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Crf450 mid to top end bogging

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I have an 03 crf 450r and the day I was going to sell It so I took the bike for a spin up the road and the bike seemed to go fine, a little tuning on the new fuel mixture screw but then onece I went to turn the throttle over half it would start to sputter and even backfire even know I have cracked it wide open a few times before and it ran good. I would think by the way it was running it was super rich. The engine just had been reshimed and I put a new plug after this happened. I did buy a 3.4 gallon tank off a friend and I'm thinking they're might have been a tinny bit of dirt. I just looked at it inside barely before I put it on. If a jet is clogged that should make it run lean, no? what do you guys think this is?

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Sounds like fuel starvation, id take the tank and carby apart and give everything a good proper clean and go from there.

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So I took off the bowl on the carb and sure examined it till I found a little spec of dirt smaller than the bore of the main jet but knowing how touchy carbs are I thought most likely it. I checked the stator and it was healthy and had a new plug in it from before. Secured down all wires and took the bike for another spin down the road. After having the bike warmed up I put the throttle back and doing the same danm thing again...

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Check the gas cap vent, Petcock flow, and check your float level. Backfire is a lean symptom.

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The vent on the tank cap is good, Petcock seems to flow ok. I checked the float and it seems to be within spec, cleaned the bowl and main jet. Still acts like a turd. Thinking about how it could run lean I decided to go for a ride down the back top with the air filter off and didn't do a thing

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The vent on the tank cap is good, Petcock seems to flow ok. I checked the float and it seems to be within spec, cleaned the bowl and main jet. Still acts like a turd. Thinking about how it could run lean I decided to go for a ride down the back top with the air filter off and didn't do a thing

Ok- Are you getting the symptom if you slowly roll on the throttle, or is it when you whack it? Have you checked your accelerator pump timing and squirt? Are you sure the valves are in spec? Don't assume they are because they were checked or adjusted recently. Once they start moving, they will continue to until you replace/reseat.

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It does it thing more if I twist it quick than slow but will do it ether way. I reshimed the valves twice as they moved the first time and check the a third time 5 hours later to do the compression release. Perhaps the coil could be on its way out? The more I think about it it almost sounds like a lean misfire... but I could be wrong. Be mindful the bike ran good then this suddenly happened. 

Edited by Dusty99

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It does it thing more if I twist it quick than slow but will do it ether way. I reshimed the valves twice as they moved the first time and check the a third time 5 hours later to do the compression release. Perhaps the coil could be on its way out? The more I think about it it almost sounds like a lean misfire... but I could be wrong. Be mindful the bike ran good then this suddenly happened. 

Did you move the TPS when taking off the carb. That could cause symptoms similar to what your describing.

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Good news! As I was looking for the primary side of the coil I realized that the bolt fell out that held the ground wire. I'm kind of susprised it sparked at all and werd how it would only cut out at when I put it past half throttle.

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Good news! As I was looking for the primary side of the coil I realized that the bolt fell out that held the ground wire. I'm kind of susprised it sparked at all and werd how it would only cut out at when I put it past half throttle.

Looks like The Kran had it right.
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