Good idle, bad in gear - 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 07-03-2011, 04:17 PM
david-b's Avatar
Dave is THAT guy
 
Last photo:
Join Date: Oct 2010
Location: Chicago
Posts: 213
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
Good idle, bad in gear

Hey all;

I swapped the Demon carb that was on my 400 off to an Edelbrock and have been getting much better results with it. It's no longer stupid rich and running decently well. My biggest problem however, is that at idle in park, I have her about 1000rpm. When she's in gear (auto) idle drops really low. I've raised the idle on the carb up some so it's higher in park and higher in gear, but I know that's wrong and need to get this figured out.

Engine is sbc400, stock bottom end. Aluminum heads, headers, Edelbrock 4bbl carb (I believe the 650 or so but could be wrong), high rise intake, 282.0 / 290.0 cam, and 2300-2700 torque converter.

Couple things to add. I was setting timing with the HEI hooked up to the vac advance, and after doing some searching here... you're not supposed to do that. When car was at 12btdc, she ran like crap. I changed around some and with the vac still on, she's running great at about 25btdc. Does this sound about right? Also I'm reading that the dizzy should be hooked to the constant, same as the trans instead of the advance. Is this right as well?

So the question really is, should I keep playing with the timing to get her to idle in gear, more so than the carb? Thanks

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 07-03-2011, 05:15 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,752
Wiki Edits: 0

Thanks: 3
Thanked 348 Times in 345 Posts
read my posts on recurving your distributor for a big cam.

You may have the wrong converter. Get a 10" 3000+ stall.

You want a minimum of 24deg base initial at idle (not including any that vac advance adds at idle) You must modify the distributor advance stop to get this. HEI is simple, search my posts.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-05-2011, 12:08 PM
david-b's Avatar
Dave is THAT guy
 
Last photo:
Join Date: Oct 2010
Location: Chicago
Posts: 213
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by F-BIRD'88
read my posts on recurving your distributor for a big cam.

You may have the wrong converter. Get a 10" 3000+ stall.

You want a minimum of 24deg base initial at idle (not including any that vac advance adds at idle) You must modify the distributor advance stop to get this. HEI is simple, search my posts.
Ok, I've been reading a lot and searching a lot. Just still confused. From what it seems, I will need to get different springs for the dizzy to allow for more/less vacuum at idle, correct? Vacuum does drop quite a bit in gear, I want to say it's at about 6" in gear, about 12 to 15" in park. I also basically lose my brakes when driving and rpms drop to idle. Also, there's no change in vac when using a gauge and adjusting the carb.

I also tried hooking the distribuator to the manifold vac, and there was no change in anything.

Again, thanks for any help.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-05-2011, 03:11 PM
Custom10's Avatar
my KARMA ran over my DOGMA
 

Last journal entry: SS
Last photo:
Join Date: May 2009
Location: Saskatchewan, Canada
Age: 49
Posts: 1,095
Wiki Edits: 0

Thanks: 15
Thanked 26 Times in 23 Posts
As mentioned ultimately you may want a bigger stall so that in gear your converter is not loading up until then you may need to live with the drop in RPM from park to drive. It will also help the cam reach peak torque properly

For timing,,,When you raise the base timing up you need to limit the mechanical advance mechanism in the HEI. Most HEI's will add 18-22 deg of mechanical advance in out of the box form.

So if you set your base at 20 lets say for sake of round numbers then add your mechanical advance once at 3000RPM you are at approx 40-42 deg advance already, then add another 16-18 from vacuum advance and you are at 56-60 Deg total,,,too much.

Find out what you have using a timing light and then post the numbers. First disconnect the vacuum advance and plug the hose, what is the base timing? at say 900RPM. Then rev the motor slowly up in RPM with the timing light on it (wheels blocked, park brake on) note the RPM that it stops advancing (should be done by 3500) and record the timing BTDC it should have increased. Then finally let the motor idle and hook up the vacuum advance to full manifold vac and take a reading. This will tell you/us what you have.

As mentioned you will most likely need to limit the mechanical advance inside the HEI as well as the vacuum advance. The springs do not limit the amount of advance they simply allow the mech advance to come in faster (lighter springs) as compared to engine RPM or slower (heavier springs). You can use bushings or a mechanical stop to set the limit depends on the HEI. This plate is used to limit the vacuum advance or fashion one up, but for 4 bucks?

http://www.summitracing.com/parts/CRN-99619-1/

At idle you could live with 30-32 deg BTDC. This would include the base timing of say 20 Deg and then another 12 added via vacuum advance on manifold vac,,,try it. You want to prevent any mechanical advance at idle so try and keep the RPM below 900 at idle.

You need allot a patients when you piss around with distributors, it really is trial and error until you have done it a few times,,,take your time it pays off
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-05-2011, 08:44 PM
david-b's Avatar
Dave is THAT guy
 
Last photo:
Join Date: Oct 2010
Location: Chicago
Posts: 213
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
Got to get to the garage today for a little.

