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Discussion Starter #1
Okay guys, 0304 636. Recent rebuilt top end. Dyno shows that it's killing fuel and spark around 6k rpm at any throttle position. Sensors have been swapped, throttle bodies and ignition coils swapped as well. Tested cam position sensor and crank position sensor. Also idles a little rough. Plugs are new.
 

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killing fuel and spark? so its getting too much fuel? start with the basics then I guess. check the air, air filter and any associated hoses. after that It may be an injection issue?
 

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Discussion Starter #3
I don't think it's the injectors, it consistently stutters at 6k rpm at any throttle position. I have changed throttle bodies, map sensors, ignitionn coils and did a fresh TB sync.
 

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How is the dyno showing what's missing? Guessing an exhaust gas sensor is in use?

Why do you think it's both fuel and spark?

Does the bike have secondary butterflies?
 

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Discussion Starter #5
Secondary butterflies are gone, dyno sensor said it was losing fuel and the sensor placed on the coil wire said spark was missing at that moment.
 

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Does it have a power commander in it? How about a quick shifter? Is the side stand nice and snug in the full up condition?
 

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Discussion Starter #7
Does it have a power commander in it? How about a quick shifter? Is the side stand nice and snug in the full up condition?
No power commander, it's stunted so kickstand sensor is deleted, tip over sensor is deleted. Everything stock other than exhaust and sprocket. Ran fine before the the second head I put on it. Mechanically sound, timing is perfect, valve clearance is perfect. No codes.
 

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I can't see why it has issues at one specific RPM. That's the unusual part. I presume it clears up above that point?

If not, I'd be looking at the fuel pump.

A glitch in a narrow range is something I would expect to be vibration related.runs poorly from a certain point and above, state of tune, fuel delivery, etc.

Since you replaced the head, what are your compression numbers? What did you set the valves clearances at? Are you sure you're not off a tooth on the timing chain?
 

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Discussion Starter #10
I set clearances a little on the tight side, haven't tested compression but that's a good place to start. It does clear up after about 8000 rpm.
 

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I'd also make sure the intake runners are properly seated on all four cylinders...... you may be fighting two problems at the same time.
 

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Reset intake runners, getting code 51 but only at 6k rpm.
What does the code indicate the problem to be? If it's giving you a code, that should point you at the problem..... If the indication only occurs at one span of rpm, either vibration is shaking a connection loose, a wire is rubbing, or a sensor has a dead spot.

What readings do you get when you sweep the TPS?
 

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Discussion Starter #15
I've changed every sensor that has something to do with spark and fuel with no change. I switched the TPS with another one I had and again it's in the same spot.
 

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Discussion Starter #18
UPDATE
I changed the cam shafts and now it runs fine past 6k rpm. Now it's like it won't go past 12k rpm whatsoever. I have not tested compression yet which may be an issue but I'm not sure.
 

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Cams? This is a interesting glitch.. several question marks in a row = ???????? smiley faces

So the original problem was 6k,, now 12k..

I'm far from a engine expert, so I'm wondering what caused you to replace the cams and why.
When you say won't go past 12k,, how does it run up to 12k and what happens at 12k.
 

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Are the valves adjusted correctly? Weird that the stutter moved in the rpm's with a cam change. I could tell in my mustang with a solid roller cam if the valves weren't set correctly and it would be noticeable at certain rpms depending if the lash was set loose or tight. I've never worked on a bike engine though.
 
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