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Hello everyone, this is my first post. I am part of SVRider and Ninjetta forum. I am happy to be part of this new forum.

Main symptoms: Bike is running on 50% power with the occasion 100%. When you power it on, it turns on fine, after about a minute, RPMS drops significantly. Causes the bike to go from below 1k rps to 2k rpms. Leave it long enough and it will turn off. When you do full throttle in N, the bike SLOWLY climbs its RPM scale.

Modification done to it: Exhaust only and K&N Air Filter. Nothing else. Slip on.

Issue started about 2-3 weeks ago. Bike was running great, I would notice it would idle kind of weird after the exhaust swap, idle would very slight drop but nothing that caused me to have any concerns. It wasn't until I performed a tune up on that the issue got really bad. I did an OIL change on it, I used Rotella oil as I like to do my oil changes quite frequently. I added iridium spark plugs on it. Everything worked great for about 50 miles and that's when the bike would run on 50% power. See video. I thought, OK maybe it did not like the iridium sparks plugs. I added stock spark plugs, worked just fine for about 200 miles and now I have the EXACT same issue.

I am about to take the sparks plug off again. What should I be looking for? Could my COILS be bad? The bike barely has 6k miles on it.
 

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I posted this elsewhere -

There are plenty of things that can cause what you are experiencing, most are pretty simple to correct.

Is the battery fully charged? Check the voltage before starting - should be 12.7V. Check it cranking - should be over 10V. Check it at idle - should be 13V or more. F.I. bikes do odd things if the voltage is low.

How old is the fuel? If there's any question, drain and refill before taking things apart. Add a strong fuel system cleaner like Techron Concentrate once per season to clear deposits from the injectors, intake valves, and combustion chamber.

Did you oil the new air filter - too much? Put the original one back in and see how it runs.

To that I'll add, check the header pipes with an IR temp gauge so you know if the issue is isolated to just once cylinder. Then you can do a swap with the coils to see if the problems follows instead of buying stuff.
 

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When it is at 50% power, is it still smooth or is there more vibration? When an engine first starts, the fuel mapping is in closed loop. Meaning it runs a preset air/fuel mixture. Once the temperature starts to rise and the ECM has finished its checks, it will go into open loop. Meaning the A/F changes in real time based upon what is happening, many times per second. A muffler can change how the engine breathes and upset the A/F mapping. But I would be surprised to lose 50% power. If someone can read the engine error codes it should identify the cause. Otherwise, I would start by looking at the oxygen sensor. Did it get disconnected /damaged when you did your slip-on?
 

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You have those terms reversed. Open loop mean it is running with out feedback as in an open loop. Closed loop means it's running with feedback.
Also the majority of US 300s don't have an o2 sensor so they are always running open loop. Even the ones with o2 sensors only run close loop at low throttle positions.
 

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Did you oil the new air filter - too much? Put the original one back in and see how it runs.

THIS.
Easy enough to check/correct, too.


To OP: for how many miles did it "run great" after you purchased the bike, before the problems started?
 

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Sound's like a bad connection or bad wire as things get warm yes by electrical flow as well the connections may be getting looser and pushed off by expansion caused by heat . Make sure plug wires are in good shape and that they connect tightly
 
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