Back Fire

[becky]

My bike back fired a few times as i turnt the throttle. i was coming down the A12 So i was going at about 60.

Anyone no what this could be?

I do have race cans on the bike, They do splutter a bit but i didnt think it was to do with them as they only do it when i roll off the throttle.

[DoGbOt]

hmm possibly over fueling, has it been set up for the cans if not there could be the route of problem<

[The Guvnor]

You sure it was the bike ?:grin2

[Lateshift]

Very likely the bike needs rejetting after fitting the cans, its just as common as the spluttering you get when you roll the throttle off.

In simple terms you will probably find that the race cans being pretty much wide open, its allowing the bike to dump the exhaust gases too quickly and with the jetting being out, the instant you open the throttle hard its causing unburnt fuel to leak into the header pipes where it detonates and causes the bang :)

If its doing it a lot it wont be doing much for the bike and almost definitely the valves ;)

[becky]

Hmmm OK. can it be done without taking it on a dyno?

[DoGbOt]

Well there is this sparkplug type gizmo that u can buy (halfords have them) called, Colourtune, u put it in instead of the spark plug & it tells you with a coloured light whether to richen or leanen the mixture (just dawned on me carbed models only probably) but i've never really had much to do with these,

http://www.demon-tweeks.co.uk/products/ProductDetail.asp?cls=MSPORT&pcode=GUN4170

Reckon the best way is a dyno tho!!

[Lateshift]

Colourtune is all well and good but it will only confirm that the jetting will need altering slightly, lets face it, if this is going to become a race bike it would be just aswell fitting the K&N filter and then getting it setup properly on the Dyno much the same as Harrie is going to do.

Granted it isnt going to make a massive difference to the power but it will sort the fueling out properly and allow it to be ridden on a smoother throttle, then get a quick action throttle fitted to liven it up slightly :)

[Webby]

Lateshift and the others are almost deff on the money here. However, it could also be a restricted airflow problem. Check airfilter and intake hoses.

Could also be a leak at the headers, esp if you have had new cans/downpipes fitted.

[fall off]

the main problem you will have if you don't sort it out , is that i can burn the valves out and cause it to seize , so be care full .

[becky]

So the main problem is, i have a trackday on saturday and if i cant getted it sorted for this is it worth taking it!!

Can it be done without taking it to get it dynod and set up. Can i just say take it to a bike shop and they sort it the best they can. JUST as a quick fix!

[Lateshift]

They can adjust the fueling for you without too much of a problem, the only benefit from doing it on a dyno is that you are able to tune the bike knowing exactly what the fueling is doing to the power :)

If this is just the occasional backfire that is happening i wouldnt worry about it as far as the track day is concerned and just get it all sorted when you get back, if its playing up all the time though it might be an idea to get the jetting sorted sooner rather than later to make sure you arent causing any long term damage.

In the meantime it wouldnt hurt to make sure that you have got a good seal at the link pipes and also the headers as Webby suggested, at least then you are eliminating everything that you can do :)

[becky]

OK thank you for all the help. i think i will ride it into work tommoro, just to see weather or not it is all the time.

[DoodleBug]

Becky, I'll be at Micks garage Thursday night, bring it along if you are still having probs, or take it to the pub tomorrow.

[ben@gerickes]

When I come down through the gears on the limiter during a fast ride my exhaust flames up for like 1 or 2 secs. You see it on sports bikes with straight through cans ll the time becky. Its not likly to have any real negative effect. If you let you bike warm up..... Hold the throttle to the stop for a few seconds you will see that it either pops or flames. My SP1 was like a flame thrower and that was on 20,000 miles when I sold it no problems!

[Lateshift]

You couldnt be further from the truth ;)

its fine on a race bike that gets overhauled every couple of races but a bike that is throwing flames out of the exhaust needs its fueling sorted.

Especially injected bikes.

Popping and spluttering badly on the over run is a sure sign that the bike is running lean in nearly all cases, running a bike lean enough that it does it constantly will burn valves and valve seats.

Fact.

Exactly the same as holding a bike on the limiter for fun is likely to cause valves to drop (seen it time and time again and i have seen first hand a 178hp RSV Factory do exactly that and lose a championship because of it!).

Unfortunately people think its cool to have a road bike popping and banging on the overrun because it sounds like a race bike, but unless you have a race team budget all's you are doing is damaging the engine unnecessarily ;)

There are a few exceptions to the rule such as Akrapovic systems that due to their slip on design, they tend to pop a little where air is allowed to be drawn into the pipework as exhaust gas is scavenged out, but

regardless, popping and banging is a bike running lean in at least 90% of cases where someone sticks a race can on an older bike without jetting it.


Oh and for the not so mechanically minded now who dont understand that holding a bike on a limiter will be guaranteed to make a bike splutter and fire (and eventually kill it (because the CDI is designed to make and break the ignition circuit and stop you killing the engine in one go) its purely down to the ignition circuit collapsing and unburnt fuel being drawn through the cylinder and exploding in the headers and exhaust, again not good for the engine.

[DoGbOt]

There are a few exceptions to the rule such as Akrapovic systems that due to their slip on design, they tend to pop a little where air is allowed to be drawn into the pipework as exhaust gas is scavenged out,


Glad you said that cos thats what i was told about my full micron system where its all spring clipped together, you can get rid of most of it with some assembly paste like i did...... but the point im making was i thought the guy that fiddled with fuel mixture & carb balancing was feeding me a line with that 1!! lol cheers............... Good Ole lateshift 2 problems 1 thread!! supermod!! haha:laugh1

[Lateshift]

You would have thought that with exhausts (which are a science in themselves) that such a loose fit which allows air to get drawn in by gas on its way out is just shoddy engineering but it is a feature of the pipework that is factored into it, bearing in mind that the gap reduces with the heat build up, however it doesnt hurt to use a smear of exhaust paste to seal it and get rid of the popping :)

[DoGbOt]

yeah, i had to do something as the dam noise was doing my head in let alone drawing unwanted attention from the plods...... still i wont hijack this thread any longer!!:laugh1`

[becky]

Your not hijacking the thread!

The pipe work for these exhausts on my bike arnt exactly fixed together properly. il try the paste stuff :grin2

[DoGbOt]

i used

"Fire Putty, Exhaust assembly paste" its good to a 1000*C,

Make sure nobody tries to tell you that "Gun Gum" will do the same job cos it just wont it makes a terrible mess & is predominantley a BoDGing trick for blowing muffler's on cars! a guy in arrow motor spares tried to sell me it instead as he didnt have assembly paste, i dont spend money there no more thats for sure!! plus gun gum is about 3 times the price!!

Remember a little goes a long way too! as latey said the pipes do expand so smear is the operative word! i have seen this stuff sqeeze out of the gaps as it was drying & it looks minging on the outside of a pipe join.

[becky]

well i left the bike at home today, because shane has done the pipes for me, Dont no how is done them though :grin2

It still backfires past 60mph! ive ran parkies and there gonna sort it out for me tommorow :grin2