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Old 01-14-2014, 10:54 PM   #17
Studly Adventurer
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Joined: Aug 2006
Location: Port Alberni
Oddometer: 625
Originally Posted by Sumi View Post
You can get an idea about it in this thread:

But IMO first check for vac leaks going on anywere near that throttle body (ports on the intake, rubber boots, TB proper seating), then I'd check the valve clearances (you are into that anyways, aren't you?) And if everything seems to be fine check the TB sync.

If I recall correctly the rear flow sensor*? (is that what it's called?) is also hooked up to that intake (at the vac port), so it can measure intake air flow or whatever - so any leak in this system could also lead to misfiring/backfiring into the TB. So check the connecting hose for any cracks. Don't know how to check though whether the sensor is working correctly - maybe swap it with the front sensor, and see if the problem shifts to the front cylinder?

*Edit: Looked it up in the fische: 61041085100 PRESSURE SENSOR.

I belive the guys who adjust the TB with TuneECU, rely on the values of these sensors, so if you also have a plugin type flow meter / other syncing tool, you can quite rule out if the problem lays somewhere in here. Also to get the job done properly, if you are really willing to dig into the deep, finding out what's going on, adjusting the sync and the TPS, you'd probably need TuneECU (and lots of free time:)). That said, it can be anything different, like the TB not providing enough fuel/shutting off all the fuel on closed throttle because of a failing TPS, or misinformation from one of the sensors (o2, pressure).. I believe it's quite hard to diagnose, so if the simple things don't solve the problem, maybe living with it is easier and cheaper than fixing it trial-by-error.
Originally Posted by jwalters View Post
My 2008 990S has dirty throttle bodies as well. I keep the valves in spec but they still acquire some varnish (50,000+ miles on the odometer). I think it's normal for these bikes. Possibly due to crank case venting some oil into the airbox?? Not sure, but that would be my guess. Regardless, I wouldn't worry about, check the valves and go from there.
It will be interesting the next time I have the filter off, I recently installed the Rottweiler intake and filter and re routed the crankcase vent hose outside the intake with its own little K&N filter. It should mean my throttle bodies will no longer have oil varnish on them. Maybe? :-)
2010 990R Adventurer.
2007 Tuono 1000R
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