Back firing

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superbond
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Joined: 17 Feb 2017, 06:03

Back firing

#1

Post by superbond » 07 Apr 2018, 14:20

So I don’t know if any of you have followed my motor rebuild issues. And if you have and replied thank you.
Well here we go again. Rebuilt my 72 351 Cleveland 2v again and converted it into a 4v. After having oil coming out of the exhaust with the first rebuild it look like it was a manifold gasket problem.
So fast forward to the second rebuild of this motor. Again it looks like the manifold gasket is leaking a bit not as bad as las time. But that is not my problem right now. My problem is the motor is back firing out the driver side exhaust. I don’t have crossover on my exhaust. So you can hear a popping sound coming from the driver side exhaust. Pop pop pop pop! It seem to be getting worse.
Anyone know what it could be?
I’m thinking maybe either my carb/manifold or distributor.
I have a aluminum edlebrock performer and a Holley 600 with vacuum secondary’s. Distributor is stock with a electronic upgrade

superbond
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Re: Back firing

#2

Post by superbond » 07 Apr 2018, 14:22

When I was driving it for the first time after the rebuild it was good but as it sat in the garage for a month or two it’s acting up and seems to be getting worse every time I start it up

superbond
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Re: Back firing

#3

Post by superbond » 07 Apr 2018, 14:25

Was thinking of putting it back to points to laminate ignition. The carb is new but it did back fire a few time with the first start up after rebuild. Distributor was out 180

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1969XR7Vert
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Re: Back firing

#4

Post by 1969XR7Vert » 07 Apr 2018, 18:10

Butch,

Was the cam/lifters you used already broken in and re-used (with the lifters in the same position I hope) or a new cam? Guessing the former. Did you use a ZDDP additive or oil with zinc (you have a flat tappet hydraulic cam, correct?)? If no to any of the above, take the PS valve cover off and see if any of the rockers are moving less than the others. If yes, you wiped out a cam lobe or three. Sorry to hear of your continued troubles, hope this helps.

Regards,

Robert
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Canted--Texan on the351cforum: "One of my most impressive attributes is that.......a lot of people don't like me.....or the horse I rode in on"

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catlover
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Re: Back firing

#5

Post by catlover » 08 Apr 2018, 08:32

To follow up on Bob's reply, you could just have a valve too tight.
There is never time to do it right, but always time to do it over

67 Cougar restomod
69 Elim. 428 SCJ orange/ white
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superbond
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Joined: 17 Feb 2017, 06:03

Re: Back firing

#6

Post by superbond » 09 Apr 2018, 09:19

I did put the used cam in and lifters in the exact spot. The only thing I changed was I put new push rods in. They were the same length and were straight.
It just seems like the issue is getting worse every time I start it up.
I torqued the rocker arms to 11-14 ft pounds with lock tight.
I’m going to switch to my old points and see if that helps

0F94M
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Location: St. Clair Shores, Michigan

Re: Back firing

#7

Post by 0F94M » 09 Apr 2018, 14:07

I would perform a compression check before continuing... maybe a valve ( or valves) are not closing. This would show up as no compression in that cylinder.

superbond
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Re: Back firing

#8

Post by superbond » 09 Apr 2018, 18:55

What would make the valves not close?

0F94M
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Joined: 07 Nov 2016, 08:07
Location: St. Clair Shores, Michigan

Re: Back firing

#9

Post by 0F94M » 09 Apr 2018, 19:10

Pushrods too long, rocker arms adjusted too tight (if adjustable)

0F94M
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Location: St. Clair Shores, Michigan

Re: Back firing

#10

Post by 0F94M » 09 Apr 2018, 19:29

Pushrods too long, rocker arms adjusted too tight (if adjustable) would be 2 reasons... compression test would be my first step here: if it checks out, then you can start chasing down ignition and carb problems. If compression check is bad, there is an internal engine, cam, cam timing problem. Also double check your firing order.

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