Top Speed

[SlowBalt]

I have a raw motor that i spin to 8200 .

I hit 45 mph with a 36 tooth thats 8600 rpm

 

[Scootmeister]

I learned while racing gokarts and motorcycles that three things determine speed: HP/weight ratio, gearing, and roll resistence which usually is determined by the quality of your equipment, especially bearings. Using this formula I built a MB with a homelite chainsaw engine, 58.2 cc, 3.33 HP, rated at 7500 RPM with a magnesium frame and chrome cylinder. Mine has a Mikuni carb, about 16mm (some came with Tillotson, Walbro). I mated this short-stroke quick reving engine to a freewheel jackshaft and 3-speed Shimano rear. With a 46 tooth rear sprocket and 15 : 1 initial gear ratio driving the 3-speed, in 3rd gear I get about 53 MPH. With a change in gearing and a final ratio of 16 : 1 I get about 50. Both are way too fast on my cantilever bike with springer front end. The optimum setup is a 19 :1 ratio which gives me a top speed of approx. 44. The Sun Rhino Lite XL wheels and sealed bearings roll true with little resistance. Running the final drive chain directly to the Shimano hub eliminates the vibration from rag joint or other extaneous hardware. My KMC BMX chain runs smoother than 415 Chinese chains.

 

[flatblack]

66cc Jet, RT carb, SBP xchamber, Puch 70cc Hi Hi head, billet intake, NGK plug/wire, 40t, 26x2.125 Duro Bricks. Still on break-in mix, I've hit 38mph on a humid 90 degree day. She'll see 40.

 

[5-7HEAVEN]

I learned while racing gokarts and motorcycles that three things determine speed: HP/weight ratio, gearing, and roll resistence which usually is determined by the quality of your equipment, especially bearings. Using this formula I built a MB with a homelite chainsaw engine, 58.2 cc, 3.33 HP, rated at 7500 RPM with a magnesium frame and chrome cylinder. Mine has a Mikuni carb, about 16mm (some came with Tillotson, Walbro). I mated this short-stroke quick reving engine to a freewheel jackshaft and 3-speed Shimano rear. With a 46 tooth rear sprocket and 15 : 1 initial gear ratio driving the 3-speed, in 3rd gear I get about 53 MPH. With a change in gearing and a final ratio of 16 : 1 I get about 50. Both are way too fast on my cantilever bike with springer front end. The optimum setup is a 19 :1 ratio which gives me a top speed of approx. 44. The Sun Rhino Lite XL wheels and sealed bearings roll true with little resistance. Running the final drive chain directly to the Shimano hub eliminates the vibration from rag joint or other extaneous hardware. My KMC BMX chain runs smoother than 415 Chinese chains.

Now THAT'S A RIDE!!

You got a clutch on that thing?

 

[Scootmeister]

Hi 5-7. Yep, chainsaws have a robust centifugal clutch that lock up pretty tight at the set speed. I simply rev the bike up, let off the gas and shift. It works pretty smoothly. The only catch is there is no engine braking, when you let off you are basically freewheeling like you would be on a single speed bike with an automatic clutch. My Hueng Sheng 4 stroke is the same way. It's something you just have to get use to. What is your ride?

 

[gera229]

Yep, chainsaws have a robust centifugal clutch that lock up pretty tight at the set speed.

I'm new and am curious what you meant by that. Do clutches slip at high speeds or something?

How much did you get your motor for?
Home light chainsaws seem pretty cheap.. are their motors reliable? How many miles is on your motor? How many miles do you ride it daily? How hard/fast do you ride it most of the time?

And I see it's a chain drive using a chain, is the motor mounted in the rear of the bike or is it mounted inside the bike frame between the pedals?

 

[Scootmeister]

Chainsaws made by Stihl, Homelite, and McCullough are manufactured to much higher tolerances than Chinese motors. Better metal is used and better bearings, rods and pistons are used. They rev higher, produce more horsepower and last longer. The carburetors are much better, especially if you get a Mikuni. Mine has a Chrome cylinder liner to extend life. I have found used chainsaws at garage sales, flea markets, and pawn shops for much less than you would pay for a Chinagirl. I've had my Homlite for 20 years with no problems. You have to be a little creative to figure out how to mount the engine, I fabricated mounts from flat hinges. It's not a "plug and play" arrangement, so most are interested. But if you march to a different drummer, the results will far surpass the kits. Good luck and let me know if I can help.

