I recently purchased a 2004 Savage with about 7,400 miles.  It's stock except for a Jardine Rumblers series slash cut slip on (currently no baffle, but considering one).  I have read the many posts on carb jetting and narrowing the needle spacer (washer, shim).  I greatly appreciate all the experience and tested fixes!  Thank you!  Here comes my specific question.

I'm in Houston, TX.  It's hot, humid, and virtually at sea level.  The bike starts and idles well and generally runs well (slight dead spot in the low/mid range especially when the bike hasn't warmed up, but noticeable otherwise too).  I am however getting some gnarly backfire on deceleration - not just a nice popping and crackling - but some kaboom style.  I have removed the plug over the air/fuel mix screw (prior owner never even tinkered with it after installing the Jardine).  It was 3 turns out as stock indicated.  With the bike hot, max idle RPM is actually at about 2.25 turns out, with no significant drop in RPM to 3.0 turns out.  Even at 3.5 turns out, still not much of a drop.

Based on my reading on the issue, here's what I'm thinking to do to tune the carb and get rid of the kaboom.  

1) Go to 1/2 spacer on the needle.  Should I go any thinner?
2) Go from 52.5 to 55 pilot jet.  I'm really questioning myself here since max RPM is achieved at 2.25 turns out.  If I go with the bigger jet, will it be too much?  Will I be able to lean it out to max RPM with #55? Will it only be 0.25 turns out or worse none (not optimized)?
3) Go from 145 to 150 main jet.  I'm thinking this is ok, but I don't want to give up mid-range snap and responsiveness.  Thoughts.

Note: I'm an older rider (60ish).  WOT is a blast, but I rarely ride that way anymore.   In my younger days, I would have been tuning all day to maximize WOT.  Nice clean, crisp acceleration with no kabooming backfire on deceleration is my main goal.  

Will thinning the needle spacer achieve most of what I'm wanting to do?  I don't mind occasionally working on a carb, but I'd rather be riding than hold my carb in my hand.

Thanks in advance!

I would definitely install a baffle in the Jardine, if not replace it with a HD Dyna muffler; depending on whether you like the sound level and performance of the Jardine.  A Dyna works very well on our engine, makes good power, sounds good, and is easier to tune. Of course an exhaust change may require a jet change/s.

With a hot engine (like after riding several miles before adjusting the pilot screw) your pilot screw is at 2.25 turns out and you have max rpm, this should be the best setting for your current setup.  You can keep the current pilot jet if you wish, you are under the 3 turn rule.
If you go with a #55 pilot jet the new pilot screw setting would be around 1.25-1.5 turns out.

I assume no air leaks in your exhaust system since you did not mention it, which can cause backfiring.  To check your system, head-header and header-muffler connections, use a candle with wick blown out, watch the smoke near the connections for disturbance of the smoke.  If you have a leak it can cause backfiring.

The white plastic spacer on the needle should be shaved by 1/2 or replaced with 3 washers to address the pause your experience as the carb transitions from the pilot circuit to the midrange.   If the engine has not warmed up yet...wait until it is.

Having a #145 main jet, I would replace it with a #152.5 first.  If it’s too rich then drop to #150.

Thank you Lancer.  I thought I would still be able to get to max rpm with the 55 pilot, but I wasn't sure.  On the main jet, I have been going back and forth in my mind between the 150 and 152.5.  My thought was baby steps so I don't end up going too far in the rich direction.  Verslagen1 doesn't think the Kaboom will go away.  I was thinking the spacer thickness adjustment might actually be the main thing to resolve it.  Hmmm...  Y'all seem to like the HD Dyna (and I'm sure I would too).  I don't mind the loudness and sound of the Jardine until the kaboom comes.  That said, I don't need super loud and thus I'm considering the baffle.  Also trying to keep the investment $$ small, so replacing the muffler isn't at the top of my list, but I will think about it.

I am going to check for exhaust leaks again.  I did have to replace one of the main exhaust head bolts.

Am I understanding that the spacer thinning won't help much?  I was hoping for a small miracle.  Note: If I turn up the idle and go 3.5  turns out and go ride, the backfiring does seem mitigated, but the idle shouldn't be at that high level.

Thanks again!  

Let me point out that the hotter and more humid it is, the LEANER you need to go.  

With that said a good way to test the direction you want to take your jetting is to ride it early in the day when it's cooler and then in the afternoon when it's hot out.  

If you are too rich, the bike will run stronger and rev out quicker in the morning.  

Also, always make sure the bike is at full operating temperature.  That can take a good 10-15 minutes.  

My bike has a 47.5 pilot and a 147.5 main.  It runs 100 times better than the 55/155 combo the previous owner had in it.   Elevations on my commute range between 400ft and 1100 ft.  Temps are between the low-60s and 70s in the mornings and the 80s to mid-90s in the afternoons.  Humidity is high this time of year.

The backfiring is annoying, but it discourages tailgaters!