Re: [Chevelle-list] distributor total-timing question - BB

[Tom Tomlinson]

I re-wired my small block two years ago, being very careful to label the wires to the proper cylinders. Even so, I switched #6 and #8 wires. The engine ran ok, but lacked power, and backfired occasionally.   Just a thought.   Tom ----- Original Message ----- From: Wayne To: Larry Williams ; The Chevelle Mailing List Sent: Monday, February 28, 2005 7:55 AM Subject: Re: [Chevelle-list] distributor total-timing question - BB Larry... Wrote " it backfires occasionally"  Vacuum Leak ? to back fire. the spark plug must fire with an intake valve open in a cylinder. You may have a vacuum leak. An easy way to check, is use an unlit propane hand held torch.(  I cut off the flame head off and attached a 4 ft length id vacuum tubing) probe around the manifold and carb base.. If the RPM increase you got a LEAK.. Recheck you timing. with no vacuum advance at low RPM under load might be your culprit. ??   Wayne. ----- Original Message ----- From: Larry Williams To: The Chevelle Mailing List Sent: Sunday, February 27, 2005 12:33 PM Subject: Re: [Chevelle-list] distributor total-timing question - BB I am doing the same thing with my BB.  I just installed a new hyd Comp Cams roller and am using a mechanical advance Mallory Unilite.  Comp Cams help line said that 36 -38 deg total was recommended w/ 8 -10 initial for my cam. The cam # is CB 290-R10.  The Mallory is set at 25 deg total advance, and is at 9 deg initial now.  I have ordered a Mallory kit to  change the total setting.  I do not plan to change the springs.  I rebuilt the 750 Edelbrock AFB.  The valves are zero plus 1/2 turn down.  My problem is that it back fires occasionally.  Could it be a vacuum leak.  The cam was installed at zero.  Have new Taylor Wires to install today.   New carb?  I'm at a loss.  Any suggestions?    ----- Original Message ----- From: Dave Studly To: Chevelle-List@Chevelles.Net Sent: Saturday, February 26, 2005 8:34 PM Subject: [Chevelle-list] distributor total-timing question Does anyone have some semi-accurate information regarding the mechanical and/or vacuum advance curves that are typical in a stock points or HEI distributor? (or typical �performance� settings in a re-curved setup?)  I�m trying to come up with a baseline for my EFI conversion.  If this darn weather would warm up, I�d get my butt in the garage and finish it.   From many of the magazine articles I�ve read, they seem to end up around 36-38 degrees of total timing on typical carb setups.  If you�re running, for example, 12 degrees of initial timing, does this mean the mechanical advance is providing 24-26 degrees of additional timing?  I assume there is no vacuum advance at WOT.  For a performance application, should I have it all in by 3000 RPM, or sooner?   As for the vacuum advance, 10 degrees sticks in my mind as the max amount that it will add.   So, if I�m running down the road at 3500 RPM, high vacuum, I could have 12 degrees initial + 24 degrees mechanical + 10 degrees vacuum = 46 degrees total timing?   -Dave