Backfiring/flames bad for a bike?

[Colinzor]

So i have just got my new bike a week or two, its a Kawasaki Z750 with a slip on simi performance exhaust, when its warmed up nicely and i hold the revs a second and hit the limiter i can sometimes make it spit a flame out of the exhaust, do this once in a while just with friends for some fun not riding around ringing the bike all he time

is this considered bad for the bike or running to rich? just a general question thanks
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CBR 125R 05 (Sold) | GSX 750F 1996 (Sold) | Kawasaki z750 2004

[grr666]

Mine does it really easily since I got the race exhaust. My bikes like a horse, you shouldn't stand behind it.

[RhynoCZ]

Open exhaust would normally make the mixture lean, as it'd be easier for the ''air'' to go through. If your Z750 is equiped with a O2 sensor, then I do believe the DFi unit should compensate the mixture accordingly.

''Hitting the limiter'': you should know that the rev limiter cripples the ignition, in most cases (definitely on carbed engines). This means, for that brief moment you get a lot of fuel getting into the engine and not enough ignition cycles happening. The excesive fuel is then burned in the exhaust system.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[definitelyinc...]

Interested to hear as considering getting a racey backfirey exhaust, was inspired by another mates bandit 1200 spitting massive flames

[howfastdoesit...]

It's basically un burnt fuel (that does not mean it is rich) fuel won't always burn in the exhaust unless it's warm and the mixture is right..

Dynojet power commander actually recommend adding fuel in some cases to stop decel pop. I am not sure if that works or not I'd have thought the opposite.

It's worth noting not all bikes run lean with a race pipe, it makes sense that they would but Some manufactures run the stock bike a bit towards rich in some cases... The GSXR1000rr 2006 can have a hell of a lot of tuning ( i.e. raised compression, cam timing, port work etc) and still run safe on the stock ECU, while barely effecting peak HP. I've run one at 200HP at the crank on the stock ECU and the power commander only smoothed out the curve.

Running a little bet less than optimum A/F can reduce snatchy throttle response and I think for some wierd reason it actually reduces some of the less obvious harmful gases from memory. It's also safer... Which is why road bikes are not set up for optimum A/F ratio.

Also if you are hitting the rev limit, it may be changing the ignition timing which can cause a back firing.

Some bikes have air injection systems... takes air from the airbox, to the exhaust headers, PAIR etc.. these usually open via a reed valve when the throttle is shut I recall. This is to make the emissions better. They tend to blank these on race bikes... to get more accurate A/F readings on a dyno.

Have these working will make a bike pop with a race pipe.

There is also something called overlap, which means momentarily your exhaust valves will be open, while your inlet valves are... which allows all the crap gas to be extracted by allowing some clean flow through...

All this can contribute to what you are describing, depending on the bike set up etc...

The main thing is, despite the fact people do it... rev'in the bike to limiter when it's in neutral is arguably not too healthy for it.. The motor does not rev that fast under normal conditions and there are lots of forces going on inside that engine.

Disclaimer: if any of the above is incorrect I am sorry, That's from memory. I am santa and I'm a little bit busy right now.

[Snowdonia Rider]

My SV has a lot of decel pop. It has a Beowulf exhaust, no baffle (lost) and no adjusted fuelling. Sometimes I feel like an advert for Rice Krispies
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[SuperMike]

I had a tuned impreza P1 a number of years ago. Used to put a cat on it for the MOT each year and then the other 364 days ran around on a wing a prayer that plod wouldn't do a full inspection of the various rally equipment I had under the hood.

Anyway, the flames. Oh the glorious flames. Being a bit young and silly I also had the tuning shop install a 'flamer kit' in the big bore exhaust - basically a spark plug drilled into the pipe that you could turn on and off with a switch. It used to pop and spit flames anyway, but with the added spark plug on a dark night you could see the road lighting up orange in the rear view mirror. Awesome fun.

Anyway, did that for 8 years and no harm done. I wouldn't stress about the odd spit from a motorbike.

[Vracktal]

It's fine.
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2007 BMW R1200R: On road
2009 BMW G650X Challenge: On road
1975 Norton Commando 850: Off road, awaiting recommissioning

[Pete.]