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2007 DRZ400sm

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Hi, I feel bad posting as I am sure the answer to this question is in the forum somewhere. I have done considerable reading to see if I can determine what could be the cause of my problem.

I have a 2007 DRZ400sm that I purchased last year. It has a FCR MX Sudco carb on it. A yosh pipe rs-2 full system and K&N air filter. The bike seems to idle O.K. now that I have adjusted the fuel screw 2 - 2.5 turns out. However at times it seems to studder a constant throttle around a 1/8 to 1/4 throttle position. The engine seems to miss, my guess is that I am running a bit lean at this position. If I flick the throttle the bike seems to rev nicely, also the bike will pull nicely under heavy acceleration.

I live in Ontario Canada and the temperature variation at this time of year is quite high. It seems like in the morning the bike runs better then when it is warmer in the afternoon.

I have no clue what the current setup is, however I would assume that it is as delivered from TT. I have at this point only been playing with the fuel screw as I am afraid to make the bike worse but just tinkering without a plan.

What are the steps that I should take to first diagnose the root cause?

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I am by no means a jetting experty. But I know the Pilot Jet controls the first 1/4 throttle openings, so your best bet would be to firstly play with the fuel screw to see if you can get rid of that shudder your talking about.

If it gets better as you turn out the screw, but doesn't completely go away. You would need a bigger pilot jet.

If it gets better as you turn in the screw, but doesn't completely go away. You would need a smaller pilot Jet.

I think thats how it works....

EDIT: Read this. http://www.thumpertalk.com/forum/showthread.php?t=327405

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if you installed as delivered the jetting is not right. you needed to install the emn needle and remove the pilot air jet.

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Alright, I will see what the feul screw shows me based on the recommended test process.

I did not install the carb, it was already on the bike and installed by a previous owner. My assumption is that the jetting was not played with.

However you know where assumptions get you, maybe within the next few weeks I will get a chance to investigate further. Was hoping that I wouldn't have to get that familiar with the carb but looks like if I want this studder gone I have no choice.

Thanks for your time.

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