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Message started by Silverhippi on 09/04/14 at 13:19:04

Title: LatestBackfireClarification
Post by Silverhippi on 09/04/14 at 13:19:04

Hello all,

I've noticed from owning the Big Single and visiting this forum that Backfiring seems to be a common thread among owners.

I just wanted to get a little clarification on what people are referring to as backfires.

When I first got my bike, an 03 LS650 hand-me-down from mom, it appeared completely stock except that the air/fuel mix plug had been removed. The bike would backfire when I turned it off. A clear, loud pop or crack. There did seem to be a connection to the idle setting and when I adjusted this I would get just a nice poof on shutdown, a backfire.

Since then, I've gone to a straight, unbaffled short pipe with K&N filter in the airbox. I wish I new my jet size but mechanic re-jetted the carb and I'm not cetain about the spacer mod. Maybe next time I'll have the courage to re-jet the carb. I also put in the Raptor petcock and plugged the vacuum port on the carb. My fuel/air screw is somewhere around 2 1/2 turns out. I ride daily to work which is a 52 mile round-trip. Lately I've been travelling the interstate at 70-75 mph because my two-lane back-road is under construction.

Here's how she runs now and where I'm wondering about backfiring... If I decelerate abruptly/rapidly without holding the clutch in I get the rumbling or stumbling from the engine consistently and sometimes when letting off the throttle to change gears I get the same rumbling/stumbling from deceleration.

Is this considered backfiring?

If it is, should I be concerned about it?

Even if it isn't backfiring should I be concerned about it?

As of today, I rarely get an actual pop or crack backfire and that is usually when down-shifting from third to second gear.

She seems to be really happy the more throttle I give her.

Any help and/or clarification is welcome.

D

Title: Re: LatestBackfireClarification
Post by Dave on 09/04/14 at 14:16:31

Short unbaffled pipes are a problem on this bike.....the engine doesn't like them, and you will most likely never be able to get it to stop backfiring with that pipe. With a baffled pipe the pops and bangs are a bit more subtle, and maybe occur a bit less often. Consider getting a DYNA or SuperTrapp muffler. Also you need to jet the engine so it runs well when under throttle.....not for what it does when the throttle is closed. Putting in large pilot jets to cure backfires makes for crappy fuel mileage.

Bangs on shut downs are a result of the unburned fuel igniting in the hot header pipe. When you turn the ignition off the spark is gone, and the fuel air mixture that is pumped through the engine while the engine is coming to a stop is pumped into the exhaust.....and if the pipe is hot it ignites. Richer mixtures burn less suddenly in the exhaust and cause a softer explosion - but you should not jet your engine based on what happens when the ignition is turned off. The engine should be jetted to run well...not to stop well.

Title: Re: LatestBackfireClarification
Post by Serowbot on 09/04/14 at 17:44:50

To be perfectly clear,... a backfire goes through the carb...
Technically,.. these booms that we get, are afterfires... they go out the exhaust...
... but nobody knows what yer' talkin' about when you say "afterfires" so we say backfires...
:-/...

Anyway,... pops, and blats, and wooble-wobble sounds on decel, are just a big thumper's way of announcing itself...
The gunshot "kerpow" sound is a problem, and should be dealt with...
It can come from being too lean, or too rich, or having too open a pipe...
... or a leaky or loose pipe or muffler...

Title: Re: LatestBackfireClarification
Post by Silverhippi on 09/04/14 at 18:33:32

Thanks for the clarification!

I think I'm ok with announcing myself with the wobble-bobble. :)