When disconnecting the vaccum line from the distrib, the car doesn't want to idle. Was showing about 14btdc at around 1000rpm. I couldn't go up since the parking brake is disabled right now and my bro wasn't going the best job holding the brake down.

Motor with vac hooked up at idle in park is about 25btdc. I tried advancing some to see if it would hold idle better in gear, and that came back negative. Died prettty quickly.

I ended up just ordering the plate... just easier since it'll be here before the next time I get out to the garage and had an order I needed to place anyways. Going to try that. So basically, I just installed that under the weights, it looks like? And it'll block the vacuum from being there at idle? Then I just raise the idle on the carb?

This is very aggrevating as I just want it to run already with no issues. Computer control FTW!
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-06-2011, 09:02 AM
Custom10's Avatar
my KARMA ran over my DOGMA
 

Last journal entry: SS
Last photo:
Join Date: May 2009
Location: Saskatchewan, Canada
Age: 49
Posts: 1,095
Wiki Edits: 0

Thanks: 15
Thanked 26 Times in 23 Posts
You would be best advised to set the base and mechanical timing first, then set/limit the vacuum advance to about 12-14 with the plate. The engine idle vacuum when connected finally to the vacuum advance canister will add advance at idle this is OK and should bring your idle BTDC to over 30 once you set the base or initial at 20ish.

The plate does not block the vac advance at idle it simply limits the maximum amount of advance the vacuum canister can add.

Look for about 20 BTDC on the base timing then add another 14-16 with mechanical for a total of about 34-36 to start. The vacuum advance will pull in and out based upon engine load.

Remember once the mechanical advance limit is set it can not be changed unless you get back in there so it is important to know how much base timing the motor wants then set the mechanical limit to get 34-36 total at approx 3000RPM.

ie if your motor likes 16 deg BTDC base then you can limit the mech to add 18-20, if the motor wants 22 deg BTDC base then you will need to limit the mech to 12-14 etc etc.

You rev the car in park to check the mechanical advance, not in drive (might be reading this wrong).

What kind of HEI? stock GM or after market?
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 07-06-2011, 09:33 AM
david-b's Avatar
Dave is THAT guy
 
Last photo:
Join Date: Oct 2010
Location: Chicago
Posts: 213
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
HEI is a basic aftermarket. No brand on it, and got the car with it already there.

Maybe I'm not understanding how this is going to help my idle. I understand the plate is going to stop vac from coming in. But how is that going to help the vac at idle?

The example of 16btdc is without the vac, correct?

Also, is there any changes that need to be made to the allen key inside the vac advance? Lastly, would you recommend full time vac or ported for this?

Again, thanks for your help.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 07-06-2011, 11:51 AM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,752
Wiki Edits: 0

Thanks: 3
Thanked 348 Times in 345 Posts
You are playing with the wrong thing. You need to shorten the mechanical advance curve from stock 20-22deg to around 10-12deg by limiting the travel. This will allow 24deg initial base tming at idle and 34-36deg at max mechanical advance. This is all done without any vacuum advance at all.

Then once you have done that,,, vac advance is used for part throttle cruisng, not for idle timing at all. You want to adjust the vacuum advance to get around and additional 10-12deg coming in at part throttle cruise at hiway speeds when engine load is low, vehicle speed is high and manifold vacuum is high.
You also want to verify that the vac advance does not add more than 15deg reguadless of how much vacuum is applyed.

search my posts on how to limit mechanical advance on a HEI.

This will allow the required base timing at idle.

You cannot do it by just swapping weight and springs.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 07-06-2011, 11:54 AM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,752
Wiki Edits: 0

Thanks: 3
Thanked 348 Times in 345 Posts
Once you have giving the motor all the idle timing (24++) it requires and the idle still drops too much when going in gear, then the torque converter is too tight.
A higher stall converter is required. Get a real 10" 3000+ high stall.



Allows easy hot starting with increased ignition timing.
Make sure the rear starter bracket is instaled on your GM starter motor.


Last edited by F-BIRD'88; 07-06-2011 at 12:00 PM.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 07-06-2011, 01:18 PM
david-b's Avatar
Dave is THAT guy
 
Last photo:
Join Date: Oct 2010
Location: Chicago
Posts: 213
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
I've seen the block out screw picture before but didn't get too far into it. After doing some searching, it seems like that's what I want, no? Not the entire lockout since I'm not boosted, but just limit it, correct?

I'm trying not to have a switch on the dash to get her started. Hopefully she'll be fine with some limiting.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 07-06-2011, 02:20 PM
Custom10's Avatar
my KARMA ran over my DOGMA
 

Last journal entry: SS
Last photo:
Join Date: May 2009
Location: Saskatchewan, Canada
Age: 49
Posts: 1,095
Wiki Edits: 0

Thanks: 15
Thanked 26 Times in 23 Posts
OK I will try to explain one more time, it is difficult to describe in detail all the in and outs, as we all know. Yes just limit the mech advance don't lock it out.

