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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 Topic: Timing, fuel delivery vacuum leak??
    Posted: Apr/05/2021 at 10:27am
I am a new member and would like to first thank all of you for taking the time to read my post. I have had a challenging time getting my 304 up and running correctly. I am going to try to explain my issues without boring the life out of you.

1975 Cj5- AMC 304 - Stage 2 Cam - Edlebrock Performer intake - DUI Distributor - Long tube Hedman Headers - (Holley) Brawler Carburetor 600 cfm (vacuum advance) - everything else is stock.

Upon initial startup from complete rebuild I could never get the timing mark to line up in and consistent manner with a timing light.  I timed it by ear and by how the engine performed and it was almost perfect. Easy to start and good drivability. It did have some lag when accelerating, this is when it all went down hill. 

I tried to do a little carb tuning and when I put the vacuum gage on it held steady at "wrong valve timing" at idle but it I revved slightly it would be in the green. (I figured this was ok since the cam is slightly bigger and the carburetor might be a tad too big for this motor. 

Once I started making small adjustments with the mixture screws and the timing again things went south... I now have a popping in the carburetor and it will not go away, nor will it get even close to starting easily or idling nicely as before. (my spark plugs foul in a matter of minutes, even when I try to lean the carb out as far as possible)  

I had checked, rechecked and checked again that the motor was set at TDC correctly and every time I had myself convinced I screwed up and set it wrong... Each time it check out correct...

Yesterday I took the timing cover off to check yet again that TDC is correct. When I clock the cam gear at 3 o'clock I have 21 pins from the dot on the cam gear to the dot on the crank gear.  The manual says this is acceptable but is it really??

I did not complete a full inspection of all the push rods yet but felt of them and there does not seem to be any anomalies there yet. 

The only other thing I have yet to think of was my fuel delivery, I have a small Holley electric fuel pump that I tested and without the engine running it is pushing close to 7 psi.  I have the Holley Red fuel pump coming in today and plan to switch those out...

It really feels like a timing issue to me but from what I can tell everything is set in accordance with the manual... I'm at a loss.... 
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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/05/2021 at 9:10pm
The first thing I would do is take a look at the mechanical fly weights in the distributor. Make sure the springs are of the same weight. 
Also are you checking the timing with the vac advance vacuum line disconnected?
Also Re verify firing order just for kicks.

On the carb side of things verify the float level first
Then run those mixture screws all the way in softly till they stop then back them out 2 turns . Now I suspect you may be checking the eng vacuum at a ported pick up point. You want to be checking the vacuum off the manifold vacuum. All vacuum is not created equal.
If your manifold vacuum is too painful to acquire you can adjust the mixture screws to highest idle as you back the throttle stop out.

My guess is it is something simple . Float level and mech advance. Good luck
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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/06/2021 at 8:18am
Originally posted by iapexl8r iapexl8r wrote:

The first thing I would do is take a look at the mechanical fly weights in the distributor. Make sure the springs are of the same weight. Done, they are correct.
Also are you checking the timing with the vac advance vacuum line disconnected? Yes, disconnected and plugged (Plugged on the carb side).
Also Re verify firing order just for kicks. I have done this a few times but will absolutely do it again.

On the carb side of things verify the float level first. As per the carb manual the sight windows show the fuel level right in the middle, while it is running.
Then run those mixture screws all the way in softly till they stop then back them out 2 turns . Now I suspect you may be checking the eng vacuum at a ported pick up point. You want to be checking the vacuum off the manifold vacuum. All vacuum is not created equal. I have attached a pic, the vacuum port I use is circled in green, The first time I had it running well the screws were out quite a bit.
If your manifold vacuum is too painful to acquire you can adjust the mixture screws to highest idle as you back the throttle stop out. If I am not checking the vacuum in the correct spot please let me know the best place.

My guess is it is something simple . Float level and mech advance. Good luck

I feel the same but it is very evasive, thank you for the reply. If I have any changes I will post.

Well I tried to add a pic...  maybe I'm too new?


Edited by 75Cj5 - Apr/12/2021 at 1:35pm
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Heavy 488 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 9:01am
Is this a new DUI with the rebuild or was it used prior?
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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/06/2021 at 9:17am
Originally posted by Heavy 488 Heavy 488 wrote:

Is this a new DUI with the rebuild or was it used prior?

It is a new DUI sir.
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Heavy 488 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Heavy 488 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 9:37am
Are you connected to the stock power feed with the resistance wire or are you on a full 12 volts?. 
Brand new chinese parts doesn't always mean fully functional either.
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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/06/2021 at 12:40pm
Originally posted by Heavy 488 Heavy 488 wrote:

Are you connected to the stock power feed with the resistance wire or are you on a full 12 volts?. 
Brand new chinese parts doesn't always mean fully functional either.

I have a new wire harness (Painless) and used the coil power wire that shows to have 12V with the ignition on as the power feed.
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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/06/2021 at 8:17pm
Ok the vac port you should be checking vacuum from is listed in the instructions as full manifold vacuum. As seen here https://static.summitracing.com/global/images/instructions/qft-199r11202.pdf . It looks like it is the inner of the two fittinGs.
 One other thing that came to Mind Is.what did your distributor gear look like when you pulled it?
Does your engine have a good ground strap? 
Which harness did you put in the car? If you have a voltmeter check to verify 12 volts at coil.
1.5 to two turns out is a standard starting point for mixture screws on every carb I have ever messed with.
-chris

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BassBoat View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BassBoat Quote  Post ReplyReply Direct Link To This Post Posted: Apr/07/2021 at 8:55am
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.
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 familar.  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.  
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 teh timing sprocket.
good luck.
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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 9:57am
Originally posted by iapexl8r iapexl8r wrote:

Ok the vac port you should be checking vacuum from is listed in the instructions as full manifold vacuum. As seen here  https://static.summitracing.com/global/s/instructions/qft-199r11202.pdf - https://static.summitracing.com/global/images/instructions/qft-199r11202.pdf . It looks like it is the inner of the two fittings. Ok this is NOT where I checked the vacuum, once i get it buttoned back up I will use this port. thank you!
 One other thing that came to mind is what did your distributor gear look like when you pulled it?
Does your engine have a good ground strap? The gears look good, there is good grove contact visibility, I will also double check the ground straps but last check they were making good bare metal contact from block to frame.
Which harness did you put in the car? If you have a voltmeter check to verify 12 volts at coil.  It is Painless P/N 10101, I have power to the coil but I have not checked the actual coil other than confirming the spark plugs were firing and they do.
1.5 to two turns out is a standard starting point for mixture screws on every carb I have ever messed with. This have been my starting point at each attempt 1-1/2 from seat. I have slowly worked my way in and out to the point I was scared they were going to fall out and to the point the engine wants to die.
-chris

Thank you Chris!



Edited by 75Cj5 - Apr/12/2021 at 1:36pm
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