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DR-Z stuttering around 71mph

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When I'm cruising around 70-75mph my bike seems to... stutter. Like jumping in and out of power for the most part. Like cutting power to the back tire for a split split second so I'm sort of jumping forward spastically.

 

My battery is dead, so I'm hoping that when I replace that tomorrow the problem goes away, but if it doesn't what might be causing this? I have an '07 DR-Z 400SM. Full aftermarket exhaust and air box mod along with some other stuff the guy did to it.

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My 2006 DRZ400S started doing that a few weeks ago. I kinda just ignored it until it got really bad last week in traffic. It also started backfiring and had a sound like the chain in the head was lose. I am riding my second bike and put it in the shop. 

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could be a lean surging. and possible solution would be by dropping needle clip .5 to 1 clip position. 

 

what is your current jetting.

 

it has happened to me before, but it turned out that my float bowl screws were loose. tightened them up and problem went away. 

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After battery replacement if it persists take a peak at your needle and clip setting, and main jet size..

Jetting wise a stutter normally indicates a rich condition....

Edited by Craig-o

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I'm getting the new battery today if things go as planned, so I will be able to let you guys know if that is the problem shortly. Thanks for the suggestions guys! The bike has 11k on it as well.

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I had smthng like this. My battery was gone and stator was producing very low voltage(It blown either). So after 5~6.000 rpm bike was stuttering.

 

Waiting for result...

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Okay so a day late, I got the new battery in.

 

Bike starts on it's own! Hooray! Now, the problem still exists, so it wasn't the battery. I also found out two more things. First, the problem occurs at a certain RPM, I'm thinking 2/3'rds throttle is where the bike starts to 'stutter'. Second, I noticed when replacing the battery and cleaning up the bike, that the vacuum line was plugged with a screw at the end, any reason for this?

 

Mods I'm aware of:

Full FMF Exhaust

3x3 Airbox Mod

K&N Air Filter

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Okay so a day late, I got the new battery in.

 

Bike starts on it's own! Hooray! Now, the problem still exists, so it wasn't the battery. I also found out two more things. First, the problem occurs at a certain RPM, I'm thinking 2/3'rds throttle is where the bike starts to 'stutter'. Second, I noticed when replacing the battery and cleaning up the bike, that the vacuum line was plugged with a screw at the end, any reason for this?

 

Mods I'm aware of:

Full FMF Exhaust

3x3 Airbox Mod

K&N Air Filter

 

Pics.?

 

Has it got a manual petcock.?

If the crab was set up by previous owner, it could be worth while to contact them and ask what settings they used

 

Probably run some electrical tests (stator) before we start ripping into the carb....

Charging system diagnoses

Edited by Craig-o

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Not sure what a manual petcock is, but I do have a little plastic piece which has a phillips tip on it that turns, maybe that's it? Here are some pics. First is the plugged hose, second is where the the hose leads, I was told it's the vaccum line. Last is just a pic of the 3x3.

 

Just noticed they're sideways, sorry. Uploaded from my phone directly.

image.jpg

image.jpg

image.jpg

Edited by RobertLindert

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The petcock is the fuel tap that sits under the back edge , LHS of the fuel tank....

 

Std is a vacuum type petcock that will have ON ,RESERVE and PRIME stamped on it.....when it turn to on or reserve the fuel flow is automatic only when the engine is started,,requiring engine vacuum to operate via the hose you have which is plugged.... on prime fuel will run without the engine running....

 

A manual petcock has On RESERVE and OFF stamped, fuel flow only occurs when the tap is turned to ON or RESERVE...with OFF =  NO fuel flow any ant time..

 

So what the fuel tap look like..?

Edited by Craig-o

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Not sure what a manual petcock is, but I do have a little plastic piece which has a phillips tip on it that turns, maybe that's it? Here are some pics. First is the plugged hose, second is where the the hose leads, I was told it's the vaccum line. Last is just a pic of the 3x3.

 

Just noticed they're sideways, sorry. Uploaded from my phone directly.

post-392354-0-03813400-1408592112.jpg

 

What the... ?!?! AFAIK 3x3 mod means cutting the air box, not the side cover plastics  :confused:

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What the... ?!?! AFAIK 3x3 mod means cutting the air box, not the side cover plastics  :confused:

 

Depending on what the air box top opening size is and current jetting ...you could have a super lean condition go'in on...

 

BTW....you should really run a cover on that CS area...

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Yeah , that venting is overkill

 

 

Depending on what the air box top opening size is and current jetting ...you could have a super lean condition go'in on...

 

BTW....you should really run a cover on that CS area...

The air filter is inside of that mesh.

 

What the... ?!?! AFAIK 3x3 mod means cutting the air box, not the side cover plastics  :confused:

It's what the guy did, and it looks kinda cool I think, I like it.

 

 

Now, perhaps the bike is running lean. I'm going to go see if I can find the petcock and take a picture of it.

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Took some more pictures here.

post-392354-0-10248000-1408627220.jpg

Robert, it is not 3x3 mod... It is smthng 3x3x3x9 !))

 

That will distrup/spoil "feed" of bike. Especially at,,,,, at every when you throttle or idle. Believe me, it will.

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Robert, it is not 3x3 mod... It is smthng 3x3x3x9 !))

 

That will distrup/spoil "feed" of bike. Especially at,,,,, at every when you throttle or idle. Believe me, it will.

I'm sorry but I don't understand how having a more exposed air filter will disrupt things. Some bikes I see have the air filter sticking right out into the open. It's not like I'm running it without an air filter, then I could see some problems arising.

 

Anyways, do you think this is what's somehow causing the stutter? I don't see why it would.

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