Need some expert opinions on a weird situation I’ve discovered with a 60 2F stalling when I push the clutch in at HWY speeds (only with the AC on)

[CenTXFJ60]

As the title states this truck stalls when you’re cruising above 60mph in 5th gear about 80% of the time once you shift to neutral or engage the clutch. Some background…the owner of this truck bought it and shipped it to a very reputable shop in CO. They spent a year putting in a rebuilt 2F, H55, all new interior, rust correction and some paint work. It’s. 1985 and very clean. This shop de-smogged the motor as well. Once he had it shipped back to TX it started falling on its face. The de-smog is not the traditional one I’ve (and most folks) used from the sticky in this section. It’s bare bones as they did not keep the HAC, fuel cut sensor and some of the vac lines were in the wrong place. I had to flat bed the truck to my shop. Sorted out what was left there post the de-smog, discovered the original carb was put back on the rebuilt 2F. Pulled the carb and had @mattressking rebuild it. I also blew out a very restricted fuel feed line along the frame. New soft lines on both the feed/return lines. New fuel filter. I’ve inspected the tank twice via the sending unit port and it’s very clean. Also did the aftermarket fuel canister upgrade from Autozone. Truck was running awesome for several months. Then the owner noticed in June (about the time he was starting to hit the Hwy with the AC on) it shutting off when he would coast to a stop light after cruising at Hwy speeds. I’ve checked for vac leaks with carb cleaner with no luck. Vac gauge holds steady at 17 (at idle). @matressking has walked me through several tests and it’s passed all. Then I swapped another recent rebuilt carb off this owners other 60 to this truck and it does the exact same thing. Instead of removing it a second time I just plugged the carb from this 60 in question onto his other 60 and it does not stall. Back to the issue…when the truck stalls I’ve pulled over several times and the float bowl is at the correct level. And the motor fires right back up and runs awesome. At least until you remove the load on the drivetrain at hwy speeds with the AC on. Nate and I have talked at length and leaning towards a decrease in the spark at that moment when you’ve been traveling at speed and engage the clutch. I swapped out the AC amplifier

 

[CenTXFJ60]

I know this is long winded and I could not add anymore text to the previous post. So I swapped in another AC amplifier from another 60 and have the same symptoms. Putting this out there to see if anyone has any recommendations on what to look at next. I appreciate any feedback or questions.

 

[klinetime574]

Interesting scenario here. If the desmog was done poorly I would check wiring to the coil, the amplifier, and to the compressor. Those wires would all be on or around the passenger inner fender. Maybe something is hooked up wrong or spliced in. I’ll be interested to see the solution.

 

[jcj_78FJ40]

Was the dash pot/throttle positioner removed from the carb with the desomg? That keeps the engine from dying when there's a sudden deceleration.

 

[cruisermatt]

Sounds stupid but is the fuel filter ok? Should be clear blue style that you can see.
My 40 was doing exactly this a few months ago and it was just a clogged fuel filter, but it was the metal filter you couldn’t see. I guess it would drain the float bowl under higher load (when you can’t see it) and by the time you would pull over and open the hood it would be filled up again.

 

[Spike Strip]

I'll second checking the fuel filter.

My 60 only had about 5K miles on a Toyota filter and was stalling. Banged my head for a while and finally changed the fuel filer just 'cuz it was easy. Fixed. Must've been a bad tank of gas. It happens.

 

[CenTXFJ60]

Was the dash pot/throttle positioner removed from the carb with the desomg? That keeps the engine from dying when there's a sudden deceleration.

I actually don’t know what the “dash pot/throttle is. Could there be another name for it. It’s a stock Aisen carb which @mattressking rebuilt for us. To my knowledge nothing has been removed from it.

 

[CenTXFJ60]

Sounds stupid but is the fuel filter ok? Should be clear blue style that you can see.
My 40 was doing exactly this a few months ago and it was just a clogged fuel filter, but it was the metal filter you couldn’t see. I guess it would drain the float bowl under higher load (when you can’t see it) and by the time you would pull over and open the hood it would be filled up again.

Hey Matt. So I’m on my 3rd Napa (opaque) filter. The second one I removed and cut open was very clean. I can shine a light behind it and get a pretty good visual on the one currently in there. I’ve been stumped by a fuel filter before and it’s not a good feeling. The difference with this situation is the truck runs awesome at all RPM ranges and through all the gears. The only time it dies is in high RPM ranges (primarily fifth gear) when you take the load off the drivetrain by slipping into neutral or holding the clutch in. It fires right back up by releasing the clutch or tapping the key. Also, it won’t die unless the AC is on. Really weird.