3 amigo's of timing

1) Base timing -this is set by turning the distributor CCW or CW and then it does not change once you lock down the dist hold down clamp

2) Mechanical advance - this is controlled by the moving spring plate and weights inside the dist. You can set or limit how much advance is added by using bushings over top the pins that slide in the top plate slots or as Fbird shows use a mechanical stop to limit the spring plate travel. The use of a screw to prevent any mechanical advance all together is also shown in the pic as well but you don't need to go there. The side kick to this mech advance is the tension of the springs used on the spring plate posts. Heavier springs hold back the mech advance as compared to engine RPM since the spring plate moves via centrifugal force, lighter springs allow the mech advance to come sooner.

3) Vacuum advance - this is controlled by the vacuum canister which is activated by the engine vacuum levels. The engine vac works upon the canister diapahram to pull the actuator rod which in turn rotates the magnetic pickup and adds advance. At high engine loads like when you rug it the vacuum level drops and the vacuum advance is all but gone. At light engine load like when cruising the engine vacuum is high and the advance is added. The canister can be hooked to full manifold vac or ported carburetor vacuum but we won't get into that just yet I don't have all day and guitar joe is on holidays lol. Some cans have an adjusting screw to set the spring range of the canister, that is a topic that we can get to once you master the mechanical advance settings...hopefully

For your application:

First work on setting up the mechanical advance, never mind the vacuum advance. When the HEI's are un modified they work with un modified engines. This is because the base timing of these engines is low say 10 Deg BTDC. When the engine revs up the mechanical advance will add say 22 deg in stock form, this is OK cause the motor ends up with 32 Deg BTDC total and is happy. Now take that stock HEI and increase the base timing to 20 and don't limit the mech adv, then add the same 22 deg adv and the motor is seeing 44 total not good. So do you see why you need to limit the mechanical advance now? We are telling you to run 20-24 deg base timing, so if you don't limit the mech advance your hooped.

I asked before what the dist was adding for mechanical advance, did you test it out?
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 07-06-2011, 02:35 PM
david-b's Avatar
Dave is THAT guy
 
Last photo:
Join Date: Oct 2010
Location: Chicago
Posts: 213
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by Custom10
For your application:

First work on setting up the mechanical advance, never mind the vacuum advance. When the HEI's are un modified they work with un modified engines. This is because the base timing of these engines is low say 10 Deg BTDC. When the engine revs up the mechanical advance will add say 22 deg in stock form, this is OK cause the motor ends up with 32 Deg BTDC total and is happy. Now take that stock HEI and increase the base timing to 20 and don't limit the mech adv, then add the same 22 deg adv and the motor is seeing 44 total not good. So do you see why you need to limit the mechanical advance now? We are telling you to run 20-24 deg base timing, so if you don't limit the mech advance your hooped.

I asked before what the dist was adding for mechanical advance, did you test it out?
Thank you for the breakdown. I think I understand it now. Very useful and paints a clearer picture.

Base idle no vac was at 14btdc @ 1000rpm in gear. I couldn't get it any higher since I have no parking break right now and brother was holding the brakes.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 07-06-2011, 02:48 PM
Custom10's Avatar
my KARMA ran over my DOGMA
 

Last journal entry: SS
Last photo:
Join Date: May 2009
Location: Saskatchewan, Canada
Age: 49
Posts: 1,095
Wiki Edits: 0

Thanks: 15
Thanked 26 Times in 23 Posts
you can get it higher just loosen the hold down clap of the dist and turn the dist CCW then recheck it you don't need brakes for this , tell your brother to go get beer and ice for the cooler it may be a long day lol
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 07-06-2011, 07:12 PM
cool rockin daddy's Avatar
1.21 giga-watts???!!!!
 
Join Date: Aug 2003
Location: wherever cool cars are
Posts: 1,535
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
You do realize that you are also going to have to adjust the idle speed as you take timing out of the engine. As the engine gets more timing, the idle speed will go up, you will have to dial it down at the carb. An automatic should usually idle around 700-800 in gear.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 07-06-2011, 09:42 PM
F-BIRD'88's Avatar
Yada Yada Yada
 
Last photo:
Join Date: Oct 2005
Location: Ontario, Canada
Posts: 9,752
Wiki Edits: 0

Thanks: 3
Thanked 348 Times in 345 Posts
Exactly what cam is in this motor?
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
Rough idle, high idle in park, stalls in gear.. Help! ratmaro Engine 18 03-23-2012 05:29 PM
Won't idle in gear newportman Engine 16 06-01-2011 02:48 PM
idle in gear ?????????? sickolds Engine 27 08-04-2010 05:00 PM
305 sbc good idle, Dies when in gear 1970Chevy Engine 40 11-08-2007 09:00 AM
Idle in Park is 1,800 RPM....Idle in gear in 900 RPM...Way too High. white66coupe Engine 11 09-10-2004 11:49 AM


All times are GMT -6. The time now is 12:16 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.