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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: sh00ter on September 02, 2012, 09:16:57 AM
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Hey All -
After replacing plugs and resynching TBs, the bike's developed a high RPM cutout (5k+) that is, to say the least, extremely disturbing.
It does a quick cut, recover, cut, recover until you let off the gas. Runs great in lower RPMs and seems to be more prominent in the lower gears, but it's done it in all. I'm guessing I must've horked up the TB balance ... would that do it? Any other ideas? I'm assuming it's starved for oxygen or fuel; the cutout feels just like the rev limiter @ the top of the range, but happening much sooner.
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Bad ballance on the TBs would not do that.
I'd be looking for a bad electrical connection that may have been disturbed first up, key, fuel tank connector, ECU plug, something like that. It is usualy the simple things don't go looking for anything too complicated to start with.
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... I'm assuming it's starved for oxygen or fuel...
Probably not lacking air unless your air filter is totally blocked. I'd try replacing the fuel filter for sure.
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Low on gas? The fuel pump is in the middle of the tank. If you're ripping on it when low on fuel then it starves the fuel pump when the gas surges to the back of the tank.
Fuel filter?
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As others have suggested and if you have not done it recently, replace the fuel filter. And, ensure there is plenty of gas in the tank (which makes changing the filter, less pleasant).
You might re-set the large FI connector under the seat too.
Tom
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hmmm ... I'll do the fuel filter, though I did it about 4k miles ago. The tank is just above half by the gauge and looking into it, It appears to have about half a tank. I've experienced what you're saying though duck, when I was running with the fuel light on < 1 gal left and it is the exact same experience, though I wouldn't consider this state "low" on gas ...
I can say it's really unnerving when you're cracking it hard and she cuts out a few times in rapid succession, the jerking is not pleasant. Especially in a corner.
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Another thing to check is the connector for the fuel level sender. Not sure why it would cut out only at RPMs though. :dunno2:
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Well, I filled it up with gas this a.m. Took 2.2 gallons. Rode it like I stole it for about 30 miles. No Problems.
This afternoon, took it out again in the afternoon heat. After I rode it a couple miles, parked it, then rode it again it started doing the cutout again.
Scenario like this: Riding 70 mph down the freeway, bike is completely warmed up, downshift to 3rd, run about 5-6k rpms slowly increasing (not cracking open) as soon as it starts doing so, it starts cutting, hard.
Another - after I get off the freeway, ride it in 1st, again slowly increasing RPMs - once up to about 6.5k or just before 7k, starts cutting out - way b4 the rev limiter.
Definitely it's not more than a gallon or gallon point five down from the top of the tank. Haven't done the F filter yet, but it's on my list. Any other ideas?
Another thing to check is the connector for the fuel level sender. Not sure why it would cut out only at RPMs though.
You mean the wiring in the tank?
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Maybe check your HES sensors with a hair dryer in the driveway. If one of them is starting to fail, it typically happens when hot, the ign will cut out.
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Maybe check your HES sensors with a hair dryer in the driveway. If one of them is starting to fail, it typically happens when hot, the ign will cut out.
Will check that, though it idle and pulls from idle just fine every time, only under top RPMs does it cut, then it cuts hard, no coughing, just cut, like the engine is stopping then recovers quickly - the whole cycle is very fast.
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Hi Sh00ter!
Question? Was it doing it before you swapped out the plugs?
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Hi Sh00ter!
Question? Was it doing it before you swapped out the plugs?
nope - i'm going to re-check the plugs wires etc. but i just didn't think it could be that. Logic would tell us though that the last thing touched ....
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Your new plugs.... Do they have the little metal caps on them? Not just the bare threaded stud?
It's happened before.
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Your new plugs.... Do they have the little metal caps on them? Not just the bare threaded stud?
It's happened before.
yep, i transferred them from the old ones. Could a mis-gap cause this pain?
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Update - ch1t.
Changed the plugs back to the old ones. Two blocks from my house the brick died, but the fuel pump didn't kick back in until I kicked the kickstand down and back up again. Could that be the source of my woes? the kickstand sensor? Or is this a red herring??
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Mechanic's Rule: look at what you last effed up. I've had cutouts, they can be quite disturbing, like when you're merging into freeway traffic.
I recently had the tank connector for the pump and fuel level go bad. It stranded me twice before I caught on. During the second event, if I held the connector just so, it would run. But that was out of the question on public streets. I don't think it's your problem but it's easy to check: run at idle on the centerstand, and mess with the connector. The bike will run 5-6 seconds at idle without the pump, but you'll easily hear the pump whine cut off if the connector is bad.
Early K's didn't have a kickstand sensor, but if yours is not one of those, pity. I read they are a B*TCH to change. I'd hardwire the thing if it was mine, but both my K's are early models unafflicted by this nonsense. They just have to put up with me instead.
A clogged fuel filter makes the pump dump fuel to avoid overpressure, it's very noticeable, the pump is suddenly about three times as loud as it used to be. Easy to tell, so I don't think that's it either.
If the spark plugs didn't need the little metal caps, you'd notice, the wires might not fit snugly. You should be able to feel them "snap" on.
HES sensor has been suggested; this might be it. I took the cover off and tested mine with a hot air blower. Hot enough to sizzle spit but still ran okay, sensor not bad.
Disconnect and reconnect your ECU. Always good for a laugh, easy to do and who knows, just might be worth what you paid for the work.
Hope you get this solved. Bike misbehaving can be a real pain in the azz.
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Well, initial reports are that bypassing the side stand switch has solved the issue. Just did 50 miles varying between gentle, but high revving and hard cracking to WOT; so far so good. Thanks to all who gave input on this.
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Forgive my ignorance but whats a HES sensor?
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