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On my 2008 rmz 450, at 1/4 throttle there's this horrible studder. It started about a month ago. The bike has about 70 hours on it i bought it later last year and never had a problem with it. The only thing that i changed on it was the header pipe it had the stock one and i tweaked it where it was making a weird noise so i replaced it with a stock one.

Things i have tried............................

New spark plug

Cleaned the air filter 

Oil change 

Checked the valves one exhaust is on the loose side but not out of spec.

I may try injector cleaner but idk if thats ok for these bikes.

Any help is appreciated thanks in advance 

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I notice you didn't mess with the carb at all. That's where I would of started.

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11 minutes ago, William1 said:

Not a jetting problem but a wear and tear one if it ran good at one times and now does not. Common wear item is the needle jet emulsion tube and needle.

 

2 hours ago, jaguar57 said:

I notice you didn't mess with the carb at all. That's where I would of started.

The bike is efi though

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Just now, William1 said:

My bad. Suspect items on EFI is a bad capacitor, bad fuel pump, or dirty injector.

Would a capacitor or fuel pump be a constant problem throughout the throttle?

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2 minutes ago, Drewbwislock said:

Would a capacitor or fuel pump be a constant problem throughout the throttle?

Could be. The capacitor has to 'smooth' electrical current and the pump keep the pressure constant. Time to dig out the service manual and follow the testing procedures. Do not just replace parts. It could also be something as simple as a bad ground or poor connection.

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2 minutes ago, William1 said:

Could be. The capacitor has to 'smooth' electrical current and the pump keep the pressure constant. Time to dig out the service manual and follow the testing procedures. Do not just replace parts. It could also be something as simple as a bad ground or poor connection.

Alright thanks ill start tearing in to it 

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Alright i know its been a month since i posted this but i took everything apart check tps, capacitor, and from the tests nothing was wrong according to the manual specs. i cleaned some connections. i then took it to the track for the first time and it seemed to have worked correctly. But i went out trail riding this past weekend and the damn bike started doing it again.... Anything else i could do? ive read that the fuel pump could cause this i may try swapping tanks with my brothers to see if it the fuel pump.

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On 7/15/2018 at 7:07 AM, Drewbwislock said:

On my 2008 rmz 450, at 1/4 throttle there's this horrible studder. It started about a month ago. The bike has about 70 hours on it i bought it later last year and never had a problem with it. The only thing that i changed on it was the header pipe it had the stock one and i tweaked it where it was making a weird noise so i replaced it with a stock one.

Things i have tried............................

New spark plug

Cleaned the air filter 

Oil change 

Checked the valves one exhaust is on the loose side but not out of spec.

I may try injector cleaner but idk if thats ok for these bikes.

Any help is appreciated thanks in advance 

1. clean/replace the fuel pump filter inside the tank. Supposed to do it every 30 hours of riding.

2. start treating all you fuel with PRI-G or similar. Unless you drain your fuel out after every ride, you need to treat sitting fuel.

3. get a tank sock or a mr. funnel and start filtering all your fuel. Pump gas is full of dirt.

4. pressure clean the injector  

 

5. DO NO ADD 'CLEANERS' TO YOUR FUEL

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