Low vacuum - Team Camaro Tech
Engine General Engine Discussion.

 
LinkBack Thread Tools Display Modes
post #1 of 9 (permalink) Old Dec 19th, 05, 11:31 AM Thread Starter
Senior Tech
 
Join Date: Jul 2001
Location: Columbus, GA
Posts: 867
Low vacuum

I just had someone help me adjust my timing and carb on my Z/28 and we noticed that it only has 5" of vacuum at idle. This is low. I adjusted the valves a couple of days later but that didn't change the vacuum. What would be the likely culprit of this? Timing, compression, etc.?

Also, since I installed a smog system, removing the passenger side rocker arm cover is a pain. I had to remove the smog tube from the manifold just to remove it. There has to be a better way. Any ideas?

Dave, member number 7704
2000 Dodge Viper GTS
drdave69 is offline  
Sponsored Links
Advertisement
 
post #2 of 9 (permalink) Old Dec 19th, 05, 01:09 PM
 
Join Date: Nov 2005
Posts: 143
Re: Low vacuum

Assuming you are using the original style camshaft the 302 cam has excessive duration,hence the lack of torque and low vacuum.There are far better solid cams on the market today that will help your situation www.hardcoreparts.ca
pro1 is offline  
post #3 of 9 (permalink) Old Dec 19th, 05, 03:03 PM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 31,755
Garage
Re: Low vacuum

With OE camshaft, should be around 8-9 in/Hg. vacuum.

I'd probably throw in alittle more initial timing to bring up vacuum, but not enough it would kick back against the starter when hot.

If the kickback happens, too small of battery cables, min of 1 AWG, plus too small of reserve battery won't help starter spin fast either. And starter condition is a factor also.

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 offline  
 
post #4 of 9 (permalink) Old Dec 19th, 05, 04:26 PM Thread Starter
Senior Tech
 
Join Date: Jul 2001
Location: Columbus, GA
Posts: 867
Re: Low vacuum

We set the initial timing at 12 degrees (this is on the OE camshaft and not planning to replace it). It starts and runs fine even after getting to operating temp. Doesn't knock upon accelerating that I can hear.

Dave, member number 7704
2000 Dodge Viper GTS
drdave69 is offline  
post #5 of 9 (permalink) Old Dec 20th, 05, 09:19 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 31,755
Garage
Re: Low vacuum

Vacuum leak somewhere?
Will it idle down further, say to 700-750? If it does, good indication of no vacuum leaks.

I suggested 8-9 jn./Hg of vacuum at idle because JohnZ offered this value sometime in the past.

I believe idle rpm is set around 900 rpm. If one revs up to say 1500, vacuum should come up. Throw a rag over the carb air horn and listen to what happens. If it dies,good setting, If ti revs up, vacuum leak or too lean.

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 offline  
post #6 of 9 (permalink) Old Dec 20th, 05, 09:20 AM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 31,755
Garage
Re: Low vacuum

Double post

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 offline  
post #7 of 9 (permalink) Old Dec 20th, 05, 05:14 PM Thread Starter
Senior Tech
 
Join Date: Jul 2001
Location: Columbus, GA
Posts: 867
Re: Low vacuum

It idles around 900-1000. The next time I have it running I'll try the rag over carb trick.
It has always had a very strong smelling exhaust but it seems unbearable now. I have 5 gallons of 110 racing fuel mixed with the 93 unleaded. The exhaust gases burn my eyes and the smell stays in my clothes/hair if I stand around the garage with it running. Could this be a too rich condition?

Dave, member number 7704
2000 Dodge Viper GTS
drdave69 is offline  
post #8 of 9 (permalink) Old Dec 20th, 05, 08:48 PM
Super Moderator
Bess-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 31,755
Garage
Re: Low vacuum

Yes. Spark plugs would be dry black if idled too long. You might try to open secondaries just hair so the primaries could close alittle more to allow more effect of mixture screws. Use the stop screw on pass side of throttle plate to open secondaries.

A slotted setscrew is only available from the bottom, meaning carb removal. Screw screw out and screw with slot on top from the top for easier adjustment.

If secondaries opened too far, curb idle won't be able to decrease to 900-1000 rpm. Trial and error setting.

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 offline  
post #9 of 9 (permalink) Old Dec 21st, 05, 12:45 PM
Senior Tech
 
Join Date: Mar 2002
Location: Austin, TX, USA
Posts: 5,277
Re: Low vacuum

Valve issues usually cause the vacuum needle to pulsate.

Dave
========================
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
dnult 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