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Discussion Starter · #1 · (Edited)
Hey Guys, I'm in dire need of someone's expertise on this one!!

Check out this video:

As you can see, there's a strange sound, almost like a misfire coming from the front cylinder. You can hear them clearly at 00:14 and at 00:28.
When I have my hand over it, I can feel warm air during the hickup.

What do you guys think it is?
 

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Can't get the video to load :s
 

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Well... that's certainly not confidence inspiring. What reaction do you get if you rev it?

If you haven't already, pull the plugs and compare thoroughly, if its no trouble, replace them as an experiment. Deposits can retain heat, cause the fresh charge to pop at the end of the intake stroke. Ditto for any combustion chamber deposits.

Second, wilder ideas.. coilpack or wiring having issues or fuel injection going randomly lean on that cylinder, allowing an auto-ignitable charge to hit the chamber, it'll pop when the charge in the chamber finally touches the plug or exhaust valves... likely around the end of the intake cycle, and valve closure. If it were a total out-gas of the cylinder's contents.. you'd not hold your hand there of an obvious reason. Does say its later in the intake cycle when this happens.. if a youtube video's audio/video sync is to be trusted.


Wife says dinner time... *hears whip*
 

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when was the last time you check the cams/valves? if you feel warm air coming from the intake, maybe a valve is not seating properly, or is sticky and not closing all the way?
 

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Discussion Starter · #7 ·
Haven't been checked in years! at least 2 if not 3

How difficult of a job is that?

And assuming that's the problem, am I ok to drive it ? or does it need fixed right away
 

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If that's what it were to be, no it wouldn't "technically" be "ok" to run it. If that is combustion gas, it'll burn the valve face/seat before long. I'd imagine it would run poorly as a result anyway, not give the impression of wanting to be ridden.
 

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That is a lean misfire. It comes up the intake on overlap. You might, indeed, have some tight valves which will magnify this...but it might be taken care of with synching the TB's.

Does it make the same sound when the airbox is on? Having the box off....along with the sensors in it unplugged can make the engine do things it wouldn't normally. Sure wouldn't hurt to check the valve clearances anyhow.

The twins will 'cough' like that sometimes at very low rpms and lean fueling too. Mine used to do it after sitting during a fuel fillup. One 'cough' 'spit' or what ever you call it when giving a little throttle to pull out. Hasn't done it lately since I've bumped up the fuel pressure and thereby increased the idle fuel a little.
 
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