#1  
Old 05-23-2022, 10:10 PM
64speed's Avatar
64speed 64speed is offline
Ultimate Warrior
 
Join Date: Jul 2003
Location: Westminster S.C.
Posts: 6,025
Default Cutting out under load

So the car has developed a problem. It has terrible acceleration and if you kick it then it flat or stumbles. Idles great, revs perfectly as long as it’s not under load.. where do I begin

__________________
468/TKO600 Ford thru bolt equipped 64 Tempest Custom. Custom Nocturne Blue with black interior.
  #2  
Old 05-24-2022, 05:59 AM
chuckies76ta's Avatar
chuckies76ta chuckies76ta is offline
Ultimate Warrior
 
Join Date: Jun 2004
Location: Canada
Posts: 3,078
Default

Fuel delivery system. What carb are you running? how much H/P is it making?

__________________
68 Firebird. IA2 block, 505 cu in, E-head, Solid roller 3650 weight. Reid TH400 4:11 gear. 29" slick.
Best so far 10.12@133 mph. 1.43 60 ft.
76 Trans am, TKX .81 o/d, 3.73 Moser rearend,
468 with KRE D-ports, Doug headers, 3" Exh.
  #3  
Old 05-24-2022, 09:07 AM
grivera's Avatar
grivera grivera is online now
Ultimate Warrior
 
Join Date: Feb 2005
Location: Just south of Baltimore
Posts: 4,889
Default

Dave - what size fuel line(s) and pump?

__________________
Will Rivera

'69 Firebird 400/461, 290+ E D-Ports, HR 230/236, 4l80E, 8.5 Rear, 3.55 gears
'64 LeMans 400/461, #16 Heads, HR 230/236, TKO600, 9inch Rear, 3.89 gears
'69 LeMans Vert, 350, #47 heads: Non-running project
  #4  
Old 05-24-2022, 09:10 AM
Bill Hanlon's Avatar
Bill Hanlon Bill Hanlon is offline
Ultimate Warrior
 
Join Date: Feb 2005
Location: Fredericksburg, TX
Posts: 2,349
Default

Quote:
Originally Posted by 64speed View Post
where do I begin
I agree with Chuckie.

I'd put a T in the fuel line right before it enters the carb. Then run a line from the T back into the passenger's compartment and mount a temporary fuel pressure gauge on or under the dash. If the pressure drops below spec you've identified the problem.

__________________
My Pontiac is a '57 GMC with its original 347" Pontiac V8 and dual-range Hydra-Matic.
  #5  
Old 05-24-2022, 02:44 PM
25stevem's Avatar
25stevem 25stevem is offline
Ultimate Warrior
 
Join Date: Jan 2022
Posts: 1,744
Default

What do you mean by using the term as you did “ developed “, was the car all good until just recently?
This detail will make a huge difference in how members once again put in there time, experience and knowledge to guide you out of this.

__________________
I do stuff for reasons.
  #6  
Old 05-24-2022, 02:51 PM
NeighborsComplaint's Avatar
NeighborsComplaint NeighborsComplaint is offline
Ultimate Warrior
 
Join Date: Aug 2009
Location: Elgin
Posts: 2,468
Default

Check your distributor advance. An engine will accelerate just fine with no load even in the absence of full distributor advance. Under load, it will want to maintain a steady state and not accelerate.

Carburetion issues are typically a temporary bog or lean out followed by normal acceleration. If too rich, the plugs foul and the car runs lousy all the time.

__________________
Triple Black 1971 GTO
  #7  
Old 05-24-2022, 02:58 PM
64speed's Avatar
64speed 64speed is offline
Ultimate Warrior
 
Join Date: Jul 2003
Location: Westminster S.C.
Posts: 6,025
Default

I called Holley tech today because like I said it just started doing it. The tech told me to back the idle mixture screws out another 1/4 turn and tell him what my vacuum said. I did and it went from fluttering to 11/12 steady. Got in it, drove it, seems fine. There is a man just down the road from me that has a 70 GT37 that runs like a raped ape all up and down the highway near my house. I am gonna go pay him a visit cause I have seen him slow down several times and look at my car. His car runs good so maybe we can tinker with mine.

