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Timing, fuel delivery vacuum leak??

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75Cj5 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75Cj5 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2021 at 10:04am
Originally posted by BassBoat BassBoat wrote:

A common problem with Holley carburetors is a backfire will damage the power valve.  I'm guessing somewhere along the tuning you got it too lean and blew the power valve.  With the power valve blown it is open all the time, adding fuel for wide F open whether you are or not.  A test to see if power valve is blown is to turn the idle mixture screws all the way in.  If it doesn't die, the power valve is bad.  I have had more frequent problems with power valves even without a backfire which I blame on the inferiority of gasoline with ethanol. This sounds very possible and I will check this once it is button back up and "running", I have only put in ethanol free fuel... now that brings up another question.. it is 93 octane.... would that cause any issues?
Secondly the HEI distributors are notorious for failing distributor gears.  I just bought a 304 car that had bad distributor gears and some of your symptoms are familiar.  Goes from running pretty good, to popping and backfiring.  My problem was the distributor would jump a tooth or two, and I chased the timing for a while before I pulled the distributor to rebuild and recurve.  The gear damage was then obvious.  Hope that isn't your problem.  There is no damage to the gear so I will assume I am good on that... it does sound like it could pass for the same problem though.
My distributor gear failed because the timing sprocket bled off all of the oil that is supposed to lubricate the distributor gears.  As my dear friend Phat said, "of course its the timing gear (bleeding off oil) they haven't made one right in 20 years".  So if you take the timing cover off again, delete the slots on the timing sprocket. By chance do you have any visual reference you can share on this? I have noticed there is oil on the timing gear when I remove the distributor so it might be alright..?
good luck.

Thanks you!


Edited by 75Cj5 - Apr/12/2021 at 1:33pm
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iapexl8r View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iapexl8r Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2021 at 1:29pm
bass boat mentioned the power valve. this may be a problem, but most newer (as of 1995) have have  power valve protection built in them.

        once you get the motor to idle,  you can time the motor to total mechanical advance. assuming you have a timing light with an adjustment for advance.. to do this you would dial in 32 deg (thats what I would do for your set up) ) on the timing light, run the rpms up until the mark in the harmonic balancer stops moving and then rotate the dist to line up the harmonic balancer mark  to the zero mark on the timing chain cover . basically what you are doing is opening up the flyweights in the dist via centrifugal force and setting the timing there. then take not of where you started timing at idle.

on another note how much are the timing marks moving around at idle?
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75Cj5 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75Cj5 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2021 at 1:50pm
Originally posted by iapexl8r iapexl8r wrote:

bass boat mentioned the power valve. this may be a problem, but most newer (as of 1995) have have  power valve protection built in them.

        once you get the motor to idle,  you can time the motor to total mechanical advance. assuming you have a timing light with an adjustment for advance.. to do this you would dial in 32 deg (thats what I would do for your set up) ) on the timing light, run the rpms up until the mark in the harmonic balancer stops moving and then rotate the dist to line up the harmonic balancer mark  to the zero mark on the timing chain cover . basically what you are doing is opening up the flyweights in the dist via centrifugal force and setting the timing there. then take not of where you started timing at idle.

on another note how much are the timing marks moving around at idle?

I am using an Innova inductive timing light.... Should I look at upgrading this? The DUI Distributor manufacture recommended finding an older dial in timing light.

Any time I could ever get the engine to run smooth and perform close to normal the timing mark would hit very consistent at idle, HOWEVER, also at idle the mark would be at approximately the 8 O'clock position as if you were standing directly in front of the balancer facing it. 


Edited by 75Cj5 - Apr/12/2021 at 1:33pm
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75Cj5 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75Cj5 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2021 at 2:19pm
Talking about the power valve reminded me of something that might be very key in this... Sorry this is just coming to mind... 

when the engine idles it pops through the carb, if I am able to bring up the RPM's the popping will reduce and subside until it is brought back to idle.
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PacerLarry View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PacerLarry Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2021 at 4:03pm
Just a thought, are you hooking the timing light up to the #1 wire (drivers side) and not #2 by mistake? 
#2 fires just before #1 and the timing light would indicate a lot of advance when the motor is running smoothly like you said was happening. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote iapexl8r Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2021 at 8:41pm
The Inova timing light comes in many different varieties, if yours has a dial or a digital screen, it is fine. If it has neither you will probably need to upgrade 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PHAT69AMX Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2021 at 9:52pm
Triple check and make absolutely sure Plug Wires #5 & #7 are not crossed or swapped at the plugs and/or at the cap...  I did it more than once... .
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75Cj5 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75Cj5 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/08/2021 at 8:23am
Originally posted by PacerLarry PacerLarry wrote:

Just a thought, are you hooking the timing light up to the #1 wire (drivers side) and not #2 by mistake? 
#2 fires just before #1 and the timing light would indicate a lot of advance when the motor is running smoothly like you said was happening. 

I have it on the driver side front plug wire, and trying to keep it clear of the other wires as well. 


Edited by 75Cj5 - Apr/12/2021 at 1:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75Cj5 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/08/2021 at 8:25am
Originally posted by iapexl8r iapexl8r wrote:

The Inova timing light comes in many different varieties, if yours has a dial or a digital screen, it is fine. If it has neither you will probably need to upgrade 
https://youtu.be/dRA4_7N7rSc - https://youtu.be/dRA4_7N7rSc 

Ok, mine just has the on/off button. 


Edited by 75Cj5 - Apr/12/2021 at 1:34pm
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75Cj5 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 75Cj5 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/08/2021 at 8:29am
Originally posted by PHAT69AMX PHAT69AMX wrote:

Triple check and make absolutely sure Plug Wires #5 & #7 are not crossed or swapped at the plugs and/or at the cap...  I did it more than once... .


Will do Sir.

Just to confirm, my manual shows this as the firing order: 1-8-4-3-6-5-7-2

Fire wall / back

8 7
6 5
4 3
2 1

distributor cap / front 


Edited by 75Cj5 - Apr/12/2021 at 1:34pm
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