Can the throttle linkage be sticky?


And, if you currently have a single spring, I highly suggest upgrading to a dual spring for redundancy- like one of these options:


If you never had a return spring break, let me tell you it’s one of the more exciting situations you’ll encounter :wink:


I just inspected the diagrams in the Chilton and Haynes. I see a ‘choke opener’ (is that what you meant when you wrote ‘pull-off’?) but no secondary anything.

The hemispherical thing that covers a helical coil that hooks over an arm that connects to the choke; the coil rotates with temperature? 20 years ago I had to drill out the rivets to put the arm back in the loop of the coil after I tried to start on a -17° morning. I reinstalled it with #6 screws. It’s still holding.

Does this require another person?

Thanks. As I mentioned earlier, when I searched on this, I found only motorcyle and Mercedes owners doing it. Odd that they need to.

I was guessing that it unstuck in a few minutes.

I don’t see instructions in my manuals for this. I’ll wait until I’ve done more diagnosis.

Your problem relates to you not seeing gas squirt out when you open the throttle and the engine is cold. Either the accelerator pump is bad or there is some other carb problem, such as a leak or a bad/mis adjusted float. It could be compounded by a misadjusted choke and or choke pull-off.


When the engine is cold, remove the air filter housing. Plug any vacuum hoses that are disconnected.

Step on the accelerator once. The choke plate should be closed.

Start the engine. The primary choke pull-off should slightly open the choke plate and the engine should idle.

Operate the throttle linkage by hand. The secondary choke pull-off should open the choke plate more each time the throttle is operated and return back to it;s original position when the throttle is released. The engine shouldn’t stall.

Let the engine idle. and see if the thermal choke pull-off slowly opens the choke plate completely.


1 Like

While you are doing what @Tester advised, I would add that when you take off the air cleaner housing, that you take a q-tip, wet or dry, and clean the window to the fuel bowl. This way as you do the tests, you can keep an eye on the fuel level in the bowl. It should stay right in the middle of the window. You may need a small flashlight to see it clearly.

Also, based on information you supplied, I do not think your accelerator pump is bad. If it was, the engine would stumble every time you step on the gas pedal, warm or cold. If it doesn’t stumble when warmed up, then it is working.

What explains the lack of gas squirting when he opens the throttle when the engine’s cold?

Throttle return springs are located on the throttle shafts.
That is not the problem unless your engine is racing out of control.

Check the accelerator pump for proper operation.

Is there a hard linkage or a cable? The steel wire inside a cable can saw a slot at the bends and cause the wire to bind erratically. Rotate the cable jacket to a new position to keep the wire inside from riding in the slot. Had a Datsun Honeybee that had weird carb problems. Found that the throttle plate had brass bushings and one was loose and could jump in and out of position in the die cast housing. When it jumped out, the engine would race. If you pressed the pedal to the floor, the bushing would jump to it’s normal position.

It stalls when it’s cold if I don’t send it gas; that’s what I mean by needing another person.

I just can’t see it. I tried all this already.

Apparently a mistake. It squirted today.

That’s a lot of springs. Are they hard to replace?

The accelerator pump squirts fuel into the carburetor. The choke is open; pressing the gas pedal closes it. My pickup starts as Dora Do-right’s car does: I press the gas pedal once, release it, ignite - then it stalls out either on its own or if I press the gas pedal. Before I leave home I just take off the top of the air cleaner and open the throttle valve, and can start again. The spring applies no tension to the throttle valve: whether hot or cold, it’s where I move it. Is that correct?

Somewhere on your carburetor there should be a fast idle cam, maybe that is not functioning properly.

If there is no problem with the throttle cable, I think I would “roll the dice” and get a new Chinese carb from Amazon, ~$100. If you do, read the return policy.

That tells me the choke isn’t adjusted correctly, and its opening too far when the primary choke pull-off opens it.


1 Like

Do you mean top plate, above any other? That is the choke. It should close just about all the way when, with cold engine, you floor it and release. Then when you start the engine it should open slightly. Then over a few minutes of running it should gradually open all the way.

1 Like

My truck doesn’t use a secondary throttle, so I’m of little to no help if the stalling when cold problem is associated with that.

I have had some stalling when cold symptoms a few times over the years , usually caused by a vacuum system leak; i.e. not a carb problem. You need an extra rich mixture when it is cold, and anything leaning the mixture can cause stalling. When I suspect a vacuum leak on my carb’d truck, engine off, I locate the source-port for the system’s vacuum (intake manifold in my truck’s case) , remove the hose and apply a test vacuum on the removed hose, using a hand-held vacuum pump. That path should be air-tight. If there’s a vacuum leak anywhere in the system the applied test vacuum won’t hold. I have to repeat this test again b/c there is more than one vacuum-source port. But none of them should leak. When I find the leak, it is often that one of the vacuum-motor device’s internal diaphragm has split, can’t be seen visually.

Doesn’t a choke either work or not? The manuals I have tell me how to evaluate it, recommend only cleaning or replacing ‘troublesome’ parts - not adjusting it.

There are 2 valves on top - are they both the choke? My manual points to only 1 of them. I thought the other was involved with the throttle.

The chokes’ butterfly valve (visible at the top of the carb) is adjusted to begin to open at a certain temp and be fully open by another certain temp. In between those two temps, it is open part way. The main choke settings on my truck are adjusted by twisting the electric choke housing cw or ccw. But there are other settings which involve the choke, fast idle for example. There’s also a settings for the choke pull-off and the choke-unloader.

