Bike would not start followed by a loud BANG!!!

[Darren27]

Hi all, need a bit of help and advice on this one.

Last week my exhaust started blowing, traced it to the joint from the real cylinder behind the shock. As a temporary fix I slapped on a little exhaust paste to seal the joint until I had time to sort it properly.

Today I got the bike out of the garage to go to work, on the side stand open the choke a little and pressed the started, the motor turned over but would not start, sounded like trying when the kill switch is off. Bit more choke and tried again, the same. Flipped up the side stand thinking it might be the cut out switch and tried again. The motor turned over briefly before there was a very loud sharp bang, which scared the crap out of me, I almost dropped the bike! several neighbours looked out of their windows trying to see where the explosion came from. I did try again after but the engine would not fire so I gave up and went to work in the car (and was late!)

Is there anyway that by sealing up the joint in the exhaust I could have stopped my engine from working and why did it go bang!

My bike is an 05 ABS model which is under a dealer warranty but the exhaust is not covered, I don't want the dealer to collect the bike then blame it all on the exhaust and charge like a wounded rhino for the repairs.

Any help would be greatfully appreciated.

Cheers

Darren

[fatowl]

sounds like it back-fired. caused by unburnt fuel getting into the exhaust, then being ignited when the engine starts. probably nothing to do with what you've do at all, it was just playing up.

[LUNLUNZAI]

Did you leave it unuse for a period of time, say 1 week?

I had the same issue with my alp and bandit 1200 and the back fire I had on the bandit was as loud as firing a gun if it is unused for a week or so.

Personally, I dont think there is anything to do with the exhaust paste.

[Zenarchy]

Dont know if this could be related, but I've heard about people hitting the killswitch then flipping it back on quickly to give pedestrians about to wander onto the road a fright (causes the bike to backfire for some reason - never tried it myself incase it caused any damage). If you were having a problem turning it over to begin with, could this be related to what happened?

Either that you've touched the kill switch accidentally when it's turning over, or if there's some problem with the kill switch (you mentioned it sounding like the kill switch was on to begin with)?

Just a wild guess and don't know enough about them to know myself, but if you're looking for options other than the exhaust it might be worth considering.

[davsato]

called a killswitch backfire, they are good fun till one day you shoot the bloke behind with the baffles from your endcan blowing out!

the backfire shouldnt be anything to do with it not starting like fatowl says, its just a by-product of turning over without starting, youre priming the whole exhaust with mixture then when it does spark the whole lot goes off like a gun.
i suppose if the Fi has a lambda sensor in the exhaust at the exact place you put the paste then you might have fouled it, but what are the chances? i doubt it.

sounds like you flooded it, do you always start it with the choke? try again, with no choke. also is your battery up to snuff?

and check the obvious, mine wont start but it will turn over with the killswitch on

[z-weiser]

er . . could be Osama bin Mouse trying to free the garage from the human invaders!!??

probably unburnt fuel in the exhaust!

mine does it every now and again!

then starts working!

go figure!?

[Darren27]

Well its still dead, I've checked over all the obvious bits, kill switch, side stand cut out, fuse box, nothing wrong there.

When I try to start it turns over strongly but just wont fire. I did notice that after only a couple of seconds on the starter with no choke or throttle there was a strong smell of petrol so I'm starting to wonder if its the fuel pump or engine management pushing too much fuel through and flooding the engine preventing it from starting. The ignition must be sparking to cause the backfire from the exhaust when the fuel mixture mixes with air in the exhaust to lean the mix.

I guess this means its going back to Honda for them to fix now, just have to hope it wont cost too much!

cheers

Darren

[davsato]

hmmm......

i would let the dealer have it back if its still got a warranty. even if its the exhaust (doesnt sound like it to me) and he wont sort it at least you will know what the problem is.

[Darren27]

Well the bike is now running fine without having to go to the dealer.

My dad happened to mention the problem to a friendly mechanic at his local Yamaha dealer and he suggested disconnecting the battery for a couple of minutes then reconnecting and trying to start the bike.

I tried this the other day and after reconnecting the battery the bike started first push of the starter as it always had. I have so far put on another 150 miles without it missing a beat.

The mechanics thought was that the ecu/fi system was compensating for the blown exhaust by enriching the mix, once the exhaust was fixed, for whatever reason the ecu was still using the rich mix and so was flooding the engine and preventing it from starting. Disconnecting the battery effectively rebooted the ecu and reset it back to factory default.

Something to be said for carbs!

[fatowl]

Glad it's sorted It's a new one to me !