Help please

Maver-Nick · Post by **Maver-Nick** » Dec 14th, '06, 12:31

Bimbo has been riding his bike (CBR 900) everyday in all weathers...

However when he tried to start it yesterday it had what he thought was a flat battery, so charged it, then when he turned the bike over there was an almighty backfire and nothing else... scared him sh!tless, so he didn't try again.

When he went to work this morning he tried again, and the same happened, massive backfire...

Help please... BUT PLEASE ONLY REPLY IF YOU KNOW WHAT YOU'RE TALKING ABOUT (moose, andrew, age, jason, chris, gav and co.) DON'T WANNA HEAR FROM THE WANNABE MECHANICS THANK YOU.

SNIFFY · Post by **SNIFFY** » Dec 14th, '06, 12:37

Nick do you know if he tried to bump start the bike, as I have known this to wreck electronic parts. Also it sounds electronic and timing as fuel is lickley to be getting through but its sparking at the wrong time.

Thats me done.

chris_1127 · Post by **chris_1127** » Dec 14th, '06, 12:55

had he been spinning it up for a while with it not starting nick? if so unburnt fuel mixture in the can/exhaust igniting makes it go with a bang. Ditto if theres a leaking/sticking float valve making it way too rich this could do the same.

bump starting wont knacker electronic parts sniffy - did you mean jump-starting off a car? very much doubt if its anything put the timing out making it go bang though - timing will be taken off the stator/crank

fjrnobby · Post by **fjrnobby** » Dec 14th, '06, 12:55

Had similar problem with a kwak I had a few years ago. Turned out to be the ECU. Took three mechanics several hours to find the fault. See if you could get one to try.

Maver-Nick · Post by **Maver-Nick** » Dec 14th, '06, 13:03

Chris, when he turns it over on the button, it spins for 4-5 seconds then backfires.
He tried bumping it, but it didn't go... I'll give that a go later.

chris_1127 · Post by **chris_1127** » Dec 14th, '06, 13:16

is it fuel injection or carbs Nick? dont know much about efi so below refers to carbs

theres fuel getting through or it wouldnt be going bang - check for any fuel leaking out of the float bowl vents (rubber tubes hanging down from carbs) or from the front of the airbox - if so its a sticking float somewhere making it really rich. the fact that its backfiring so regularly as well suggests that theres too much fuel getting through somehow.

if hes been trying to start it for ages and the plugs have got really wet with fuel this could be compounding the problem too. is it easy to whip out the plugs on a blade and check/clean?

its also sparking/firing on at least one of the four pots, as this is whats igniting the unburnt fuel and causing the bang. might be worth checking that its not a coil gone down (in which case either the outer or inner pair of cylinders will both not be sparking) - plug an old plug into each ht lead in turn and check for a spark. i'd have thought it would still start and run on 2 - mine does - but dunno if blades are same like that, and its an easy one to check.

Post by **TLS-Moose** » Dec 14th, '06, 13:19

It could be one of several things, either mechanical or electrical ..... the one thing you obviously do have is fuel, hence the backfire

Why did he think the battery was flat - did it turn over (just) but sound laboured, or spin up just not fire, or not do anything at all

What was it running like when it was last used

Unlikely to be ignition timing, as that is unadjustable on most bikes ..... most obvious thing to do is get a plug or two/three/four out and check them for sparks. If no sparks, check the plugs on another bike, and if still no spark replace them.
If plugs ok but no spark, or just a pair arren't sparking, swap the coil leads ovr and see if the others spark - replace dodgy coil.
If coils OK, next logical step is test the ECU, then the ignitors ........ but before that go round and check EVERY electrical connector ..... easy/cheap things first

Do you know anyone else with a similar bike

if so best way is to swap parts around and see what sorts it ...... ECU's don't come cheap, even on e-bay

Just remember do things in a logical manner, and work from the plugs back.... leads, coils, ECU, ignitors, etc. ......

mechanical things which can do something similar would be cam timing or valves

if it was over-revved a couple of dropped / bent valves or the cam-chain slipping could create similar symptoms, but i'd think that unlikely ....

graham22 · Post by **graham22** » Dec 14th, '06, 14:21

Check air-box/carb mountings; Carb'd Fireblades are known to blow carbs off of inlet rubbers - usually after someone blips the throttle (gassing up the inlet) when turning motor off.

Mine used to blow the carb balance rubber bung off of No4, my mates actually blew his carbs off, just enough for it to not run.

As a result, I always shut down motor at tick-over and hardly ever had this problem.

Mike Daytona600 · Post by **Mike Daytona600** » Dec 14th, '06, 19:08

1st and i've no doubt you've already checked this Nick, make sure the kill switch is on. On Hondas the starter will turn over when the kill switch is off.

Check you've got a good spark. If you've got a dodgy coil, lead, conection,cap etc you might get the odd spark making it backfire. But it's a four so it's probably something common with all four, unless sods law says more than one of the above has gone down. Basically what Moose said.

Like others have said you're getting fuel cos of the backfire, so might be worth getting the box of tricks checked, you can do a basic check with a multimeter and a workshop manual.

If the ECU has gone down you can get them repaired. I will get a number for you from work tommorow.

Good luck

age · Post by **age** » Dec 14th, '06, 19:35

As it has been said the backfire is just unburnt fuel in the Exaust etc. It does deffo sound like an ecu problem.

When was it last serviced ?

nip it in to S P and get them to sort it, Nothing is easy when it comes to electrics You need all the kit and know how to sort it.

Age

gixerdrew · Post by **gixerdrew** » Dec 14th, '06, 22:11

Mike Daytona600 wrote:1st and i've no doubt you've already checked this Nick, make sure the kill switch is on. On Hondas the starter will turn over when the kill switch is off.

It would'nt be the first time for something like this to happen to someone. That was my first thought too.

zx10r · Post by **zx10r** » Dec 15th, '06, 14:30

sounds def like unbunt fuel
the zx7r use to do it all the time when batt was low
so when you charged batt up the first thing it would do was go bang on the first start. i just kept changing the spark plugs now and then which helped

miler · Post by **miler** » Dec 16th, '06, 10:57

occasionly get a backfire on mine especially if i open the throttle when starting,

is the battery ok, Nick are the headlights staying bright.

Have you got it sorted yet?

Maver-Nick · Post by **Maver-Nick** » Dec 16th, '06, 14:13

JEEZZUS H CHRIST...

No wonder Bimbo said he sh!t himself...

I was expecting it, but left the floor when it backfired, I've heard loud sounds before (used to work with bomb disposal) but this rates up there with all of them.

No normal backfire believe me, it happened everytime I turned it over, after 4-5 seconds...

Told Bimbo to take Age's advice, and get SP to pick it up, as neither of us know much about mechanics...

Will update and tell you what they find.

tomr6 · Post by **tomr6** » Dec 16th, '06, 17:37

Nick, I dont know what model it is but the early blades have an issue with the reg/rec and the connectors. If this is not in 100% condition it can cause a weak spark and big backfires. Also, plug gaps can cause the same issue. I've ripped a few of these apart over the years so gimme a shout if you need some advice. If you know how to use a multi meter and carry out basic checks I can give you a few pointers of where to look for faults.