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09-22-2019, 06:00 AM | #41 | |
Junior Member
Join Date: Oct 2018
Location: Oamaru New Zealand
Posts: 20
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Re: 292 y-block distributor puzzler
Quote:
Can you do a vacuum/pressure check on both of the lines going to the vacuum advance diaphragm? Something is causing it to go to ATDC. I've checked vacuum at idle and there is none (500 ~ 550 rpm) The timing at idle should not change when the vacuum lines are connected.. |
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09-22-2019, 08:49 AM | #42 |
Senior Member
Join Date: Aug 2012
Location: IN A 'GALAXIE' FAR FAR AWAY
Posts: 6,475
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Re: 292 y-block distributor puzzler
If one goes to the SPECIFICATION CHAPTER of the SHOP MANUAL. the vacuum signal levels will be given at the appropriate engine RPM.
Example - DIST RPM - 200 - DIST Degrees 0 DIST RPM - 500 - DIST Degrees 3 1/2 - 403/4 So there is a modified MANIFOLD VACUUM SIGNAL @ idle. It supplies the signal to advance the breaker plate. This is why the vacuum signal is removed when adjusting base timing. On the 1956 DUAL DIAPHRAGM SYSTEM (not all 56 engines used it), there are two signals, one modified manifold vacuum (this gives advance) and constant MANIFOLD VACUUM which operates the outer surge diaphragm (which retards breaker movement). You can see vacuum advance operation/movement with a timing light and revving an engine unloaded. This is one of the checks performed during a tune-up. The same is true on a DUAL ADV DIST, whether using PORTED VACUUM, MANIFOLD VACUUM or a mixture of both. If the timing shows retard @ idle, it is most likely a bad breaker plate or vacuum diaphragm. You guys are beating yourselves to death.
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