Hesitation off idle, secondaries won't open - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
LinkBack Thread Tools Display Modes
post #1 of 9 (permalink) Old Jul 11th, 10, 02:20 PM Thread Starter
Tech Team
Kelly
 
Join Date: Apr 2009
Location: cary, NC
Posts: 62
Hesitation off idle, secondaries won't open

Car all but dies when you get into gas. Once speed is up, the car is fine. Found a vaccum leak and resealed it. No more leaks but the problem is still there. I did the "paperclip" test method to see if the secondaries were opening, no dice. Did a lap around the block, got into it (as much as she'd let me) secondaries stayed close the whole time. I've got the lightest spring in the canister, canister works (applied suction to hole and secondary rod pulled in as advertised).

Any ideas? and could the secondaries not opening be the cause of the off idle stumble?
Force61 is offline  
Sponsored Links
Advertisement
 
post #2 of 9 (permalink) Old Jul 12th, 10, 03:01 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 32,167
Garage
Re: Hesitation off idle, secondaries won't open

Increase timing, either by adding to initial or having full manifold vacuum onto vac advance.
Increase squirter size by two numbers until gone.

Secondaries won't open until needed as determined by engine demand; light car, might not come open until after 6k rpm.

Give a man a rescued dog for the health of both their souls. May 2017 ROTM Winner - Thank you!
'
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
CUBS - 2016 World Series Champions - Thank you, Joe Madden enjoy your next chapter.
Everett#2390 is online now  
post #3 of 9 (permalink) Old Jul 12th, 10, 07:53 AM Thread Starter
Tech Team
Kelly
 
Join Date: Apr 2009
Location: cary, NC
Posts: 62
Re: Hesitation off idle, secondaries won't open

So I've done a little research. Apparently when you have a bigger cam (which I do) you run into the problem of opening the butterflies too much when trying to set idle mixture. In all the back and forth of tweaking idle set screws and idle speed screw, you open the butterflies way to much exposing the idle transition slot far more than normal. From what I understand there should be NO MORE than .040 of the idle transfer slot exposed. I'm on the road, but when I get home I'm going to pull the carb (again) and see how much of this slot is exposed.

I also read that if the accelerator pump arm should actuate as soon as the throttle is actuated, no slack at all. The only slack shoult be about a .015 inch clearance at WOT on the pump arm.

I'll go ahed and admit that I've been messing around with the idle mixture while chasing this stumble around. I bet the butterflies are open too much at idle. I'll check it out and report back.
Force61 is offline  
 
post #4 of 9 (permalink) Old Jul 12th, 10, 08:23 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 32,167
Garage
Re: Hesitation off idle, secondaries won't open

While you have the carb off, unscrew the secondary setscrew on the pass side of the throttle plate and install it from the top.

This way, you can adjust it from the top and without having to rremove the carb and adjusting.

I did have to adjust the secondaries open a hair for air bypass so the primaries could be closed more for idle circuit action.

Give a man a rescued dog for the health of both their souls. May 2017 ROTM Winner - Thank you!
'
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
CUBS - 2016 World Series Champions - Thank you, Joe Madden enjoy your next chapter.
Everett#2390 is online now  
post #5 of 9 (permalink) Old Jul 12th, 10, 10:56 AM
Senior Tech
Alan
 
Join Date: Oct 2007
Location: SoCal
Posts: 3,905
Re: Hesitation off idle, secondaries won't open

The suspense is killing me. What is the paperclip test?

alan
alanrw is offline  
post #6 of 9 (permalink) Old Jul 12th, 10, 01:03 PM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 32,167
Garage
Re: Hesitation off idle, secondaries won't open

The paper clip test is install a paper clip on the vac diaphram rod at the bottom of the vac diaphram.
If the diaphram pulls open the secondaries, the action will slide down the paper clip on the rod.

Give a man a rescued dog for the health of both their souls. May 2017 ROTM Winner - Thank you!
'
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
CUBS - 2016 World Series Champions - Thank you, Joe Madden enjoy your next chapter.
Everett#2390 is online now  
post #7 of 9 (permalink) Old Jul 12th, 10, 01:56 PM
Senior Tech
Steps
 
Join Date: Dec 2005
Location: New Zealand
Posts: 13,321
Re: Hesitation off idle, secondaries won't open

You can get to the sec adjust screw by flaten the end of a rivet, square off as a screwdriver blade then put a 90 degree angle in the shaft.

My Spelling is not incorrect...it is creative

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Steptoe is offline  
post #8 of 9 (permalink) Old Jul 12th, 10, 02:02 PM
Senior Tech
Alan
 
Join Date: Oct 2007
Location: SoCal
Posts: 3,905
Re: Hesitation off idle, secondaries won't open

Quote:
Originally Posted by Everett#2390 View Post
The paper clip test is install a paper clip on the vac diaphram rod at the bottom of the vac diaphram.
If the diaphram pulls open the secondaries, the action will slide down the paper clip on the rod.
Thanks Everett, for some reason, I was visualizing unbending a paper clip and trapping it in the butterfly. If the butterfly opens, the clip falls in which wouldn't end well for the engine.

alan
alanrw is offline  
post #9 of 9 (permalink) Old Aug 2nd, 10, 09:25 PM Thread Starter
Tech Team
Kelly
 
Join Date: Apr 2009
Location: cary, NC
Posts: 62
Re: Hesitation off idle, secondaries won't open

Ok, here's an update. Figured out the problem!!! The engine dying on throttle input was due to the accelerator pump drowning the motor. When I rebuilt the carb and set it up to Holley specs, the accelerator pump actuated as soon as throttle was given and there was a .015 gap (at the accelerator pump arm) at WOT. Apparentley this was too rich for the engine. I backed off the adjustment screw that actuates the accelerator pump and presto! the engine runs mint! So now the accelerator pump doesnt get actuated until around 1/4 throttle or so, maybe more.

This leads me to a couple other points. First, the car must be running rich if the accelerator pump kills the motor at the slightest actuation off idle. So does this mean that I have too much carb (750cfm for a mildly cammed 396 BB)? or is the CFM fine and the squirter is too big? By the way, my idle adjustment screws are only about 1 1/4 turns out to give maximum vaccum at idle. Idle transfer slots are less than .040 exposed.

I think the real answer is to get an A/F ratio guage installed and see what the ratio is at idle and all through the RPM band and go from there. But I'm looking for something a bit easier (and less expensive).
Force61 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
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.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



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

 
For the best viewing experience please update your browser to Google Chrome