But if it passes the basic visible tests already mentioned above, you problem doesn’t seem like it is a choke setting issue, unless it is involved with the dual throttle system already mentioned.

1 Like

I probably misunderstand. There are 2 valves at the top of the carb. I thought the one on the passenger’s side was the choke. It seems to behave properly: is open when I stop, closes when the engine is cold when I step on the gas, seems to open when the car warms up. The coil that opens it when the engine warms up became disconnected from it 20 years ago, so it never opened, so I backfired. I fixed that.

This is the first time I paid attention to the valve on the driver’s side. Is that also part of the choke? I notice that, although it has a spring on it, the spring seems to apply no tension: I move it, and it stays whither I move it, hot or cold. I don’t know about in between.

When I drove yesterday it stalled at every stop, as it would if the idle was low, so I turned up the idle (I set it properly after I rebuilt the carb.) and it stopped stalling. I don’t know why the idle would be low. When the accelerator pump was leaking I had to turn it up, but it’s not leaking now.

Referred to as the choke thermostat. The choke thermostat closes the choke using spring pressure. As the engine starts, vacuum is applied to the choke pull-off, this opens the choke plate to a calibrated setting. The gap created by the choke pull-off is to be measured with a gauge, a drill bit of the same measurement will work. This needs to be precise, you can’t guess.

The factory choke pull-off setting is a starting point, this can be adjusted to compensate for elevation or fuel quality: excessive ethanol content.

Advanced carburetor adjustments are probably above you pay grade. But just as minor environmental differences can affect drivability during choke operation, so can fuel quality. Gasoline that is more than a year old, plus the old gasoline that was in the tank before you last filled up has lost the lighter petroleum chemicals through evaporation. The result will be poor performance during cold engine operation.

No, that is a secondary air valve, it is closed using light spring pressure and not connected to the choke thermostat. The throttle valve on that side of the carburetor remains closed until you go beyond half throttle. The secondary air valve restricts air flow in order to prime the venturi nozzles with fuel as you floor the accelerator. You shouldn’t need to be concerned with that side of the carburetor at this time.

The two butterfly plates at the top of the carburetor are NOT throttle plates. The throttle plates are near the bottom of your carb. You have a two barrel carburetor with a primary throttle and a secondary throttle.

The secondary throttle is sequential, it starts to open when the gas pedal is pushed about 3/4 the way to the floor and opens completely at wide open throttle (WOT), i.e. when the gas pedal is pushed to the floor.

The butterfly plate above the primary side is your choke. It appears to be the one on the right in your photo. This is the one that should partly open after start up with a slight touch of the pedal.

The plate over the secondary is vacuum operated. When you push the gas pedal to the floor at low RPM, it remains closed because the vacuum in the manifold is zero, or close to zero. It prevents too much air, and fuel from entering the manifold and flooding the engine. As RPMs build up, the manifold will start to build up a vacuum, which will in turn open that plate and allow more air and fuel into the manifold. In other words, when you go WOT when warmed up, it keeps the engine from stalling. You should never go WOT on a cold engine, but I think you know that already.

BTW, since you have to manually open the choke plate a little after starting to make the engine drivable, that pretty much says the choke pull off is bad.

There are three different kinds of idles and all are rpm adjustable , at least on my truck’s carb:

  1. Don’t know the mechanic’s name for this one: Warm engine, electric solenoid off. This is set so the engine doesn’t run-on (diesel) after turning the ignition to “off”. Intended to solve a common problem for 1960’s engines using a mechanical fuel pump.

  2. Curb idle: Warm engine, electric solenoid active (on). This is the usual term for “idle”, what the warm engine idles at in normal operation. A little faster than number 1. The increase in rpm from 1 is due to an electric solenoid pushing the throttle slightly more open when the key is in the “on” position.

  3. Fast idle: Separate adjustment, independent of the solenoid, set to spec when the engine is cold. Intended to prevents stalling when cold.

Suggest to double-check all three. The rpm spec’s should come w/the rebuild kit.

I have to adjust my truck’s curb idle from time to time. Sometimes up, sometimes down. I presume there are two causes: the first is something slightly clogging the carb’s idle-fuel circuits; and the second is slight leaks allowing unmetered air into the engine . Any air that bypasses the carb is unmetered air. I seldom have to adjust the fast idle. Sometimes the cold engine idles too fast and causes a jerk sensation when shifting from park to drive, then I’ll adjust the fast idle a little lower.

fyi: I’ve had a couple of weird choke-related problems over the years requiring fixing:

  • There’s an electric heater over the choke’s thermostatic coil spring, intended to cause the choke to release sooner after starting a cold engine, presumably to improve HC emissions. That heater failed, open-circuit.

  • There’s a sort of thermo-siphon/vacuum loop arrangement that also heats the same coil spring, but using engine heat. The heat is sourced from an exhaust manifold cover. The tube distorted & fell out of the hole in the exhaust manifold cover and needed to be replaced. The other end of the path from the coil spring to the air intake has to also be clear so the warm air is pulled through the entire loop. No failures on that part so far … knocking on wood … lol …

It starts up as it should, then stalls out. I can’t get it restarted. The choke is closed, so is the secondary air valve. I open the secondary air valve, it starts, then stalls… I repeated this until I ran the battery down, so I’m off to the Zone of Auto for a jumpstarter.
I have to push the pedal all the way down to get it to run, then it races. If I put it into gear it stalls out.

Does this mean anything to you? It’s as though the engine is sticky; I changed the oil 619 miles ago.