Bike won't start

Hi,
I've been trying to start the engine but I'm having issues, I had a loud noise , a bang coming from the exhaust in the best case scenario. Battery new, fuel pump working, fuel filter new, air filter clean and cleaned the pipe air filter too, full choke won't start the bike, I can hear the starter cranking, second gear push start method also failed. Do I need to clean the carbs, change the spark plugs? I've already cleaned one spark plug but nothing changed.

Is the battery connection good and tight?
Is there a rev counter error code?
Is there fuel in it?!
You may have flooded it, in which case try cranking it over with full throttle and choke off. This probably won't start it but may help clear the excess fuel.
Leave it a while, then try again with your normal starting regime.
If this yields nothing, then it's time to suspect things like the coil(s), CDI and associated wiring.

Was the spark plug wet when you took it out?
How old is the fuel?
Did you test for spark?
Did this happen after you changed the fuel filter and the cleaning of other bits?

That bang could be a bit worrying - I had that once but I was able to get the bike started, eventually, but it never ran properly. Turned out the 'back fire' blew back into the carbs and managed to dislodge one of them. If you can move the airbox, chances are it could be that. This scenario is the least likely to be the case though

I'm suspecting something to do with the wiring and CDI, or is it the carbs that need cleaning? Maybe it's a fuse or something?
I have removed the excess fuel by blowing air thru the air filter pipe coming below the airbox and still nothing changed, I get backfire if I use full throttle and full choke with many retries.
Battery new bought this summer Yuasa and fully recharged.
No idea how could I diagnose and see a rev counter error code.
Yes fuel is pumping when I turn the key, I can hear the clicks and the carbs are filled with fuel.
Steve, what do you mean by moving the airbox?
I have opened the air filter box and there was nothing wrong.
No the spark plug wasn't wet, but electricity passes when I start the engine thru the spark. I'm considering getting new iridium NGK, she has plain NGK now, but I haven't changed those, so they could be old. This happened after I changed the fuel filter and pipe but I have started the bike a couple of times since then.
The fuel is new, the tank was recently cleaned from rust also, it stayed about two weeks in the garage in dust cover in rainy weather, I haven't filled the tank but there is enough fuel coming to the fuel filter and the valves. The fuel pump is clicking normally, I only get an exhaust backfire when I constantly try to start the engine, the battery gets wasted after many retries, I need to recharge it again.
Thanks for all the input!

I wouldn't worry about the airbox / carbs off at the moment - think mine was an extreeme case and you have said the backfire occurred after full choke and throttle.

You'd notice error code on the rev counter, if the needle jumps from 0 to 3k or 8k and back to zero then that is an error - one is for the Throttle position sensor and the other relates to the fuel level sensor, most of the time that comes up when you have the tank off and have disconnected the cable.

I wouldn't put Irdium plugs in, they do nothing for performance and are not designed for the 'Cat - the plugs really need a fuel injection system to keep the mixture spot on as well as - I think- a higher voltage. They don't last longer, if anything they may have a shorter life span.

Silly question maybe, are you sure the carbs are being filled with fuel? You can hear the pump priming for a number of seconds then stop, if you turn off the kill switch and back on again (or the ignition key) do you hear the pump priming again?
I'd have expected to see wet plugs from all the full throttle/choke - flooded engine. Can you smell un-burnt fuel from the exhaust?

It might be worth checking all the HT leads for a spark - if you have a spare plug use that rather than take all the plugs out. If they all spark then that pretty much eliminates the coils and the CDI. Could still be duff plugs, but for more than one to go just like that isn't that likely.

The fuel valve under the tank isn't half open is it?
I'm thinking the odd backfire might be not enough fuel getting to the cylinders.

A pinched fuel tank breather hose might also cause it to starve (simple check is to open the filler cap and let it breathe through that).

Did you take air pipes and fuel pipes off? If so did you put them back the right way round. Check throttle cable just in case pinched somewhere and stuck open. Look round carbs for fuel leak, Can you smell excess ful when trying to start? Smell the exhaust can, does it smell of fuel? check coil packs for spark to all flugs. Ground against frame and do one at a time dissconnecting all leads from plugs so engine doesnt start (or not)

Sounds like its over fueling and then igniting causing the back fire.

HT leads in the right order?

Yes if numbered check you have them in the right order first off as this could be the issue as well

has a mouse or other form of rodent set up home in your muffler and causing back pressure? lol

Don't hold a cigarette lighter up to the end of the pipe to check though or you could become part of an urban myth (like that Doctor and the bloke with a hamster up his arse).

Richard Gere?

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'Armageddon!'

I'm going to get some new spark plugs, I think it's and ignition cause, no I haven't changed anything and the fuel is getting there, the air as well, but the plugs are old enough and should need replacement, I don't know if these are the symptoms of old spark plugs though. So I'm getting at least one NGK CR9e 6263 to swap and I will report back. The Leads are ok, I haven't removed anything so it's in the right order, could be a mouse burger now in the exhaust .

Eddie990 wrote:'Armageddon!'

That's the one.

Swapping the plugs certainly won't hurt HeZoR.
Standard ones last for ages, iirc I got about 30k out of my last set.

I have the new NGK CR9E 6263 spark plugs here, however the gap size is 0.30mm and the ones already installed. The manual of the 'cat has the gap at 0.70mm to 0.80mm, that's far from the factory setting of the pre-gapped spark plugs. Any recommendation before installation would highly be appreciated.

If those are the plugs stated for the cat then the gaps are pregapped (is that a word?) So should be fine to use.

Thankfully, it was the spark plugs.
I swapped two of four and the bike started, also it felt like it is starting faster. I'll have to change the other two plugs from the right side of the bike, when I'll have some spare time.

Well done! Always good when it's an easy(ish ) fix.

I've learnt my lesson now with plugs, they are relatively inexpensive, will be doing mine more often. I left an iridium in a bit too long and the plug got stuck in the engine - ended up with a 'new' engine.

Stevecat. ... how long was too long? Just out of interest?

If I remember correctly, it was about 2 years. I think the bike stood for a few months, unused, before I bought it so the plugs might have been in the engine longer (they had only done a few miles when I collected the bike).
It was then I discovered one of the plugs would not come out, the others were replaced and the stuck plug (the threaded part exposed in the engine became damaged) died about 10 months later.

I should add that a few years ago I was in the habit of racking up a fair mileage. Not that would contribute to the damaged/stuck plug, but would explain the relatively short life span.

In the four years and 44000 miles I had my cat I didn't change the plugs, still ran perfect

SteveCat wrote:... I discovered one of the plugs would not come out ...

Some people will overtighten their plugs, a half turn is enough.

That's good to know then. It's just I've got the iridium ones on mine but they've only been in there about 8 months and only seen about 2000miles. I will be changing them in a few months anyway just to play it safe

wouldnt be over keen to swop them out, maybe after a couple of years but 10 months is a bit of a waste of decent spark plugs. If your getting no issues with them i wouldnt worry about it. If your concerned then maybe loosen, then tighten by hand then just a qtr turn and bobs your uncle.