Quick Re-jetting question

[upsguy]

I just bought a 2004 GS500F last week and it runs well.  Yesterday I cut off the stock exhaust at the midpipe and installed a stubby 9" Delkevic exhaust.

It still runs fine with no issues (yet) with power and performance being fine, however when decelerating, it now does the loud popping thing (snap crackle pop).  My understanding is that this bike already runs lean from the factory and by using the Delkevic without the baffle in, it is almost a straight pipe now so it's probably super lean.

My home town ranges from 120'-160' above sea level (in Connecticut).

Questions:
1) Do I NEED to rejet?  If I don't are we talking just having to change the plugs more frequently or are there other drawbacks?
2) If I take the plunge and tear this thing apart to rejet the carbs, my understanding is the stock jets are: Pilot 17.5, Mid Main 60, Main 130.   Keeping the stock air filter, does this sound right: Pilot 20, Mid Main 62.5, Main 142.5 ?  How many turns? Do I NEED to shim with washers?
3) If I put the baffle in the exhaust do you think it will add backpressure and reduce the crackle on deceleration?

Thanks in advance.

[mr72]

That muffler is not going to make it run noticeably more lean.

I'd bump the pilot to a 20 and maybe go up to 132.5 for the main.

You hear the popping because the muffler is louder. It's normal.

[Kookas]

Both my GSes did the popping and crackling thing whilst engine braking. As I understand it, vacuum continues to draw fuel through the throttle, which will always be open at least a little bit in order to idle, but now the momentum of the bike is turning the engine faster than the actual combustion process is, so some of that mixture goes unburnt through the exhaust and explodes out there when it hits the open air. An EFI bike can detect this condition and cut out the fuel entirely and it's probably possible to do something with the ignition on a carbed bike that prevents the mixture going unburnt, but our GS will just push that air-fuel mixture back out there.

You just don't realise it with the stock exhaust till you open up your visor or a flip-face and look back!

[alpo]

I've found adding a little more fuel helps reduce the popping. Raise the needles, or larger mains. However, you have to tune for it - lots of trial & error. 

Here's a good tutorial on how to go about tuning a bike with CV carbs.

[upsguy]

Thanks guys.

[upsguy]

P.S. Josh, I love your blog.  I was reading a really helpful entry earller today.