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Wayne S.
Wayne S., Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 1255
Experience:  Experienced and Licensed Motorcycle Mechanic - all sizes and brands welcome.
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I have a late 2004 polaris sportsman 400 that breaks

Customer Question

hello i have a late 2004 polaris sportsman 400 that breaks up from half to full throttle. it also runs out of power going up hills. i have cleaned / rebuilt the carb replaced the ecm i found the spark plug wire pinched in between the gas tank and frame so i replaced it still having issues. the atv seems to run great for the first minute and than all of the above starts to happen. i should also mention that the speedometer is missing
thank you
Submitted: 2 years ago.
Category: Motorcycle
Expert:  Wayne S. replied 2 years ago.
Have you checked the charging system voltage?What is the plug color after running in the "break-up" throttle range?Compression is good?Thanks---
Customer: replied 2 years ago.
90 pounds of compressionThe plug is a little dark and slightly wet
I have not checked the charging system will check and get back with you.
Expert:  Wayne S. replied 2 years ago.
The 90 lbs psi compression is very low. Even worse for a four stroke engine. Check your valve clearance and if that does not help
see if the compression improves with a small bit of oil added through
the spark plug hole. If the pressure goes up alot then you need
new rings, piston, valves checked.
Low compression might account for the loss of power you are having.
Customer: replied 2 years ago.
That was my first thought but I'm not sure it will with in range of the service manual attached
Expert:  Wayne S. replied 2 years ago.
Ok, the compression figure they list there is likely with an engine decompressor working on it. That psi is low but once the engine starts the decompressor should disengage and allow the engine to run at a higher compression ratio.
If you run the engine at the problem rpm and then quickly stop it
then the spark plug color can be analyzed. Warm up the engine first.
If the charging is okay then go by the plug color to determine what
might be happening at that rpm. Black is rich, whitish is lean, tan is okay. Might be misfiring due to a lean main jet or if black might be compression or over rich fuel problem.
Get back to me with any findings.
Customer: replied 1 year ago.
Wayne my issue was with the speedometer if u recall I had asked about that with my opening question so you kind of sent me back for a couple of days
Expert:  Wayne S. replied 1 year ago.
Yes we have to cover lots of bases here without actually seeing the machines. Mistakes are often made but sometimes things work out in the end if we can help eliminate most of the common problems first.
Thanks for using our service anyway, enjoy riding.

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