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Cameo Ivory 1967
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Discussion Starter · #21 ·
I think you are a bit lean lean Army. Yes rich can do it also. But lean is more common. At cruise with a light pedal you are getting a lot of timing which you need to burn the lean cruise mixture. But yours may be a tad too lean for your setup.

when you slowly push the clutch down you also slowly “Decrease the load” on the engine by letting your foot off the gas pedal. Youkinda work those feet at the same speed. When you clutch easy your foot comes up easy andwhen you shift hard your foot comes up fast.

So depending on the speed where this happens an enrichment of that carb circuit may be called for.

say at 3000 Rpm you are at 60 mph light throttle. That will be on your main jets and idle circuit. ( because idle circuit never really stops, it is just overdone by th email jets.

then I would increase the main jets two sizes and see if the after fire changes.…then see what the AFR is if it is gone.
Ive always (for decades) kept my AFR's on the lean side (as you may or may not recall). But the manual trans exploited it, so I did bump up two stages richer, earlier in the week, but then the new exhause went on, so I'll pay close attention to the AFR's.

It's definitely in the 13's, but it has four mufflers now. I also am battling a s slight header gasket leak, at the head... so lean would make sense.
 

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It's happening because you changed to a stick and are now closing the throttle between shifts. Which means higher intake vacuum and richer mixture, temporarily. You may have a slight exhaust leak, and the combination of combustible fuel in the pipes and added O2 from the exhaust leak= BOOM. I remember a lot of stick cars I worked on in the early 80's had de-cel valves on the carbs which delayed the throttle closure on let-off just to keep emissions from getting too rich. Annoying to drive, as the rpm 'hangs' for a bit on the shifts.
In your case, I would verify exhaust leaks. My old stick GTO's and Corvette don't backfire between shifts. Yours shouldn't either.
 

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Discussion Starter · #27 ·
Was the exhaust "quiet" before the cam change?
There was noticable difference in the heartbeat, between the two cams, but no, the exhaust has always been far too quiet for me, before and after.

My new exhaust still maintains a humble idle, but now you know that its angry. Before it just sounded tame.

Videos will be up soon.
 

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Discussion Starter · #28 ·
It's happening because you changed to a stick and are now closing the throttle between shifts. Which means higher intake vacuum and richer mixture, temporarily. You may have a slight exhaust leak, and the combination of combustible fuel in the pipes and added O2 from the exhaust leak= BOOM. I remember a lot of stick cars I worked on in the early 80's had de-cel valves on the carbs which delayed the throttle closure on let-off just to keep emissions from getting too rich. Annoying to drive, as the rpm 'hangs' for a bit on the shifts.
In your case, I would verify exhaust leaks. My old stick GTO's and Corvette don't backfire between shifts. Yours shouldn't either.
Here's my only data:

I put 2000 miles on the manual, with no afterfire. My 70 Vette had none either.

I put 50 miles on the car, the night before I did the exhaust, and it was missing the front two driver side header bolts the entire time... it didnt afterfire at all. Ive since replaced the bolts, but not the gasket...

Which leads me to believe (but not sure) that it's being caused by my new exhaust mods.

I opened the cutouts and then added a 17" long piece of 2.5" pipe, with homemade baffles inside them, and then resonators on the end. They're just prototypes at this point, but they did what I wanted them to do.
Gas Cylinder Auto part Metal Wood

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Here's my only data:

I put 2000 miles on the manual, with no afterfire. My 70 Vette had none either.

I put 50 miles on the car, the night before I did the exhaust, and it was missing the front two driver side header bolts the entire time... it didnt afterfire at all. Ive since replaced the bolts, but not the gasket...

Which leads me to believe (but not sure) that it's being caused by my new exhaust mods.

I opened the cutouts and then added a 17" long piece of 2.5" pipe, with homemade baffles inside them, and then resonators on the end. They're just prototypes at this point, but they did what I wanted them to do.
View attachment 153489
View attachment 153490
I've never had after fire on my 4spd even with the cutouts open that are right before the muffler. Probably due to the vacuum leak and that the exhaust exit is so close to the motor maybe.
 

