hesitation problems (vacuum adv.?) - 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 07-25-2007, 02:45 PM
Almost there
 
Join Date: May 2006
Location: nashville
Age: 28
Posts: 56
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
hesitation problems (vacuum adv.?)

hey guys im here again for some help. ok. so i still have this 74 f100 with a 390 in it. i set the timing on it today and it runs a lot better but i still can not punch the throttle and it stay running. it cuts out like it wants to die on me and then smooths out again. any suggestions?
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 07-25-2007, 03:09 PM
speedydude's Avatar
Registered Cruiser
 
Last photo:
Join Date: Apr 2007
Location: Sedona, AZ
Posts: 271
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
It would be nice to have more info.........engine, carb, etc. What's your fuel pressure?? Accelerator pump working??? Fuel filter changed recently???
Thx, JD
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 07-25-2007, 03:36 PM
Jmark's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Sep 2003
Location: phoenix
Age: 60
Posts: 4,787
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
My first suspect would be the accelerator pump OR the power valve, depending on the carb. Could also be "one of those things" where the engine/trans/gearing just won't allow you to mash it and go screaming away from a dead stop.

Other thing could be ignition problems. Do you still have points or is it electronic? Does the engine have enough compression to get that beast moving quickly from a dead stop?

The vac advance does nothing when you "mash the pedal down". Manifold vacuum goes to zero and there is no secondary vacuum signal either, so you can rule out the advance as the problem.

Mark
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 07-25-2007, 09:27 PM
Almost there
 
Join Date: May 2006
Location: nashville
Age: 28
Posts: 56
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
i. more info... this truck had not ran is 6 years. i cleaned out the gas tank new fuel filter, new points, new solenoid,new master cylinder, new wires and plugs and a new carb (2bbl).the motor is a 390 wi 56,000 miles. also all of the cylinders have great compression.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 07-25-2007, 11:36 PM
speedydude's Avatar
Registered Cruiser
 
Last photo:
Join Date: Apr 2007
Location: Sedona, AZ
Posts: 271
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
2 bbl on a 390??? Ok but a 4 bbl would be nice. Got a feeling it's starved a bit. At least that's my first reaction, but it's getting late here and I'm checkin out. Carb is new or rebuilt??? Float working properly??? Do you have a vacuum gauge to see what's happening at idle and higher rpm??? Bear in mind it sat for 6 years........there's a host of things that could be an issue. Me and "old fuel" have had issues in the past.

Any way to get a fuel pressure reading???? None of us are leaning over the engine so it's a bit hard to diagnose from a stinkin computer. Will check back in the AM.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 07-26-2007, 12:02 AM
aka Duke of URL
 
Last wiki edit: Finding vacuum leaks Last photo:
Join Date: Oct 2001
Location: Rockville, MD
Posts: 4,821
Wiki Edits: 1

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by Jmark

The vac advance does nothing when you "mash the pedal down". Manifold vacuum goes to zero and there is no secondary vacuum signal either, so you can rule out the advance as the problem.
The vacuum advance feature operates from a ported vacuum signal and will cause tip-in hesitation as will a bad accelerator pump. Check diaphram operation and breaker plate binding. It has mechanical points so make sure they are adjusted correctly.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 07-26-2007, 08:15 AM
Almost there
 
Join Date: May 2006
Location: nashville
Age: 28
Posts: 56
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
yes it is a new carb not a rebuild. the points was gapped properly with a feeler gauge. and like i said the gas tank was cleaned not drained. could vacuum have anything to do with it at all? i know that the vacume lines are messed up. i thik the previous owner pluged them up to wherever he thaught they should go
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 07-26-2007, 10:42 AM
speedydude's Avatar
Registered Cruiser
 
Last photo:
Join Date: Apr 2007
Location: Sedona, AZ
Posts: 271
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
What carb are you running??? First, I would disconnect the vacuum lines and plug. Plug the ports on the carb where removed. Set base or initial timing. Do you have a timing light??? Check mechanical advance to be sure it's coming in correctly. Visually inspect all vacuum lines and fittings for deterioration or leaks.

If you have vacuum leaks you can usually get it to idle but it will crap out when you add additional F/A mixture. (too lean). Also look in the carb throat , open the throttle and make sure the accelerator pump is giving a good squirt.

