Backfire

[camp upshur]

Nobody has mentioned flat cam lobe yet??
(exhaust lobe)

[GT350AUS]

Don't think so because it runs fine from cold start to cruising. Problem comes up when under harder acceleration. Flat cam lobe would be evident from start up.

[shelbydoug]

Others should be aware that 68s have a different vacuum footprint then other years and potential for weird vacuum issues as a result.

[GT350AUS]

Backfire is gone!!!

Problem was timing and point gap.

Once checked, found the harmonic balancer has  moved on the rubber so the standard readings are useless.

Starts up fine. Runs perfect. Accelerates hard and no backfire or pinging.

Pulls hard as a Jet.... a Cobra Jet!!!!!!

A great Easter present for me.

Now all i need to do is drive it before winter hits here in Australia.

Thanks to all you guys for your suggestions.

[Rbwiii]

Don't think so because it runs fine from cold start to cruising. Problem comes up when under harder acceleration. Flat cam lobe would be evident from start up.

My experience with a flat lobe is it starts and idles fine, revs fine, when you drive it, give it gas and put a load on it, it feels like a miss fire , or runs like crap....no back firing in my experience.

[Rickmustang]

Post 7. Timing 😁

[GT350AUS]

Yep you were right but timing marks gave the wrong reading and point gap had to be reduced from standard due to movement in the dizzy shaft.

All in all a great result and good info for anyone else chasing a difficult to diagnose problem.

That's the benefit of this forum.....

[corbins]

Yep you were right but timing marks gave the wrong reading and point gap had to be reduced from standard due to movement in the dizzy shaft.

All in all a great result and good info for anyone else chasing a difficult to diagnose problem.

That's the benefit of this forum.....

Now all you have to do is go out and buy a new balancer and dizzy

[Shane]

Yep you were right but timing marks gave the wrong reading and point gap had to be reduced from standard due to movement in the dizzy shaft.

All in all a great result and good info for anyone else chasing a difficult to diagnose problem.

That's the benefit of this forum.....

Thanks for sharing the cause and outcome, especially since this is not on the shortlist for most!

[1967 eight barrel]

So the root cause is a rotten elastomer strip that allowed the outer damper ring to slip?  I have seen it a couple times.  I didn't think about points as most of us have got away from them. Especially those with dual points. I'm glad you have it sorted and can enjoy it before it gets put away for the season.
                                                                       -Keith

[GT350AUS]

Spot on Keith.

Starts first kick every time nw and I can enjoy the drive before the weather turns sour.

Thanks again

Ross

[1967 eight barrel]

I'm glad you're not dealing with my issue.  Machinist that don't know their way around an FE and the common core shift  issues.
It's an expensive proposition to do right.
                                                                    -Keith

[Bob Gaines]

I would like to know how you determine slippage of the outer ring ? Was it crooked or other distinguishing factor?

[shelbydoug]

This is a common occurrence these days on Fords which largely have un-bonded rings.

I haven't looked at any in a while but I seem to remember that the Clevelands have a cut notch in the ring that is keyed to the crank key.

There are a few exceptions. My Boss 351 for instance has a bonded ring. That probably is because of the expected higher rpm use and the greater mass of the ring.

The 427 Fords are similar but not as massive as the Boss balancers. I can't remember the exact weight right now but the ring is two inches thick. That's in most cases twice as thick as a 4v balancer and considerably thicker then my 67s ring.

The plus of this is that they are all "re-buildable" and bondable. If you are building an engine now with a used balancer it would be highly advisable to send them out to have rebuilt for high performance use.

[1967 eight barrel]

The 427 and 428PI  weigh in at about 18 lbs. Both have an incorporated single groove pulley. The PI has the beveled edges  and timing marks where the 427 damper simply has small v groove on the front edge of the pulley. They are about 7 X 2.2" and is  massive. To my recollection they weigh more a Boss 351 damper.
The are the heaviest harmonic damper I have seen. Interestingly enough I was surprised that it wasn't chosen for use on the CJ nor the SCJ. Both wound up with the thinner FE damper and the SCJ wound up with the small counterweight in place of the spacer.
                                                                                            -Keith