Floating Idle after Carb Rebuild on Desmog'd FJ60

[Gordo]

I rebuilt my carb this weekend, the byproduct of replacing my exhaust manifold gasket (while it's off I ought to...).

Pleased that it started right up but found that the idle fluctuates around 400-500 RPMs (currently 900 to 1400 RPM) and the engine misses intermittently (mild miss but noticable).

On the good side it definitely pulls like a new truck, strong all the way up to 4k RPM!

I haven't started to troubleshoot yet, just looking for some upfront suggestions where to look.

Thanks, Gordo

'87 FJ60, Desmog'd

BTW, what a weekend for the TLC:
-Replaced driver's side broken motor mount.
-Replace 3 year old exhaust/header manifold gasket (I don't recommend the SOR kevlar gasket).
-Rebuilt the carb.

 

[soggy60]

all the little vac hoses correctly reconnected - those removed as part of desmog properly capped. verify ya didn't snap on of the two 'plastic' temp sensing vac control valves on side of thermostat housing....

 

[beaufort-fj60]

take pics of your desmog; left and right side of engine, and close up of carb area. post them

 

[Gordo]

Pics

Would like to post pics but the last time I tried I think I was out of space...

Beaufort like B-yew-fort, SC or like Bow-fort, NC?

Thanks for the suggestions,

Gordo

 

[BlueBoxFJ60]

a verify ya didn't snap on of the two 'plastic' temp sensing vac control valves on side of thermostat housing....

not to change the subject but what do they do and what happens if one is broken?

 

[Gordo]

Nothing on mine...

Mine are capped off as part of my desmog.

The Bi-Metal Vacuum Switching Valve (BVSV) on the side of the t-stat housing works as part of the spark control system/part of your overall emissions control system.

In short, it delays application of vacuum to your distributor advance until the vehicle is warmed up.

In my application I run a vacuum line from the carb's advancer port to the vacuum advance diaphram on my "performance" distributor (or whatever you call the older, points type, vacuum advance distributor - mine's no longer points type BTW; Crane XC optical pick up in place).

Yes, my engine is significantly modified/in most cases simplified. Still trying to figure out if it makes troubleshooting harder or easier...

Thanks, Gordo

 

[beaufort-fj60]

B-yew-fort, SC

everyone desmogs differently, there is no text book way that i have seen. a desmog link is in the tech links above.

 

[soggy60]

The comment about all the tiny hoses....

there's a choke-opener and a choke breaker that runn off vac lines; they can have a similar effect ( hunting) if the vac feed has a leak.

same can occur with the 3 (4?) vac fittings on side of carb ( air-rail side).; a small leak can cause the wandering of idle r.p.m.

last but not least : float adjustment.....idle mix adjustment....
come to think of it, maybe these should be checked first . . .

 

[Gordo]

Odd

Not sure what happend but I removed my air cleaner assembly yesterday to observe fuel flow down the barrels (confident my truck isn't backfiring...). When I replaced the air cleaner and fired it up it has smoothed out: my fluctuating idle is gone. Very odd.


Gordo

 

[Gordo]

Thinking it Might Be Fuel Cut Solenoid Related

Going to wire it up so it's always open/on when the key is turned on. Symptoms appear to be in line with the description that the emissions manual describes when you are testing the fuel cut.

Gordo

 

[beaufort-fj60]

i'm not positive, but i would guess that unpluging the cut-off would do the same thing as a re-wire. i think the "computer" on the 60 is more of a "yes" or "no", not a "if", "and", "or".

 

[kevinmrowland]

If you jump the green wire from the solenoid to ground, the black/yellolw wire will get the "engine on" signal that it needs. Your engine would not run if that b/y was not getting power. This will effectively cut out the decel cut function.

If removing the air cleaner, then reinstalling seemed to fix the problem, was it possible there was just a leak around the seal? To much air getting in? Did you remember to reinstall the rubber doughnut on top of the air horn? Could happen.
Did you try spraying things with carb cleaner while the engine was running to see if the RPMs change?

 

[Gordo]

It Was the Fuel Cut

Another oddity but I confirmed it was the fuel cut causing my fluctuating idle and hesitation. Odd because it didn't have this problem prior to the carb rebuild and the fuel cut solenoid checked out fine during the rebuild.

I tried to ground it but may have been grounding the wrong wire. Ended up just rewiring the soleniod to a switchable power and ground.

Problem fixed runs smooth. Now onto checking into what appears to be an inop secondary activation.

Appreciate the feedback.

Gordo