Check back, JD
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 07-26-2007, 11:25 AM
Member
 
Last photo:
Join Date: Nov 2004
Location: Lakeland FL
Age: 65
Posts: 4,110
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
here's a very handy trouble shooting link....

click on "feels" then "engine hestiates" for a prioritized causes listing.....

http://www.autozone.com/UseCase,S001...tInTheZone.htm

because it sat so long you really should put a clear plastic Purolator gas filter ($5) on the the fuel hose line into the fuel pump to catch the crap from the tank and fuel lines.....common for the first one you put on to be to be plugged full of crap (filter is totally full of gas) in just 200-500 miles
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 07-26-2007, 01:06 PM
Almost there
 
Join Date: May 2006
Location: nashville
Age: 28
Posts: 56
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
fuel pump

o.k. so i went out this morning and did a pressure test on the truck. the fuel pressure didn't even read on the gauge. so i am going to change it and see if that fixes my problem. what i don't understand is how could it stay running is the fuel pump is not working
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 07-26-2007, 01:12 PM
Not A T 25's Avatar
Takes Guts To Cut One Up
 
Last photo:
Join Date: Sep 2003
Location: South Central Illinois
Age: 57
Posts: 354
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by Tryin2MakeIt
o.k. so i went out this morning and did a pressure test on the truck. the fuel pressure didn't even read on the gauge. so i am going to change it and see if that fixes my problem. what i don't understand is how could it stay running is the fuel pump is not working
It will transfer some fuel just not generate pressure or volume I would look for a fuel filter up line from the pump it could be blocked. If no filter blow back thru the line to the tank to make sure there is no sludge or blockage could be a starved pump.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 07-26-2007, 02:09 PM
speedydude's Avatar
Registered Cruiser
 
Last photo:
Join Date: Apr 2007
Location: Sedona, AZ
Posts: 271
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I've always liked the clear fuel filters, easy to see what's happening. And ditto to T-25
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 07-26-2007, 02:56 PM
400smb_s10's Avatar
Back Yard Junky :)
 
Last photo:
Join Date: Mar 2007
Location: Around the Corner from the middle of nowhere... Arden Ontario
Age: 28
Posts: 368
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
IMO I would fix all the fuel problems then unbolt the 2 bbls and intake and drive to the closest lake and throw them in it and bolt on a 4bbl set up. Theres nothing better then hearing the 4 bbls open up at 3000 rpm when you mash the gas and leave 40 ft of rubber

But thats just my opinion

Ed
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 07-26-2007, 03:08 PM
Not A T 25's Avatar
Takes Guts To Cut One Up
 
Last photo:
Join Date: Sep 2003
Location: South Central Illinois
Age: 57
Posts: 354
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by 400smb_s10
IMO I would fix all the fuel problems then unbolt the 2 bbls and intake and drive to the closest lake and throw them in it and bolt on a 4bbl set up. Theres nothing better then hearing the 4 bbls open up at 3000 rpm when you mash the gas and leave 40 ft of rubber

But thats just my opinion

Ed
Theres nothing better than an armchair hot rodder He obviously put the 2bbl on there for a reason "Duh what he wanted" bet he beats your gas mileage
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 07-26-2007, 03:26 PM
400smb_s10's Avatar
Back Yard Junky :)
 
Last photo:
Join Date: Mar 2007
Location: Around the Corner from the middle of nowhere... Arden Ontario
Age: 28
Posts: 368
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Yes thats for sure but you still cant beat the sound of 4bbls opening up when you smash the gas and 40 people are watching you smoke the tires off that 390 ford I have no beef with 2bbls I used to have a 1984 ford branco with a 302 with 2 bbls and YES it was stupendisly great on gas Untill it rotted out the frame and I had to can it for a street vehicle.. I welded the frame put a 4 bbls intake and carb on it and jacked it up and put 44 inch swamper boggers on sold it as a non road werthy vehicle to my buddy for $9000 and hes won many many mud drags/bogs with it. I miss the old truck because I could put 50 bucks in gas in it and it would last me a week and a half but now Im hooked on my new truck a 1978 chevy stepside with a 400 sbc pushing 425 hp with super 40s on it oh my gooses I think I love it more then my girl friend. I dont even turn on the radio when im on a long drive just listen to the 1 5/8 headers straight into super 40's then into 5" blue chrome tips

anyways thats my .02 cents

Ed
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
Vacuum advance hooked up directly to manifold....is this bad????? Steve-0321 Engine 69 03-10-2014 05:10 PM
Vacuum Secondaries Won't Open Fully leejoy Engine 11 08-28-2006 12:30 PM
68 charger lights T-bucket23 Electrical 5 08-14-2006 05:07 PM
Timing ?'s, Idle Speed and Ported vs Manifold Vacuum JoeS Engine 5 11-03-2004 12:34 AM
vacuum problems APACHEMAN Engine 3 09-29-2004 11:32 AM


All times are GMT -6. The time now is 09:39 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.