Here's my Hawk in stock form. These are wonderful little bikes, with handling far beyond the power they put out. They also lend themselves to hopping up and racing (no, family, don't worry, I'm not racing - this year;). The Hawk (RC31) has a 647cc 52 degree V-twin with crank spacing that makes the cylinders fire like it is a 90 degree V-twin. It also has a single-sided-swingarm that makes changing the rear wheel easier than pie. It has a rigid twin spar (extruded) aluminum frame that can handle almost anything - many raceHawks have 70+hp and run slicks or sticky DOT radials.

So much for stock. Modifications:

• Engine:
  
• Intake: I took the stock airbox lid and introduced it to my favorite holesaws. Repeatedly. I also noticed the stock air filter had only a small surface area of material, so I made my own filter. I took another stock filter and trimed the plastic back, especially over the two carb intakes, trimmed the restrictive sheet steel with holes, but left he back-fire screen in place, and glued in some foam from a few performance filters I had lying around. Presto. Freed up intake & a honk on full throttle that sounds delicious.
• Carbs: Instead of buying a jet kit, I decided to try it myself. Being in Colorado Springs at about 6500ft, I didn't think I would need the same jet sizes anyway. I reamed the Pilot Jets from 42 stock to 43. The next size Kehin makes is a 45 and most references thought that was too big except for all-out race engines. I enlarged the mains from 132/138 (yes, they were different front & rear) to 140. I also bought a bunch of stainless M2 (or M3?) washers and mic'ed them to get two of them to measure 1.25mm and placed two under each needle to raise it. The result is crisp, smooth carburetion at all rpms & throttle openings.
• Exhaust: I got a good deal on an ex-racer's Two Brothers Racing exhaust. Problem was it was an early non- tapered design that had large-diameter primaries that apparently caused a mid-range flat spot. I didn't want that so designed around it. I made some anti-reversion stubs & had them welded in at the port-primary interface (thanks, Rob). They are the same size as the port and extend about 1.5" into the primary. They operate by allowing forward flow unrestricted, but restrict reverse flow when the reverse pulse pressure wave tries to push exhaust gasses back into the combustion chamber. David Vizard has documented this design and it's power additions on 2.0L OHC Ford engines and small-block Chevys. The other thing I tried was purely theory (or BS). I noticed a lot of motorcycle exhaust manufacturers tying primaries together on 4cyl bikes. They claimed it helped midrange through softening the reverse pulse strength. So, I tried it. I got a short length of 3/8" brake line w/fittings and had two bungs welded on the primaries (thanks Rob). I bent it up to go between the pipes and Viola! I have a pipe with no flat or soft-spots. Of course I haven't control- tested for these variables, but either way, it works great, so I like it. I also packed the cannister with stainless steel "scrub boys" instead of fiberglass so it will never blow out. Nice and throaty V-twin roar with a melodious burble on decelleration. I also had (Guess who - thanks Rob) weld a bung on the collector to mount an oxygen sensor for my air-fuel ratio gauge.

• Suspension:
  
• Tires: I ran stock size tires for a while, 110/80R17 front and a 150/70R17 rear in a Metzler MEZ1 front, MEZ2 rear. That made a world of difference over the hard tires that came with it. I have since upgraded to a MEZ1 rear in a 160/60R17 size. I like the better stick, as it is less likely to "walk around" while cranked over, but because it's a little softer, probably won't last as long. I have a 120/70R17 MEZ1 front, but am waiting to put that on until I have the wider CBR 600F2 front wheel installed.
  
• Forks: First thing I did is to lower the front end by raising the forks in the triple clamps. I moved mine up about 1cm which steepened the rake angle and reduced trail to quicken the steering nicely. I recently redid the front end, changing the fork fluid from stock 5weight to 11wt (mixed 10 and 15 to get it). I also cut 2 coils off of the fork springs and made slightly longer preload spacers from 1" sched 40 pvc. This has nicely firmed up the front end, making it a little less dive-prone and a litle more planted while heeled over. Next on the list is a complete CBR F2 front end with dual disc brakes and all.
  
• Rear Shock: I got a deal on a remote reservoir Progressive shock that is adjustable for compression and rebound, but is the same length as stock. I am going to have it rebuilt before installing it, and have them extend the mounting points .5" for a little increased rear ride height.

• Body:
  I put on F2 clip-on handle bars which are a few inches lower than stock, and give it a nice cafe-racer feel, along with getting me lower and a little more forward on the bike.
  I also installed shorty front & rear turnsignals I picked up at the local shop. I mounted the rears in the stock location (benefiting from rubber vibration isolation) and the fronts I mounted into the aluminum headlight brackets. Cleans up the looks nicely. I also shortened the rear fender and removed the two extra reflectors. I may completely remove the license light and mount the plate right under the taillight, but for the amount of attention the local constabulary has been giving me, we'll leave it for now.
  I got a LockhartPhillips copy of a Corbin gunfighter seat from a racer that crashed for next to nothing. I had a local cycle specialist (thank you Patsy) reupholster it in all black with squareweave and smooth vinyl. Much more comfortable. The pillion is much smaller, but none of my passengers have complained yet. (of course they were probably too busy hanging on to notice!)
  The tank has a few dings, the front fender is scratched, and the rear cowling is thrashed. I could just buy new, but where's the fun in that. I love the black Hawks I have seen but I want something a little different. Soooo, I think I will do black bodywork and wheels, with a stripe of my family's tartan (plaid) from Scotland down the top-middle. We'll see.
  I also met Jay Wright, a very nice guy in Woodland Park who specializes in single cylinder racers, doing crazy downdraft head conversions and such. I am trying to find a spare tank to modify for increased capacity. Basically, cut the stock one open and have Jay weld in some sections to be able to ride for longer than 120 miles in one sitting.

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