__________________
468/TKO600 Ford thru bolt equipped 64 Tempest Custom. Custom Nocturne Blue with black interior.
  #8  
Old 05-24-2022, 04:31 PM
25stevem's Avatar
25stevem 25stevem is offline
Ultimate Warrior
 
Join Date: Jan 2022
Posts: 1,744
Default

Ok, once again in your first post you had said that it idled fine, when actually it did not.

It’s good that you have the idle better now with a 3 minute adjustment, but the idle mixture screws will not cure a lean stumble or a bog as you have posted about.

Note that there’s a HOLLEY carb tips thread posted up near the start of this street section, it might be a good time to start Thumbing thru it.

__________________
I do stuff for reasons.
  #9  
Old 05-24-2022, 05:30 PM
ta man ta man is offline
Ultimate Warrior
 
Join Date: Apr 2006
Location: Clinton,Ontario,Canada
Posts: 5,348
Default

What does your fuel system consist of? Line sizes and fuel pump. What carb?
A weak coil can also cause the same symptoms.

__________________

466 Mike Voycey shortblock, 310cfm SD KRE heads, SD "OF 2.0 cam", torker 2
373 gears 3200 Continental Convertor
best et 10.679/127.5/1.533 60ft
308 gears best et 10.76/125.64/1.5471

Last edited by ta man; 05-24-2022 at 05:53 PM.
  #10  
Old 05-24-2022, 07:22 PM
64speed's Avatar
64speed 64speed is offline
Ultimate Warrior
 
Join Date: Jul 2003
Location: Westminster S.C.
Posts: 6,025
Default

Well I dont know what you considered idled fine but this thing is pretty rowdy so its hard to tell whats smooth and whats not. It smoothed out a little I guess but it didnt turn into a Caddy. It has ALWAYS free revved fine, even when the plugs were black. I put 65 miles on it today. Seems to be better. If it does it again I will explore further. After driving I pulled a plug and they seem to be fine too although I am no expert at reading plugs they arent black like the ones I took out. Man you gotta cut me some slack, EVERYTHING on this car is new. Not a damn part but the seats and steering wheel and speedometer and gas gauge was reused and they were recovered,recast, and rebuilt. I do not have it sorted out totally and I wont for a long time. It may leave me on the side of the road tonight but right now the Holley tech said adjust the idle mixture screws, I did, it runs. I do have a spare coil I will carry with me in case thats what it is. I just took my wife to the parts store with me to return some stuff from the flywheel swap and scared the hell out of her at how fast it is and its still under break in, I gave it like 2/3 throttle.

__________________
468/TKO600 Ford thru bolt equipped 64 Tempest Custom. Custom Nocturne Blue with black interior.
  #11  
Old 05-24-2022, 09:02 PM
NeighborsComplaint's Avatar
NeighborsComplaint NeighborsComplaint is offline
Ultimate Warrior
 
Join Date: Aug 2009
Location: Elgin
Posts: 2,468
Default

1/4 turn wouldn't really do anything. That's your mixture at idle with the throttle plates closed. It really has little to no effect once your throttle plates are into the transfer slots off idle.

__________________
Triple Black 1971 GTO
  #12  
Old 05-24-2022, 09:11 PM
64speed's Avatar
64speed 64speed is offline
Ultimate Warrior
 
Join Date: Jul 2003
Location: Westminster S.C.
Posts: 6,025
Default

Quote:
Originally Posted by NeighborsComplaint View Post
1/4 turn wouldn't really do anything. That's your mixture at idle with the throttle plates closed. It really has little to no effect once your throttle plates are into the transfer slots off idle.
So what do you think it could be?

__________________
468/TKO600 Ford thru bolt equipped 64 Tempest Custom. Custom Nocturne Blue with black interior.
  #13  
Old 05-24-2022, 10:32 PM
Bill Hanlon's Avatar
Bill Hanlon Bill Hanlon is offline
Ultimate Warrior
 
Join Date: Feb 2005
Location: Fredericksburg, TX
Posts: 2,349
Default

Quote:
Originally Posted by 64speed View Post
So what do you think it could be?
Don't know, but it'll be back.

