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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: Scaryfastatx on April 03, 2024, 09:22:46 PM

Title: Dualjet cruising lean hesitation
Post by: Scaryfastatx on April 03, 2024, 09:22:46 PM
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!

Title: Re: Dualjet cruising lean hesitation
Post by: Captkaos on April 04, 2024, 02:56:46 PM
Steady speed cruising, acceleration at that rpm?  What do the plugs look like?
Title: Re: Dualjet cruising lean hesitation
Post by: JohnnyPopper on April 05, 2024, 11:23:07 AM
Sounds like ignition.
Title: Re: Dualjet cruising lean hesitation
Post by: Scaryfastatx on April 05, 2024, 05:20:24 PM
Quote from: Captkaos on April 04, 2024, 02:56:46 PM
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
Title: Re: Dualjet cruising lean hesitation
Post by: Scaryfastatx on April 05, 2024, 05:21:51 PM
Quote from: JohnnyPopper on April 05, 2024, 11:23:07 AM
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
Title: Re: Dualjet cruising lean hesitation
Post by: JohnnyPopper on April 05, 2024, 09:58:06 PM
What year? HEI? Points?

How long has it been since you replaced the ignition components?
Title: Re: Dualjet cruising lean hesitation
Post by: Scaryfastatx on April 06, 2024, 05:02:55 PM
Quote from: JohnnyPopper on April 05, 2024, 09:58:06 PM
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
Title: Re: Dualjet cruising lean hesitation
Post by: JohnnyPopper on April 07, 2024, 09:23:16 PM
So your Pontiac coil is HEI too.

Well, give it a shot.