Actually,... after-fire theory,.. (most often referred to as "backfire")...
A real "backfire",... goes backwards... blowing up through the carb...  (this is most often caused by a valve/spark timing issue)...
What we refer to as backfire, (the gunshot out the tailpipe),.. is correctly called an after-fire...

This is caused by a hot pipe, igniting unspent fuel in the exhaust...
Why does it happen?...
1.  you have unspent fuel in the pipe... (this could be too rich... or too lean... either will cause inefficient burning in the cylinder... one, will leave the cylinder with not enough fuel to give complete combustion, and the other will have too much)...
2.  the hottest engine, is the one with the best combustion.... and that will expel heat into the pipe that can reach combustive levels... but, it shouldn't cause a big one,... because there shouldn't be that much fuel in there...
3.  an air leak... in the exhaust pipe will introduce fresh oxygen into the pipe, and this will make a nice secondary combustion chamber...

What are some clues?...
a. if it's mostly upon shutdown... there must be unspent fuel in there... a "poof" could just be the final cycle of the engine after the ignition is shut off... That would be normal...
A huge "Kappowww!" at shut-off should indicate rich... (there's too much fuel in there)....
b. if it's more upon decel and downshifts,... but not so much on shutdown,... I'd guess lean...(a lack oxygen in the combustion chamber is causing inefficient burning in the chamber and when you close the the throttle there is a momentary richness, caused by the throttle plate blocking air before the fuel flow is reduced, causing a boom in the pipe on throttle chops)...
c. all the time... (yer' so screwed)... jest kiddin'...
You are probably rich,...the gunshot afterfire is still indicating an excess unspent fuel...

Basically,.. what I'm proposing, is that judging rich or lean, by your pipe is not a good way to go...
It's very popular... but, often wrong...
Rich, or lean, can cause popping, afterfire, and blueing...
...and, when your engine is working best, it is burning hottest... (at least in the combustion chamber)...

The best indicator of your engine's tuning/jetting is the environment...

If popping/afterfire increases in...
thinner air
hotter  air
more humidity
higher altitude
...  go leaner...

...if popping/afterfire increases in...
thicker air
cooler air
less humid
lower altitude
... go richer...

If your bike is generally disturbed more when the weather/or conditions are unusual in either direction,... then it stands to reason, that it is jetted for best performance in normal conditions,... and this is where you want it...

... and, if you live in Florida... where it's hot, humid and flat...all the time... yer' jest so screwed...
I guess you just gotta' change jetting, up and down to alter the mix conditions, because nothing else ever changes...
...
Same rules apply though... you'll just have to alter your engine conditions, rather than observe the environment...

... and... I'm probably wrong here somewhere... but, it's my theory... and it's roughly based on science... and I'm sticking to it...
...

So,.. take advantage of the next muggy, or humid,.. or hot or cold, or mountain or valley ride,.. and observe your bike's behavior...
If popping, and backfire/afterfire increase, that's a good sign...
You tune your bike for what is usual... ...

S'bot, I've always found the biggest bang on shut down was when the idle mixture was set at optimum.  And all it takes to get rid of it is an 1/8 to 1/4 turn richer.

Bubba wrote on 04/15/13 at 07:57:09:


Snorkle?  

Vacuum at the jet is produced by air movement, in either direction, past the orifice in the carb throat. The orifice for the idle jet (which is what you tune with the air screw) is located right where the edge of the butterfly rests when closed. Because of valve overlap, etc, when the engine's at idle air is pulsing back and forth past the edge of the butterfly. So the idle jet sees more than one suck for each intake and hence is tuned lean to deliver a correct mixture.

On the overrun the butterfly's closed but higher revs smooth out pulsing in the carb: the idle jet's now seeing only one suck per intake and is delivering a lean mixture. When a couple of other variables line up, particularly revs dropping past a critical point, this produces banging and crackling as unburnt fuel ignites in the exhaust.

The "temporary enrichment" valve on the side of the carb is supposed to address this - it gets sucked open by high vacuum on the engine side of the carb, opening another circuit to the low speed jet. Cleaning this out can help.

Going one size up on the low speed jet reduces backfiring, so long as you've also ensured there are no leaks in the exhaust system for air to get in. Another step is to alter or replace the spring on the temporary enrichment valve diaphragm - a softer one means the valve stays open longer - but it sounds as if this has upset other aspects of the carburation.

