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xr650l jetting issues? No power. . .

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I have a 07 xr 650 pig. I have bebuilt the motor with a .50 over piston stock compression. hotcam stage 1. I have all uncorked modes done. full xrs only exhaust. running the stock carb. I have tried all different combinations of jets, yet it still feels like its not all there. I get a little hesitation on axcell. and it just seems to not have all the power it should have. My question is the carb I wondering if it canot handle the fuel and air mix required by the motor. Has anybody ran inton a problem like this? Any help would be great.

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This is my take on it, you went with stock compression and a cam with big tube header

It's going to run poorly, with the cam and header it needs some compression the more the marrier..at lest 10.1 for a start.

You can jet it til the sun doesn't rise anymore, but until you put some comp into the gal she's not going to love you back.

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i dont think more comp is the answer, but it wont hurt you. the oversize piston really aint done anything and the cam is small. check the timing. adv= more bottom end power and returd= more top end power. what does the plug look like? that should tell you alot

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also,with a cam that small, your not going to see what you think in power gains. you got to remember, were dealing with a motor that puts out around 40hp from the factory, so the piston,cam and pipe are only going to make 4 or maybe 5 hp more. kind of hard to feel it in the seat of your pants

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i dont think more comp is the answer, but it wont hurt you. the oversize piston really aint done anything and the cam is small. check the timing. adv= more bottom end power and returd= more top end power. what does the plug look like? that should tell you alot

Why wouldn't more comp be an answer?

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comp is the the FIXALL answer. like i said, it cant hurt

A well setup motor typically gets 1hp/cubic inch and slightly more on torque. 39.60 cubic inches = 650cc's....The computer model shows 8hp difference between 8.5 and 10.5 compression, experiance has shown this to be more like 10-12. It also shows corrected pressure (based upon when the intake valve closes) to be 7.27:1 for 8.5 and 8.94 for 10.5 using the stage one cam. 9.1-9.4 is what I like to see for a street motor using 92 octane pump fuel. To achieve this would require 10.7-11.0 mechanical compression.

My larger concern would be that the 8.5 comp version would not support the that cam very well. The torque may be flat and low with the HP curve shifted closer to the rev limiter (still climbing at max rev and never reaching peak, typical for an overcamed motor).

Another, less complex, option would be a narrower cam that would make more cylinder pressure as a function of the earlier intake closing. Overall HP would not match more cam/compression but the torque curve would be better than the 8.5/Stage one combo. Last the low compression version will run cooler, be more forgiving on fuel quality, less sensitive to ignition timing and theoretically last longer but will be dogy and low on tq.

If the OP has done the correct jetting which he says he's done than the motor is not setup correctly to maximize the componets that he's using.

Now If the OP has not done the correct jetting that's a whole other debate.

And for more comp as the fixall like you stated, yes more comp will is the answer when adding big tube headers and a larger cam with different lobe centers and more duration.

More comp will overcome many downfalls when it comes to poor cam and exhaust/carb selection.

Fourstrokes love compression..........:thumbsup:

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I have a 07 xr 650 pig. I have bebuilt the motor with a .50 over piston stock compression. hotcam stage 1. I have all uncorked modes done. full xrs only exhaust. running the stock carb. I have tried all different combinations of jets, yet it still feels like its not all there. I get a little hesitation on axcell. and it just seems to not have all the power it should have. My question is the carb I wondering if it canot handle the fuel and air mix required by the motor. Has anybody ran inton a problem like this? Any help would be great.

The carb is plenty big for a low compression motor like yours, the cv carb works much better once you pump some comp into the gal.

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