__________________
My Pontiac is a '57 GMC with its original 347" Pontiac V8 and dual-range Hydra-Matic.
  #14  
Old 05-25-2022, 10:31 AM
geeteeohguy's Avatar
geeteeohguy geeteeohguy is offline
Ultimate Warrior
 
Join Date: Dec 2009
Location: Fresno, California
Posts: 5,313
Default

Agree that the idle mixture circuit is out of the equation as soon as the throttle is cracked open. It would have nothing to do with crapping out under load. It could be a fuel issue or an ignition issue.

__________________
Jeff
  #15  
Old 05-25-2022, 10:59 AM
Bill Hanlon's Avatar
Bill Hanlon Bill Hanlon is offline
Ultimate Warrior
 
Join Date: Feb 2005
Location: Fredericksburg, TX
Posts: 2,349
Default

Quote:
Originally Posted by geeteeohguy View Post
It could be a fuel issue or an ignition issue.
I'd start with fuel because ignition wouldn't care (much) if under load or not.

__________________
My Pontiac is a '57 GMC with its original 347" Pontiac V8 and dual-range Hydra-Matic.
  #16  
Old 05-25-2022, 11:23 AM
Scott65's Avatar
Scott65 Scott65 is offline
Ultimate Warrior
 
Join Date: Jan 2002
Location: Houston, Texas
Posts: 1,991
Default

Quote:
Originally Posted by Bill Hanlon View Post
I'd start with fuel because ignition wouldn't care (much) if under load or not.
I've found that not to be true always. Low voltage will support no load/light load and bang like crazy under high load.

__________________
'65 Tempest 467 3650# 11.30@120.31
  #17  
Old 05-25-2022, 11:58 AM
64speed's Avatar
64speed 64speed is offline
Ultimate Warrior
 
Join Date: Jul 2003
Location: Westminster S.C.
Posts: 6,025
Default

Fuel pressure is too high and is blowing the needle and seat I think. The problem came back, changed black plugs, went away.

__________________
468/TKO600 Ford thru bolt equipped 64 Tempest Custom. Custom Nocturne Blue with black interior.
  #18  
Old 05-25-2022, 12:16 PM
Scarebird's Avatar
Scarebird Scarebird is offline
Ultimate Warrior
 
Join Date: Nov 2002
Location: ABQ, USA
Posts: 4,998
Default

Quote:
Originally Posted by Scott65 View Post
I've found that not to be true always. Low voltage will support no load/light load and bang like crazy under high load.
A cracked distributor cap will idle and rev perfectly but under load sputter and miss.

You won't see the crack.

The Following User Says Thank You to Scarebird For This Useful Post:
  #19  
Old 05-25-2022, 12:27 PM
Scott65's Avatar
Scott65 Scott65 is offline
Ultimate Warrior
 
Join Date: Jan 2002
Location: Houston, Texas
Posts: 1,991
Default

Quote:
Originally Posted by Scarebird View Post
A cracked distributor cap will idle and rev perfectly but under load sputter and miss.

You won't see the crack.
Yeah, now that you mentioned it, my Dad had that issue once. I was young, but remember it being confounding for him by the vocabulary lesson...

__________________
'65 Tempest 467 3650# 11.30@120.31
  #20  
Old 05-25-2022, 02:10 PM
Scarebird's Avatar
Scarebird Scarebird is offline
Ultimate Warrior
 
Join Date: Nov 2002
Location: ABQ, USA
Posts: 4,998
Default

I was lucky - I worked at a gas station and they had all sorts of spare parts, replaced the cap and voila'

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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

Forum Jump


All times are GMT -4. The time now is 09:21 AM.

 

About Us

The PY Online Forums is the largest online gathering of Pontiac enthusiasts anywhere in the world. Founded in 1991, it was also the first online forum for people to gather and talk about their Pontiacs. Since then, it has become the mecca of Pontiac technical data and knowledge that no other place can surpass.

 




Copyright © 2017