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B200F Idle Speed & Timing?

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Old Mar 31st, 2020, 23:16   #1
CosmicBike
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Default B200F Idle Speed & Timing?

I'm intrigued by a couple of things with my 240. A 1993 Tors, so the 2.0 lump and LH2.4.

I've read that the timing cannot be adjusted, and that the LH2.4 system deals with it. Now I just replaced the timing belt, the old one was 1 tooth out, which must have affected the timing by virtue of the aux shaft driving the dizzy. The dizzy mount is slotted, which suggests adjustment is available. Can anyone confirm or deny this?

Also wondering what defines idle speed. Appreciate it is managed by the IAC valve when the TPS says the engine is off throttle, but what defines the desired rpm, which I assume is measured electronically, again presumably via the CPS?

Just trying to get to grips with how it all works...
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Old Apr 1st, 2020, 16:11   #2
Clifford Pope
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I've just posted a query on controlling the timing on your other thread. I'm not sure.

On the idle speed, I think it is ultimately determined by the gap between the throttle butterfly and the side of the throat.
There is an idle stop screw which is factory-set, but people often turn it, in the traditional way, if the idle seems wrong. But it only wanders off setting if the throttle body is gumming up with carbon. So if as a new keen owner you clean up the throttle body and plate you then find the idle speed is mysteriously too high.
I've always started by cleaning everything properly, including removing the TB, and the IAC, and then re-set the idle screw to the proper speed - 900 rpm? After that if it wanders off then it can only be something else, usually the IAC or the TB carbonning-up again.
I think there might be a procedure for setting the butterfly gap with a particular size drill.
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Old Apr 1st, 2020, 17:50   #3
CosmicBike
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The LH2.4 did away with the idle control screw on the throttle body, so not an option.
I've already stripped and cleaned the TB, set the butterfly to close fully, thus allowing the IAC to govern airflow at idle. Since it is post MAFF, I would imagine the engine fuels according to what the MAFF determines. I can only imagine the idle speed, as in what the ECU wants it to be, is set by the ICU and governed by the IAC.
I think I'm going to have an experiment with the mechanical movement available on the dizzy, see what happens..
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Old Apr 1st, 2020, 18:46   #4
Clifford Pope
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Quote:
Originally Posted by CosmicBike View Post
The LH2.4 did away with the idle control screw on the throttle body, so not an option.
.

How odd. I've had three 240s with LH2.4, 1991, 92 and 93, and all have had the screw.
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Old Apr 1st, 2020, 20:00   #5
CosmicBike
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Originally Posted by Clifford Pope View Post
How odd. I've had three 240s with LH2.4, 1991, 92 and 93, and all have had the screw.
Are you referring to the black one on the throttle body? Mine doesn't have it, not sure where the idle adjust would be? I can adjust the throttle body butterfly stop, but it's already fully shut.
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Old Apr 2nd, 2020, 10:01   #6
Clifford Pope
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Originally Posted by CosmicBike View Post
Are you referring to the black one on the throttle body? Mine doesn't have it, not sure where the idle adjust would be? I can adjust the throttle body butterfly stop, but it's already fully shut.

That's it - the screw stop that limits how far the butterfly stays open a fraction when the accelerator is fully released.
I don't think yours sounds right, which could be the cause of the uneven running. Yours sounds as if the IAV is trying to control all the air at idling in order to produce a smooth idle. I don't think it's meant to do that. My understanding is that the preset gap in the butterfly plate supplies most of the idling air, and the IAV then does a fine adjustment by feeding in a little more.

That's how all mine have appeared to work, anyway. I suspect your IAV is being asked to do all the work.

(You don't mean the cable adjuster at the end of the throttle cable? There is meant to be a tiny bit of take-up free movement there, before the TB moves at all. If the idling were being controlled by the cable length then it would dither about as the engine wobbled.)
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