I am not sure that "Loud Pipes Save Lives".....but I am certain that they tick off the neighbors, aggravate the general populations, and tend to make people hate motorcycles and those that ride them.  I have alwys been a fan of "Less Sound = More Ground" from my old dirt biking days.

Your bike is not running rich when it backfires after you close the throttle......it is running lean.  When you close the throttle it closes the fuel jets and the mixture becomes so lean the spark plug cannot ignite it....and it gets ignited by the hot exhaust header or the next power pulse from the engine where it is ignited by the spark plug.

You can get a freeze plug at the auto store (I believe it is 1" diameter), and drive it into the muffler between the front and rear holes where the original center baffle used to be.

Open or straight through exhaust are hard to get jetted right, and may make less power.
Serowbot has added this video to the Dyna Muffler thread in the Technical Section if this link doesn't work:
http://www.youtube.com/watch?v=KjKUKhHQLHg

I used to think the same way you do about the mixture when you shut the throttle.  I assumed that when you chop the throttle and the vacuum increases dramitcally....that it would pull a lot of fuel through the jets.  What I failed to take into account was that the closed slide or butterfly puts the jets on the opposite side of the carb from the high vacuum, and the slide needle has dropped down and closed off the main jet.  When I was jetting my carb I installed an Oxygen Sensor and guage on my bike, and I was surprised to see the mixture go lean whenever the throttle was closed.  The TEV device on our carb is supposed to add fuel to prevent help reduce the backfire....and I suppose with the stock muffler it helps.  It is not up to the task of stopping backfires when we put on free flowing muflers.

The reason that I don't believe that loud pipes do much to keep you safe, is that in most cases they only hear you when you are passing them.  When you are approaching an intersection the sound is behind you and they really don't hear you coming....they hear you going.  On the highway when driving my cage, with the windows up and the air conditioning on and the radio playing, I can only hear the motorycle when it is right beside me......so I suppose that might keep me from changing lanes while you are beside me.

I do live about 2 miles from a major highway....and I can hear the loud pipes from bikes and semi trucks 24/7.

On my bike the engine ran very lean just off idle.  With a baffled DYNA muffler and a SuperTrapp my best jetting was a #50 pilot, #150 main and the needle installed with 2 metal washers on top of the needle instead of the white plastic spacer.  I tried a #52.5 pilot with the 3 washers and it did not correct the lean condition, and when I went to 2 washers I had to back the pilot down to a #50 for smoother running.

It sounds to me like your engine is too lean at the lower throttle settings where the pilot jet and needle jet control the fuel mixture.  This is the throttle position (1/4 or less) where most of your riding is done....unless you are over 50 mph and needing more than light throttle.

What happens if ya pull the choke to 1/2? Full?

If you can richen it a bit & knock some KerPOW out of it, then its better for the motor.

My 2005 was factory stock when I installed the Dyna Muffler.
When I fired it up it ran poorly and had the same nasty popping sounds
and afterfires that yours has, danjray.
So i pulled the brass plug, adjusted the screw for highest idle speed,
then turned the throttle stop screw to set the idle at 1100 RPM.
Those two adjustments made the bike ridable until the jets and spacer
were changed.
You'll need to pop the brass plug for tuning as part of your jet changes
so you might want to try that now while your waiting for them.

Yea I got a Dyna that was open too, the freeze plug trick did the trick    

justin_o_guy2 wrote on 08/07/13 at 13:49:44:


I tried this out yesterday, it helped quite a bit, luckily my jet set comes in tomorrow so I shouldn't need to limp along by this method much longer! I was wondering if there is any correlation to using 1/2 choke to what jet size I would need to go to. With the 1/2 choke I still had some popping and after firing but it was better, at this point I'm guessing I'll go up a half size in the pilot and a full size in the main and go to 2 washers (based on the carb posts I've been reading) does that seem like a reasonable place to start?