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testing ignition components: distributor

 
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rfaass924  



Joined: 04 Aug 2020
Posts: 2
Location: seattle

PostPosted: Wed Aug 05, 2020 10:21 am    Post subject: testing ignition components: distributor Reply with quote

Working on my 79 924: it does not rev up well.

Studied the book:

3 degree ADC with vac hoses installed @950 rpm

vacuum degrees -7.5 - 12.5

mechanical 13 degrees

Total advance max 13 + 20 = 33 degrees (I am optimistic here)

This full advance test should be 41 degree @ 4500 rpm with no vacuum hoses attached

When looking at the graphs on page 131 I am wondering where there is a typo, because there is no way other th an moving the distributor by hand (difficult during driving) to get to the 41 degrees as specified by the test...

When observing the timing light, my mechanical advance does not work at all, my vacuum advance is good.

Is the 41 degrees test correct and what am I missing here?

TIA, Robert.
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Raize  



Joined: 18 Sep 2013
Posts: 136
Location: Scotland

PostPosted: Wed Aug 05, 2020 7:48 pm    Post subject: Reply with quote

All the numbers on those graphs have to be doubled as they're in camshaft degrees for some reason but we normally talk about ignition timing in crankshaft degrees, which rotates twice as fast.

Also note that the timing for US 1979 model is to be set with hoses attached so that will effect your calculations too.

Try twisting your distributor rotor with the cap off - you should feel some resistance and it should twist a few degrees if the centrifugal advance is working. If it's stuck or it has no spring back then that could be your problem. Or someone has locked the timing because racecar.

I'm not entirely sure how the dual port vacuum canisters on US cars are meant to work. Maybe someone else can explain that.
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rfaass924  



Joined: 04 Aug 2020
Posts: 2
Location: seattle

PostPosted: Thu Aug 06, 2020 9:48 am    Post subject: Reply with quote

Ahhhh that explains it. Yes, I now set it at 41 degrees btdc and found a broken egr mounting wich made the idle too high. The distributor was new but did not work, I put in an old one and it is running great! Thank you for the education!
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