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Discussion Starter · #1 ·
I recently had my quad modified. It's now a 686 with 12.5:1 compression, webcam stage 2 cam, proflow filter, lte dual exhaust, stock ignition and jetting was done using a dyno...it was only making 36 horsepower and I had the mechanic look into the problem bc he said it was my exhaust which I thought was bs. My dad is keeping an eye on it and I forget what he said but it had something to do with the valves and compression...can the valves be choking my raptor up this much? Thanks in advance for the help!
 

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A damaged valve could certainly cause you to lose power, as could the wrong timing, poor piston clearances, improper cam orientation with respect to timing, etc.

And if the dyno-tuned jetting was done when the bike was having this problem then it could be way off as well.


From your post on ATVC I know that the shop that dynoed the bike is also the one that installed some or all of the parts. Looks to me like it needs to be taken back to the shop and trouble shot and fixed free of charge unless they can prove it wasn't their fault or unless the bike has run flawlessly since they installed the parts and has just recently lost all that power.
 

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Discussion Starter · #3 ·
Well here's how it went down...they worked on it, dynoed it and it made 36 hp...I took it home rode it and it was running like dogs**t so I took it back and told them something is wrong and 36 hp isn't right so he said he is going to look at it and break it down so I'm in college now and my dad said that the guy said it has something to do with the valves (hopefully that's it).. I was just wondering if valve clearance or anything like that could cause that much loss in hp.
 

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Ok, that's a little clearer. In order for simple valve lash to be so tight or loose that the bike would produce such low power they'd have to be so far out of adjustment that you likely wouldn't be able to get the bike to start in the first place.

A bent valve is common when piston-to-valve clearance isn't checked during installation or when timing or cam orientation is incorrect. These could cause such a lack of power. Also if your valve seats are leaking like there's no tomorrow you could expect to be down on power.
 

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Hmmmmm
If you have the stock carbs......
did you try the diaphragms to see if they were ruptured? One may be opening all the way and the other not or you may have both working impartially. Symptoms would include things like
>Engine runs great but flattens out or no top end
>great gas mileage
Take the tops of the diaphragm covers off and very carefully inspect them(the rubber diaphragms) . The diaphragms can be in-op but the bike still runs 'ok'. HAd it happen to me. IF you need info e-mail me [email protected]
 

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have them ck the automatic decompression mechanism it is probably installed 180 degrees out which does not allow the pin to retract.It will still run just not very good.I have seen many people make this mistake.
 
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