Help with missing/backfire-like issue?

[el_loco]

2002 m750, stock except for a K&N airfilter and kickstand bypass switch.  It has Remus exhaust which I had heard were not the stock pipes? 
Bought it with about 7000 miles on the clock, I have just over 8000 now.  Rode great the first couple hundred, then one ride, while accelerating up a slight hill I hear a "snap" sound accompanied by what felt like a miss or hesitation.  It felt like the motor could have cut out completely but instead it picked back up and kept on going no more problem, except starting right then the temp readings started fluctuating badly.  I rode it like this for a week or two, with the temp readings fluctuating wildly once it warmed up to 200 or so, but not before.  I finally figured out I needed to tighten the oil temp sensor connection (it was very loose) and I heven't had a temp readout fluctuation since. 
HOWEVER, Now I can start the bike and ride for awhile, usually without incident unless AFTER it's warmed up to 200 or so I turn it off.  When I re start it once it's warm and start riding, within a few minutes I have the issue.  Seems to happen more going uphill (and always while accelerating in first or second gear) around 3k to 4k RPM it will make a "snap" sound while it loses power for a split seond, accompanied by a hiss from the airbox, then it picks up and off I go.  The temp readings are still stable, no more fluctuating.  However, I am wondering if the motor is running a tad on the rich side, because I can smell exhaust more prominently while warming her up and while sitting at a red light or something.  It's also been popping on decel which I didn't remember it doing when I first bought it.
So, any thoughts?  I was thinking perhaps when the oil temp sensor was freaking out it was damaged and is throwing some mixed up data to the ECU.  I noticed a very small area of black soot on a connection at one of the exhaust pipes, could be a slight leak?  Maybe a faulty kickstand switch?  I'm hoping someone here has some helpful experience!

Thanks

[Howie]

An exhaust leak might be the cause of popping on deceleration. 

Remus is a supplier of both OEM and aftermarket exhaust.  A photo will help.

The temperature sensor in question is not a computer input, it is only for the temperature read out .

Is your airbox open or does it have a cover?  When was the last service done?

[el_loco]

Airbox has cover.  The 6k mile service was done by MotoCorsa, Portland when the bike had 7100 miles on the clock.  The bike then sat for about a year. 

[el_loco]

I was trying to rationalize the weird stutter thing as perhaps something to do with the bike sitting for a year, but I've run through at least 6 tanks of gas and it's not gone away.  Also, It's strange that it happens only once or twice, and only after the engine is run and warm, stopped for a few minutes, then started and run again? 

I'm in Portland so once the weather dries up more here I'll ride more with a deliberate objective of trying to get a more specific idea of when this issue occurs and what's happening at the time.  The bike runs great other than that, so I hope it's nothing that's going to damage components, engine or electrical?

[♣ McKraut ♣]

i'm *still* trying to properly seal the joints on my exhaust to help eliminate popping on decel...

[DaFoose]

I'm no pro, but sounds like a fuel/air issue of some sort. When was the last time the air filter cleaned? Do that unless it's been recent. Also are you wide open when it happens? If so, do you go wide open a lot and it susually doesn't happen?

It could also be electrical too, perhaps the ECU is somewhat exposed to the heat, and once warmed up, gets goofy at a certain RPM range?

[el_loco]

I'll clean the air filter, was planning on doing that anyway.  

No, not wide open when it happens, usually no more than half open, and always in 1st or second gear at low RPMS (somewhere 3,000 to 4,000)  Though next ride once it happens I'll try flogging it a few times in 1st/2nd to see if it happens.

Electrical is what I'm leaning toward, though also suspicious of the fuel filter since the bike sat for a year un ridden.  Your idea about the ECU exposed to heat is interesting, though the tricky bit is that the 'hiccup' is not consistent.  It'll happen once, then the bike will ride fine after!

Thanks to everyone who's posting, it's good to hear idea's from folks, stuff I hadn't thought of yet!

