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Accelerator lags when cold

The accelerator lags for a few minutes when I start cold (after a few days). Since it starts working after a few minutes, rather than persists, I think that means it isn’t the accelerator cable. Because it doesn’t backfire I think the choke is working. The idle speed is correct. What else could it be?

'87 gas, carburetor, 2wd

Do you mean if you press the gas pedal while idling, the RPMs don’t increase? Is it the Aisin carb as used on pre-1985 Toyota trucks? 22R engine?

Worse: they decrease and I stall, or come close.

I re-built it a couple of years ago. I forget the details. I’ll have to look it up.

22R engine.

It works properly when I start; it’s at the first few stops afterwards.

Is the temperature under 36* and if so is the hot air intake on the breather operating? Without that hot air intake you might have carburetor icing. And even with the hot air supply you still might get icing until heated air is getting to the carburetor.

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Your 5 year old gasoline doesn’t atomize well when cold.

No. It’s been unseasonably warm.

I bought gas last year - November 13.

Unless you drained the tank you may have had 3 to 4 gallons of old fuel in the tank. I have been though this before, adding 10 gallons of fuel to an “empty” tank of old fuel results in 200 miles of use with bad fuel.

Also with old fuel you can expect to need to clean out the carburetor ever few years.

When left idle for months at a time e-15 gasoline can cause some big problems. Especially in older models

First guess would be the choke mechanism.

What choke malfunction would cause that problem? I repaired it once, 20 years ago.

Binding linkage (spray that down with cleaner), failure in some emissions-related add-on to the choke system, mis-adjusted linkage, etc.

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Choke pull-off (echoing from decades-ago Car Talk answer.) IIRC it’s vacuum controlled and should open the throttle just a tad once the engine starts and vacuum is produced. You could just connect a rubber hose to it and suck on it to see if it does crack open the throttle a bit.

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No E-15.

What linkage? If it bound, would it bind open as often as closed? It only lags, not runs fast.

Hmmm… I’ve heard this term but don’t see it in Chilton or Haynes. There’s a ‘choke breaker adjustment’ in Chilton.

The choke closes when the engine’s cold, opens when it’s hot. There’s no backfire. It seems to operate correctly after a couple of minutes. It passes the ‘test’ in Chilton .

WAG here, it appears you have a throttle cable, watch the action when cold vs normal, probably a cheap part, try a new one?

A choke breaker is another name for the choke pull-off. If the diaphragm in the choke breaker were leaking the choke will not open to the calibrated amount, the engine would run very rich and will stall at idle, this does not sound like your vehicle’s problem.

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Carb may have an AAP Auxiliary Accelerator Pump that over enriches the mixture when the engine is cold. IIRC it’s a dome-shaped appendage held onto the side of the carb by 3 machine screws. A vac hose goes to it. Engine vac is applied to that hose when the engine is cold and when the accelerator pedal is pressed, the AAP system gives an extra shot of gas. The AAP diaphragm under that dome may be broken - I replaced mine a couple times over the years I had my 1979 Toyota 4X4 truck with the 20R engine. Eventually I disabled the AAP system - the simplest way is to pinch that vacuum line, or plug it with a ball bearing or the like. Try disabling it and see what happens. Good luck!

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The throttle cable is 33 years old. It may have gone bad but probably didn’t start out that way.

About 15 years ago the choke became disconnected (probably on that -17° day), stayed shut, ran rich, backfired. On mine the choke cover is riveted on. I had to drill them out, put the arm back in the loop at the end of the coil. Would I have backfire if it were a leaking choke breaker?

It does. I replaced it when I re-built the carb a few years ago. I’ll try this. Thanks.

I decided to disable my AAP and the engine ran better. I think today’s gasolines are more volatile than those in the 1970s when that carb and its ancillaries were engineered. Extra fuel from the AAP system is unneeded and detrimental.

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“Carb may have an AAP Auxiliary Accelerator Pump”

That’s exactly the what solved hesitation (when cold) with my '79 Celica’s 20r.

I actually found gasoline in the vacuum hose leading to the AAP diaphragm. Changed out the diaphragm, problem went away.

A bunch of carburetor cleaner and spray lube solved the problem. I should have tried that before asking.

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