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I have a 2003 predator 500 that I bought 3 years ago. It used to be very fast and I would always beat my friend's 400ex by a lot. About 6 months ago I put in a K&N air filter and rejetted it by dropping the clip on the needle jet one notch and putting in a 175 main jet. After I did this it was much fast, however, recently it has lost almost all of the top end power it used to have but still has the low end it had:dunno::dunno: (if you have ridden a predator you know they have a lot of top end and hardly any low end power). I always change the oil on time, and I just recently had the compression and valve clearance checked and they were both fine. Spark plug is also new. I haven't done anything to the carb since I rejeted it. The top speed has also decreased significantly, I clocked it at 80mph after the filter and now its top speed is only 63mph and getting beat by a 400 is not something I am going to get used to. Any thoughts would be greatly appreciated, the mechanic can't even tell me what is going on.
 

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What was the stock main jet on your Predator? Have you done a compression test on it? Sounds like to me you need to do a compression test! What oil do you run in it? Sorry for your troubles but that is probably long overdue for a piston kit.

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Stock main jet was a 150

Check the belt and clutches - either it just needs a belt, the clutches need to be serviced or both
 

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Stock main jet was a 150

Check the belt and clutches - either it just needs a belt, the clutches need to be serviced or both
Predator 500s have belts and clutches? LOL!!
OK - I didn't check before responding, but it still has a clutch; it's just that the clutch is probably not the problem in this case, unless the engine revs in the taller gears without accelerating.
 

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That's about right! On my 400ex Honda I did a custom built slip on and K&N with outerwear. Went from 48 to 52 pilot and 152? 178 main! DS 650, cut the spark arrest or out and K&N with outerwear I don't remember the jets in this 2001, I went up on on the pilot and like 175 main. I did have to move the needle up(clip down one groove). Our local Honda shop was installing pipes, K&N with outerwear and lowering the clip one/ going up one on main jet. They were pissed when I beat them at 280lbs. There plugs were white, most didn't want my help!

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