Idle Mixture Screw - 87 T4 SR5

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Jonymoto
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Posts: 296
Joined: Wed May 06, 2015 9:39 pm
My tercel:: 1983, DLX 4wd wagon with 4.1 manual gearbox, tow bar). Manual steering. 313,000 kms. Tercel 4WD SR5, 1987, 500,000kms. Other car - 2003 Rav4, AWD, 2l manual, Peugeot 407 Diesel (93,000 miles) in Ireland for use when on holiday there.
Location: Melbourne, Australia

Idle Mixture Screw - 87 T4 SR5

Post by Jonymoto »

My recently purchased 1987 T4 is idling very fast, around 1,500 rpm even when its warmed up. Adjusting the idle screw completely out doesn't make any difference. This Aisin carby appears to be missing an idle mixture screw which would be the second thing I would adjust. Has anybody else come across this problem?
DSCF2662.JPG
DSCF2660.JPG
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When you lose, don't lose the lesson - The Dalai Lama
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Mark
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My tercel:: 1984 Automatic, 1981 sedan
Location: Victoria, B.C.

Re: Idle Mixture Screw - 87 T4 SR5

Post by Mark »

I think the idle mixture screw is not meant to be adjusted. It is sealed with a plug that has to be drilled out. My wagon idled high when I got it and the idle speed screw didn't help just like yours. It turned out to be a few vacuum leaks in the diaphragm housings causing too much air to be sucked in, acting like the throttle was slightly open. When I plugged/replaced the components with vacuum leaks (almost always the auxiliary acceleration pump), the idle went down to normal. I keep my idle at about 800 rpm now (it's an auto), but once I adjusted it down to about 500 rpm just to see if it still ran and it was fine.
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Jonymoto
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Posts: 296
Joined: Wed May 06, 2015 9:39 pm
My tercel:: 1983, DLX 4wd wagon with 4.1 manual gearbox, tow bar). Manual steering. 313,000 kms. Tercel 4WD SR5, 1987, 500,000kms. Other car - 2003 Rav4, AWD, 2l manual, Peugeot 407 Diesel (93,000 miles) in Ireland for use when on holiday there.
Location: Melbourne, Australia

Re: Idle Mixture Screw - 87 T4 SR5

Post by Jonymoto »

Thanks Mark. My 83 Tercel has an idle mixture screw which is why I'm puzzled with this one. At first I thought I had a vacuum leak. I've replaced all the vacuum hoses. Checked that the carb is screwed down tight and even cleaned out the egr valve as it was completely blocked. I'll check the aux pump operation as you suggested.
When you lose, don't lose the lesson - The Dalai Lama
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Mark
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Posts: 883
Joined: Mon Apr 22, 2013 9:49 pm
My tercel:: 1984 Automatic, 1981 sedan
Location: Victoria, B.C.

Re: Idle Mixture Screw - 87 T4 SR5

Post by Mark »

Here's the info from the FSM. It mentions regulations. Maybe that didn't apply to Australia in '83 so that one wasn't plugged?
carb.jpg
I noticed there's a vacuum line disconnected in the picture of your carb.
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Jonymoto
Top Notch Member
Posts: 296
Joined: Wed May 06, 2015 9:39 pm
My tercel:: 1983, DLX 4wd wagon with 4.1 manual gearbox, tow bar). Manual steering. 313,000 kms. Tercel 4WD SR5, 1987, 500,000kms. Other car - 2003 Rav4, AWD, 2l manual, Peugeot 407 Diesel (93,000 miles) in Ireland for use when on holiday there.
Location: Melbourne, Australia

Re: Idle Mixture Screw - 87 T4 SR5

Post by Jonymoto »

Mark - I did that on purpose to show where the idle mixture screw should be in the photo, otherwise that hose would've been in the way. I removed the AAP diapragm and it looked ok. I replaced it with one from another carburettor that I have from a 4AC engine and it didn't make any difference to the idle. I'm now thinking of dismantling the carbie and overhauling it with a new carbie kit. This car has done 503,000 kms. It wouldn't do it any harm, I guess. I'm even thinking of converting it to a Weber. At the moment I'm waiting for a new brake master cylinder to arrive from Rock Auto (the old one was leaking inside the booster) so that I can check the rest of the car. I'm not dependent on this car - I'm just fixing it as a hobby because I love the Tercel and want to get it back on the road.
You are right. My 83 Tercel was made to run on leaded petrol. The 87 on unleaded 91octane. Unleaded wasn't introduced here till 86. Today I run the 83 T4 on unleaded 95. Anything less makes it ping. Thanks for the info from the FSM.
When you lose, don't lose the lesson - The Dalai Lama
User avatar
Jonymoto
Top Notch Member
Posts: 296
Joined: Wed May 06, 2015 9:39 pm
My tercel:: 1983, DLX 4wd wagon with 4.1 manual gearbox, tow bar). Manual steering. 313,000 kms. Tercel 4WD SR5, 1987, 500,000kms. Other car - 2003 Rav4, AWD, 2l manual, Peugeot 407 Diesel (93,000 miles) in Ireland for use when on holiday there.
Location: Melbourne, Australia

Re: Idle Mixture Screw - 87 T4 SR5

Post by Jonymoto »

And Happy & Prosperous New Year Mark.
When you lose, don't lose the lesson - The Dalai Lama
User avatar
Jonymoto
Top Notch Member
Posts: 296
Joined: Wed May 06, 2015 9:39 pm
My tercel:: 1983, DLX 4wd wagon with 4.1 manual gearbox, tow bar). Manual steering. 313,000 kms. Tercel 4WD SR5, 1987, 500,000kms. Other car - 2003 Rav4, AWD, 2l manual, Peugeot 407 Diesel (93,000 miles) in Ireland for use when on holiday there.
Location: Melbourne, Australia

Re: Idle Mixture Screw - 87 T4 SR5

Post by Jonymoto »

Hi Mark, I managed to fix the idle speed issue by simply (1) backing off the accelerator cable at the carbie and (2) adjusting the high idle screw.
I checked everything else on the carbie and I'm now wondering why I didn't think of these two first. On the bright side I've learned a lot about the Aisan /Aisin.
Thanks
When you lose, don't lose the lesson - The Dalai Lama
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