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Discussion Starter · #1 ·
Hi there,
for the last years, i'm cruisin on my '96 fatboy.:cool:

Great bike, got a jetkit, K&N airfilter, and cam.
My mufflers are empty.

since some time now, there's a 'POP' sound coming from the exhausts, (or a backfire) everytime i close the throttle when the engine is hot and running High RPM.:dunno:

I've been told that its probably caused by an 'airleak' in the exhaust system.

...searched alot, found nothing.
Is there a better way to find this leak ?
Anyone?

The winner might get a weekend in our belgian countryside....?:wootdnc:
 

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After changing exhausts I always hold a burning cigarette up around the flanges and any joints in the pipes to see if I've got good seals. Its pretty easy to see the disturbed smoke and know if you've got a problem.

If a pipe is actually cracked somewhere that would probably be a different issue.

Tom
 

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I'm pretty sure you are describing a lean running condition. More likely a leak on the intake manifold, if you convinced it's a leak.

I'd read the plugs and see if they are lean...

I'm sure others, who know more than I, will chime in soon.

Is airfare to your place included???:brows:
 

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Sounds like yopu are experiencing the phenomenon known as "reversion". It happens when a rich mixture of unburnt exhaust gasses in the exhaust pipe meets an oxygen rich source. The unburnt fuel then ignites and you get a pop or backfire. It is not going to hurt anything other than your neighbours ears, but if you want to get rid of it, then try putting the baffles back in your pipes with the applicable packing material. You should also check for exhaust leakage at the headpipes and any other joints in the exhaust where ambient air could be drawn into the ehaust system during the scavenge portion (when the piston passes top dead center and the intake valve begins to open) of the ehaust stroke.
Hope this helps...

On a side note, a couple plane loads of Belgian Air Force guys just arrived here in town for a 2-3 month stay. -I'll do my best to welcome them...:cheers:
Cheerz,
DyNasty
 

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Humpin One Leg at a Time
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TLeath said:
After changing exhausts I always hold a burning cigarette up around the flanges and any joints in the pipes to see if I've got good seals. Its pretty easy to see the disturbed smoke and know if you've got a problem.

If a pipe is actually cracked somewhere that would probably be a different issue.

Tom
Never thought of using a cigarette, good idea. cough cough
 

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All of the above. :) Running open pipes is one of the worst thing you can do to your engine. The reversion can be severe enough to cause major damage when the cold air gets sucked into the combustion chamber through the exhaust valve (thermal shock). It's even worse with long duration cams with a lot of overlap. What cam are you running?

On some bikes I've worked on with open drag pipes, you could actually feel the exhaust sucking back into the rear pipe when you hold your hand over the end while idling. This is NOT GOOD for the engine!!

The only bikes that run halfway decent with open pipes are the older pre-EVO machines. You are also killing a LOT of torque by not using a good exhaust system. It's gonna be almost impossible to tune correctly, too. Put some baffles back in or change to a real, tuned exhaust system.

Those so-called AR (anti-reversion) cones are basically worthless. I've tried them on a few bikes and ended up throwing them out. If you want the most torque out of your engine for excellent street performance, then you would have to go to a 2-1 exhaust. There are a few 2-2 systems that perform almost as well, though.

The best way to check for exhaust leaks is to just change the gaskets. Make sure you torque the pipes at the head BEFORE tightening the support brackets. If they don't line up, bend or shim the brackets until they do. For intake leaks, use WD40 using the red nozzle that comes with the can. Idle the bike, and spray around the intake seals. If the engine speed changes slightly, they you know you have a leak. Some people use other methods, but this one is fool-proof and much safer and more accurate than using propane, brake cleaner, or some other highly explosive substance. Propane can actually get sucked into the air cleaner while doing this, so it's not very reliable.
 

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Discussion Starter · #7 ·
I have to disappoint you concerning the airfare, but once you get here, You'll get a nice introduction in our famous Beerculture... who am I kiddin... we'll just drive to my favorite bar and get drunk.
 

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Popping

I had the same thing happening on my 95 Heritage. I installed a set of thunder monsters and had it dyno-tuned and had no more problem. I actually have better drivability now - no more dead spot in the low RPM range.

Gunnar
 

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Discussion Starter · #9 ·
thx

Thanks guys,
I'm going to see my dealer next week and we'll talk about the matter.
The exhaust is basicly a standard 2-2 pipes with a crossover. It's only the mufflers that are hollow. Originaly it were SE's but I did'nt like their sound.
And that, my fellow listeners, is excellent right now.... not hearing the poppin'sound..

Whatever the problem was, I'll keep you posted.
Thx for all the tips
c u next time.

PS.: whenever you should visit Belgium, give me a sign and I'll tell you the do's and don'ts of tourisme here.
 

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Exhaust leak or lean fuel

Recently, I installed the SE-AC and SEII slip-on mufflers to my 05' Softail Standard. With the H-D download and a dyno run I soon learned that the engine was too lean (Refer to "Lean fuel and pipes" in the stage one sucks thread). When I took the bike in again the dealer mentioned that some of my decel popping could be caused by an exhaust leak. In the course of having the SERT installed they did find a leak on the front flange of the interflow tube. When I picked the bike up I inspected the techs work and saw that he had done a custom fix on the flange. He explained that the SEII pipes have a manufacture defect on the front pipe and that the interflow flange is too big for the tube. Has anyone else heard of this? His fix was not sloppy, it was quite clean. He used two gaskets, trimming one of them to slip higher on the interflow connector. The bike has started to decel and shift pop like crazy, especially in this Kansas heat of 100F. I spoke to the tech yesterday and he wants to check his work on the exhaust. I took the liberty to do a smoke test on the pipes myself and found nothing. An incense stick works as well as a cigarette. I am going to take it in and have the exhaust checked, and once it is all clear I am going in for a custom map on the SERT. My air/fuel ratio is still too lean. My question is, is it the pipes/exhaust leak or leaness?
 

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I have this condition despite the fact that my bike is tuned to perfection:wootdnc: It is caused from a leak between where the two head pipes cross over joins. I have fixed this gasket so many times that I finally realized that on a rubber mounted evo motor, the fix would never last. I finally put in a new gasket sealed with exhaust high temp silicone. It still leaks ever so slightly but the alternative is to go with a different head pipe. The performance on my stock head pipe with cycle shack mufflers is too good to compromise. A little rumble and popping when throttling down on steep hills is ok with me! Sounds like a Harley!
 

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My '01 Fatboy popped abit until I put the PCIII on. I just upped the values a little at 0 throttle from 2000rpm to 3500rpm. Popping is gone now.
 

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fire baaad, back pressure goood....
 

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I had the same problem when I put on my aftermarket pipes and full flowing air filter. I say that your carb isn’t jetted right for your set up and I would change my idle jet lower by one. You do need an exhaust system that provides some back pressure for more power off idle in your power band.
 
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