M4MC carburetor connection questions

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Old Oct 15, 2024 | 07:26 PM
  #1  
illumined's Avatar
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1978 Ninety Eight
 
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M4MC carburetor connection questions

After reinstalling the carburetor back onto the engine (403 V8) there were two external springs, one I was able to figure out one of them was the throttle return spring. But I'm at a total loss for the other. I vaguely remember it is connecting the secondary lever to *something*, which makes sense since the secondaries don't seem to open when i simulate wide open throttle. I get the sense I'm missing something very very obvious, but as I'm new at this not everything is as obvious as it should be.

I also wasn't able to find where the AC idle solenoid connected to. I've plugged in everything on the wiring harness except what I believe is the low coolant level sensor. It's too short to reach much but unless I'm missing something obvious (again) there doesn't seem to be anything to connect to.

I didn't take a picture prior because I figured the chassis service manual would show where it goes, but I was unable to find it on both counts. The wiring diagram doesn't even show the AC idle solenoid at all.

By the way I did circle back to the fuel filter situation from before, as it turns out it did have a filter in the inlet, and it had an external inline filter. I have no idea why, I replaced the rubber fuel line and I'm not seeing a need to put back on another external fuel filter.
Old Oct 15, 2024 | 08:07 PM
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Fun71's Avatar
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Originally Posted by illumined
the secondaries don't seem to open when i simulate wide open throttle.
That is 100% normal as the QJet secondaries are a “demand” system and don’t open with no load (as in revving while in park or neutral).
Old Oct 15, 2024 | 08:56 PM
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illumined's Avatar
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1978 Ninety Eight
 
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Originally Posted by Fun71
That is 100% normal as the QJet secondaries are a “demand” system and don’t open with no load (as in revving while in park or neutral).
Ok that makes sense. Then the spring must be some kind of return spring for them?


BTW I also belatedly realized the connection I thought was for the coolant level sensor as it turned out was for the idle solenoid. One mystery down.
Old Oct 15, 2024 | 08:57 PM
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Are the springs similar to each other, does one fit inside the other? If yes, they may both be throttle return springs.
Old Oct 15, 2024 | 09:00 PM
  #5  
illumined's Avatar
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1978 Ninety Eight
 
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Originally Posted by Sugar Bear
Are the springs similar to each other, does one fit inside the other? If yes, they may both be throttle return springs.
I admit that thought never occurred to me, I will have to try that when I work on it again this weekend. Thank you.
Old Oct 16, 2024 | 04:57 PM
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There are two return springs for redundancy. One goes inside the other.



Old Oct 16, 2024 | 05:53 PM
  #7  
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Originally Posted by joe_padavano
There are two return springs for redundancy. One goes inside the other.


You can say that again...
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