2007 YZ450F Jetting with stock exhaust

I just got a 2007 YZ450F with some engine mods, but the guy I bought it from sold it to me with the stock exhaust as opposed to the DRD he was running.

The bike has NO bottom to mid pull, so my question is would this stock exhaust be the culprit to the power loss and if I go to a DRD would this solve the problem?

The engine mods are as follows:

-Modified Head - ported and polished

-Web cams

-Carb work by Tokyo Mods

-New HC piston and rings

Carb settings:

main jet - 165 was running a 170 with DRD before I bought it.

clip position = center position

Fuel/air screw = 2 1/4 turns out

Any help or advice would be greatly appreciated.

The pipe may not be helping you, but it isn't hurting that much, either. The cams are likely the problem. If you switch to a stock set, especially one for an '06, your low/mid power should improve.

You may want to verify that the cams are timed correctly, too.

Thanks for your help.

Well I checked the cam timing and the markings are as per the manual at TDC. The exhaust markings at 9 and 12 o'clock and the intake at 12 and 3 o'clock.

I also checked the valves while I was there and all are in spec.

I'm new to the 450's so I'm gauging the low to mid range on my '07 YZ450F to my friends '09 YZ450F all stock, and the '09 has much more pull in the mid range, while my '07 feels like it has no mid and revs out very quick.

I'm not sure what to try first.

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