I'll add a bit of info I read about intake spacer length. Says a lower geared quick revving motor does better with a shorter carb to head spacer length. The Hawk, mine at least, was geared far too low from the factory, it had 15/45 sprockets, I put a 17 on the front and I can tell zero difference in power, as in there was no loss of power, it made the bike far better to ride and greatly increased the top speed.
The 167FMM isn't a fast revving engine but it does make decent amounts of torque in it's mid range, so this is where we'd benefit most from our efforts to increase power, the 17/45 sprocket combo seems to do a good job of targeting this mid range power. My research says that a longer intake tube between the carb and head is exactly the type of setup you want for an engine that's a little slower revving. Since there is more mass of air/fuel flowing you get a better cylinder fill from that setup. Too long of a distance from carb to head and you'll get fuel pooling in the head. There's also some sciency bits, I'll quote them here:
Quote:
The intake system on a four-stroke engine has one main goal, to get as much air-fuel mixture into the cylinder as possible. One way to help the intake is by tuning the lengths of the pipes.
When the intake valve is open on the engine, air is being sucked into the engine, so the air in the intake runner is moving rapidly toward the cylinder. When the intake valve closes suddenly, this air slams to a stop and stacks up on itself, forming an area of high pressure. This high-pressure wave makes its way up the intake runner away from the cylinder. When it reaches the end of the intake runner, where the runner connects to the intake manifold, the pressure wave bounces back down the intake runner.
If the intake runner is just the right length, that pressure wave will arrive back at the intake valve just as it opens for the next cycle. This extra pressure helps cram more air-fuel mix into the cylinder
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Might be worth a shot to experiment with this. Also, the intake tube running up to the carb definitely benefits from keeping a uniform circumference throughout it's length. The Hawk airbox would seem to wreck any benefits gained from this as the tube opens up into a box. You'd be better off running the intake tube into the box and having a round style filter on the end of the tube, merely using the box to keep water/debris out, tossing aside the Hawk's lawn mower filter.