[el_loco]

Here's one of the plugs I pulled to see if it looks like it's running rich.  One side of the insulator is very light grey, the other is very dark and has small amount of buildup (sorry, low quality pic, you can't see the detail)




What does it look like to you guys?

[seevtsaab]

Cherry, u sure that plug was used? Doesn't look fouled anyway.

But -  pull them both.

[el_loco]

Ha!  Yeah, I'm sure it's used

No, it definately doesn't look fouled, but it's pretty black on the one side.  My experience reading plugs is more with 2 stroke engines, so I expect the margins are different.  This would be a pretty good plug for a vespa, but those suckers run rich pretty much as a rule!

[el_loco]

Okay, thanks again to everyone who's been following.  I have some additional details to clarify things:
Other than K&N airfilter (not an open air box) Bike is stock
The 6k service was done by Motocorsa about a year ago
The "cough" happens, it appears, between 3750 and 4000 RPM.  It's now occured in 1st, 2nd and third gear.

If I hold the RPMS around the problem range, the motor is a little bumpy at times, but nothing too worrisome.  I cannot replicate this problem at will.  I rode for 45 min. today after getting the engine up to 210 degrees+, and purposely kept running through the gears, winding up through the problem RPM range both slowly, moderately quickly, and balls to the wall.  It doesn't seem to happen more frequently at any specific rate of acceleration.

There is a bit of a "pop' sound accompanied by no power to the motor for a split second. I can hear a bit of hiss from the airbox and what sounds like a loud "click" from the front of the bike/instrument panel.
I'm wondering if the TPS needs to be cleaned or re-set?

[Mr Earl]

My M800 experienced a similar set of symptoms.  The pop/click/hesitate thing seemed to be a backfire through a throttle body.  I'd recommend these steps:

 - check compression.  You can get a suitable gauge set at Harbor Freight for about $25 and do it yourself.  Cross your fingers that it's OK.

 - pull the air filter and look down each bore with the throttle opened.  See if there's a carbon ring at the butterfly closed position on the bore.  If it's there, pull the box and clean it out with a rag with some carb cleaner on it.

 - it didn't help me, but you can pull the injectors and soak them clean.  Ducati officially recommends Yamaha Carburetor Cleaner Dip.

The permanent solution for this problem on my bike was a TFI fuel manager.  It was just running too lean above about 3000 rpm and that appeared to cause the hiccup.

Good luck, and I hope this is less frustrating for you than it was for me 

[el_loco]

Cool, thanks for that I'll give the airbox a look.  How much $cratch did the TFI fuel manager run you?  I'm about a half step away from dropping the bike off at Motocorsa.  They did the 6k service and all services for this nike before I bought it.  The thing runs so good that the compression doesn't seem like it'd be an issue, and given that the shop did a full 6k service on it less than 1,000 miles ago I assume they would have caught any compression issues!

What kind of air filter were/are you running?

[el_loco]

I had a thought:

When I changed my oil I overfilled and ended up draining some out, but I rode it to work and back first.  This is when I first noticed the issue.  I drained a good amount of oil out but even now when it's warm the level is just a hair above the top line.  Could oil be reaching the throttle body and messing with the induction at a particular RPM range?

[Mr Earl]

Cool, thanks for that I'll give the airbox a look.  How much $cratch did the TFI fuel manager run you?  I'm about a half step away from dropping the bike off at Motocorsa.  They did the 6k service and all services for this nike before I bought it.  The thing runs so good that the compression doesn't seem like it'd be an issue, and given that the shop did a full 6k service on it less than 1,000 miles ago I assume they would have caught any compression issues!

What kind of air filter were/are you running?

The TFI is about $200, maybe a bit more, if you look hard.

I have a BMC Sport filter (pretty much a K&N) plus Leo Vince slip-ons.

Motocorsa must be a better shop than the one I used, they didn't bother to check compression.

A shade high on hot oil level won't cause these problems, IMHO.