Inconsistent idle (trying to adjust idle mixture)

[Freeborn]

Continuing to work out the bugs on my rebuild. Current task: idle mixture + any other carb adjustments.

Prereqs: 1978 FJ40, 2F, Aisin carb, smogged (as in I have a smog pump - always confusing to me), and I live in Denver

Trying to get the idle mixture dialed in. When it idles, it doesn’t keep a consistent rpm and sounds like it skips a time or two every 1s-ish. RPMs fluctuate up and down maybe 50 RPM on a couple-second cycle. I’m fairly positive I have all the vacuum lines going somewhere that makes sense - one at the base is plugged. The only vacuum ports that are open are a couple off the top of the air cleaner. When I try to adjust the idle speed screw (base of the carb, vertical, firewall side) it seems to do nothing. Adjusting the idle mixture (base of the carb, exhaust manifold side) it seems to do nothing- even screwed all the way closed.

I was reading through this thread, and the last post about the transmission speed sensor caught my attention as the leads on mine came off during the tranny rebuild and are disconnected:

'78 FJ40 carb adjustment

I have a '78 FJ4 that is running pretty good now that I have the electrical issues sorted out. (It was the ground.) However, now that I have been driving it around an issue has popped up. It idles too high. I've looked at some threads here, and this one in particular has been helpful...

forum.ih8mud.com

Thoughts? Am I missing something vacuum-y? Is the tranny sensor a big deal? Any work-arounds or diagnostic procedures?

You want any specific pics?

 

[Freeborn]

Maybe the transmission wire is a non-issue according to this thread:

78 FJ40 - Transmission mystery wire

Hi Mudders, Just finished up rebuilding the 4 speed transmission and broke off this black wire connected to a switch on top of the transmission. Could it be a ground? Haven't had much luck figuring out what it is and where to find a new one. Any input would be greatly appreciated. Thanks! Jim

forum.ih8mud.com

 

[devo]

My instant answer is: because this happened to me after a carb rebuild the fuel or vacuum porting could be blocked or clogged ?



devo

 

[Freeborn]

My instant answer is: because this happened to me after a carb rebuild the fuel or vacuum porting could be blocked or clogged ?



devo

Could be. I’m a little dubious. Fresh rebuild on the carb. Freshly made fuel lines. Is there a good way to figure out which line is the problem child (assuming it’s vacuum)? I’m new to the carbureted car world. Please forgive my ignorance.

 

[Freeborn]

...also all new vacuum lines.

Does anyone have a better diagram than the FSM for how the vacuum lines hook up to the ports on the computer (or whatever that is on the driver side of the engine compartment)?

 

[devo]

See if you can get Mark, @65swb45 . He somewhat of a carbureted man stuck in a fuel injected world.
He knows some stuff.
I’m over my head!





devo

 

[thebigredrocker]

If you are trying to get a lower idle speed and the idle speed screw is no longer affecting the idle, then something else is 'holding up the show.' The first thing I would suspect would be the choke linkage, which also has an adjustment screw. You might want to try backing that off as well.

If that doesn't work, try manually pulling on the horizontal linkage of the bellcrank towards the drivers side fender, which should also slow the idle. If this works after you take your hand off, then either something is binding to prevent this from happening naturally, or your return spring is weak.

Hth.

 

[thebigredrocker]

If you pull your air cleaner, at idle shine a light down the primary(nearest the valve cover). If you can see fuel spray that's indication the idle circuit has a problem.

What's your timing set at and do you have a vacuum gauge to get a vacuum reading. Vac at idle should be steady and 18hg+.

 

[Freeborn]

If you pull your air cleaner, at idle shine a light down the primary(nearest the valve cover). If you can see fuel spray that's indication the idle circuit has a problem.

What's your timing set at and do you have a vacuum gauge to get a vacuum reading. Vac at idle should be steady and 18hg+.

Timing is set to 7 deg before tdc. I don’t have a vacuum gauge, but I’m guessing there’s one in my future.

