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Sparkiewalt 08-23-2013 03:26 PM

351 Cleveland popping when accelerating
I have a 1973 Mustang grande with a 351 cleveland 2v engine and automatic 3 speed tranny. It has headers, a 4 barrel vac secondary summit 750 carb and weiand alum intake. All this was on the car when i got it. It did not pop then. Both header gaskets were leaking and needed replacement, which I did.

I replaced plug wires with street fire spiral 8MM from oriellys. And a new set of plugs accel 0576S-4 with a 045 gap. It started the popping after I fixed the intake gasket which was blown out when I got the car. I am pretty sure I put the distributor back just like it was. The car has a GM HEI distributor. The weird thing is when I went to check the timing I have to connect my light to the number 5 cylinder to line up with the marks on the harmonic balancer. I am not sure how this happened.

Any way the engine cranks and runs great and it has good power, I can do a good burn out. but when I give it hard to mid range acceleration it starts a slight popping sound that is worse at first then almost goes away after I build up some speed. The pops have about a 1 sec interval. The distributor cap and rotor seem to be in fairly new condition.

The popping is not as bad since I changed the plug wires and plugs. timing set a 6 BTDC is better than 10 BTDC. 2 BTDC is about the same as 6.

67mustang302 08-23-2013 04:22 PM

You need to verify the timing marks on the balancer first. Sounds like the timing could be way out.

Sparkiewalt 08-23-2013 06:53 PM

If the timing was way out the engine would not run correct??

dawson1112 08-23-2013 07:07 PM

Those HEI distributors will run even if the plug wires are mixed up.

IF you have to have the timing light on the number 5 wire to light up on the mark then you likely have the dizzy out 180. I know its messed up but those hei dizzys will jump spark all over inside that cap.

Bring the number one cylinder up to TDC pull the cap and see where the roter is pointing I would bet you are way out. .
There is no way you should have to clip the number 5 wire to read timing.

Sparkiewalt 08-23-2013 08:50 PM

So you are saying that my engine will run and produce full horse power with the timing 180 degrees out???

67mustang302 08-23-2013 09:01 PM

If it's misfiring to other cylinders, it's possible. It would act like a DIS wasted spark system, fire to multiple cyl at once, and only 1 of them makes power.

HEI's seem to cause a lot of problems for a lot of people.

dawson1112 08-23-2013 09:03 PM


Originally Posted by Sparkiewalt (Post 8270983)
So you are saying that my engine will run and produce full horse power with the timing 180 degrees out???

I don't know.. I know that my gmc pick up with a 350 ran when the wires were all mixed up . The HEI dizzy jumps spark all over . Are you getting full hp ? I don't know.

I do know that if you only able to see the timing mark using the number 5 wire something is way off.

The biggest clue is that you say you are pretty sure the dizzy was put back in the way it came out.

Verify this by bringing numer 1 up to tdc and see where the rotor is pointing. You either didn't get it stabbed right or the wires are all mixed up .

boogerschnot 08-24-2013 12:43 PM

Just pull the number one plug and rotate the engine by hand to verify. Either way, the things timing is definately off somewhere. You shouldnt be running at 2btdc. Does the popping sound like marbles in a tin can?

Sparkiewalt 08-24-2013 08:19 PM

The popping sounds like a small back fire. I took the timing chain off, it was pretty slack, I am going to replace it with a Zoom double roller set. But when I took off the valve covers I think I may have found some real problems, both the 6 and 8 had loose rockers. The previous owner "rebuilt" the heads so he said. I hope he did a better job on the valves than He did on the rockers.

Sparkiewalt 08-24-2013 09:18 PM

I will re-time the engine correctly and see what happens.

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