backfiring

[Funbaldguy]

21,500 miles. I bought at 4,500 3 seasons ago. no po info. been fine till this last oil change. I have been changing every 3,000. new plugs every 8,000 or so. after about 500 miles into this oil change I'm getting backfiring? any ideas ? All else seems fine except for brake side exhaust has some how separated inside. it still flows out fine but when the pipes are off they have a wiggle to them?

[Jess from VA]

Has your bike been desmogged?

When my (desmogged) bike started backfiring, almost exclusively at high(er) speeds then dropping the throttle to decelerate quickly, it was a real surprise to me, and all the vehicles around me (who I believe thought they were being shot at).

The vacuum caps, stuck on the inside intake nipples in replacement of the vacuum lines (except #1 to the OE petcock) had big cracks in them or blown in two.  Even without desmog, maybe the OE vacuum lines back there have cracked at or around those nipples.  The fun part is, it's hotter than hell sticking your fingers back there feeling around when the bike is warmed up.

The longer you go, with cracked/blown apart vacuum lines or caps, the worse it gets.  All the air pressure on a hole or crack makes it get worse.

One of those headband led lights will come in handy, even in daylight. 

[LB]

If the exhaust manifolds are wiggling inside the muffler, you've broken the welds which will let air leak inside when you let off the gas... and it will backfire.

[MarkT]

The place where defective OEM pipe's welds break is at the header collector.  And these will be defective to fail at such low miles.  The welds are inside where you can't see them.  I have seen a number of them with poor welds - looks like they are welded manually and some welders were new, doing OJT on production pipes.  I have fixed all such pipes I've done my work on, by mounting the pipes on a jig that holds them in correct alignment, lightly welding on the outside on opposite sides of each pipe, then cutting them apart and welding thoroughly inside.

If they have just broken, they will likely backfire such that you can hear it.  Also they may have been backfiring before the break, just too quiet to hear.  They can backfire for a number of reasons, chief among them too lean - often from a vacuum leak due to cracked rubber hoses below the airbox.

[Funbaldguy]

Have not desmogged. I was considering buying a used set to use and have while these can get fixed. The question I have is he said rear baffles are out. Would this effect much? Or would it be fine. I like quiet pipes. Would I think them too loud? I want to thank you all for your input also. Sorry too take so long. I guess I’m busier than I think lol

[cookiedough]

Have not desmogged. I was considering buying a used set to use and have while these can get fixed. The question I have is he said rear baffles are out. Would this effect much? Or would it be fine. I like quiet pipes. Would I think them too loud? I want to thank you all for your input also. Sorry too take so long. I guess I’m busier than I think lol

My 98 tourer with cobra exhuast backfires horribly any gear except 5th gear when letting off the gas especially the higher rpm revs in each gear, mostly the left side exhaust though but is enough to scare the crap outta anyone around including me the driver.   guessing my 30 avg mpg has something to do with it as well as gas smell.....