OK so I have to give the techs at Dirt Wheels full props .....

I went and did their z400 mods: a Motoworks slip-on, and a Power Now carb insert. No jetting and kept the air box lid on....just as they did on the DW z400 mods.....

I know it might sound silly but I did not want to re-jet..... I really don't want to use any more gas then I have to these days ($4.71 for 91 octane is insane) and I ride in too much gunk to take off the air box lid......

Now first let me say WOW on the Motoworks exhaust...... this is one VERY nice piece of engineering... these guys are for real in the game and I am glad I gave them a chance...(I've always been an FMF guy).....the SR4 mounted up so easy I could not believe it..... slips right on, one bolt and done....... it looks great, very nice attention to detail...... and it sounds excellent..... not ear splitting loud at all..... in fact at idle it is almost quiet....just a nice sound...... when you get into the throttle it barks nice and firm, again not overly loud but you can hear it.... has a nice tone and impressive growl..... I could not be more impressed with this exhaust.

The Power Now insert, while not a major mod really does allow you to get away without jetting with just a slip on and the box lid still on.......I know these things are controversial but I could tell the difference with the thing in and out...... when it was out there was a slight break up, but with it in the break up was gone and the engine pops right off idle......

The net results?

I could not be more impressed...... the thing runs excellent, you can notice a significant power increase through the entire range, much stronger low-end and the mid-range barks even better then before. Top end seems to fall off about the same place as stock, maybe a sight increase but not much.....but I got exactly what I was looking for......you can really notice the pull in the low RPMs, same throttle position has more torque, the engine does not fall off under load at all in the low end which enables you to ride at a lower RPM in the tight woods.......

All in all a very nice set of mods for the money..... easy to do and well worth it....

 

if you added an exhaust you NEED to rejet, not rejetting can damage your motor. its not about saving fuel, with a new exhaust your motor NEEDS more fuel to operate properly. REJET IT>

 

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I agree with this guy!!!!!!!!!!