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Message started by madmikesmech on 05/18/17 at 13:24:26

Title: backfire when engine is shut down
Post by madmikesmech on 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?

Title: Re: backfire when engine is shut down
Post by verslagen1 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. 8-)

Title: Re: backfire when engine is shut down
Post by SALB on 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. ;)

Title: Re: backfire when engine is shut down
Post by springman on 05/18/17 at 14:50:19

I personally enjoy it! ;D

Title: Re: backfire when engine is shut down
Post by madmikesmech on 05/18/17 at 15:13:17

283B2C2D323F393B306F5E0 wrote:

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. 8-)

Thank you!
Idle mixture? Ido not see a mixture screw.how do I richening it up a bit?

Title: Re: backfire when engine is shut down
Post by madmikesmech on 05/18/17 at 15:16:23

3635372C2B2228242B450 wrote:

I personally enjoy it! ;D

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)

Title: Re: backfire when engine is shut down
Post by verslagen1 on 05/18/17 at 15:16:58

look up idle mixture plug in the index

Title: Re: backfire when engine is shut down
Post by Dave on 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).

Title: Re: backfire when engine is shut down
Post by George Palickar on 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.

Title: Re: backfire when engine is shut down
Post by buster6315 on 05/18/17 at 20:04:35

706374756A6761636837060 wrote:

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. 8-)

Mine also gives a shut-down poof, & I enjoy it!

Title: Re: backfire when engine is shut down
Post by 1st2know 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

Title: Re: backfire when engine is shut down
Post by bobert_FSO 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? 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.

Title: Re: backfire when engine is shut down
Post by Dave on 05/19/17 at 02:57:17

030E03041315610 wrote:

"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.

Title: Re: backfire when engine is shut down
Post by buster6315 on 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.

Title: Re: backfire when engine is shut down
Post by madmikesmech on 05/19/17 at 06:34:50

2D6F682E7772736B1C0 wrote:

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!!!!!

Title: Re: backfire when engine is shut down
Post by madmikesmech on 05/19/17 at 06:40:02

7D464B5C4D415A5C474F425D2E0 wrote:

I totally agree, the engine SHOULD be tuned for running not shutting down.
I suspect I could go a tad richer tho, as I once in the while, if I get on it sudden and hard it pops also, so richening it up should help thst too.

Title: Re: backfire when engine is shut down
Post by stewmills on 05/19/17 at 06:45:05

In case it wasn't already noted, here (see link below) is the air/mix screw location and how to remove the plug if it hasn't already been removed. BE CAREFUL AND SLOW about drilling the plug as you can go too deep and booger up the flathead tip of the brass air/mic screw. The plug is also soft brass and once the drill bit breaks through (which it will easily and quickly) you can push too hard and hit the screw. It is down there just a bit deeper (maybe 3mm) than the plug, but not too much.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1221818822

Title: Re: backfire when engine is shut down
Post by justin_o_guy2 on 05/19/17 at 06:58:57

Tape on drill bit.

Title: Re: backfire when engine is shut down
Post by madmikesmech on 05/19/17 at 09:21:59

160512130C0107050E51600 wrote:

look up idle mixture plug in the index

THANK YOU

Title: Re: backfire when engine is shut down
Post by Steve H on 05/20/17 at 06:35:20

I pulled up to the Waffle House last night to get something to eat and when I shut mine off, it made a nice very loud bang. The security guard had just walked out the door and almost hit the dirt, looking everywhere for the shooter.

I just grinned and went on in.
Embrace the 'bang'.

Title: Re: backfire when engine is shut down
Post by badwolf on 05/20/17 at 06:55:22

They have a security guard at the Waffle House? Must be in a rough neighborhood!
Do the waitresses still smoke while they take your order?

Ever heard of the Hattiesburg, Miss. Waffle House fire?

https://www.youtube.com/watch?v=MxaNUp6-O5k

https://en.wikipedia.org/wiki/Reverend_Billy_C._Wirtz

Title: Re: backfire when engine is shut down
Post by Steve H on 05/20/17 at 07:47:52

They have them on weekend nights around here. Seems like just about everything that gets robbed is on the weekends at night...so.

They can't. County ordinance...no smoking in restaurants. They have to go outside now.

This is probably the quietest area in town but they still have some problems. Most of the time the guards end up rousting drunks that get to roudy, drug users that come in and occupy the bathrooms, etc. But we are no 5 on the list of most violent places in the country. Here's a link.

http://abcnews.go.com/Business/worst-neighborhoods-violent-crime-us/story?id=19087850

Have not heard of the fire. I will read the article.

Title: Re: backfire when engine is shut down
Post by Steve H on 05/20/17 at 09:05:51

Hey BadWolf,

That guy's crazy. I listened to several of his songs.
I'll remember the Waffle House fire next time I go. ;D

Title: Re: backfire when engine is shut down
Post by badwolf on 05/20/17 at 10:07:15

Ah yes, with Rev. Billy or Rodney Carrington you WILL BE ENTERTAINED!

Title: Re: backfire when engine is shut down
Post by madmikesmech on 05/24/17 at 17:36:02

Well I finally got out and looked closely and the anti tamper cap HAD BEEN removed. I cleaned the road grime debris out with PB Blaster and let her sit over night. Put the correct size flatblade in the slot and attempted to turn ccountercockwise... no luck, then tried to turn clockwise...again no luck.
The slot was not real deep to begin with, wonder if when cap was drilled it got "milled" by a careless drill operator!!? As previously stated :( now I'm screwed, IF I can get the mixture screw out, I may have to change it, unless I can think how to repair the slot to accept a screwdriver.
Any & all tips on adjustment or removal would be GREATLY APPRECIATED
Thanks,
Mike

Title: Re: backfire when engine is shut down
Post by Dave on 05/24/17 at 17:39:00

Unfortunately.....those little threads can be corroded, and it locks the adjusting screw in there pretty tight sometimes. Even if you drill the old one out - you can't get the new screw to go in until you clean out the threads. I have the proper tap to clean up the threads if you get that far along, and I can loan it to you.

Title: Re: backfire when engine is shut down
Post by madmikesmech on 05/24/17 at 19:06:54

Well Dave, thank you VERY much for that most generous offer! I have some left handed drill bits IF it comes to that. I would presume the carb SHOULD be off for this type of proceedure correct.

Title: Re: backfire when engine is shut down
Post by justin_o_guy2 on 05/24/17 at 21:07:12

Build a tool to clean the thread.
Mix 50/50 trans fluid and acetone.
Carb on bench, get penetrating oil in on the threads, give it some time, keep it wet, carefully start working on the carp in the threads.
Piano wire from the hobby shop, bent, tip shaped on grinder.