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How to stop the backfire (Read 134 times)
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How to stop the backfire
07/14/20 at 13:11:59
 
I would like to stop my 2015 LS650 from backfiring.

I've read on this website that this can be done.  However, it sounds like it involves more than simply adjusting the fuel idle screw (ie lean-rich fuel mixture screw) on the carburetor.  If I read the procedure correctly, it sounds like I also have to open the carburetor, change some internal washer spacers, etc. also.
 
I would prefer not getting into the carburetor.  

So, will the backfiring stop, if I simply adjust the fuel idle screw ... or will it require getting into the carburetor also?

Thanks for your help.

Ron G
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Re: How to stop the backfire
Reply #1 - 07/14/20 at 14:11:04
 
depends why it's backfiring.
there are a lot of reasons why it might be backfiring (technically afterfire, backfire is out the carb... you don't want that).

how you fix it depends on whether you care about fuel mileage, overheats, or flames out the tailpipe.
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Re: How to stop the backfire
Reply #2 - 07/14/20 at 14:36:59
 
For me it was leaning out the pilot jet slightly.  The white spacer mod didn't have much affect IMO.  I still get a mild "puff" at shutdown that can be eliminated by using the choke right as I kill the power.
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Re: How to stop the backfire
Reply #3 - 07/14/20 at 21:14:12
 
I just run mine out of fuel. It quits quietly without a whimper. And the float drops away from the needle relieving the pressure.
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Re: How to stop the backfire
Reply #4 - 07/15/20 at 03:21:32
 
If your pilot screw cover plug has been removed (if not remove it) then adjusting the pilot screw may help some.  Before adjusting it the engine needs to be completely warmed up, like 10 minutes of ride time, then adjust the screw for the highest rpm possible, the re-adjust the idle screw to bring idle rpm back to 1000-1100.
Do not turn the pilot screw out more than 3 turns, it could loosen and fall.

A carb running too rich or lean, and an air leak between the head/header and header/muffler can cause blasts out the pipe as well.
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Re: How to stop the backfire
Reply #5 - 07/15/20 at 05:37:15
 
If its backfiring while riding I would inspect the exhaust pipe flange at the head to ensure that the nuts are tight.
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How to stop the backfire (Part 2)
Reply #6 - 07/15/20 at 12:24:09
 
Thanks for everyone's response to the original post.

Just to clarify (for verslagen)... As we all know, the LS650 has a natural tendency to backfire occasionally on deceleration because it has been tuned to run lean from the factory.  That's what I am trying to resolve.  My bike has no issues regarding additional reasons for backfiring (has only 6800 miles on it).  It's running perfectly other than the fact that the manufacturer has tuned it lean.  This occasional backfire when decelerating (ie closing down the throttle) is what I hope can be resolved by adjusting the pilot screw.  

So, from what I am reading from everyone, by adjusting the idle screw (ie pilot screw or lean-rich fuel mixture screw) there is a good chance it will reduce the backfiring?  Again, I have no interest in getting into the carburetor.

If this works, I have only one other question.  I've read from this site how to take the 'cap' out in order to get to the pilot screw.  (By using a drill to make a hole in the cap and then inserting a sheet metal screw in the hole to pop out the 'cap'.)  So by using this method to pop the cap out, will the cap come out easily or is it quite 'stubborn' to remove? (Just wondering what I'm up against).

Thanks for your help.
Ron G
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Re: How to stop the backfire (Part 2)
Reply #7 - 07/15/20 at 12:42:49
 
Your biggest concern is allowing the drill bit to go too far and mess up the screw.

Wrap the bit with tape just behind where the bit stops tapering.
And dont push hard.

Run a sheet metal screw in (but not too far) and yank with pliers..
Its not in hard,,
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Re: How to stop the backfire (Part 2)
Reply #8 - 07/15/20 at 12:52:43
 
Others will disagree, but I don't think it really runs all that lean and I don't think that's why it backfires.

The person I got my bike from had it jetted really rich (55/155) and it backfired much more than it does after I rejetted it.  I took it to stock (52,5/145) and then went two jet sizes up and down.  First with the main jet and then the pilot.   I think I ended up one jet larger than stock on the main (147.5) and two sizes leaner on the pilot (47.5).  My bike is stock except for the HD dyna muffler.  You'll often see 50/150 pilot/main sizes recommended as a starting point.  

I use my bike for commuting and put 6-7k miles a year on my bike.  I regularly ride in temps as low as the mid 30's in the late fall and early winter. I get almost no decel backfire and only a minor puff at shutdown.  The bike runs stronger in cooler weather than it does when the temps get above 85* and humidity rises.   At that point it's slightly rich up top.  Almost all of my riding is done between 500'-1200' of elevation.

Bottom line is that you really need test and see what works best for you.
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« Last Edit: 07/15/20 at 18:54:51 by ohiomoto »  
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Re: How to stop the backfire (Part 2)
Reply #9 - 07/15/20 at 13:02:36
 
Chdeck the exhaust flange bolts, certainly..Do it with it cold, and dont get horsey with it. Youll be pulling a motor and hauling it to a machinist.
Gently see if they are Not Snug,, These arent head bolts, stripping or breakin them is a HUGE screwup.
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Re: How to stop the backfire (Part 2)
Reply #10 - 07/15/20 at 13:44:25
 
rong wrote on 07/15/20 at 12:24:09:
Thanks for everyone's response to the original post.

