Asha'man

As it's warming up, it idles high like carb'd trucks do, around 2000rpms. However, starting a couple days ago, when it's warm it refuses to kick down and idle at 900 like it's supposed to. Instead, it just keeps revving at 2000. I can kick the pedal as much as I want to and nothing happens. I tried spraying some carb cleaner around and in the carb, just in case there was something sticking, but there was absolutely no change. This started completely randomly too; it ran just fine before the other day.

Any ideas?

third coast cruisers

your floats are sticking.

is it a toyota carb or weber?

take off the air cleaner and spray some carb cleaner in the carb whle it is running. may un stick it.

otherwise time for replacement floats if thay are the plastic kind.

Asha'man

Stock Toyota carb. Are the floats visible from the top? How hard are they to replace?

drew303

I don't think your float is sticking, if it were you'd have different symptons like a crappy running motor and black smoke, or nothing running at all. A float is just that, a float, its a valve that is controlled by the level of gas in the bowl. As the bowl fills, the float moves up pinching off the gas supply, if its stuck there, you get no gas, if its stuck open, then your carb floods. It'd be pretty bizarre to have one stick shut tho.

I'd check your throttle linkage first. Sometimes the cable can get hung up on the connection at the carburetor. Check the linkage on the back of the carb and use your hand to adjust the throttle while the motor is running. Push/pull up on the throttle arm. (its where the cable attaches, yo'll figure it out)

I'd say the choke breaker or the bvsv that controls it is shot but this would be true if the idle just didnt drop down till you hit the pedal, but you said you can kick the pedal and it wont jump down so something mechanical is binding up or sticking.

goodluck

abecedarian

what drew303 said. (and I'll add my 72 firebird's float sticks shut all the time, but the needle valve is rubber-tipped and it didn't get driven a lot... but that's a different beast and doesn't really apply here)

and you can check the float level by looking in the sight glass on the side of the carb. the fuel level should be in the middle of the window.

I'd be looking at the throttle cable and linkage and the choke linkage to see if any of it is binding / sticking. Have you checked with the engine cold that the choke is closing and the throttle shaft is hitting the high-idle step? Since the choke mechanisim is basically a bi-metallic strip (heated externally) that moves the linkage as it warms up, even if it did not have voltage it should eventually release once the carb warms up to normal temperatures. And if you're seeing the choke butterflies open when the engine warms but it still idles high, then I'd guess it's either the throttle sticking open or a vacuum leak somewhere.

Asha'man

I thought it might be the throttle cable, but I played with it along its length (at least in the engine bay) and revved it by hand a few times and nothing appeared to be sticking. I suppose it's possible that something might be off-kilter under the dash - I'll look at that tomorrow.

Where is the choke and its associated mechanisms? I'm really not very familiar with carbs; having never owned one or planned on owning one I never learned much about them. As I understand it, the choke allows the motor to warm up (somehow), so it logically follows that if it was sticking, it would never kick down. I can't believe how little I know about this.

The fuel level in the sight glass is fine, btw - appears to be right in the middle or slightly above it every time I've looked at it.

abecedarian

normal procedure with a carb is to tap down on the gas pedal before starting. this causes three things to happen: a short burst of fuel provided by the accelerator pump then the choke butterlies close and the throttle shaft turns causing linkage connected to the choke butterflies to make the throttle stick slightly open.

Choke operation:
The choke butterflies restrict the amount of air entering the engine. When operating, there is linkage that causes the throttle to be held slightly open. Having the throttle held slightly open causes the engine to rev higher and suck a little extra fuel. Between the choke butterflies restricting some air flow and the throttle being held open, the engine will idle higher and with a slightly rich mixture which it needs to idle smoothly until the engine warms up enough for the normal carburetor functions to operate properly.
In a carbureted engine, when cold, the fuel released through the carburetor tends to form 'droplets' which don't like to burn easily. By adding extra fuel and restricting airflow, the choke system (when working properly) provides enough atomized fuel for the engine to idle smoothly, albeit at a higher rpm.

Give me a few, and I'll put up some pics of the choke.

Asha'man

Any luck on those choke pics? I kinda need something to go off of here, cuz I really don't know where to start. Been a while since I've been this unfamiliar with an automotive system!

Asha'man

So here's one for my fellow dumbasses. I was screwing around with the truck the other night and a stray thought crossed my mind, the gist of which was that perhaps the throttle and butterfly linkages and such were just gummed up. I went inside and grabbed a can of CLP from my gun box, went back out and sprayed it on the throttle cable, the throttle, down into the carb throat onto the butterflies, and pretty much everywhere that looked like it might be sticking. Sure enough, I tapped the gas and the revs dropped right down to where they should be.

For future reference - make sure things are lubed!

abecedarian

good to hear you fixed it.
and sorry I didn't get back with pics. things have been a little crazy what with my wife's truck having issues.

hellfire

my truck has done this a few times, but hasn't done it lately...

thanks for the helpful info.. i will do this next time it does this.