2F carb clogging (I think) - need help with ID'ing source

[playedout]

I have a '84 FJ60 with rebuilt stock carb and most smog equipment intact. Truck has run great for years but has recently started clogging the carb from what I can tell. Truck will start stumbling and bucking, struggling to idle, requires significant feathering of gas to get it back home. Last couple of times I've been able to get things running nicely again by going through a full on-vehicle carb clean-out (carb cleaner in fuel inlet, bowl drains, idle mixture screw hole, and all around the main carb throat). I haven't been super diligent in attempting to catch whatever I'm clearing out but I'm not noticing anything significant getting flushed out. I've replaced all soft fuel lines, toyota fuel pump over the past couple of yrs. Changed out fuel filter a couple of times and again not seeing anything too diagnostic in those.

Took it into an indy Toyota shop recently and they weren't much help. Guy just recommended slapping a Weber on it - sure didn't sound like he put much thought or effort into it and if we're dealing with a clog, that obviously wouldn't do a thing.

Wondering if anyone has any thoughts on next steps for diagnosing culprits for clog source? Should I be looking forward of the fuel filter? Any candidates to check/replace? Or could there be things small enough to slip by the filter that could be causing the issue? Fuel tank removal/replacement a place to start? I'm not seeing any rust-like stuff in the fuel filter. Appreciate any thoughts!

 

[trainbufftony]

Check for vacuum leaks first.
Spray carb cleaner at the intake gaskets and anywhere there may be vacuum and listen for a change of RPM. If that checks out, I'd compression test the engine, just to be 100% certain we're dealing with a good engine. Also check timing.

Pull the fuel line at the carb and check the fuel pumps ability to deliver fuel into a coffee can.

If all of these things check out, then consider rebuilding the carb.

 

[mattressking]

Fuel cut solenoid and emissions computer are a good place to start.

Once you can truly verify that the solenoid clicks reliably and emissions computer board doesn't have notable cracking (reflow all visibly cracked solder points). You will need to go through all of your existing smog equipment and test vacuum at idle when hot. Anything less than 18inHg is a leak that needs resolving. Fix all of those items first if you find failures. Back to smog equipment - there's a chance your egr is sticking. Run the truck at idle and put a long piece of vac hose on the egr port, suck on it and if the engine dies instantly, it should be just fine. If it doesn't, you have a sticky egr that isn't opening/closing reliably and causing a major vacuum leak.

Download the 2F emissions manual from cruisercult.com and run through every item on your truck. Don't skimp, don't half ass it. Then report back.

 

[CruiserTrash]

Listen to @mattressking, don’t go slapping new carbs on or looking for particles that may not be there. Eliminate the vacuum leak and EGR variables first - those are much, much more common.

The only finer point I’d put on it is your idle vacuum can vary with altitude. I live at 5200’ and have 17inHg which is pretty good here. That would be around 21inHg at sea level. Test by running the vacuum gauge hose to your AC idle up port on the intake manifold (comes off the brake booster vacuum source near the back). If you’re factory non-AC, then put the hose onto the triple-nipple thing screwed into the intake manifold near cylinders 2/3 (Toyota calls it a “gas filter”).

 

[KevinHardy]

Fuel cut solenoid and emissions computer are a good place to start.

Once you can truly verify that the solenoid clicks reliably and emissions computer board doesn't have notable cracking (reflow all visibly cracked solder points). You will need to go through all of your existing smog equipment and test vacuum at idle when hot. Anything less than 18inHg is a leak that needs resolving. Fix all of those items first if you find failures. Back to smog equipment - there's a chance your egr is sticking. Run the truck at idle and put a long piece of vac hose on the egr port, suck on it and if the engine dies instantly, it should be just fine. If it doesn't, you have a sticky egr that isn't opening/closing reliably and causing a major vacuum leak.

Download the 2F emissions manual from cruisercult.com and run through every item on your truck. Don't skimp, don't half ass it. Then report back.

Hi and thank you. What do you mean emission computer board? Where is it and what does it look like?