Backfire on overrun

[MR&MRS.P]

So my lovely 1150gsa has a very irritating backfire at just under 2k rpm on overrun in every gear. It's bad enough to surge forward and off balance the bike. Almost dangerous in low speed 2nd gear corners.

Now, the end can to link pipe connection has a slight leak and no matter how I tighten the clamp I cannot stop it (appreciate tips for this). Is this likely to cause the backfire/surge?

Bike is completely standard, I think it has one of those accelerator things but I haven't tried taking it out...

Appreciate your help

 

[Fanum]

Learn to love it

 

[MR&MRS.P]

How did I know that was coming? Ha!

 

[Micky]

You shouldn't be on the 'overrun' in second gear corners

Air leak in exhaust system ... as Bill says "Learn to love it"

 

[nick.ct]

The backfire on the overrun on my 1100 turned out to be faulty ignition components. I changed the coil and leads and the transformation was so obvious and I was so pleased to have fixed it that I didnt bother to find out which component was the cause. Also improved greatly was the hesitation at low throttle openings.

The fault was a weak spark that didnt always ignite the mixture on the overrun allowing the un burned fuel air mixture into the exhaust system where it backfired.

A leaking exhaust can also cause the backfire

 

[MR&MRS.P]

Thanks Nick, well the bike runs lovely. Very strong everywhere, no real surging, no flat spots.

So can a leak at the end can cause this or is it more likely to be closer to the front?

 

[mspenz]

My GSA used to do the same thing and it could shake the whole bike sometimes, usually when you were least expecting it as well
I was convinced that it was the tail pipe connection and replaced the clamps with Mikalor jobbies but still the same, it eventually became so bad that it was banging almost every time I closed the throttle and it turned out to be a stick coil breaking down. Doesn't backfire now...ever

Hope you get sorted out.

 

[MR&MRS.P]

Is it strange that it is the same rpm every time, around 1900rpm?

 

[mspenz]

It might just be a 'quirk' of the bike as they all tend to have their own 'character'!
Has it always done it or is this something new? Any changes been made recently?

Can you get access to another GS of a similar age and try swapping some electrical components around?

Try using some silicon exhaust seal on the tail pipe, also used for flues and boilers, this stays flexible as it heats and contracts unlike Firegum.

 

[Decster]

mine does it with my stubby and i love it.

 

[hank]

My 1150r used to do it when I was running with a y pipe and standard can. The boys used to love it when I arrived at work on dark winter mornings, blipping the throttle would make it backfire and shoot flames out the end of the exhaust.

 

[Steptoe]

Is it strange that it is the same rpm every time, around 1900rpm?

That's because the clever ignition/fuel injection shuts off if you close the throttle at higher revs until it drops down to 2000rpm when it kicks back in.
Hence the bang.

Try just lightly feathering the throttle as the revs drop down near the 2000rpm mark.

I can get my bike backfiring to order through a combination of throttle position and revs. Very handy for scaring old biddies as they attempt to run across the road in front of me.

 

[Roger 04 RT]

+1

There are two conditions that start and end Overrun Fuel Cutoff on deceleration. Check this for detail: http://bmwsporttouring.com/ubbthrea...9029&Words=roger+04+rt&Search=true#Post769917

OFC on decel occurs above 1800 RPM but throttle less than 2 degrees.

OFC on decel ends when either the RPM drops to 1800 or below, or when you crack the throttle open a tiny amount to 2 degrees.

When OFC ends the injectors turn back on with a couple slightly longer than normal fuel pulses. If your injectors don't atomize the fuel well (cleaning) and/or there is an air leak, there is fuel to ignite in the exhaust. Bang!

 

[mspenz]

I think that Fanum said 'learn to love it'....go with that answer as it's less complex


Anyway, my GSA twin spark does not backfire no matter how hard I try so all the old ladyees can relax and people suffering from OFC/OCD should really get that seen to.

My CCM however is very handy for clearing the way through a Tesco car park

Happy banging...

 

[Fanum]

Anyway, my GSA twin spark does not backfire no matter how hard I try so all the old ladyees can relax and people suffering from OFC/OCD should really get that seen to.

Loosen off the clamp on the front of the silencer just a tad (or use a 1.0 mm steel drill ), tweak up the TPS setting to .38-.40 volts, find a tunnel and learn to love banging

 

[MR&MRS.P]

I may be naive to the boxer twin engine but all other bikes and engine types I have ridden have backfired but that has purely been in the exhaust. The gs is extra ignition in the cylinder... No bang just a rather annoying lurch forward just as I am about to tip into a bend.

 

[Mr K]

I may be naive to the boxer twin engine but all other bikes and engine types I have ridden have backfired but that has purely been in the exhaust. The gs is extra ignition in the cylinder... No bang just a rather annoying lurch forward just as I am about to tip into a bend.

See post #12. Steptoe explained it.

I'd suggest your revs need to be higher going into a bend.

 

[topcat2006]

Loosen off the clamp on the front of the silencer just a tad (or use a 1.0 mm steel drill ), tweak up the TPS setting to .38-.40 volts, find a tunnel and learn to love banging

How does that work? I've a stubby and no backfires. My 1100 didn't either but my 1200 did.

 

[Zx9man]

Back fire is standard on a gsa I think it's free with 16 k of your money lol lol lol

 

[mspenz]

Loosen off the clamp on the front of the silencer just a tad (or use a 1.0 mm steel drill ), tweak up the TPS setting to .38-.40 volts, find a tunnel and learn to love banging

Love it !