Timing as usual - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 12-10-2010, 06:47 PM
Registered User
 
Join Date: Dec 2010
Location: California
Posts: 7
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Timing as usual

I have a 75 GMC 4x4 that I am trying to get tuned in. I have a 350 (not sure what the crank is) but it was a rebuild I bought from my neighbor. He said it was high performance but not a stroker, so whatever that means. I set the initial timing at 16btdc and rpm around 550-600 at idle with the vacuum line plugged off. I revved it up to 3500-4000 and got the timing at 36 total with the advance back on. Then put the idle back to 750-800 and it is good at idle. When I put it in gear it dies unless you keep on the throttle. I think it runs good, it jumps up a little if you get on it which is cool but if you get to a stop sign it will die. Any ideas?

Wes
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 12-10-2010, 06:58 PM
DoubleVision's Avatar
Not Considered a Senior Member
 
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 40
Posts: 10,643
Wiki Edits: 0

Thanks: 13
Thanked 56 Times in 53 Posts
With vac advance disconnected and plugged, set the base timing to 12 degrees before top dead center. Lock distributor. Reconnect vac advance to a manifold vacuum source (one that pulls vacuum full time, including idle) recheck timing, it should be around 20 - 24 degrees at idle. The idle issue sounds like either it`s got a vacuum leak, idle mixture out of adjustment or trash in the idle circuits. Set the idle screws with a vacuum gauge, simply adjust them to the highest vacuum reading. I would also make sure it`s not flooding at idle, shine a light in the carbs throat at idle and see if you see any fuel coming out of the boosters. You may also want to check the carbs float height.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 12-10-2010, 07:08 PM
Registered User
 
Join Date: Dec 2010
Location: California
Posts: 7
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Thanks, it just got dark on me and I'm frustrated so I'm gonna get some sleep and check it out in the morning. Thanks for the advice, I'm gonna get it done tomorrow. Once, I check the timing at the full time port, do I disconnect it and hook it back to the carb? Also, how do you set the idle screws with a vacuum gauge? Where do you hook it up at?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 12-10-2010, 11:22 PM
DoubleVision's Avatar
Not Considered a Senior Member
 
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 40
Posts: 10,643
Wiki Edits: 0

Thanks: 13
Thanked 56 Times in 53 Posts
You connect the vacuum gauge to any vacuum port that`s pulling manifold vacuum which is any port that pulls vacuum at full time, including idle.
As for the vac advance I`m not understanding what you mean. So I`ll start over.
Disconnect the vacuum advance and plug it.
Set the base timing to 12 degrees before top dead center.
Lock the distributor down.
Reconnect vacuum advance to a full time manifold vacuum source (one that pulls vacuum full time including at idle. Can be on the carb or the intake. Either works fine)
Recheck timing at idle, it should be 20 to 24 degrees before top dead center.
If the timing is still at 12 degrees the vac advance cansiter is ruptured and will have to be replaced pronto.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 12-11-2010, 07:07 AM
Frisco's Avatar
Glad To Be Here
 
Last photo:
Join Date: Nov 2002
Location: Canton, North Carolina
Age: 72
Posts: 2,244
Wiki Edits: 0

Thanks: 0
Thanked 7 Times in 7 Posts
Quote:
Originally Posted by wes1976
I set the initial timing at 16btdc and rpm around 550-600 at idle with the vacuum line plugged off. I revved it up to 3500-4000 and got the timing at 36 total with the advance back on.
There is something wrong with the figures you posted.

Using a GM HEI non-computer distributor and setting the initial timing at 16 degrees BTDC with the vacuum advance dis-connected and plugged and the engine RPM below 800 is a good starting point. However, when increasing the engine RPM's to 3500-4000 the built in mechanical advance should have added an additional 20 degrees totaling the 36 degrees you posted without re-connecting the vacuum advance. Adding about 15 degrees for the factory non adjustable vacuum advance should have brought the total up to 51 degrees total mechanical + vacuum timing.

Either your vacuum advance is not working or the mechanical (centrifugal) advance is sticking or being limited internally.

Read DoubleVision's post again and follow it.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 12-11-2010, 10:53 AM
Registered User
 
Join Date: Dec 2010
Location: California
Posts: 7
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
well,I did have it hooked to the manifold once and seemed to really smooth things out but a buddy of mine told me it goes on the carb. So, I have a holley 600 and it has a few ports on the passenger side, one is pcv and I thought the one at the top was for the dizzy, there is one more on the bottom that I hooked the dizzy to but it doesn't pull as much as the manifold. So I decided to plug the tranny into it next to the big port for the pcv. So now I just have to start over at the 12degree and try that out. My question about the vacuum for the dizzy, was is it supposed to stay on the manifold all the time or does it ever go to the carb? Thanks by the you guys are cool, I just signed up here yesterday!
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 12-11-2010, 11:12 AM
DoubleVision's Avatar
Not Considered a Senior Member
 
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 40
Posts: 10,643
Wiki Edits: 0

