jlfenner

My 85 with 22r has been sitting for a two years while I worked outta state. Came back, drained the old gas, oil, water. Put in fresh. Started up first turn (just like always) and fast/choke idled for a minute or two. Once the choke disengaged and dropped idle, she appears miss slightly and almost want to die. Tried again and the same thing. Figured I'd do a tune up. Plugs, wires, cap rotor, fuel filter, air filter. Also checked and rechecked all the vacuum lines. Feel kinda like I replaced all good parts cause it still does the same thing. Funny thing is, when I put my foot in it, the truck comes alive and sounds great. Not just good...it sounds great. No noticeable miss above around 1500 rpm. Peppy, very responsive.

Now, I can turn a wrench and have a ok grasp on the basics of this fine engine but when it comes to vacuums, and diaphragms, and carb related issues, I'm in the dark. I researched a bit last night on here about the issue but nothing I found seemed to be of any great use.

My question would be, is there a vacuum that's supposed to open/close or a switch that is supposed to engage/ disengage when the operating temp reaches the level for the automatic choke to disengage?

Appreciate any suggestions.

slow-mo

Your answer will be in this long explanation:

the choke system on the 22R Aisan carburetor is an Automatic Choke, not an electric choke, as it has been called on this forum. That means that the choke coil does not require any 12 volt power to engage the choke. The choke coil is a bi-metal spring that is affected by ambient temperature. To engage the choke, the driver would pump the gas pedal (twice, so says the Toyota owners manual) which will do three things. One, it will free up any friction on the choke linkages to allow the choke valve to close. Second, this will engage the Fast Idle Cam. The Fast Idle Cam will forcibly hold open the throttle valve to aid in faster warm up time. And third, fuel will squirt into the primary barrel to aid in start up.

So...let's say on a cold morning, the choke coil spring will rotate to close the choke valve. When the engine is started, 12 volt power, via the alternator, is then routed to the choke coil spring. As the choke coil is heating from the resistance of electrical power, the coil spring then acts upon the choke valve to progressively open the choke valve.

"So does that mean that the choke coil spring is always heated even when driving for 2 hours?", you ask. No. Built in-line (in series on the ground side) is a positive temperature coefficient thermistor (PTC) whose resistance increases with temperature to prevent unnecessary 12 volt current flowing when the engine is warm.

Once engine coolant temperature has reached operating temperature, a bi-metal vacuum switch valve (BVSV) will switch the vacuum going to the Auxiliary Acceleration Pump (AAP) to the Choke Pull Off. This will forcibly remove any and all remnants of the choke circuit, i.e. the choke as well as the Fast Idle Cam. This action knocks down the high idle at start up.

Even though the choke and the Fast Idle Cam are connected indirectly via the linkages, the opening of the choke is not enough to remove the high idle of the engine. Therefore, the choke pull-off forcibly removes all of this. The vacuum exerted on this choke pull-off diaphragm is applied full time once switched over.

jlfenner

Ok. I get that. Guess sometimes it's all in how the info is explained.

Pops taught me about the automatic choke/stomp pedal thing and it always worked so I never looked into the specifics. Anyways...

So since the idle drops when warm does this mean the bvsv is switching the vacuum to the aap and pulling the choke off and my issue is with something else? I can't remember with thread it was but another member mentioned something about the vacuum advance on the distributor. When testing the vacuum advance, are both the advance and retard supposed to hold vacuum?

slow-mo

Well first, on a cold engine the BVSV defaults, if one wants to call it that, to routing the vacuum to the AAP. Then after the engine warms up, it then switches off the AAP and over to the choke pull off.

Yes, both diaphragms are suppose to hold vacuum. If the diaphragm that controls the idle advance is faulty, the timing will not be adjusted correctly (anywhere from 5° to 12° advanced) and you could have the symptoms you are experiencing. Best thing to do is to check your timing at idle.

Another thing is because the vehicle has been sitting for so long, you may have developed a clog in the idle circuit of the carburetor, since your symptoms seem to occur at that point. You could try some in the fuel tank fuel cleaner for carburetors.