Bogs on throttle - 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 09-26-2010, 06:51 PM
Registered User
 
Last photo:
Join Date: Apr 2010
Location: NC
Posts: 108
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Bogs on throttle

I have a rebuilt 350 with T350 auto tranny that bogs and sputters if I press the gas. In park I can rev it fine with no issues. In gear I barely press the gas and it drives along fine but if I press on the gas it start to bog and sputter and never gets past this point.

What should I be looking at, vacuum leak, carb?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 09-26-2010, 07:08 PM
Registered User
 
Join Date: Sep 2010
Location: saraland,al.
Posts: 12
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
what carb is on it
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 09-26-2010, 07:11 PM
sqzbox's Avatar
My pipes are my music
 
Last photo:
Join Date: Sep 2009
Location: indiana
Age: 64
Posts: 2,938
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Sounds like a bad accelerator pump.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 09-26-2010, 07:32 PM
Registered User
 
Last photo:
Join Date: Apr 2010
Location: NC
Posts: 108
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
It's got a Holley 750 CFM. Acc Pump was my first thought but I thought that would be bad only through the transition between the idle circ and the primary. If it is bad would it keep doing that even when running on the primary circuit?
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 09-26-2010, 07:43 PM
sqzbox's Avatar
My pipes are my music
 
Last photo:
Join Date: Sep 2009
Location: indiana
Age: 64
Posts: 2,938
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
The acc. pump operates all the way through the primary's to cover the opening of the throttle blades to keep it from going lean. If you notice, when you open the throttle 1/4 way open there is still some pump arm travel left that the pump cam will continue to operate until the primary's are fully opened.
That's why manual secondary's have another accelerator pump on the back 2 barrels. With vacuum secondary's a secondary pump is not needed as the secondary's will only open as far as needed by engine load and vacuum signal to the diaphragm.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 09-26-2010, 08:16 PM
bubbahotep's Avatar
Registered User
 
Last photo:
Join Date: Aug 2008
Location: NYC
Age: 42
Posts: 487
Wiki Edits: 0

Thanks: 1
Thanked 1 Time in 1 Post
Have to agree with the accel pump. You might just need to adjust the arm. Theres a bolt with a spring on it that presses down on the accelerator pump arm, if its NOT solid on the arm you will get a stumble. Then again you might just need a different pump cam.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 09-27-2010, 04:50 PM
Registered User
 
Last photo:
Join Date: Apr 2010
Location: NC
Posts: 108
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I got a rebuild kit today but while researching this furher I found the following info. Mine bogs and stumbles at at RPM speed, from start to cruising. I am going to warm the engine up and shut off, then manually open the accl and see if fuel squirts from the pump. If it does it should be good right?

"Bog from a cruise RPM may be caused by a defective advance mechanism, but on 4 barrel carburetors is often caused by the secondary side opening too soon. Most original equipment 4 barrel carburetors have “on-demand” secondaries (I use this term rather than vacuum, as some early 4 barrels used vacuum to accuate the secondary, while most 4 barrels from about 1960 up used either spring tension or weights to control the secondary). The Carter AFB uses weights, and therefore never goes out of adjustment. Other 4 barrel carburetors such as the Carter AVS, Carter TQ, Rochester 4GC, and Rochester Q-Jet have a tensioned secondary spring. As the spring fatigues, the air valve will open too soon, creating an instantaneous lean condition, and a bog. These units, when rebuilt, should virtually always have the tension spring replaced, and adjusted to factory specifications. A defective accelerator pump will rarely cause bog from cruise."
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 09-28-2010, 02:44 AM
sqzbox's Avatar
My pipes are my music
 
Last photo:
Join Date: Sep 2009
Location: indiana
Age: 64
Posts: 2,938
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
But, you have a holley. So what you going to do now?
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 09-28-2010, 06:49 AM
bubbahotep's Avatar
Registered User
 
Last photo:
Join Date: Aug 2008
Location: NYC
Age: 42
Posts: 487
Wiki Edits: 0

Thanks: 1
Thanked 1 Time in 1 Post
The accel pump should always shoot gas when the car I'd off , even cold. No need to warm up. It holds 30cc typically

just because it shoots doesn't mean it's adjusted for your particular car. The accelerator pump cam controls how fast or slow it shoots. Changing the pump cam will change the performance for good or worse.

I would check the pump operation, it might be a simple tightening of the bolt

what model carb is it? If it's a 4160 vac secondary then I highly doubt you have secondary issues.

What's your timing, idle rpm in gear?
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 09-28-2010, 07:39 AM
Registered User
 
Last photo:
Join Date: Apr 2010
Location: NC
Posts: 108
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
The carb is a 3310 or 750 CFM. It was running fine and then while driving test miles after a rebuild it just started doing this after a while. I am going to remove the carb today and check it out.

I am not sure of the timing at this point. Last week I removed the dist and manifold to replace a lifter. Then I reinstalled the manifold and went through the process of reinstalling the dist. I marked the dist location before removal and of course when I reinstalled I had to work it where when the gears meshed it ended up pointing the rotor to #1.

At this point I used a light to set initial timing to 11 deg BTDC as a starting point. The engine started fine but would not stay on in gear at all. I advanced a little more until it idles good and run fine in gear. My thought is that when I got the dist reintalled it is not exactly lined up with the damper mark so what the timing light was showing is not accurate. After it stops raining I am going to hit it with light again and see.
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:
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
acceleration flat spot in carb. corvettetonybone Engine 17 04-13-2013 08:31 PM
Throttle Linkage vs throttle cable 65comet Engine 2 06-02-2006 01:56 PM
I'm going to make a bonfire out of my car blown69stang Engine 36 08-22-2005 03:36 PM
Jeep 2.5L throttle body to 4L throttle body. Parisienne66 Engine 2 07-10-2005 08:35 PM
Proper throttle spring placement willys36@aol.com Engine 1 11-13-2002 07:19 PM


All times are GMT -6. The time now is 12:02 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.