Thanks: 13
Thanked 56 Times in 53 Posts
A manifold port doesn`t mean as in a port on the intake manifold. Both the carb and the intake have manifold ports. It`s called manifold because it pulls vacuum full time including idle. So yes you can connect it to a carb`s manifold source or a direct source to the intake, either way will work one in the same.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 12-11-2010, 12:10 PM
Registered User
 
Join Date: Dec 2010
Location: California
Posts: 7
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Still Dying

I did exactly what you guys told me to do... I did it at 12 and hooked up the dizzy and got a 20 or so jump, I also did it at 16 and got the same thing around 36 total. No matter what I do it dies when I put it in gear. My idle is around 800-850 in park and it seems like it sounds good but as soon as I go into gear it dies immediatley, just bluh bluh blu then dead. I don't get it...???
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 12-11-2010, 03:12 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,181
Wiki Edits: 0

Thanks: 2
Thanked 292 Times in 289 Posts
If this motor has a long duration cam in it it will not idle in gear until you modify the distributor advance curve to allow much more initial base timing at idle.

Shortening/limiting the mech advance curve will allow this.
Typically you want 24deg at idle and 34-36deg at max mechanical advance.
(shorten the mech advance curve to 10-12deg)

Set the motor up to idle correctly without any vac advance.
then connect the vac advance to either the ported source or full vacuum source which ever you prefer.
If the cam is 230 @.050 or higher you will need a high stall torque converter and the carbs power valve will need to be changed to allow correct idling while in gear.

Ask your neibour what the cam specs are.

Check for and fix any carb/intake manifold leaks.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 12-11-2010, 04:03 PM
Registered User
 
Join Date: Dec 2010
Location: California
Posts: 7
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
so firebird, if it is set up at 24 degrees without the advance hooked up and i get that straight, then plug in the advance and it goes to 34-36 - do I just leave it there if it runs good? I am going out to try it right now. I have checked for leaks and can't find any. Also, if it is at 24 degrees should the rpm still be around a 1000 at idle? Thanks...
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 12-11-2010, 04:12 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,181
Wiki Edits: 0

Thanks: 2
Thanked 292 Times in 289 Posts
Quote:
Originally Posted by wes1976
so firebird, if it is set up at 24 degrees without the advance hooked up and i get that straight, then plug in the advance and it goes to 34-36 - do I just leave it there if it runs good? I am going out to try it right now. I have checked for leaks and can't find any. Also, if it is at 24 degrees should the rpm still be around a 1000 at idle? Thanks...
You have to modify the mech advance curve length to allow the increased idle base timing and avoid excessive max mech advance.
(24+/- base at idle, 34-36 at max mech advance)
Then, try both/either (ported or full) vac source for the vac advance. Use what works best for you.
There are no rules.

Big cams need more (base) timing at idle.

Big cams need a looser high stall converter. A stock low stall converter will pull the engine rpm down too much when going in gear.

If the motor does have a big racey cam in it and you don;t want to change the torque converter, change the cam.
A big racey cam is a mismatch for 4x4.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 12-12-2010, 07:56 AM
Frisco's Avatar
Glad To Be Here
 
Last photo:
Join Date: Nov 2002
Location: Canton, North Carolina
Age: 72
Posts: 2,244
Wiki Edits: 0

Thanks: 0
Thanked 7 Times in 7 Posts
Quote:
Originally Posted by wes1976
No matter what I do it dies when I put it in gear. My idle is around 800-850 in park and it seems like it sounds good but as soon as I go into gear it dies immediatley, just bluh bluh blu then dead. I don't get it...???
You may have your idle RPM set too low.

Apply the parking brake. Get a buddy to hold the foot brake fully. Block the rear wheels. Start the engine and allow to fully reach 'normal' operating temps. With the wheels blocked and brakes fully applied, put the automatic trans in DRIVE. Set the RPM to around 650-750 when in DRIVE. NOTE: The engine RPM will increase when in PARK. Do NOT increase the RPM while performing this procedure. Check/set the timing while in DRIVE and the RPM below 800. Do not have the vacuum advance hose connected when checking/setting the timing. It should also be plugged. After checking/setting the initial timing, re-connect the vacuum advance hose. If you use a full manifold source for the vacuum (either at the carb base or the intake manifold), the engine RPM will increase. Re-adjust it so that it is just below 800 RPM with the trans in DRIVE.

You will notice that the engine RPM at idle with the trans in PARK will be around 900-1000. It will drop to around 650-750 when in DRIVE.

As others have previously stated, using a more radical cam will necessitate the need for a higher than stock stall speed converter and a slightly higher engine idle RPM than what I have posted above.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Distributor Tuning and Theory - Part 1 Rick WI Engine 35 04-26-2011 12:38 AM
Low buck 355 sbc not running correctly, wanting to much timing. ForceFed86 Engine 68 04-13-2011 12:35 PM
sbc timing question 350pano Engine 8 05-15-2009 10:30 AM
Timing Timing Timing bigcountry1009 Hotrodding Basics 6 01-20-2009 05:47 PM
Do I need vacuum advance? (Long Post) Chevy21 Engine 49 10-25-2007 12:51 PM


All times are GMT -6. The time now is 02:05 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.