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Discussion Starter · #1 ·
Ok, I've got a 99 gsxr750. I did the airbox mod, put a tbr full system on, put a [email protected] filter on, took out the middle head gasket, and have the tre mod done. The bike is running really rich and thought I needed to have it tuned on the dyno. The shop guy told me that my powercommander was bad. I've unhooked it and it still is missing badly around 4500 rpm. It was a little flat before I put the pipe on and once on, it became much worse. I thought for sure it needed remapping. He told me it should run fairly good without the powercommander. Do you think he knows what he's talking about? It pulls really good above 5000 rpm, but is really twitchy down low as well. Please help. Anyone have some maps I could try?
 

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Ok well first off.. Let me tell you something about the head gasket... get a new one and put it back to stock.. there has been a lot of problem with not enough piston to head clearance... So unless you checked it, I would open it and put a stock gasket in before your motor ends up like mine..


Also, as far as the flat spot, i would look for something else... Like maybe a bad TPS... if you take the PCII off and map it with a yosh box, try running a +5 +10 +5 setting... It should run just fine without a to many flat spots...

John
 

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Discussion Starter · #3 ·
Hey John,

What's the deal with the head gasket? Did your motor fail because you sucked a valve or what? I put the powercommander back on, because I don't think that's the problem. Just looking for some maps to try. Another thing, why would the motor be running richer after I put on the TBR pipe? It doesn't make any sense. The TPS checks fine as well.
 

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I have been told that the head gasket could have cause the valve to break. I dont know how true it is, but it isnt worth it to me... I know that stock our bike come with about .026-.027" of clearance, and you should not go less then .025". The center of the head gasket is .009". so when you do the math, it isnt enought... I would take a look at it just in case..


As far as the PCII... Have you had the bike since day one? Or did you get it used?

John
 

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Discussion Starter · #5 ·
I'll look into the head gasket deal. No, I bought the bike used and added the powercommander. I put a low mileage head on it once I got it. The timing and valves are fine. I also synched the throttle bodies. It's just a really weird thing I guess. It's got 10,000 miles on it. The compression also checked good.
 

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If you can get to a YOSH box I would hav them set it back to 0 0 0 if you can.. this way you know for sure that the ECU is stock. (Do it without the PCII hooked up)

That would be a good place to start..

Also, how do you know that valves are good on the new head? Did you lap the valves? Did you even take the valves out of the head? It may sound funny but there might be a valve guide seal that is leaking..

Why did you change heads? when you changed them did you pull the block off?

If you old head is still good and you to ship it to me, and buy the new guide seals (about 75 bucks) I can clean up the head and make it run really nice..
Let me know if you want to talk more about that.

John
 

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Oh BTW what was your comp at? You said it was ok... but what were the numbers?

Also, hav you done a leak down?

John
 

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Discussion Starter · #8 ·
The compression is 165 psi across the cylinders. The mechanic zeroed the ECU with the yosh box. I didn't check the valves, but the combustion chambers were all a nice tan and I put a little WD-40 in the head to check for leaks around the valves before I threw it on. Like I said it runs great above 5000 rpm, but the new pipe aggravated the flat spot (4k-5k) and low rpm drivability.
 

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Have you done a TRE?

John
 
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