 

[CenTXFJ60]

Hey Matt. So I’m on my 3rd Napa (opaque) filter. The second one I removed and cut open was very clean. I can shine a light behind it and get a pretty good visual on the one currently in there. I’ve been stumped by a fuel filter before and it’s not a good feeling. The difference with this situation is the truck runs awesome at all RPM ranges and through all the gears. The only time it dies is in high RPM ranges (primarily fifth gear) when you take the load off the drivetrain by slipping into neutral or holding the clutch in. It fires right back up by releasing the clutch or tapping the key. Also, it won’t die unless the AC is on. Really weird.

I do plan on clearing both the fuel lines again just to be certain

 

[jcj_78FJ40]

I believe it's linked into the fast idle screw. It's been awhile since I have worked on these carbs. Maybe someone more knowledgeable can chime in.

Here's Google AI spiel..
The throttle positioner on a 1985 Toyota Land Cruiser (equipped with the 2F or 22R engine) prevents the engine from stalling when you let off the gas pedal. It acts like a soft cushion for the throttle valve. It slows down how fast the valve closes, letting the engine RPMs drop gradually.

 

[CenTXFJ60]

View attachment 4173572

I believe it's linked into the fast idle screw. It's been awhile since I have worked on these carbs. Maybe someone more knowledgeable can chime in.

Here's Google AI spiel..
The throttle positioner on a 1985 Toyota Land Cruiser (equipped with the 2F or 22R engine) prevents the engine from stalling when you let off the gas pedal. It acts like a soft cushion for the throttle valve. It slows down how fast the valve closes, letting the engine RPMs drop gradually.

Ah yes. It’s still on both the carbs involved. Thank you for clarifying.

 

[Godwin]

Another off the wall thought - could running the AC interrupt the electrical signal to the fuel cut solenoid causing the problem?

 

[bhsdriller]

fuel cut solenoid would only really affect idle? It's happening at highway speeds

 

[toy_tek]

You’ve confirmed the AC idle up is working?

Is the AC clutch actually disengaging when it shuts down?

You mentioned weak spark theory and also rust correction & paint - check for clean unpainted chassis ground for igniter / volt regulator / etc ?

 

[CJF]

fuel cut solenoid would only really affect idle? It's happening at highway speeds

...at hiway speed with the clutch pushed in and when coasting to a stop.

 

[CenTXFJ60]

Another off the wall thought - could running the AC interrupt the electrical signal to the fuel cut solenoid causing the problem?

Good thought Jim and don’t hesitate to keep throwing ideas out. The fuel cut solenoid checks out. I thought having the fuel cut relay (vacuum connects to the backside of the carb) deleted during the de-smog could be impacting this. Was told this has no impact. The previous shop capped this port on the carb.

 

[Godwin]

fuel cut solenoid would only really affect idle? It's happening at highway speeds

Yes, except when it happens he's shifting gears thus transitioning into an idle state.

 

[CenTXFJ60]

You’ve confirmed the AC idle up is working?

Is the AC clutch actually disengaging when it shuts down?

You mentioned weak spark theory and also rust correction & paint - check for clean unpainted chassis ground for igniter / volt regulator / etc ?

Yes sir. At idle in the shop I get close to a 200 increase in RPM’s when the ac button is engaged. Great suggestion on checking igniter connections. I’m also going to advance the timing a few since it’s fully desmogged. Right now it’s at the factory 7 degrees.

 

[CenTXFJ60]

Yes, except when it happens he's shifting gears thus transitioning into an idle state.

Jim, this is a great point. I thought about the solenoid being negatively impacted at operating temps or possibly based on load/demand, but when I switched the carb from this gentleman’s other 60 over to this truck in question, the same symptoms presented themselves. Then I put the carb from the truck in question onto his good running 60 and it runs as it should with zero issues.

 

[CenTXFJ60]

One note to consider is this 60 only shuts down at HWY speeds with AC on and clutch engaged. Another discovery I’ve made is shifting through the gears (at lower speeds) with the AC on you can watch the tach every time you push the clutch in and the tach drops down towards 100-200, then bounces back up to 5-600ish before I release the clutch. I discovered this by counting 1 Mississippi…2 Mississippi, then release the clutch. With the AC off it does not drop below 500. This is not normal driving behavior but I’m doing all the things I can think of to pinpoint the issue.