Re: [Chevelle-list] distributor total-timing question - BB
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?) Im trying to come up
with a baseline for my EFI conversion. If this darn weather would
warm up, Id get my butt in the garage and finish
it.
From many of the magazine
articles Ive read, they seem to end up around 36-38 degrees of total
timing on typical carb setups. If youre 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 Im 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
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?) Im trying to come up with a baseline for my EFI conversion. If this darn weather would warm up, Id get my butt in the garage and finish it. From many of the magazine articles Ive read, they seem to end up around 36-38 degrees of total timing on typical carb setups. If youre 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 Im 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
RE: [Chevelle-list] distributor total-timing question - BB
If your car pops or backfires when you whack the throttle the problem could be the accelerator pump. Make sure the accelerator pump is flowing fuel through the whole throttle stroke. A bad accelerator pump will cause a temporary lean condition which will cause the engine to pop. Also, try your timing a little higher. I would start at 12 to 15 degrees and see if you get any pinging. Retarded timing can also cause a backfire. I run my 454 at a total of 40 degrees timing. Mine is actually set at 20 degrees initial with the mechanical advance putting in another 20 degrees by 4000 RPM but I don’t run a vacuum advance on mine. Bill Vander Werf -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Larry Williams Sent: Sunday, February 27, 2005 12:34 PM To: The Chevelle Mailing List 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?
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?) Im trying to come up with a baseline for my EFI conversion. If this darn weather would warm up, Id get my butt in the garage and finish it. From many of the magazine articles Ive read, they seem to end up around 36-38 degrees of total timing on typical carb setups. If youre 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 Im 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
