PITA Rough idle...need help

[4thwheel]

OK here is the story....

Rebuilt 2F, newly installed 250 mi ago... Ran good with a higher idle speed setting for break in. Then lowered RPM at Idle to 650. Still ran pretty good...just a bit rougher than I expected with a balanced motor.

So I decided to Change oil/ filter, retorque Head bolts, reset valve clearences, and set timing and Idle mixture. After all this...It chuggs and surges just a bit at 650 RPM and ran rich.

I figured it was all about the idle screw setting (The PO removed the plug ) So I attempted top use the FSM lean Idle drop method to set the idle.

Only problem was the to do this you must have all vacuum hoses and air cleaner assy. installed. With air cleaner installed I cannot get to the mixture screw....go figure.

Next I decided to check out the idle mixture factory setting from a non rebuildable carb I have on hand. Drilled out the plug, and turned the screw in exactly 3 turns. So, I figured this is the factory setting...changed out the idle screws, dialed in 3 turns , installed air cleaner, vacuum hoses and started her up.

Runs more lean and seems great at high RPM but still idles rough at 650-800 RPM.

So I figured vacuum leak...checked all hoses (new 3mm lines) and all connections, retorqued manifold gaskets and still rough idle.

Help me out if you can...Im getting pretty frustrated!!

New carb kit/rebuild
New vacuum lines
new air filter
new fuel pump and inline filter
new plugs /dizzy cap/rotor
Timing set to the ball 7 degrees btdc
Valves carefully adjusted with warm engine...almost hot!

Thanks...Im wanting to hit the trails on Sunday

1981 FJ40
complete engine overhaul
man a fre RV cam
too much else to list

 

[Magnum44]

I know you checked for vacuum leaks but have you tried spraying some starting fluid around the base of the carb, manifold etc. I have had good luck finding leaks this way. Sounds like you've covered all of the bases. it's probably something very minor. The first L/C I restored everything was new. Couldn't get it started for anything. finally I found the new condensor was bad. Changed that and fired right up. Good luck I know it's frustrating.

 

[ocdbeetle]

The vacuum gauge is a must have for dialing in a carb...idle mixture....

I had a similar problem a couple days ago although I run a 1bbl.......Everything I tried and adjusted was fruitless.....

I read somewhere in the anals of the mudship to put my hand over the carb when it was running and let the momentary suction unclog anything that may be lodged in somewhere....well...I adjusted the the throttle screw where it would rev above the idle circuit and put my hand over the top....It pulled my palm, almost choked, then I moved my hand.....did this twice.....Whatever was clogged was gone and it runs better than it ever did.....It was that easy....this time anyway.....I was due for an easy one....

 

[Pin_Head]

Make sure the idle fuel solenoid is grounding. Ground the yellow/green stripe wire and see if the problem goes away. If not, remove the solenoid and verify that it is operating and not clogged with a piece of O-ring or other junk.

You can go ahead and adjust the mixture with the air filter off. If the idle changes with the filter on, you have a bad filter.

 

[4thwheel]

HMMM...

Thinking valve adjustment might be the problem as I hear a uneven firing at the exhust pipe that is in time with the "chugging" I hear up front.

Question: how critical is the valve adjustment...I may have a couple exahust valves too tight. I always try to get the perfect balance between no tick and no leaks...would this make it run rough as in a true idle/carburator problem

To awnser pinhead...the fuel cut soleniod is fine and connected properly. Thanks for helping out

 

[Pin_Head]

Connected properly is not the same as getting grounded when it needs to be.
I dubt that valve adjustment is your problem. They would have to be so tight that they would prevent the valve from sealing.

 

[ocdbeetle]

I'd have to try cleaning/unclogging the carb....sounds like the idle circuit is blocked somewhere....especially since its great at higher rpms...Otherwise I'd work between the throttle and idle adjustments...