Hi all, I need a little feedback. I just took the stock muffler off and installed one I picked up off e-bay. First thing I noticed is the sound (way louder and lower but not ear-splitting). Wasn't even sure I liked it but now that I've ridden it around a bit I think it's growing on me!

It is pretty much a straight through but does have baffles/resonator? built into it. They look like this:


I've done nothing to the carb except turn the air mix screw out 2 full turns from all the way in. Runs strong right now but when shutting down the throttle I get some backfires. I live a mile high and the stock setup ran fine with 1 1/8th turns out.
My questions are:
1) If I reduce the white spacer size would that possibly give me enough fuel to eliminate the backfire? Can it be done without removing the tank?
2) It's an '06 so I think the Main is 145 and the pilot is 52.5. If I need to move up a jet size should I go to a 150 as a starting point? and leave the pilot as it is?
3) can the jets be changed out w/o removing it from the bike?

Any thoughts would be welcome.
Thanks

Thanks serowbot...I think I'll try the white spacer mod first.
If that works then great, if not, I was wondering about a dial-a-jet. Anyone have experience with a dial-a-jet on our bikes?
Thanks

I can tell you from direct experience that the white spacer mod reduces backfiring.  I had NO backfiring after taking the spacer completely out of the stock carb.  

With another carb I was running a DAJ and it didn't help with backfiring no matter what the setting.

Pilot jets, the mixture screw, and the needle height are your best bets.

Trimming the white spacer 50% made mine run perfect, but it didn't change the backfire one bit. If you are not rough (lean) running in the intermediate 1/4-1/2 throttle range, I can't believe you would touch the spacer. And if you are smooth running in the other ranges, I wouldn't touch the jetting either. From some posts I have read, I think some have gotten themselves in real trouble messing w/ jetting while not really knowing what does what. Remember that running at 1 mile high elev, has already richened your jetting quite a lot.

Thanks for all the input everyone! This is the greatest forum on earth!
Woohoo, my first real wrenching on this bike!

I worked on it last night. Removed the tank, then, fiddled around to remove the screws that hold the spacer in the diaphram (they were tight! stripped the head on one but still managed to remove it...*tip-I replaced them with 2 itsy-bitsy screws from an old hard drive!!!), then inserted a #4 nylon washer in it's place.

For now, everything is back in place and (thank god) it still runs! I plan to try Lancer's recommendation of turning out the air mix a bit more and see where I am from there. If that doesn't work then I'll follow his advice and bump the pilot jet up a size.
I do have a very, very small air leak at the muffler/header joint but I've shimed it with some HVAC sheet metal and I plan to put a (small) amount of sealer there to close it up.

I still have the old spacer and have documented everything I've done up to now so if I screw up I should be able to get it back to where it was.
The reason I mentioned the DAJ is because even though I live at a mile high I still ride up into the mountains and can see a gain or loss of 5-6,000 feet in 30-40 minutes of riding. If I understand correctly, the higher I go the richer it runs??? Is that right?
Thanks again

BTW, this pipe I'm using is really starting to grow on me...sounds like a real bike now but the wife thinks it sounds broken...

Carburetors respond to volume flow, not mass. The air volume at altitude is the same, but at higher altitudes the air mass is less. The carburetor meters the same volume of gasoline to the same volume of air, but the mass of the liquid gasoline doesn't change, so the mixture goes rich. Electronic fuel injection actually measures mass air flow and adjusts fuel flow to match. There is still a power loss, but at least the mixture stays correct.

In the old days,... you used to flip over the lid on your car's air cleaner, to lean the mix in the mountains...

Man,... I'm old....

The CV carburetor, sometimes called a "Constant Velocity", or "Constant Vacuum", or in Brit-speak a "Constant Depression" carburetor, cannot really correct for air density. That is because it controls air flow (with the slide) and fuel flow (with the needle),  and the two are rigidly fastened together. The idea behind the CV is that it won't allow the engine to stumble or die if the throttle is whacked open suddenly from idle. With a manually controlled throttle, suddenly opening the throttle at low engine speed causes the venturi vacuum to drop (the venturi gets bigger and the airflow is still slow) so the metering signal goes away and the fuel doesn't get sucked into the airflow. That's why accelerator pumps were invented - they squirt a shot of fuel into the airflow to make up for the temporary leanness until the airflow speeds up. The CV uses the airflow to control the slide.

Unfortunately, no matter what you do to the airbox, you are going to lose somewhere around 3% of the power for every thousand feet above sea level. That's even with a perfect mixture, because air density drops about 3% per thousand feet. The amount of power the engine produces is almost a direct function of the amount of air it burns. The only way to get the power back at altitude is a supercharger of some sort.