My bike got 52kph on the flat standard, after some basic tuning and drilling some holes in the exhaust. With the shift kit, I can get about 70kph max on the flat and about 80kph on a gradual downhill. I only weigh 50kg, though.
If you accurately calibrate your speedo by sitting on the bike and rolling forward one turn, then entering that value / pi as the diameter, you can calculate rpm from your speed using JPilots Gear Ratio Calculator.
The primary ratio is 20:82, (4.1:1) and the secondary ratio is 10:44, (4.4:1), for a 44 tooth rear sprocket. (Adjust to suit your rear sprocket.) Leave the third field at 1:1.
You'd find that any further refinements of the pipe would result in minimal gain. You'd get a much better improvement with some balancing and a high-compression head at this stage, along with a decent carby. Not CNS etc, but Mikuni or similar quality.
I have a Rock Solid Engines billet head, but at 16:1 CR compared to the stock 6:1 it makes the engine very hard to turn over.
yeah, i could be anywhere between 35 to 55 on the flat before i did any tweaking, but most of the time in the lower regions.... only another 16 kg here
temperemental? yes. right time of day when the humidity is just right, she would scream, then a few hours later? hmmph. the sort of times you wish you had spent some time setting up the derailleur properly... cant do much in granny gear.
interesting that with the now much leaner settings, its less grumpy, and in fact, sorta prefers the heat... i shall see as the days get longer i suppose, if it stays that way...
80 on a pushie.... nah, ill wait til i get my license back to do 80+ again
one last thing while i think of it.
indexing spark plugs. ideally, the open side of the gap should face the exhaust port. i have no idea why, but its one of those things that can make a marginal difference, and is far more noticeable as the cylinder size increases. i noticed my head was on 180 degrees out.
shame i always have to make three or four tweaks at a time so i can never really point at one thing alone.
Hi Steve, heres some info for anyone who ever wants to split the cases or replace the main or countershaft bearings. Case bolt torque setting 75inch/pound, crank end float 0.003" to 0.008". Recomended to change all the case fasteners for automotive grade or high tensile socket head. Cheers
I think the 66cc had a 40mm stroke with an 89mm conrod, as where the 48cc has a 38mm stroke with a 85mm conrod. The piston diameters seem correct, but you might want to add these: http://www.spookytoothcycles.com/images/engines/engine-ID.jpg
They should all have a 38mm stroke/85mm conrod other than the 66cc.
That's an easy question to answer: cut a half inch wide strip from the top of a cereal box, approximately 3 inches long. With the magnet is in the horizontal position, slide the cardboard strip around the magnet and along the upper and lower arms of the magneto coil.
Now with the magneto coil screws loosened, turn the crankshaft so that the magnet is in the vertical postion. Tighten the screws and remove the cardboard strip.
Here are the measured distances from the top of the stock cylinder: engineexhausttransfersintake* piston skirt**
48cc 28mm 32mm 55.5mm 44.8mm
60cc 28.7mm 33.1mm 56.3mm 45mm
66cc 29.3mm 33.1mm 57mm 44.7mm
* measured to bottom of intake port
** measured from top edge of piston
(66cc is the cylinder the factory calls 80cc. It is 66cc when measured the most common way.)
Assuming a .7mm deck height (distance from top edge of piston to top of cylinder at TDC) here are the port durations in degrees: engineexhausttransfersintakeblowdown*
48cc 140.7 110.3 113 15.2
60cc 135.7 100.6 116.8 17.6
66cc 141.6 114.7 117.6 13.5
* blowdown is the number of degrees that the exhaust gas has to exit the exhaust port before the transfers open. For this engine 20 degrees is perfect if ported per my recommendations.
To have perfect 157/117/120 degree port durations and 20 degree blowdown change the distances to these: exhausttransfersintake or piston
25.6mm 31.2mm 56.8mm 44.5mm (48cc, 60cc)
26.9mm 32.8mm 57.1mm 44.6mm (66cc)[/FONT]
whaaa? like valve overlap, lift, open degrees, and all that jazz?
noone seems keen on doing that sort of mods to the huasheng, and as the predators are a "race" motor from briggs and stratton, with plenty of upgraded cams etc available, the info for them will be elsewhere.
such as here. there appears to be roughly 100 camshafts to choose from.