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2012 RMZ 250/270 NEED HELP PLEASE!

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Big bore 270 with stage 2 hot cams, FMF full exhaust and Moto Labs ECU remap.  Bike runs great!! Until I did a top end (used to own a bike shop so I've done hundreds but never dealt with fuel injection issues) .  Soon as I got it back together it took forever to get started and is popping and crackling like firecrackers in the muffler right off idle (idles fine). I have an hour meter with a tach and it idles about 2200.  Soon as I bring it up a notch, about 4000/4200 is when the problem starts. Runs fine on the top end but EXTREMELY lean on the bottom.  Within seconds the header is glowing.  I have realigned cams a dozen times, changed cams, unplugged every plug and cleaned them, disconnected hot start (thought it was a vacuum leak), sprayed carb cleaner all over the motor and throttle body while running to check for vacuum leak too, checked the valves and they are spot on and nothing changes. No water loss and no oil loss.  I keep leaning towards some sort of vacuum issue because it runs fine on top. I'm just about at the point of having to just tear the whole thing down and start over? I'm at a loss and any help would be greatly appreciated.

 

Charlie 

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Id check all the connections. Make sure air sensor at the airbox is plugged in. Temp sensor on cylinder? Basically just gotta go through everything. Do a process of elimination. Same spark plug? Did the tps get bumped? That could happen if the tps is not set properly. You can loosen torx and just turn tps by hand and see. You can mark it to get the original position reference. Is the header sealed to cylinder ok? There is a crush washer there.

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Exhaust crush washer good, ohmed out TPS.  One thing I did find was that one of the plugs on the harness side of the Temp sensor had pushed out of the back of the plug.  I thought for sure that was the problem, that maybe it was arcing and not a good connection.  I cleaned it all real good (along with every other plug on harness) and got the little silver plug to lock back in place.  Plugged it in and made sure it didn't push out again but the same result.  Could that have shorted out the Temp sensor if it had a loose connection? 

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I had the same issue after a rebuild and what I found was that I had failed to push the throttle body fully into the intake boot. Also, make sure the notch is centered in the groove on the boot. Hopefully that's all it is. IMG_0407.JPG

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Exhaust crush washer good, ohmed out TPS.  One thing I did find was that one of the plugs on the harness side of the Temp sensor had pushed out of the back of the plug.  I thought for sure that was the problem, that maybe it was arcing and not a good connection.  I cleaned it all real good (along with every other plug on harness) and got the little silver plug to lock back in place.  Plugged it in and made sure it didn't push out again but the same result.  Could that have shorted out the Temp sensor if it had a loose connection?

Doubt it shorted out sensor. However, if a sensor isn't working- ecu will go to a default "limp mode" where the bike will run but not well. Only other thing I can think of is the cam chain tensioner failed?? Only time I had missing and the bike acting up was when I had a bad coil but that was caused by an oversized rank I was messing with and the fuel pump rubbed the spark plug boot. Good luck.

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Just wanted to follow up..........I messed with it some more on Friday and found that TPS was out of wack.  Not sure if maybe it got bumped and moved a little or if that is a "wear" item, but I moved it one direction and it started right up but killed as soon as I touched the throttle (yes I marked my starting point); so I moved it in the other direction about 1/2 the thickness of a penny and it purred like a kitten.  No popping when I hold it above idle and revs smooth.  So thanks to those that chimed in to help.  I appreciate it!

 

Charlie

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