Shooting flames when starting

[Q777]

The last time I started the S4RS last night, it cranked over for about 4 seconds before briefly shooting a foot long flame. It continued to crank over, starting without a problem a second later. I have the 50mm Termi / ecu kit. It has never done this before, and Murphys Law made sure I was walking behind the bike putting my gloves on as it happened. I just about sh.t myself!!!
Does this happen to others from time to time?

[herm]

never heard of such a thing.

sounds pretty cool.

[Holden]

Does this happen to others from time to time?

I wish!

[corndog67]

My S4 does that every now and then, just a pretty goog POP! out the exhaust and then starts right up.   I'm assuming residual gas in the exhaust catching (maybe)?  I think it shouldn't do that with injection, but who knows.

[the_Journeyman]

My M750 does this sometimes.  The flame is usually only visible if it's nearly dark out.  It's usually accompanied by a backfire/boom that sends people running for cover in the immediate area.  It usually happens if it's cool, I'm using full choke, and she doesn't start straight away.

JM

[ducrider45]

This happend to my old 620 once. It was pumping fuel while it was cranking, then it all ignites and BOOM.

[corey]

You're probably running a little lean...
The Air/Fuel mixture isn't rich enough, so it's not always getting a good clean burn... thus some unburnt fuel get's sucked out the exhaust valves and into your exhaust system...
Add heat/spark... viola, flamethrowers...

[EEL]

Wait, I'm confused.. running lean means not enough gas in the combustion chamber. How could you have less gas and more fuel in the exhaust pipe. I'm probably not understanding the mechanics but more rich would result in fuel leakage right?

Please explain.

[corey]

When you're running lean, their is not enough fuel in the mixture to initiate a complete proper burn when the spark is applied.
Imagine that their are little clouds of fuel vapor floating around in there. Because the mixture is too lean, sometimes there are little AIR clouds that separate the FUEL clouds. Because the clouds aren't touching, sometimes only some of them get burnt up when the spark hits...
This leaves fuel vapor/mist that is left unburnt in your combustion chamber, which is then sent through the exhaust valve and into your exhaust.
This exhaust vapor that is now in your pipes collects, and sometimes combusts (backfire) due to heat.
This is what creates that really dark black, sooty appearance inside some pipes.

This is how it was explained to me recently.

[Porsche Monkey]

I wish I had this problem.

[EEL]

When you're running lean, their is not enough fuel in the mixture to initiate a complete proper burn when the spark is applied.
Imagine that their are little clouds of fuel vapor floating around in there. Because the mixture is too lean, sometimes there are little AIR clouds that separate the FUEL clouds. Because the clouds aren't touching, sometimes only some of them get burnt up when the spark hits...
This leaves fuel vapor/mist that is left unburnt in your combustion chamber, which is then sent through the exhaust valve and into your exhaust.
This exhaust vapor that is now in your pipes collects, and sometimes combusts (backfire) due to heat.
This is what creates that really dark black, sooty appearance inside some pipes.

This is how it was explained to me recently.

But running lean creates a greyish white color not dark black soot, that is done w/ a rich mixture. I'm not an expert but I'm sensing there's something weird here with your statement..perhaps someone else can chime in.

See link below for reference

http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

[Howie]

Running lean can cause flames out the tail pipe, usually with completing the show with backfire, but not usually on start up.  More likely in this case there is raw fuel in the exhaust that is being ignited on start up since this happens only on start up.  Could be a leaking fuel injector.  I would start with checking residual fuel pressure, which requires equipment most of us don't have and is probably best left to a good shop.

[the_Journeyman]

I *know* mine's rich.  Anybody with a working nose knows it too.  That and my muffler tips are very very black.  Granted it's carbed and doesn't start as easily as the FI bikes and I figure it spits a little fuel into the pipe the on the first few spins before it catches.

JM

[Autostrada Pilot]

A flame throwing monster is something we all want   


On a serious note.....get it checked out, and if it's not hurting your engine, keep it as a mod.