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Top End Power Seemingly Flat..............

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I swap bikes a few times a week between the DRZ and a KTM SuperDuke.  The power difference is SOOOOO great that it is sometimes hard to tell if the little DRZ is on its game.

 

When I left work yesterday on the DRZ, I did my usual wheelie down the street.  I had to cut it short and it landed pretty hard.  When I got to the next intersection and pulled away, it could be my imagination, but it now seems to be reluctant to pull into the upper rev range where before it would pull hard all the way to the top.

 

My setup is an 08SM, JD kit with 155 main, 3X3 with Twin Air filter, E cams, FMF Q4 w/bomb, 14/41 gear with 4500 miles on it.  Valves were adjusted 2 months ago with only 1 exh 1 step tight.

 

I dunno exactly what happened, but it became apparent after the hard landing.

 

It starts, idles, and runs fine, just seems reluctant to rip to the top.  One thing to possibly note is that a couple of weeks ago, I ran out of fuel and when I switched to reserve, it was a no-go.  I have a Chinese gravity feed petcock that has seemed to work fine up until recently.  Another thing to note is that I recently removed the ears from the lock assembly on the gas cap.  When I did this the gap now fits much more snuggly to the tank without the thickness of the ears in the mechanism. 

 

Is this possibly affecting the tank venting?  On the way to work this morning, I reached down and released a couple of airbox cover fasteners and it might possibly have gotten a bit better, but not appreciably. 

 

I can't imagine this being a timing or ignition issue as it starts and idles perfectly.  Could the o-ring in the petcock be limiting fuel flow, not allowing it to run to the top?  Could the slam down have loosened trash in the tank?  

 

What are your thoughts?   Fuel? Air? Fire? Timing?

 

Thanks a bunch!

 

David

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Check the usual suspects.

Fuel tank petcock. Drain the tank and remove it to look for crud.

Check the air filter and the air boots to carb. Did something shake loose to cause a bit of a lean condition.

 

Does your gas tank pressurize? Does it go "pop" or hiss like a jerry can when you open it up. If so, then it's not venting properly.

 

Arm chair diagnosis is tough. You have to do the wrench work to figure it out.

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Thanks Stuwy!  I found it last night, but didn't post it.  I pretty much knew that it was starving for fuel, but with the history of stator gremlins, I thought someone might have experienced similar symptoms and would chime in.  Over a hundred views and you're the only response, so I guess not!  LOL

 

The bike sat for 5 years before I bought it in January.  The petcock was rotten and there was a buncha crud in the tank.  I cleaned on it with CLR and pea gravel pretty good, but didn't get it all.  I pulled my Chinese EBay petcock and it was ugly!  I cleaned the tank for about an hour more and cleaned the carb and all is well again.  I can really tell a difference between the morning ride in at 65F and the evening ride home at 100F as well.  I'm wondering what might happen if I stepped up to a 160 main?

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It reasonably quiet, pound or 2 lighter, and flows a bit better than the stock SM headpipe would allow.  Prolly would flow just about as well with just the Bomb header, but I think the FMF is one of the nicer looking pipes.

photo 1 (1).JPG
Edited by KTMDark
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