Smooth idle; bogs when revving in neutral

[BigRedNomad]

Hello! Long time reader...thanks for all the knowledge!

I have a 1987 FJ60 (220K miles) that starts and idles very smoothly, but sputters and wants to die when the throttle is opened. The sputtering problem is load-independent and occurs with the gearbox in neutral.

Some other background:
-Replacing the fuel filter did not solve the problem.
-I can see a steady stream of fuel running from the tank into the filter (filter is translucent). There are a few bubbles in the fuel stream and the filter fills to about the bottom of the filter element.
-Spark plugs appear normal and aren't fouled.
-Distributor cap is clean.
-I disconnected the EGR and AI systems during troubleshooting; they aren't causing the problem.
-Engine runs a steady 17"hg at idle.

Based on the foregoing, I'm thinking this is either a carb issue, a fuel pump issue, or a distributor issue (some on the boards have mentioned a shaft bushing that goes bad causing excessive advance). The head and carb were recently rebuilt, but maybe one of the jets clogged after the rebuild.

Any guidance you can provide is much appreciated. Thanks!

 

[LAMBCRUSHER]

search for oakie rebuild. look for disconnected vacuum line. What is your elevation? steady vac sounds like no leak, but could still be...Check that choke is opening. maybe do a cold baseline on the carb and search for lean drop setting...I've been driving the EFI so long, I'm sure I'm forgetting some carb tricks...you know that carbs suck, right? I mean, that's how they work...

 

[Output Shaft]

Everything is pointing to the carburetor. Gunk can make it past the needle valve screen (which may be shot) and foul up a jet. I'm thinking something could maybe be blocking the primary main jet. The primary jet is THE oriffice in which 98% of the gasoline flows through.

If an Okie Rebuild doesn't clear things up you can do a little cleaning of the main jets without actually taking the carb apart. But the carb should come off to do it easier.

If you decide to take the carb off, unscrew one of the bowl plugs on the same side as the sight glass, and spray carb cleaner, with a straw, directly into the hole. Poke the straw all the way in. Spray around and let the stuff pour out by tilting the carb. Carb cleaner is very toxic stuff, so protect yourself and your lungs.

Then bolt it back up and try again. If no go, time for a proper carb rebuild.

 

[BigRedNomad]

Thanks for the helpful replies!

In the end, the Okie rebuild did the trick. Rig is running better than it was before the problem! There had been some midrange throttle hesitation, which is now gone; I missed those early symptoms until the problem got really bad. Will continue to monitor in case the needle valve screen is shot, as Output Shaft suggests may be the case. The carb was profesionally rebuilt this spring, so I'm hoping the crud was trapped during the rebuild and everything will be fine from here on out.

Here's hoping the rig will pick up a few MPG with clean jets

Thanks again, Lambcrusher and Output Shaft! I really appreciate your help!