Chevy 350 lost power with new intake manifold and carb - 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 04-27-2011, 06:16 PM
valtiel43's Avatar
Registered User
 
Join Date: Apr 2011
Location: Ohio
Posts: 44
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
Chevy 350 lost power with new intake manifold and carb

I have a 1980 Corvette, 5.7 auto. When I first got it I thought it was all stock. It still had all the old emissions stuff on it and everything. I tried to put an Edelbrock Performer for pre-86 sbc's on it, but it didn't bolt up right. So a mechanic I know told me it's because those aren't the original heads on the motor. He said they are obviously post-86 cast iron heads. And that the slightly lumpy idle is infact from a hotter camshaft, and not a motor problem like I originally thought lol. So I ordered a Holley Street Dominator that bolted up good.

So I got the new intake on, topped it off with a new Holley 600cfm double pumper (I know this carb is running good because I ran it on my t/a for a few miles and it worked great). Stuck a Spectre air filter on that and thought I was done. I also threw out the old smog pump, blocked off the egr and crimped the air tubes going to the stock exhaust heads (which will be replaced with headers here soon).

I start it up, get it timed in good because I had to take the distributer out. It seems to be running really smooth. I take it out for a drive and just have no power. I floor it and it's like driving a granny mobile. The car had more *** to it when I had all the old crap on it. What gives? I added the exact same carb and intake to a Monte Carlo with a stock 305 a long time ago and that thing ran like a whole new car. I do it to this 350 and it's like I poured tar in my motor.

My gas pedal felt weird at first, so I took some slack out of the throttle cable, and made sure my springs and brackets are good. My fuel psi is up around like 9, I'm going to get a regulator later and drop it down to about 6 because 9 is super high. I'm also going to see if the timing needs tweaked a little more.

I know this is a wall of text. I'm confused right now as to how my whole powerband could have gotten weaker when I bolted on things that should have brought the power up. If someone reads all this and can help me you will be doing me a huge favor. Thanks

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 04-27-2011, 06:21 PM
DoubleVision's Avatar
Not Considered a Senior Member
 
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 40
Posts: 10,654
Wiki Edits: 0

Thanks: 15
Thanked 58 Times in 55 Posts
What is the timing set at? What`s the vac advance connected to? A manifold or port vacuum source? 9 psi is too high, I agree it needs to come down to about 6. Are the float levels set correctly? Are there any vacuum leaks?
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 04-27-2011, 06:27 PM
Registered User
 
Last photo:
Join Date: Dec 2010
Location: williamston sc
Posts: 319
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
What type carburetor and intake did you take off of it?
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 04-27-2011, 06:37 PM
eloc431962's Avatar
Evil Wicked Mean And Nasty
 
Last wiki edit: Pilot bearing and bushings
Last journal entry: roof repair
Last photo:
Join Date: Nov 2008
Location: back in the garage.
Posts: 13,762
Wiki Edits: 37

Thanks: 50
Thanked 28 Times in 24 Posts
I would say bring the pressure down to 5psi or no more then 6psi and tweek the timing and if there are no vacuum leaks you should be ok. JMO


Cole
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 04-27-2011, 07:13 PM
valtiel43's Avatar
Registered User
 
Join Date: Apr 2011
Location: Ohio
Posts: 44
Wiki Edits: 0

Thanks: 1
Thanked 0 Times in 0 Posts
The timing is supposed to be 6 degrees before tdc. I was messing with it for what seemed like forever and never did get the marks to line up on the scale. I used a white paint marker on my balancer to mark where the line is, unless there is two lines on there I'm not sure, but I never saw it line up on my scale. I'll go mess with it more tomorrow as I'm almost sure now that it's out of time.

My Vacuum advance plugs into the port on my carb.

The floats are all set right.

I'm not sure if there are any vacuum leaks. I'll use my gauge tomorrow and check.

The carb I took off looked like the original it was an Edelbrock. The intake was a big cast iron piece. It seriously weighed like 45lbs.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 04-27-2011, 07:20 PM
Registered User
 
Last photo:
Join Date: Mar 2011
Location: hamilton ont. canada
Age: 39
Posts: 180
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
did you make sure to disconnect the vacuum advance and plug the hose while doing the timing?

10-13 deg would be better for timing that engine
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 04-27-2011, 07:32 PM
DoubleVision's Avatar
Not Considered a Senior Member
 
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 40
Posts: 10,654
Wiki Edits: 0

Thanks: 15
Thanked 58 Times in 55 Posts
Since this is a smog engine, don`t set it by factory spec timing. With the Vac advance unplugged and capped, set the base timing to 12 degrees before top dead center. Lock the distributor. Reconnect vac advance, it should be connected to a full time manifold vacuum source (one that pulls vacuum full time including idle) Recheck timing, it should be 20 - 24 degrees before top dead center. Next check mechanical advance, it should have 36 to 38 degrees, all in by 3000 RPM.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 04-28-2011, 06:02 PM
Registered User
 
Join Date: Sep 2006
Location: Kansas City, MO
Posts: 134
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
350 lost power

Have someone get in the car and hold the throttle to the floor (ENGINE OFF).
You take your flashlight and look down the carb to make sure the carb is wide open. I fixed one customers car by adjusting the throttle linkage about 1 inch. He had been driving the car that way for 6 years.

Nine times out of ten checking the basic's will fix the problem.

Ron
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
Will intake manifold make a power difference? proge Engine 3 10-11-2008 09:40 AM
Intake Manifold and Carb Ozz1967 Engine 9 12-29-2005 12:34 PM
4-71 with intake manifold and carb chevyhotrod Engine 3 08-02-2005 01:22 AM
Spacer between carb and intake manifold?... doc_rage Hotrodding Basics 2 02-06-2004 07:40 PM
carb/intake manifold 1969 CAMARO SS Engine 2 06-17-2003 02:20 AM


All times are GMT -6. The time now is 01:50 AM.


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.