As far I as can tell from my reading on this forum, if you have the stock muffler and air cleaner, you will get better performance and less backfiring if you replace the white spacer with one that is half as thick and adjust the idle mixture.

If you add a high flow muffler and a high flow air cleaner or either, then you'll get a lot more air to the combustion chamber. That will cause a lean condition which will increase backfiring and make the engine run hotter. The only solution is to increase the size of the main jet which will add more fuel and "richen" the misture.

I installed a HD Dyna muffler weekend before last.  The engine was running very lean and backfiring more.  

I did both this weekend for my 97.  I found a #4 nylon washer at the hardware store that is exactly half the thickness of the original spacer. I installed that with a 152.5 jet. I also removed the snorkel.  

The engine runs much smoother with those mods. Seems to have more power too.  I just got back from a short ride. to test it out. As I approached home in second gear, I decided to roll on the throttle to see how it would respond.  The front raised up and I thought I was going to pop a wheelie for a second.  

So why did you buy a new stock carb?

Steve

See the Mid-Range Power & the White Spacer (Backfire) and Carb Specs. threads in the Tech forum.

The procedure is pretty simple.  You do have to remove the seat and fuel tank to get the top of the carb off but heck, you almost need to remove those to do anything.

Steve530 wrote on 12/31/69 at 16:00:01:

Hmmm... I didn't remove the carb.  I just worked on it in place.

Savage_Rob wrote on 12/31/69 at 16:00:01:


I needed to remove the carb to dip it anyway.

How did you manage to get the screws out of the top of the carb while it was on the bike? With it in my hands I still stripped three of the for screws. And I would have thought the top tubes would block access to the carb.

Steve

BS37066 wrote on 12/31/69 at 16:00:01:

That's the trick. Rotate the carb. I did mine with the carb on the bike. Remove the tank and seat and it's not so difficult. I stripped several screws, but the pointy vice grips took them out no problem. The screws are too soft. Replaced them with stainless steel allen heads and all is well.

i have a bone stock 1999 ls650 and i just purchased at dyna HD muffler, but should i rejet to 155 or 152.2 which one is better? keep in mind i currently have a stock air intake, i will get to the k&n after the rejet and pipe is installed.

simplyput2600 wrote on 12/31/69 at 16:00:04:

It's so easy to swap 'em, you'll probably wind up trying both.  When I was playing with mine, I couldn't tell any difference between a 152.5 and a 155 so far as how she ran.  The only noticeable difference was that I got better mileage with the 152.5.  I was using a MAC muffler and a K&N replacement filter on mine, so you may get different results.  I'd bet on the 152.5 though.