No. I thought that was for 6 volt systems, so thanks...ARH

Valves.
 

To get back to a subject that I think I know something about, let's talk about valves. And the importance of checking valve clearances as soon as you get your Hawk, or any other bike that uses the same engine. You have an investment of more than a thousand dollars to protect, and the utter joy of riding a motor cycle that runs a treat. That's worth protecting, too. With the valve cover off, it is easy to find top dead center on the compression/firing strokes. Makes it even easier with the spark plug removed. Now, as the very charming, and beautiful Michelle Pfiefer said to Sean Connery in the movie, "Russia House", 'Every Hedgehog Knows' that an engine has to have compression in order to run, and do work. In order to have compression, both valves have to be closed. Ah, but here is the fly in the ointment. These engines come from the factory with the valves set so tightly that the valves usually leak, so reducing compression. But, to get back to the procedure. With the plug out, I prefer putting the bike in high gear, and getting the rear wheel off of the ground with either blocks of wood under the rear of the engine, or the centerstand. That way I can rock the engine back and forth until I am sure I'm on top dead center. How do I make sure it is at top dead center? I stick some thing in the plug hole that will touch the piston. I used to use a sliver of wood split off of the edge of a wood shingle. When those got hard to find, I used a chopstick that I purloined after eating in a Chinese resteraunt. You could use a drinking straw, but those are now made of plastic, so I prefer a chopstick. If you break a small piece off in the cylinder, it is not likely to be a serious problem. Wood burns, either in the cylinder, or in the cat converter. Plastic leaves a gooey sticky residue when it burns, so I don't use it. So rotate the engine until both valves are closed. You can tell by the valve springs being at maximum length. That's why you are rolling the engine over with the rear wheel, so you can see the valve action. When you have this fimly in your mind, and both valves closed, introduce the chopstick theough the spark-plug hole until it touches the piston. I usually put a mark on the chopstick at the plug hole edge, and very gently, move the rear wheel a little bit and see if the chopstick line has moved. If the line disappeared, you are past top dead center. If it moves up, you are still before TDC. So, gently, move the rear wheel until the stick is as far up as it will go. Most people, me included rock the engine back and forth until we are certain we are at top dead center. Now, with the .003 and the .004 inch feeler guages out, check, with the .003 feeler guage, the intake valve. The intake valve is at the carburetor side of the head. If you have trouble or cannot get the guage in there, the valve is too tight. When you look closely at the rocker arm, you will see a lock nut, and an adjusting nut. Back off the locking nut a turn, then loosen the adjusting nut until the .003 guage goes in, but has no slop. Hold the adjusting nut with one wrench, and tighten the lock nut. Check the clearance again. The adjustment nut wants to creep a little as you tighten the lock nut. It is important to get the adjustment right, just be patient, you'll get it. Then do the exhaust valve with the .004 guage. When you are sure of your valve settings, remove the choptstick from the plug hole, put in the plug, don't forget to put the plug wire back on, put the valve cover back on. Your engine will thank you by idleing better and running better in every way. And you will have a feeling of accomplishment from learning a new skill, courtesy of Ariel Red Hunter's School of Greasy Fingers and Barked Knuckles....ARH

Rpm.
 

Someone asked the question; how can I tell how fast the motor is turning at 60 mph. Here is the answer. Divide 336 x mph x gear ratio by wheel diameter in inches. Not rim diameter, wheel diameter. Assuming the rear tire is very close to the 4.10X18 non-tubeless tire, it might work out like this: 4.10 x .92 (the aspect ratio) is 3.772. That, plus the 18 inch rim is 21.772. Oopsie, we forgot the part of the tire under the fender, so, 25.544. Now to the gear ratio. The book says the primary ratio is 3.33. So all we need now is the final drive ratio. 16X40 is what the original guy was asking about, soooo, 40 divided by 16 = 2.5 X 3.33 = 8.325. Now, if I did this all right, 336 X 60 X 8.325 = 167832. And divided by wheel diameter, we get 6597.17 rpm at 60. Of course there has to be a fly in the ointment, and it is the Asian fascination with all indirect drive transmissions. 5th gear output is 0.9545, so multiply the 6597.17 rpm by 0.9545 and we get 6297 crankshaft rpm....Phew...ARH

and if you dont want to turn the back wheel the hawk has a cover that can be removed to put a ratchet on to spin the engine with the spark plug removed and a cover to look down into the crank to see the tdc marks. that way your right there at the engine without having to reach back or raise the bike

With my 17/43 sprocket combination (2.53:1) on a 120/80-18 tire - a 25.56" diameter tire (smaller diameter than the stock tire) My bike sits at about 6300rpm (via tach cluster) at 60mph. Something seems off with your math to come up with the same rpm on a stock tire and gearing.

