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Old 09-03-2012, 01:49 AM   #21 (permalink)
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having same problem with my 12 flstc just joined and was reading your post did you ever fix it? put on bassani slip ons and got a download from harley but still pop pop.. any advice would be greatly appreciated
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Old 09-22-2012, 04:29 PM   #22 (permalink)
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If the slip ons etc reduce back pressure, wouldn't that move the gasses further down stream faster so the popping which I think is unspent fuel occur near the muffler rather than near the head?

and therefore no damage to the engine from decel popping?
In order for the unburned fuel to ignite causing the pop there also must be air. If a bike is runing lean, the exhaust will have some oxygen but no fuel. If a bike is running rich, there will be some unburned fuel but no oxygen. Both have to be present in the pipe for the unburned fuel to light off. Air leaks can occur where the header pipe attaches to the exhaust port. When you reduce the back pressure you increase the chance air will be drawn in through a possible leak causing the unburned fuel to light off. A loose clamp or ill fitting muffler can allow air in too but at that point the exhaust gasses have lost alot of heat by then and are less likely to light off.

Removing a muffler from a header pipe sometimes requires some wrestling of the muffler to remove it. This could cause a leak at the exhaust port where non existed before. Cold air leaking in near the exhaust valve at a time when the valve is open can cause the valve to bend and or burn. Cold air leaking in near a muffler clamp is less likely to cause damage.

Lower backpressure does allow the exhaust out at a higher velocity so much so that there is a momentary negative exhaust pressure at the cylinder head. On deceleration some of the exhaust gas can be drawn back into the cylinder. If air gets drawn in with it, poping and valve damage can occur.
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Old 09-22-2012, 05:23 PM   #23 (permalink)
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Quote:
Originally Posted by JPR View Post
If the slip ons etc reduce back pressure, wouldn't that move the gasses further down stream faster so the popping which I think is unspent fuel occur near the muffler rather than near the head?

and therefore no damage to the engine from decel popping?
No.

Reduction of backpressure slows exhaust speed.

A 3" hose has less backpressure at 100psi, than a 1" hose.

The same 100psi will move faster through the smaller 1" hose.

Decel popping doesn't harm the engine, but it's an indication of an engine that's not running "tuned", and if lean, will raise cylinder temps, shortening engine life and possibly causing engine damage, depending on what's causing it.
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Old 09-22-2012, 06:02 PM   #24 (permalink)
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My $.02 is that my 06 came out of the dealer with screamin eagalet slip ons, K/N air filter, stg 1 dwn load, and decell poppin.

Re-downloads, 3 sets of injectors (diffrent spray patterns), new fuel lines n fuel filter, new header donuts 2wice, and then DD fat cat 2-1 with of course new donuts again (much attention paid to attempting to insure good seal each time) and its still poppin.

Bike runs ok, but if not premium fuel and cool weather it has spark knock when under load. (makes me cringe in the mountains n packed)

Right now its got around 60,000 miles on it like this.
Next up grade I'm considering is a efi control that will let me do some tweaking. Any suggestions on that?
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Old 09-22-2012, 06:41 PM   #25 (permalink)
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My $.02 is that my 06 came out of the dealer with screamin eagalet slip ons, K/N air filter, stg 1 dwn load, and decell poppin.

Re-downloads, 3 sets of injectors (diffrent spray patterns), new fuel lines n fuel filter, new header donuts 2wice, and then DD fat cat 2-1 with of course new donuts again (much attention paid to attempting to insure good seal each time) and its still poppin.

Bike runs ok, but if not premium fuel and cool weather it has spark knock when under load. (makes me cringe in the mountains n packed)

Right now its got around 60,000 miles on it like this.
Next up grade I'm considering is a efi control that will let me do some tweaking. Any suggestions on that?
No straight HD download to the factory ECU will stop popping.

HD's download merely restores the bike to the 14.7:1 AFR, and doesn't add any more fuel to stop decel popping with an aftermarket pipe and air filter application.

The only way to get around that, and get to a mid-13:1 ratio is to ADD fuel beyond the OEM AFR, and that's with a fual management system, or at the least, XEIDs inline with the O2 sensors for 2007-up models.
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Old 09-22-2012, 08:40 PM   #26 (permalink)
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I just got s 2005 ultra classic with 5000miles on it. a stage 1 was done on it a few years ago. Samson slash mufflers were put on it. I was told it is quite an experiance riding behind me. This bike blasts away when i let up on the gas. At high speeds, 60 or faster it is ok. Back roads, down hills all hell lets loose. My 2001 road king did it too, but not as bad. Dealer told me it had to be retuned, long job. Is this true or just a con.
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Old 09-22-2012, 10:12 PM   #27 (permalink)
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I have an 2007 ultra classic with stage 1, S.E.R.T, Samson slip on's and Screaming Eagle filter, and stock headers. Mine pops on deceleration. I personally like the sound. Looking at my spark plugs at each oil change I see normal wear. I have over 36k miles on mine and no issues with the deceleration popping.

I am contemplating buying the Cobra Fi2000 auto tuner, as I am about to go to true dual exhaust.

Glenn Williams
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Old 09-22-2012, 11:16 PM   #28 (permalink)
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Originally Posted by Dave63 View Post
No.

Reduction of backpressure slows exhaust speed.

A 3" hose has less backpressure at 100psi, than a 1" hose.

The same 100psi will move faster through the smaller 1" hose.

Decel popping doesn't harm the engine, but it's an indication of an engine that's not running "tuned", and if lean, will raise cylinder temps, shortening engine life and possibly causing engine damage, depending on what's causing it.
If one is reducing backpressure by increasing the header diameter then yes the same volume of exhaust gas will travel at a slower speed. However if you reduce backpressure by reducing the restriction at the end of the same diameter header pipe (the muffler) the exhaust speed should at least remain the same or increase somewhat due to the lesser restriction at the end.
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Old 09-22-2012, 11:21 PM   #29 (permalink)
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No, Dave is right, eliminating the restriction will slow down the exhaust gasses. Think of a garden hose; when you want to spray further, you place your thumb over the opening. Same principle here.

It may be that the only purpose for your life is to serve as a warning to others.
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Old 09-22-2012, 11:47 PM   #30 (permalink)
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No, Dave is right, eliminating the restriction will slow down the exhaust gasses. Think of a garden hose; when you want to spray further, you place your thumb over the opening. Same principle here.

It may be that the only purpose for your life is to serve as a warning to others.
Dave didn't touch on restriction. He compaired a 1" pipe diameter to a 3" pipe diameter. I agree that the same volume of anything pushed out with the same amount of force will travel slower through a larger diameter tube. I believe the OP changed his mufflers not his header pipe. so the exhaust speed through the header pipe should be at least the same. now as it enters the lower restriction muffler it may indeed slow down there. As for the garden hose the velocity of the water increases only at and after the thumbed end of the hose the water speed remains the same through the hose itself. if you went from a 5/8" dia. hose to a 3/4" dia. hose the water would travel slower through the larger diameter hose.
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