My wife had a 86 and 96 Savage and they had a heavy putt sometimes but our 09 sounds like a canon anytime you "decelerate" from 5th. to 4th. or 4th. to 3rd.!!! I'd be really HAPPY to get the backfire down to a less decible level for sure. It's bad when your riding a poker run with a bunch of "straight piped" Harley's and our supposedly to quite Japanese scoot get's the "Evil Eye"!

Good explaination on it.  I just keep a little screwdriver with me and depending on the weather, I might have to adjust the carb screw a half turn either way to fix this problem for me.

Yep, that's the one...it really isn't a big deal to remove the plug...just make sure ya read up on it and don't go all crazy, otherwise you'll mess up the screw head that lies under it.
After hearing the horror stories about the dealerships I wouldn't let them touch it...I'd just ask what the "fix" is and do it myself...

There is tons of discussion about the Savage backfire issue and I'd like to add my experience in case it might be helpful.

I have a 2001 Savage with low miles that has been reconstructed as a cafe racer (photo attached). It has a fairly free-flowing air filter and a very free exhaust but otherwise stock. The exhaust header is 1-5/8" ID, 31" long and flows into a 9" long glass-pack muffler which empties into a 3" dia turn-out. ID in the glass-pack is about 1-1/4". This bike is fairly loud and now revs way more freely under WFO than when stock. So I'm pretty happy with the main jet.

I reside in Phoenix which is about 1200 ft elevation. In reading all the guides on jetting, I started with a 155 main, 52.5 pilot and cut the thickness of the white spacer on the needle by half. But the bike would backfire on almost every shift from first through third and anytime if you chopped the throttle. Two ways I found to stop the backfire were to roll off the throttle slowly or to be on the gas hard between shifts. The slow roll-off is cumbersome, counter-intuitive, and just BS and you can't always be on the gas, like in heavy traffic. So POW. POW, POW. Some guys like the backfire, I do not.

Ryca uses a 55 pilot at sea level, so I though I'd try that and also bought a 57.5 pilot. Started making one change at a time; the 55 almost immediately stopped the backfiring. After a good warm-up and pilot screw adjustment, it was still popping from time to time, so I installed the 57.5, readjusted the pilot screw and took a long ride.

With the 57.5 pilot it backfired just as badly as the 52.5 and now it would stall after down shifting to a stop light, perhaps TOO RICH now. Overall, worse than the 52.5 pilot by far.

I did some more reading, one thread suggested throwing out the white washer but that opinion was contested pretty heavily and to my thinking, when you chop the throttle, you're almost instantly back to the idle circuit anyway, so I re-installed the 55 pilot, rechecked the exhaust for leaks, warmed up the bike, and re-set the pilot screw.

But this time I turned the pilot screw out till the idle began to stumble and then just turned it back in until it picked up and smoothed out. Only about 1/2 turn in and presto, almost no back fire at all.

I've taken a couple of 10-mile rides and made sure the bike was completely warm, (it was 107-deg ambient), and it is now very hard to get a back fire. Only did it once in 20-miles. Now when I shift and/or chop the throttle, no pops, no back fire, just the same kind of sound I get on my XR200 between shifts, a sweet little rumble.

So, my observations seem to support the conversations you can find here and elsewhere that the back fire is the ignition of unburned fuel in the exhaust which may happen if the mixture is too lean OR too rich. This seems to be my experience.  My conclusion is that you can stop the backfire but that it is a very sensitive issue; get the pilot jet and pilot screw adjustment JUUUUUST RIGHT, and you're cool.

I thought that Lancer's notion of going up on the pilot jet when you screw out the air screw more than 2-turns was a good idea and a good guide for sizing the pilot jet. It really seemed to help me.

Anyway, now the bike is a sweet ride, sounds like a thumper should, with a good rumble between shifts or when you chop the throttle. I'm not an expert tuner but I've been wrenching on bikes for about 5 decades and I have to say, this was a head-scratcher. I can't guarantee that my experience will dictate yours but my hope is that it may help someone out there.

My recommendation is use Lancer's logic on the pilot jet selection and then turn the pilot screw out till the idle stumbles and just back in till it picks back up. Try that. God knows it won't work for some one but it worked for me and it may be worth a try.

Best of luck.

Bitterswede.