SuzukiSavage.com - backfire when engine is shut down

madmikesmech Full Member Offline SuzukiSavage.com Rocks! Posts: 227 Olean ny Gender:	backfire when engine is shut down 05/18/17 at 13:24:26 Hello all, My bike runs great, but when I shut it down it gives one lone loud backfire? Does this indicate a rich mixture?
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verslagen1 YaBB Moderator ModSquad Offline Where there's a will, I want to be in it. Posts: 28884 L.A. California Gender:	Re: backfire when engine is shut down Reply #1 - 05/18/17 at 13:47:18 No, lean at shutdown. You can tune it down a bit by richening up the idle mixture. or you can pull the choke at shutdown. or you can enjoy it.
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SALB Serious Thumper Offline FSO Posts: 668 Whittier, AK Gender:	Re: backfire when engine is shut down Reply #2 - 05/18/17 at 14:04:34 Check for exhaust leaks, as they make it more likely to backfire both at shutdown, and when you snap the throttle shut while riding.
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springman Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 2217 Spring, Texas Gender:	Re: backfire when engine is shut down Reply #3 - 05/18/17 at 14:50:19 I personally enjoy it!
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madmikesmech Full Member Offline SuzukiSavage.com Rocks! Posts: 227 Olean ny Gender:	Re: backfire when engine is shut down Reply #4 - 05/18/17 at 15:13:17 verslagen1 wrote on 05/18/17 at 13:47:18: No, lean at shutdown. You can tune it down a bit by richening up the idle mixture. or you can pull the choke at shutdown. or you can enjoy it. Thank you! Idle mixture? Ido not see a mixture screw.how do I richening it up a bit?
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madmikesmech Full Member Offline SuzukiSavage.com Rocks! Posts: 227 Olean ny Gender:	Re: backfire when engine is shut down Reply #5 - 05/18/17 at 15:16:23 springman wrote on 05/18/17 at 14:50:19: I personally enjoy it! Oh I like it too, but I wondered if others experiance it too. The lean mix makes sense, as I have a "drag" pipe, (no baffle)
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verslagen1 YaBB Moderator ModSquad Offline Where there's a will, I want to be in it. Posts: 28884 L.A. California Gender:	Re: backfire when engine is shut down Reply #6 - 05/18/17 at 15:16:58 look up idle mixture plug in the index
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Re: backfire when engine is shut down
Reply #7 - 05/18/17 at 18:44:57

The bang on shutdown is a result of you turning off the ignition......which causes the spark in the cylinder to stop - while the engine continues to turn and pull air through the carb....where it picks up fuel.....then the fuel/air mix gets pumped through the engine and into the exhaust. The unburned fuel/air mix is now in the hot exhaust system....and within a few seconds after shutdown the fuel/air mix has become hot enough to ignite and create the explosion in the exhaust system. If the fuel/air mix is a richer....the explosion is less violent and more of a rumble - if the mixture is a bit leaner the explosion is louder and more violent.

I believe you should be adjusting your carb for how it runs when the key is turned on and the engine is running - not for what it does when you turn the key off. If your idle is high - it pumps more fuel/air into the exhaust when you turn the key off....so the noise will be louder. If you shut the bike off immediately after getting off the highway - the exhaust system will still be hot and more apt to ignite the mixture (allowing the engine to idle for half a minute might let the exhaust cool down enough to avoid the bang).

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George Palickar YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 48 Near Scranton, Pennsylvania Gender:	Re: backfire when engine is shut down Reply #8 - 05/18/17 at 19:06:28 I just deal with the pop. Not many road bike are singles. If they were, we would all be used to the pop. Lowering the idle before shoutdown mellows it out. When I had a louder Jardine pipe the pop was too big. I think what the forum folks are saying is that it's part of owning a savage.
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buster6315 Senior Member Offline SuzukiSavage.com Rocks! Posts: 353	Re: backfire when engine is shut down Reply #9 - 05/18/17 at 20:04:35 verslagen1 wrote on 05/18/17 at 13:47:18: No, lean at shutdown. You can tune it down a bit by richening up the idle mixture. or you can pull the choke at shutdown. or you can enjoy it. Mine also gives a shut-down poof, & I enjoy it!
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1st2know Senior Member Offline Currently between Savages Posts: 295 Seattle, WA Gender:	Re: backfire when engine is shut down Reply #10 - 05/18/17 at 22:14:46 If it's a really loud bang (people duck, birds scatter), then you should check your petcock. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1251932429/1
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Re: backfire when engine is shut down
Reply #11 - 05/19/17 at 02:15:26

"Not many road bike are singles. If they were, we would all be used to the pop."

A question... Why would a shutdown pop be limited to singles? A 1200cc twin has cylinders approx the size of a 650 savage, and many twins are even larger than that. If carburated, they also have the same characteristics that would cause a muffler explosion, especially if the exhaust system is two separate pipes without a crossover (like a lot of Harley aftermarket pipes). The carb still injects fuel as the engine winds down. The exhaust pipe is just has hot.

My Savage was jetted a little on the rich side and it hardly ever popped on shutdown. If it did, it was because I was riding hard, stopped and immediately shut the engine off. Even then, it was just a soft poof. I did get a couple of gunshot explosions before I rejetted.

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Re: backfire when engine is shut down
Reply #12 - 05/19/17 at 02:57:17

bobert_FSO wrote on 05/19/17 at 02:15:26:

"Not many road bike are singles. If they were, we would all be used to the pop."

A question... Why would a shutdown pop be limited to singles? .

One contributing factor is that the Savage has a double header pipe....it has a smaller 1-1/4" pipe inside the chrome 2" outer pipe. This makes the inner pipe run much hotter than a single layer pipe, and that makes it more apt to ignite the mixture. (Harley's have a chrome guard over the pipe to make it pretty - but the exhaust pipe behind the guard is not completely wrapped like it is on the Savage). Another contributing factor is that Harley riders tend to keep their idle speed really low - and that helps to keep to reduce the chances of the "afterfire". Smaller displacement - multi cylinder bikes just pump a lot less fuel/air into the exhaust at shut down.

This situation is not just limited to motorcycles. A lot of lawn mowers have an electric solenoid built into the carb that shuts off the fuel flow when you turn the key off - as lawn tractors would sometime make a huge explosion when the owners shut them off.....without the fuel shut off they had the same afterfire situation that we experience on the Savage.

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buster6315 Senior Member Offline SuzukiSavage.com Rocks! Posts: 353	Re: backfire when engine is shut down Reply #13 - 05/19/17 at 03:09:33 The after shut-off back fire is not limited to singles. My 1400 Intruder did the same thing.
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madmikesmech Full Member Offline SuzukiSavage.com Rocks! Posts: 227 Olean ny Gender:	Re: backfire when engine is shut down Reply #14 - 05/19/17 at 06:34:50 1st2know wrote on 05/18/17 at 22:14:46: If it's a really loud bang (people duck, birds scatter), then you should check your petcock. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1251932429/1 Got a 660 raptor replacement petcock inroute... expecting it TODAY!!!!!
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