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Discussion Starter · #30 ·
Well it's interesting that I did put beefier springs on the needles, the day before.

On the Eddy carbs, you can externally swap needle springs, to cater your transition to your engine vacuum. I put the heaviest spring in there, which means at low vacuum, my mains are wide open... I should look at my vac gauge when it's firing and see if that might be it.

But I assume Im at high vacuum when shifting at cruise, so that wouldnt be it. Tonight I can test!
 

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I was going to email you a clip so you could use it as your doorbell. It's incredible how quiet it is inside the car. The baffles that I put inside the cutout almost work too well
Keep in mind that the cut-outs are not a diverter valve sending all the exhaust out the cut-out pipes. Some exhaust/sound still flows out the mufflers and tail pipes. Maybe you should just go with uncapped headers...............ah, never mind, you'll just insist that they aren't loud enough.

Got an idea, however. I am willing to post a "Go-Fund-Me" page for you so we can buy you a set of hearing aids and then you can hear how loud the exhaust really is. Whatta ya say???? ;)
 

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Discussion Starter · #38 ·
Keep in mind that the cut-outs are not a diverter valve sending all the exhaust out the cut-out pipes. Some exhaust/sound still flows out the mufflers and tail pipes. Maybe you should just go with uncapped headers...............ah, never mind, you'll just insist that they aren't loud enough.

Got an idea, however. I am willing to post a "Go-Fund-Me" page for you so we can buy you a set of hearing aids and then you can hear how loud the exhaust really is. Whatta ya say???? ;)
Yes as the video points out, there's a substantial and equal volume of exhaust coming out the tail pipes! And as I showed, my cutouts are not just open pipe... they are essentially additional mufflers.

Do you guys really think it's loud? Yes I know that riding a Harley and being a performing bass player for 35 years, has taken it's toll on me, but every Chevelle and Mustang I hear is sooooo much louder.

In the world of muscle cars, people use sound to determine what is the baddest, and Im tired of silently creeping through these car shows, where everyone stares to see the cool GTO, and then struggles to hear it over the Mustang.
 

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Yes as the video points out, there's a substantial and equal volume of exhaust coming out the tail pipes! And as I showed, my cutouts are not just open pipe... they are essentially additional mufflers.

Do you guys really think it's loud? Yes I know that riding a Harley and being a performing bass player for 35 years, has taken it's toll on me, but every Chevelle and Mustang I hear is sooooo much louder.

In the world of muscle cars, people use sound to determine what is the baddest, and Im tired of silently creeping through these car shows, where everyone stares to see the cool GTO, and then struggles to hear it over the Mustang.
You are running 3" pipes, right?

Compression ratio, cam specs, and overall HP will make a louder sound. The position of the muffler will change sound. Place your mufflers right at the end of the headers or thereabouts and see what happens. Did that on a stock '54 Buick and then had turn downs. Was enough to get pulled over for loud exhaust. My 409 had factory cast exhaust manifolds that were very streamlined for 1965, then ran 3" pipe, turbo mufflers, and then a 4" pipe just past the rear axle put to the bumper. You could here the car coming 1/2 mile away, and so could the cops. They would challenge me and I'd tell them it is legal - mufflers & tail pipes. They would always suggest a resonator.

Think about the "big rigs" with their 4", 6", and 8" stacks how loud they are with no mufflers compared to the guy who simply removes the muffler and runs a connector pipe in place of the muffler - no comparison in sound as the larger pipe guys drown him out.

Pontiac's are not "other" makes. Each manufacturer engine has its own sound and sound level. Hmmm, how can I get my Honda motorcycle to sound like that Harley with straight pipes. I know, I'll install a Kerker Header and pipes and it'll sound better than a Harley - NOT.

Have you not ever heard a Harley that was a street bike as opposed to one with an S&S built engine - apples & oranges in sound.

You are chasing after the Holy Grail and not going to find it. You are putting a lot of effort & time into your system and coming up empty. Pull that Pontiac engine and drop in an old school Big Block Chevy LS7 and I think you will have the sound you are looking for. (y)

In the meantime, check out this video:


AND, if all else fails, you can install these to the tail pipes:

 
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