Are you people taking the tire compression under weight into account..
12mm of compression make one hell of a diffrents to the running dia...



..

Rotational inertia can often counteract the compression at higher rotational speeds, and is more prevalent on larger diameter wheels even with a slower rotational speed. The stiffness of the tire carcass also has an effect on this. My Shinko 705's are a much stiffer carcass than the stock knobby tires, and deform much less even at a lower pressure. Even if you took these factors into account it wouldn't change the outcome by more than one or two hundred rpm at most. His method of calculation is good for a general rough estimate at RPM vs. wheel speed.

with the 17/50 combo i am at 55 at 7000 rpm

I didn't have a wheel to measure, so calculated it for illustration purposes, I came up with a diameter very close to yours. Also, the guy who asked the original question was running a 16/40, which is, (I think) 2.5. So the final drive ratios are also very close. So, I'm not surprised the rpm numbers are so close....ARH

Was that calculated, or did you check it on the road? And did you actually measure your rear wheel?....ARH

thats on the road stock wheels

In that case the math is dead on lol

Ports and cams.
 

Ports are easy to modify. But they are not easy to modify correctly. Ideally, the port area should open up from the carburetor exit to the valve pocket area at around a 2 degree angle. Because we want to maintain a cohesive gas flow right on through to the valve seat, and beyond. I think this is important because as a dual sport, we want the broadest possible power band. A short hand version of this is we want higher BMEP right from 2500 rpm to 7750, or so rpm. An engine that comes on the cams at 7000 rpm, and signs off at 8000 rpm might work on a road racer, but is hard to ride off road. A 28 mm carb (1 3/32 inch) is mucho carb for a 250, but it should do the job ok with a very carefull porting job. May need a square slide carb to get enough action coming off a closed throttle. A round slide would not be as "sudden", so that's the way I would go. Needless to say, the exhaust side has to be opened up to get the best possible "blow down" in order to get even better cylinder filling. It is easy to over cam an engine to where all the power is at the top end, and low end is not as good as stock. And if the low end is soggy, too much clutch fanning, which overheats not just the clutch, but the oil in this type of engine, will be required. Like certain over-tuned two strokes in days of yore. Unlike a Bultaco Matador, the sweetest running two stroke I ever rode, off road....ARH

Things I don't like about newer motor cycles.
 

Number uno on my list is a kickstand no start switch. Useless, but annoying. Lights that tell you what gear you're in. Why do you care what gear you are in? You either are happy at the speed that you are going, or you want to go faster or slower, right? If you want to go faster, lift the shift lever up. If you want to go slower, push it down. If you're happy, leave it alone. Gas guages. Hey, it isn't like a car. You don't have to get out and put a stick in the tank to see how much gas is in it, The tank filler is right in front of you. Stop, and look in the tank. If you don't see any gas, rock the machine back and forth from side to side. If you don't see any gas, get some. It does have a reserve, Right? Nuetral light. It doesn't do any real harm, but you don't need to be playing with the shift lever with your eyes looking for the nuetral light to come on, you need to learn how to find nuetral by feel, looking at your surroundings, not focusing on a light bulb. While some snowflake on his/her cell phone plows into you. If the bike comes with a no-start interupter, and you go off road, disconnect it or wire around it. What an advantage electric start is, if you can re-start it off road when the engine flames out without having to find nuetral first. And the other pain in the butt, that can-start-it-from-the-house thingy where if you start it that way, you can't turn it off with the key. Sheese. What a winner....ARH

I sorta like the gear indicator cuz I'm constantly looking for 6th.