Need help with engine problem - Pontiac GTO Forum
User Tag List

 2Likes
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 22 (permalink) Old 09-28-2019, 10:49 AM Thread Starter
 
Join Date: May 2012
Location: River Ridge,La.
Posts: 14
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Need help with engine problem

I have 389 tri-power.On the way home from a cruise night i goosed it a few times playing with a Mustang and as i got to the next stop light the engine died. It cranked up and ran fine to next light and died again. It cranked up, ran fine to next light as i stopped the RPM's would just keep dropping.{Like when you unplug vacuum but keeps dropping till dies].I had to turn idle screw up to keep it idling.I tapped on center carb,checked timing,checked for vacuum leaks,all was ok. Out of nowhere it started idling fast and i set idle screw back. A few weeks later i had to move it out of shop,all seemed ok. When i cranked it to put back in shop it wouldn't idle again with out setting idle screw up.I never know when it will die at idle or be idling too fast.I changed PVC valve and that didn't help.One guy says its the fuel pump and another says no its not fuel pump.Need help on what may be the problem. Seems to run fine except for this problem.
Thanks,
Larry
mcguiremcd is offline  
Sponsored Links
Advertisement
 
post #2 of 22 (permalink) Old 09-28-2019, 01:21 PM
 
Join Date: Jul 2016
Location: North Louisiana
Posts: 592
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 65 Post(s)
Is there a choke on that center carb ?

Sorry !'m not familiar with Tri-power carbs.

I do know that some Q-jets have a high idle screw, connected to the choke. It's supposed to hold butterflies open enuff to idle, when cold, then release the butterflies, when engine warms & choke opens completely. The screw adjusts this mechanism. So, there can be some sort of malfunction of the choke mechanism.

Again, this may not apply to your carb.

Since adjusting the throttle screw increases your idle speed, that pretty much rules out a fuel supply to the carb problem, IMO, since if the problem was fuel supply, just turning the screw would not increase fuel supply to the carb.

I just read a post that said when you are chasing an idle problem, it's best to remove the end carbs & seal off the holes with block plates. Then solve your idle problem BEFORE putting the end carbs back on. Sounds reasonable to me.
bigD is online now  
post #3 of 22 (permalink) Old 09-28-2019, 02:59 PM
 
Lemans guy's Avatar
 
Join Date: Oct 2014
Location: Nashville, Tennessee
Posts: 728
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 68 Post(s)
I would check for any vacumn leaks at base of carb or intake runners,.....squirt some carb cleaner around base of carb and intake see if idle speeds up, a smoke machine is better, but however you do it check.

Also make sure your fuel filter is not blocked. I would add a bottle of Redline S1 Complete fuel system cleaner to a full tank of gas, nothing better, and it will help clean any gum or clogs..

Then I would clean the center carb with gumout and like big D said you can block off secondary carbs. Even just tightening the throttle plates up a bit so you have no leaks there

reset the center carb back to basic setting, 1 1/2 turns out throttle to just showing the transfer slot. And begin again.

Sounds like a lean stall at the lights, maybe from a vacumn leak or through secondary carb throttle plates, when you open the throttle screw you are increasing the mixture being pulled through,

It is faster more vacumn pulling through the idle and transfer slots and it overcomes the leaner mixture which was stalling.....Maybe

Those are a few things to check, but weak coils and ignition can cause similar stalling. To start with I would be working with the mixture and if the car sits a lot the gasoline phase separates and water makes for poor running. That is where that Redline will help.

Also make sure your choke linkage is not sticking, causing a stall and then causing it to run fast it can do both if it sticks.

You will get it!
Lemans guy is online now  
 
post #4 of 22 (permalink) Old 09-28-2019, 11:37 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,646
Mentioned: 1 Post(s)
Tagged: 1 Thread(s)
Quoted: 390 Post(s)
Garage
Quote:
Originally Posted by mcguiremcd View Post
I have 389 tri-power.On the way home from a cruise night i goosed it a few times playing with a Mustang and as i got to the next stop light the engine died. It cranked up and ran fine to next light and died again. It cranked up, ran fine to next light as i stopped the RPM's would just keep dropping.{Like when you unplug vacuum but keeps dropping till dies].I had to turn idle screw up to keep it idling.I tapped on center carb,checked timing,checked for vacuum leaks,all was ok. Out of nowhere it started idling fast and i set idle screw back. A few weeks later i had to move it out of shop,all seemed ok. When i cranked it to put back in shop it wouldn't idle again with out setting idle screw up.I never know when it will die at idle or be idling too fast.I changed PVC valve and that didn't help.One guy says its the fuel pump and another says no its not fuel pump.Need help on what may be the problem. Seems to run fine except for this problem.
Thanks,
Larry

Flooding.
PontiacJim is offline  
post #5 of 22 (permalink) Old 09-29-2019, 10:53 AM Thread Starter
 
Join Date: May 2012
Location: River Ridge,La.
Posts: 14
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Choke seems fine.
Fuel supply makes since.thanks
I have the end carbs unhooked but like the idea of blocking off.
Thanks
mcguiremcd is offline  
post #6 of 22 (permalink) Old 09-29-2019, 11:01 AM Thread Starter
 
Join Date: May 2012
Location: River Ridge,La.
Posts: 14
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Thanks guys for all the info.
Post above for BigD. I'm still working on how all works on here.
Not the best with computors.
Will look at all things mentioned.
mcguiremcd is offline  
post #7 of 22 (permalink) Old 09-29-2019, 12:45 PM
Super Moderator
 
BearGFR's Avatar
 
Join Date: Aug 2008
Location: Springtown, TX
Posts: 5,742
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 122 Post(s)
Garage
Check and verify your float levels in all 3 carbs. Make sure the pivots/hangers for all the floats are installed correctly and are situated how they're supposed to be. If you're not sure about the condition of your needles, and seats - consider replacing them in case they're leaking. If you've got brass floats, check them for leaks (pull them out and shake them - listen for sounds of gasoline inside them. Submerge them in a container of gasoline and look for bubbles.) If you got polymer floats, look for signs of nicks cracks that might be allowing them to soak up fuel and sink. If all that checks out ok, check your fuel pressure at the carb inlets. If it's too high it can force the needles open and allow flooding.

I'm a big fan of using wide band air/fuel meters, either permanently installed or one of the hand-held types like the ones from Innovate. Knowing for certain what your air/fuel ratio is under all conditions is extremely valuable information.

Bear

BearGFR
Springtown, TEXAS
BearGFR is offline  
post #8 of 22 (permalink) Old 09-29-2019, 04:46 PM
 
PontiacJim's Avatar
 
Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
Posts: 3,646
Mentioned: 1 Post(s)
Tagged: 1 Thread(s)
Quoted: 390 Post(s)
Garage
Do you have power brakes?
PontiacJim is offline  
post #9 of 22 (permalink) Old 09-30-2019, 09:37 AM Thread Starter
 
Join Date: May 2012
Location: River Ridge,La.
Posts: 14
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Thanks Bear.Will put on list to check. Mike W rebuilt carbs 4yrs and 1300 miles ago.
Jim, no don't have power brakes
mcguiremcd is offline  
post #10 of 22 (permalink) Old 10-02-2019, 05:58 PM
 
Join Date: Nov 2010
Location: Michigan
Posts: 5
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Have you held your hand over the throat of the end carbs while running?
40flier is offline  
Sponsored Links
Advertisement
 
Reply

  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Complete Engine Compartment Discussion

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Pontiac GTO Forum 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 for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 5 (4 members and 1 guests)
1968gto421, David Shuff, Ghostpilot, LATECH
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