Just to clarify (for verslagen)... As we all know, the LS650 has a natural tendency to backfire occasionally on deceleration because it has been tuned to run lean from the factory.  That's what I am trying to resolve.  My bike has no issues regarding additional reasons for backfiring (has only 6800 miles on it).  It's running perfectly other than the fact that the manufacturer has tuned it lean.  This occasional backfire when decelerating (ie closing down the throttle) is what I hope can be resolved by adjusting the pilot screw.  

So, from what I am reading from everyone, by adjusting the idle screw (ie pilot screw or lean-rich fuel mixture screw) there is a good chance it will reduce the backfiring?  Again, I have no interest in getting into the carburetor.

If this works, I have only one other question.  I've read from this site how to take the 'cap' out in order to get to the pilot screw.  (By using a drill to make a hole in the cap and then inserting a sheet metal screw in the hole to pop out the 'cap'.)  So by using this method to pop the cap out, will the cap come out easily or is it quite 'stubborn' to remove? (Just wondering what I'm up against).

Thanks for your help.
Ron G

This is difficult, one man's pop is another KERPOW!

if it's a pop, then I wouldn't worry about it.  it's a feature   Grin
it says, hey, I'm slowing down, get outta the way!

if it's a duck and cover KERPOW, then there's something to be done.
it can be carb and you can try the idle mixture screw to see if you can make it better.
but most likely it's inside the carb and nuff said, you don't want to go there.
Sometimes cleaning will fix the issue.

Air leaks can cause popping.  check with the motor running, wave a lit candle around the joints (header and muffler) or blow smoke if you do.
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Re: How to stop the backfire
Reply #11 - 07/16/20 at 04:05:01
 
When I was jetting my carb, I installed an oxygen sensor in the header pipe and it was attached to a fuel/air mixture gauge.  This allowed me to see exactly what happens when I changed jetting.  What was really a surprise to me is that the mixture ratio is not constant - but it changes constantly as the throttle is moved.  At a steady cruise and steady throttle setting the mixture stays the same - but anytime you open or close the throttle the mixture goes slightly leaner.

When you open the throttle the amount of vacuum in the venturi drops and therefore a bit less fuel is pulled out of the float bowl......but this is just a temporary sag and the proper mixture recovers quickly.  This is why we have a CV carb on the Savage - it helps to keep the vacuum from dropping too much when you open the throttle too quickly.  (Some carbs have an accelerator pump that squirts a bit of fuel into the venturi to add the missing fuel).

When you close the throttle the engine vacuum increases on the engine side of the throttle butterfly - but the amount of air flow on the other side drops dramatically and as the slide drops the jet needle is closing off the fuel flow in that circuit.....the only fuel you are getting is from the pilot jet (idle) fuel circuit.  The mixture goes really lean when you are decelerating and the throttle is fully closed - the TEV (Throttle Enrichment Valve) on the Savage carb is supposed to open and add more fuel to reduce or prevent the mixture from going so lean - but it does not work as well as it should.  I am not sure if the valve was designed to work with E10 fuel - perhaps it would work better with pure gasoline.

You should not be jetting your carb for what it does with a "closed" throttle - your carb should be jetted for how it works while the throttle is open and the engine is making power......if your engine runs well, then don't screw around with the carb or jetting.

SUGGESTED SOLUTION -  It is relatively easy to reduce the noise out the muffler while you are decelerating.  

This is a primitive bike and a primitive engine and carb, and good Savage riders adapt their riding style to work with the bike.  You need to become the "computer" that adjusts the fuel mixture as you ride - this bike will not do it for you like a modern fuel injected bike will.

As you shift gears don't slam the throttle fully closed.  Gently roll the throttle off and leave the throttle open slightly so that you avoid the lean mixture and backfiring that occurs when the throttle is fully closed.

When you are decelerating and the popping/banging begins - open the throttle a crack just until the noise stops.  You don't need to open it up so far that you begin to accelerate and need more brake - just enough for the noise to be reduced or eliminated.

With a little practice this will become second nature when you are riding your Savage.  I have a Mikuni Round Slide on my bike, and it doesn't have a TEV or a CV slide - the slide opens/closes when I turn my wrist.  If I ride this bike and allow the throttle to close fully when shifting or decelerating it really is noisy - it pops and bangs and backfires just like a poorly tuned Harley with open pipes.......but it I ride it and use my right wrist to control the lean condition while decelerating I can make it quiet.

There have been several riders on this forum who have had the same comment as you, and they have discovered they can easily control the noise when they adapt their riding style to better suit what Suzuki has given them.  Maybe someday we will figure out how to make the TEV valve provide a bit more fuel when the high vacuum condition occurs - but for now we just have to adapt to the bike.

Try it! Wink      
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Re: How to stop the backfire (Part 2)
Reply #12 - 07/16/20 at 04:10:40
 
justin_o_guy2 wrote on 07/15/20 at 13:02:36:
Chdeck the exhaust flange bolts, certainly..Do it with it cold, and dont get horsey with it. Youll be pulling a motor and hauling it to a machinist.
Gently see if they are Not Snug,, These arent head bolts, stripping or breakin them is a HUGE screwup.



Yes, yes, yes......the exhaust flange bolts are screwed into aluminum, and should just be snug.  I use one hand on a 1/4" drive ratchet/socket - they should not be Gorilla tight.
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Re: How to stop the backfire
Reply #13 - 07/16/20 at 12:31:36
 
Thanks everyone for your responses.  Appreciate it!

Ron G
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Re: How to stop the backfire
Reply #14 - 07/17/20 at 12:21:58
 
Wanted to thank those of you that suggested looking at the bolts connecting the engine to the header.  I had one bolt that was very loose.  Could help the backfiring somewhat.

This symptom must be common since multiple people suggested looking at this.  Will now be checking them occasionally.

Thanks again.
Ron G
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