Massive bangs from exhaust?

[nathaniel2910]

Guys I started my bike about a hour ago and it already takes a while to start, starter motor has to build up speed before the engine kicks, anyway hen engine usually kicks into life there was a loud bang, I stopped had a look around everything as normal, started again no abnormal noises u till a massive bang and a flame shot out of the exhaust according to the other half, so started a 3rd time and it fired but was running lumpy and there was a misfire so I just turned it off and put it back in the garage.
It's a 03 bike completely stock, recent service including replacing valve shims as were out if tolerance.
Millage unknown but roughly 10k
I'm thinking maby only once cylinder was firing and the other dumping fuel into the exhaust?
What do you guys think?
If it happens tomorow I will video it

[bmf]

Was the valve maintenance just done, or was it done sometime before?


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[nathaniel2910]

The clearance was done 50-60 miles ago

[Turd Ferguson]

Yeah, I'd start by checking spark on both cylinders.  Sounds like it could be a dead cylinder if it was misfiring and lumpy idle.

However, recent valve adjustment could mean an exhaust valve isn't closing.  I'm no expert in that area, I'll let others give their thoughts.

Dan

[nathaniel2910]

Cheers, plugs are fine, maby a tad lean but nothing bad, the exhaust valves won't be tight as there currently about 0.09mm
And the intake is about 0.07mm.
I'm thinking it must have been due to the engine cranking so slowly it takes 15-20 seconds to actually pick enough speed up to catch and fire.
Now I'm unsure why its doing it but I will start by charging the battery and take it fr there

[Jimbob]

When i had a bad battery the bike would be hard to start and then every few times i tried to start it there would be a loud bang i believe it was something about the starter motor getting stuck or something because there was not enough power. Once I got a new battery never had that problem again