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Problems with nsr250 mc21 help.


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Alidis

 
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Problems with nsr250 mc21 help.

Sun Aug 14, 2011 4:55 am » Post: #1 » Download Post

Going about 80mph on the highway and then flat lined( cut off ). Went to the side to start and got backfire. Towed the bike and had spark plugs replaced, started fine but with the backfire and something strange. Open throttle and it was jumping from 0 rpms to 2000rpms and kept jumping back and fourth. So I took the carbs off and cleaned them piece by piece in the ultrasonic cleaner. Second, took the top ends off to clean any carbon on the pistons, heads and valves. Put all back together and was doing the same thing. Idles and starts fine but when I open the throttle its still jumping from 0-2000 rpms with never going over at full throttle. Also at full throttle I feel the air and small amounts of fuel being pushed backwards. Did a pressure test and got 120 psi readings from both pistons. Pre mixing 30:1 ratio and at idle smokes just a bit. When the throttle is fully open and it's jumping , sounds like there's no build up of air. Haven't checked the crank seals yet or can it be electrical. Please help.
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Dave Ett
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Mon Aug 15, 2011 9:33 pm » Post: #2 » Download Post

Is the bike completely standard or modified in any way?

That kind of behaviour sounds like an electrical fault to me.

When did you last check that the power valves rotated freely, and weren't sticking through carbon build up?

Check the throttle position sensor is firmly screwed to the right side of the carbs, and get a multimeter on it to check the resistance changes smoothly as you slowly rotate the throttle.

Check the plugs to the PGM (in the seat hump) are firmly attached.

Could also be an earth fault, so check the battery cables, and earthing lead to the frame are making good contact.
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Alidis

 
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Thu Aug 18, 2011 12:43 am » Post: #3 » Download Post

Thank you for responding, bike is all stock. Checked coils, tsp works fine in all throttle pulls. Checked the cdi, everything looks fine in that area. Wires have not been cut in any way. As for the valves, they were clean with new top end. Have to agree, it's got to electrical due to me doing everything when it comes to the engine....! Can it be just looking for a new cdi...? Any thoughts.
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Alidis

 
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Thu Aug 18, 2011 2:22 pm » Post: #4 » Download Post

Checked the coils with the bike on......well, when I was pulling the throttle the meter was jumping from the ranges of 0.02-18.00-10.48-2. ...just flashes on the screen? Does that sound right. Also the pulse generator has no reading when the bike idles.? Took a video of the bike and what's going on. I can email you the video, so you can see what I'm dealing with.
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Thu Aug 18, 2011 6:16 pm » Post: #5 » Download Post

There's no way a digital mutimeter sampling rate is high enough to make sense of things when the engine is running. You either need an analogue meter or an oscilloscope to accurately measure anything.

Were you trying to read voltage or resistance?

Low or high tension side?

Since you're down by the coils, check that the spade connectors are nice and clean with no blackening or corrosion. They have a tendancy to open out a bit, which makes for a bad connection. Clean them up with a bit of sandpaper and if they're too wide to firmly grip the terminals, close them up GENTLY with a pair of pliers.
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shmokica

 
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Fri Aug 19, 2011 7:23 am » Post: #6 » Download Post

Have you checked the voltage across the battery terminals when the bike is running?
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Alidis

 
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Fri Aug 19, 2011 1:42 pm » Post: #7 » Download Post

Dave, thanks for taking the time to help. ...checked the coils, every wire is nice and firmly tight. There is no signs of corrosion or discoloration on the connections.
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Alidis

 
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Fri Aug 19, 2011 1:45 pm » Post: #8 » Download Post

As for the battery..... when the bikes key and switch are turned to the on position, the battery reads 12.50 and 14.44 at idle.
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Fri Aug 19, 2011 4:02 pm » Post: #9 » Download Post

Have you checked the earth connections to the battery, engine and the frame?
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Alidis

 
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Fri Aug 19, 2011 10:04 pm » Post: #10 » Download Post

Checked all 3 grounds that you pointed out......the neg terminal on the battery, on the side of the frame (seat area) and one more that is located under the tank. Un-bolted all screws and sanded for good contact.......nothing.!
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shmokica

 
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Sat Aug 20, 2011 12:30 am » Post: #11 » Download Post

Check the voltage as the revs increase, ie slowly increase the revs, the voltage output should stabilise around 14.5V. 14.4V seems high for idle. The reason I ask is if the voltage regulator is faulty, the voltage will just continue to increase. This increased voltage level will in turn alter the way that the electrical circuits operate, ie timing, coils etc.
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Dave Ett
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Sat Aug 20, 2011 10:11 am » Post: #12 » Download Post

Agreed. Check that next...
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Alidis

 
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Sat Aug 20, 2011 2:12 pm » Post: #13 » Download Post

Due to the fact the bike won't let me rev it up, I checked the battery again at 1,200 rpms (idle position) reading 14.44 steady. Like I stated, the bike idles fine it's when I pull the throttle it starts jumping from 0-2,000 rpms. So testing it when it's acting up, reading jumps around from 14.62-14.28. Have a cbr 900rr, grabbed the regulator from that. Readings are 14.62 steady at 1,200 rpms and when pulling the throttle jumps from 14.42-14.72. Both regulator are burning hot after just a few moments of testing.
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Sat Aug 20, 2011 3:49 pm » Post: #14 » Download Post

They do get hot, as that's how they dissipate the energy - the alternator can kick out up to 70 volts, and it has to go somewhere!

Those readings do seem a little high, but if the reg / rect from the Blade is fine then I'd suspect it's not that.

What resistance readings did you get from the TPS?
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Alidis

 
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Sat Aug 20, 2011 6:16 pm » Post: #15 » Download Post

With unplugging the tps and turning the key and kill switch on, the reading is 3.90 and second wire is 4.66. When I connect the two plugs together to check the tps the reading are 4.18-0.93 when the throttle is pulled fully open. The second wire reads 4.58.
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