracked the case

[Shifty]

Todays rubber is doo-doo....

[JohnnyPopper]

So when will we know Mr. Scary??? Great detective work BTW. 

[Scaryfastatx]

WELP!

that was not the problem. I ordered some clear gas approved tygon tubing and a tee fitting, gonna check for bubbles, flow and pump down

Also thinking to swap to an old Edelbrock carb I have just to do a comparison and see if maybe something is wrong with the carb that the rebuild didn't fix (power valve?)

[Scaryfastatx]

https://youtu.be/hCZ_xpEzpoM?si=hVvwvJLpUs1R86FU

https://youtu.be/S5igtSmeQI8?si=a9ofp4CSbUAeODge

Brand new Delphi pump has a bad return valve

So frustrating