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Discussion Starter · #1 ·
Hey guys, just bought a 2005 TRX450R and it has this flat spot issue when I flatten the throttle, like it just gives up on life for a bit. Happens at about 1/4 throttle and is really bugging me. Im thinking its to do with the actuation of the accelerator pump but I could be wrong. I dont know what jets are in it or what engine mods it has. Its just a real pain in the ass when you want power and its not there.

Any help would be greatly appreciated!

Thanks Sam
 

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Hey guys, just bought a 2005 TRX450R and it has this flat spot issue when I flatten the throttle, like it just gives up on life for a bit. Happens at about 1/4 throttle and is really bugging me. Im thinking its to do with the actuation of the accelerator pump but I could be wrong. I dont know what jets are in it or what engine mods it has. Its just a real pain in the ass when you want power and its not there.

Any help would be greatly appreciated!

Thanks Sam
Does it do this easing into the throttle or only when stabbed wide open? If it does it easing into it, then it's a calibration or fuel quality issue. If it does it stabbing from low speed to full throttle, then it's an accelerator pump or fuel quality issue. Since it might be fuel related, what kind of fuel are you using (brand and grade) and how fresh is it? Finally, it might be a spark plug issue. Before diving into the carb, install a new spark plug (any brand other than Champion) and just so you know; heat range of the plug is not a factor. Heat range only comes into play when the engine is at full operating temperature - too cold and it might foul - too hot and it could induce pre-ignition.
 

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Discussion Starter · #3 ·
Does it do this easing into the throttle or only when stabbed wide open? If it does it easing into it, then it's a calibration or fuel quality issue. If it does it stabbing from low speed to full throttle, then it's an accelerator pump or fuel quality issue. Since it might be fuel related, what kind of fuel are you using (brand and grade) and how fresh is it? Finally, it might be a spark plug issue. Before diving into the carb, install a new spark plug (any brand other than Champion) and just so you know; heat range of the plug is not a factor. Heat range only comes into play when the engine is at full operating temperature - too cold and it might foul - too hot and it could induce pre-ignition.
Thank you for your help. It only happens when I stab the throttle wide open. The guy I bought it off was running 100 octane in it and I have no idea how old it was. I have tested fresh 91 octane in it but the same issue occurs. I took the spark plug out whilst it was running on 100 octane and it was really clean looking, no sign of fouling or anything like that. I will pull the plug today and check it again. I have also heard from Facebook that running a bigger pilot jet fixes it.

What do you propose from here?

Thanks again, Sam
 

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The pilot is only for idle - if you install a larger pilot jet, you will have to readjust the fuel screw to get it to idle the same and it ends up being the same fuel to air ratio as with the std pilot jet - the plug would be nice and clean with 100 octane as it is still burning when the exhaust valve has opened - the engine would only benefit from 100 octane if the compression was upped substantially and the spark timing advanced. 93 to 94 octane is as high as you want to run and 91 is fine as long as no pre-ignition occurs. Raising the slide needle one notch might help and adjusting the accelerator pump will probably be the cure. Also, if it has a K&N air filter, ditch it and install an oiled foam filter in it. Changing the filter could be the cure if it has a K&N in it.
 

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Discussion Starter · #5 ·
The pilot is only for idle - if you install a larger pilot jet, you will have to readjust the fuel screw to get it to idle the same and it ends up being the same fuel to air ratio as with the std pilot jet - the plug would be nice and clean with 100 octane as it is still burning when the exhaust valve has opened - the engine would only benefit from 100 octane if the compression was upped substantially and the spark timing advanced. 93 to 94 octane is as high as you want to run and 91 is fine as long as no pre-ignition occurs. Raising the slide needle one notch might help and adjusting the accelerator pump will probably be the cure. Also, if it has a K&N air filter, ditch it and install an oiled foam filter in it. Changing the filter could be the cure if it has a K&N in it.
Oh ok thank you for that. By raising the slide needle, does that lean it out? It has a foam air filter that probably needs to be replaced as it is starting to split. Yes I will look into adjusting the accelerator pump.

Thank you so much for your help, I will play around with it and get back to you. Thank you mate.
 

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Raising the slide needle (lowering the clip) enriches the mixture from just off idle through out the RPM range and it could affect idle a little too although usually not.
 
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