 

[4Cruisers]

If you pull your air cleaner, at idle shine a light down the primary(nearest the valve cover). If you can see fuel spray that's indication the idle circuit has a problem.

What's your timing set at and do you have a vacuum gauge to get a vacuum reading. Vac at idle should be steady and 18hg+.

Vacuum is affected by altitude, so the proper vacuum in Denver would be less than 18 in Hg. Here at 7,240 feet I'm good at a little over 15 in Hg. Someone posted info here on MUD on how you can determine vacuum changes as altitude increases.

 

[Solace in Solitude]

Vacuum should be 15-21, depending on elevation, and should hold steady at idle.

Get yourself a vacuum gauge... in fact, I have one on the dash... I find it very handy to keep an eye on it, to see issues as they begin to deteriorate.

This is quite helpful and is in the FAQ —> Vacuum 101 - Land Cruiser Tech from IH8MUD.com

This thread includes desmogged schematics for 1978 —> layout for 78 2F desmog

 

[Dizzy]

Is it possible that you are partly idling on the Slow Circuit because the idle speed screw (throttle stop screw) is too open and the fuel mix screw is too closed? This would be a more common issue for our carbs at higher altitudes.

Try opening up the fuel mix screw, then closing the throttle stop screw until you get the right rpm?

Disconnect the idle cutoff solenoid and see if it stops the engine.

 

[Freeborn]

Vacuum should be 15-21, depending on elevation, and should hold steady at idle.

Get yourself a vacuum gauge... in fact, I have one on the dash... I find it very handy to keep an eye on it, to see issues as they begin to deteriorate.

This is quite helpful and is in the FAQ —> Vacuum 101 - Land Cruiser Tech from IH8MUD.com

This thread includes desmogged schematics for 1978 —> layout for 78 2F desmog

Is there a similarly clear diagram for a "smogged" 78? The FSM is not terribly helpful for my feeble brain.

 

[thebigredrocker]

Here's a few 78 smog related photo's

Brad love all the cruiser pics shes a beautiful TLC!

Should you decide to re-smog your 2f in the future please let me know as I'll be glad to help you sort things out and also locate missing parts.

Here's a vacuum diagram for your reference:

Please make these changes now prior to driving:

Connect PCV hose to intake manifold "NOT Carb"

My '78 40 had some emissions issues when I first got her, however, with the help from our MUD brothers was able to bring her back to EPA standards.

 

[samwise]

Not sure if its been mentioned, and youve likely already replaced, but PCV valve is a cheap and easy part to see if involved in your problem.
Best wishes.

 

[Solace in Solitude]

Is there a similarly clear diagram for a "smogged" 78? The FSM is not terribly helpful for my feeble brain.

This thread has two views of 1978 Federal Specs Vacuum Schematic

1978 fj40 vacuum hoses

can anyone tell how the vacuum lines hook up or where to get a diagram that will show me :doh:

forum.ih8mud.com

 

[Solace in Solitude]

Is it possible that you are partly idling on the Slow Circuit because the idle speed screw (throttle stop screw) is too open and the fuel mix screw is too closed? This would be a more common issue for our carbs at higher altitudes.

Try opening up the fuel mix screw, then closing the throttle stop screw until you get the right rpm?

Disconnect the idle cutoff solenoid and see if it stops the engine.

^x2^ These are great thoughts!!

 

[Freeborn]

Update on the idle issues...

Got a vacuum gauge involved. Here’s a video of what that’s like at “idle”


I put “idle” in quotes because it’s not actually using the idle mixture. When it’s at an idle and actually running the idle speed screw is in far enough that gas is squirting in the primary. Backing out the idle speed screw enough to reduce that flow kills it no matter where the idle mixture screw is.

 

[Solace in Solitude]

Unscrew the brass idle mix screw and make sure the tip isn’t deformed, from being screwed down too tight.

When you screw it back in, do the “lean drop” method, in the last section of this page Cruiser Carb Info - Land Cruiser Tech from IH8MUD.com

There’s a ton of good info in this page.

 

[mtman86]

I haven't heard anyone mention possible cracked intake manifold.....