Some Carb Questions

[Honger]

Recent work I did hooking up the choke cable generated a list of questions for me regarding my carb.

1. If I pull the choke all the way it closes the choke plate. That should kill the engine, right?

2. Is there a way to determine if the lower chamber (as seen in this photo) actually works under heavy acceleration?

3. And finally, what is this (the fitting on the manifold with a piece of hose that is plugged with a screw)?

 

[Weber Sarge]

If you pull the choke shut while warm , it will only raise the idle speed a fair bit and cause the plugs to run very rich - causing it to chug and foul the plugs . Close it when cold , it draws fuel in faster and enriches a cold engine to start . No , it does not shut the engine off - that carb as any other will allow air to be pulled in from the secondary under high vacuum . To see if the secondary throat is working , which is actuated by engine vacuum under a load - put a paper clip on the linkage arm just under the diaphragm - if it's working under engine load it will move about an inch .

The port on the intake is for emissions circuits on most models .

Sarge

 

[Honger]

Thanks! Very helpful.

So mine does die when the choke is closed all the way. The idle obviously picks up but if I go to full closure it sputters and dies. Any thoughts or suggestions?

I'll try the paperclip idea... good one.

 

[77wagon]

You might want to verify that your choke breaker diaphragm is functioning. This will prevent full choking from stalling the vehicle.

 

[Pin_Head]

The choke also has a high speed idle adjuster screw that needs to be set to give 1,500 RPM when the choke is all the way on.

 

[FJ40Jim]

Ignore the Americans, they know not of ROW Cruisers.
Honger's Arab-spec carb is not fitted with a choke breaker, so when the choke is pulled all the way it will close the choke blade totally, choking the engine to death. Don't do this.

As Pin mentions, the choke speed screw should be set to give 1800RPM when choke is fully on.
But this kills the engine you say!
No problem, drop a stubby screwdriver in the primary barrel to prevent the choke blade from closing completely, yank the choke knob, adjust high idle screw (on back of carb in the linkage) to the 1800 spec.

Dunno why it has a manifold vac fitting in the intake manifold. Best to remove it and install 1/8BSPT allen plug.

 

[micruz60]

... And clean up your linkage, appears pretty dusty, which can prevent optimal running.

 

[Honger]

- put a paper clip on the linkage arm just under the diaphragm - if it's working under engine load it will move about an inch .

Thanks for the pointer on the paperclip trick. Jumped on the highway and got the 40 up to 80kph and then floored the accelerator til I hit 100kph. Did that a few times. I just wrapped up that test and sure enough I got about an inch of movement.

You might want to verify that your choke breaker diaphragm is functioning. This will prevent full choking from stalling the vehicle.

Yeah, I don't have a choke breaker.

The choke also has a high speed idle adjuster screw that needs to be set to give 1,500 RPM when the choke is all the way on.

High speed idle is adjusted to 1800RPM at full choke as per FSM recommendations.

Ignore the Americans, they know not of ROW Cruisers.
Honger's Arab-spec carb is not fitted with a choke breaker, so when the choke is pulled all the way it will close the choke blade totally, choking the engine to death. Don't do this.

This is fantastic info. Thank you! I knew I had no choke breaker but thought that maybe it was supposed to work some other way. I only did this twice. Once on accident and a second time to confirm the results were consistent.

As Pin mentions, the choke speed screw should be set to give 1800RPM when choke is fully on.
But this kills the engine you say!
No problem, drop a stubby screwdriver in the primary barrel to prevent the choke blade from closing completely, yank the choke knob, adjust high idle screw (on back of carb in the linkage) to the 1800 spec.

Yeah, the screwdriver trick is exactly what the FSM said to do and that's how I did it.

Dunno why it has a manifold vac fitting in the intake manifold. Best to remove it and install 1/8BSPT allen plug.

The engine is a donor form a 1984 FJ40 or FJ60 and I presume the intake came from the same place. So that fitting likely served a function in its original Cruiser.

... And clean up your linkage, appears pretty dusty, which can prevent optimal running.

Yes... lots of dust issues here. Any recommendations on cleaning? I was thinking of just getting a stiff paintbrush and scrubbing it down. Is there a suitable liquid for washing it down?

Thanks for all the input gents!

Some may wonder why all the fuss over the choke given the consistently warm climate here. Well, I've noticed that the engine sometimes runs a bit rough when it's cool (when it's not at operating temp). Obviously once it's warmed up it idles quite nicely. So I wanted the choke for slightly higher RPM's until it's up to temp. That's worked well. Plus, it's just part of getting the truck working as it was intended.

 

[Weber Sarge]

I never knew engines in that market wouldn't have a choke breaker - odd given the cooler temps at night in such a climate . I'll file that in the cobwebs along with much of the other stuff I tend to forget ....lol .
Sarge