| [GMCnet] Timing question [message #184478] |
Fri, 14 September 2012 16:13  |
glwgmc
Messages: 1014
Registered: June 2004
Karma:
|
Senior Member |
|
|
I have a new Dick Patterson HEI distributor on my 455. My carb is a Rochester Quadrajet off of something other than a GMC motorhome. It was installed by Mark McNeal at the DynoShop in Santee, CA, when he rebuilt this motor for the previous owner. It has been really strong for over 60,000 miles and still runs like a champ. My timing issue is that the timed vac port on this carb (drivers side front just above the throttle plate) shows 12 to13" of vac at idle instead of the zero that I thought all QJs read on this port. I no longer have the temp controlled valve that switches between timed vac port at low water temps and manifold vac at high water temps. Manifold vac at idle is 16 to 17" and goes well over 20 on downgrades. Cruise is normally 14" to 16" at 60mph flat and level. The engine uses/leaks a quart of oil about every 2000 miles and is very strong.
I can't reach Dick for his suggestion, so will ask the collective wisdom here. He has this distributor set for 10 degrees initial, 20 degrees at 3000 rpm centrifical, zero degrees vac adv at 6" of vac, going up to 10 degrees at 12" for a total of 40 degrees. He said to time it by unplugging and blocking the vac line, reduce idle speed to 400-500 rpm, set initial at 10 degrees BTDC, reconnect the vac line and resetting idle speed to 700 to 800 rpm. I don't know if he was thinking the timed vac port would read zero at idle or not, hence my question.
Since I get 10 degrees of advance at idle just on the timed vac port alone, where should I set the initial when the vac line is disconnected and blocked? If I set initial to 10 degrees then with vac at idle the engine will be seeing 20 degrees of advance and up to 40 degrees at cruise. Under load (low vac) the engine will see 30 degrees at 3000 rpm (the initial 10 plus the 20 centrifical). What is the correct way to time this engine?
Jerry
Jerry Work
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
glwork@mac.com
http://jerrywork.com
541-592-5360
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Jerry & Sharon Work
78 Royale
Kerby, OR
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
