Dualjet cruising lean hesitation

[Scaryfastatx]

Hey all, before I start tearing into the fuel system. I'm having a head scratcher

Truck details, 305, dualjet M2ME, TH350, 4.11 gears

My truck had been running like a champ, then all of the sudden started getting some random hesitation mostly during higher speed cruising usually between 2k and 3k rpm

I lift and most of the time it comes back but refuses to go faster, in a few cases it's died at idle. It will start right back up with some throttle input so pretty sure it's a lean hesitation.

 I noticed the vacuum pull off died so relaxed that and it was back to normal until it reached 3k. Next day got worse. I adjusted the carb according to a manual I found online for a 78 dualjet.

Started and idle was perfect, at no load and heavy throttle it was fine, but again higher speed cruise it stumbles

It's a brand new carter mechanical fuel pump, new carb filter, added an inline filter on the frame rail where the girl lines go across the bed.

Carb has not been rebuilt

Any common stuff on these to look for first?

I was gonna start with plugging the return line, then check the filters and then the check valve in the fuel inlet

Thanks!

[Captkaos]

Steady speed cruising, acceleration at that rpm?  What do the plugs look like?

[JohnnyPopper]

Sounds like ignition.

[Scaryfastatx]

Steady speed cruising, acceleration at that rpm?  What do the plugs look like?

From a stand still it pulls hard up to the speed limit, but then starts sputtering

But I'll adjust the carb to limp home and the point where it sputters move around

I'm gonna pull the plugs this weekend to check them

[Scaryfastatx]

Sounds like ignition.

Think so? Like the module starting to give up?

I have a coil from my old Pontiac I'll swap it and see

[JohnnyPopper]

What year? HEI? Points?

How long has it been since you replaced the ignition components?

[Scaryfastatx]

What year? HEI? Points?

How long has it been since you replaced the ignition components?

It's an 81 and has HEI, it has new plugs, wires and cap and rotor but the rest I have no idea been a while

[JohnnyPopper]

So your Pontiac coil is HEI too.

Well, give it a shot.

[Scaryfastatx]

Well tried everything, cracked open the carb cleaned it all out, rebuild it and set the float up a little

New filter, swapped ignition

Still lean hesitation and it's getting worse

Today I capped the return line and it's starting up and idling with the choke much better

Starting to think my brand new Carter fuel pump is the culprit

Who makes a decent pump not made of Chinesium?

[Shifty]

None of the names we've grown up with, we gave it all away.   

Delphi is about the closest thing to quality....

[Scaryfastatx]

None of the names we've grown up with, we gave it all away.   

Delphi is about the closest thing to quality....

Sheesh, all in the name of corporate profits

I'm gonna pull the trigger on the Delphi one and see how it goes

I went for a little cruise with my kiddos just now and it starts up and idles much better with the return line plugged

If I accelerate hard from a stop it runs strong until like 30mph then stumbles. I let off for a bit and runs good again

If I accelerate normal it will go up until 50 then hesitate

Pretty sure it's the pump not giving the flow rate needed for the carb

[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. 

[Scaryfastatx]

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

[Mike81K10]

I remember the days of changing out ignition points and the condenser. Long gone!

[JohnnyPopper]

I remember the days of changing out ignition points and the condenser. Long gone!

I still have a 1966 Gem, stock points/condenser combo. Still use my dwell meter...

I know I know, In time I'm going to upgrade to HEI or MSD.