 

[Scootmeister]

Gera229, I didn't answer a couple of your questions. The engine is mounted above the lower bracket just like Chinagirls. It fits well because I removed all of the extraneous stuff like the handle, the bar mounts, the oil tank, etc. Are they reliable? Ask a logger how often they wear out a good chainsaw. They work in water, in mud, covered in oil, they are nearly bulletproof. My engine probably has 500 hours on it, maybe more and it's like new. As far as centifugal clutches slipping: the clutches are made to engage at a fixed RPM. This is controlled by the strength of the clutch springs. The larger the diameter of the clutch housing, the stronger the "bite" when the springs extend. My Hueng Sheng 4 stroke engine has a tiny centrifugal clutch, the Homelite is much bigger and locks up tighter and is less likely to slip. I hope this helps.

 

[gera229]

How much do you ride your engine daily in miles? How many total miles do you have on it (Not including the use of the chainsaw, just riding the bike)? Looks like a crazy used engine on a chainsaw. I hope these are CARB approved, but either way it would not matter.
How hard/fast do you ride it most often? (Some reported reliable china engines with full throttle running 10s of miles without problems so I'm asking about this).
Do you have any problems with your Homelite overheating? (Btw those homelight chainsaws are only 180 new for a 42cc at home depot).

By the way, how much did you spend on everything to mount the engine? Also does it have a pull lever clutch?

What would the max speed be on a 44 tooth rear sprocket without any gear shifting, but just 1 gear? 3.33 hp seems far more than these China engines can produce. What's the max RPM for China engines?

So yours is 58.2cc, 7500 rpm, and 3.33 hp? Any modifications on it?
What model is your engine? Homelight 360? I found a homelight 360 for $50 on craigslist. But still curious about what model you have because it seems hard to find a brand new 58cc engine, others that are selling new are 42cc and under.

Do you have pictures of the engine installed on the bike?

Thank you!

 

[Scootmeister]

You can use the smaller engine,, but you will have to gear your bike lower which means you need a small front sprocket(countersprocket) and a larger rear sprocket. You'll probably need a 20:1 gear ratio. I don't know how high Chinagirls will rev, mine is a Grubee 66 cc and it doesn't seem to have a very wide band. That could be because of the way it's tuned with the original carb and jetting. I probably have 500 miles on my Homelite bike, I don't ride it as much as some because I have a Whizzer and two motorcycles. I live 3 miles from a fishing village and that's as far as I ususally ride. I'll send pictures as soon as I can get my camera charged. I'm currently cleaning up my bikes thanks to Hurricane Irene who deposited 18" of salt water in my garage. I didn't see any need to modify the engine. I even used the original choke and air filter that came with the chainsaw. I did fabricate a manifold that holds a 1" diameter exhaust pipe that has a pipe fitting on the end so I can use a Chinagirl muffler for quiet operation or screw on a Briggs muffler for free breathing. With the Briggs muffler it sounds like a Bultaco dirt bike!!!

 

[gera229]

Your whizzer has what engine on it. Just curious.
Approximately how fast will a 20:1 gear ratio max out at on flat ground?

And thanks for the information.

 

[Scootmeister]

Whizzers have a 138cc engine. Mine is modified and will go faster than most.

 

[gera229]

Oh so that's why. They go pretty much faster than motor bikes I assume then. And costly I believe.
Thanks for the input.

 

[5-7HEAVEN]

Oh so that's why. They go pretty much faster than motor bikes I assume then. And costly I believe.
Thanks for the input.

I traded my son's used laptop for a 2006 Whizzer two years ago. The bike had been sitting awhile and needed a rubber fuel line.

Then I bought my son a new laptop.

 

[atombomb232610]

If you have not already done it or had it done..... engine disassembled, bore check, deck height check, head check, porting check. If any of your surfaces are iregular(not flat) or you still have casting flaws you have to fix this issue.
These engines were made by cross eyed 5 yr olds with antique machines. Nothing is ever perfect. If you take the time to have your engine corrected you should also replace all of the original bearings and hardware. In addition refer back to older books on 2 stroke exhaust and figure for gearing,bicycle weight,rider weight and the most important riding conditions. Your exhaust
is a great tuning tool when used correctly. And yes the motor is ready to blow and screaming like a banshee at 52mph. This was flat land in full board
track tuck. (yes i know i looked real stupid as I PASSED YOU!) Take your time, do it right and you will have one of the cheapest, most reliable and fun forms of transportation available today. gearing and close tolerances with minimal drag will net you speed. And I flip the finger to useless mods like boost bottles and dry nitrous( you might as well just leave the oil out of the mix because all it does is lean your motor to the point of meltdown.)
If anybody is in milwaukee,Wi and needs help feel free to e-mail me @ [email protected]

 

[GasMonkey]

Grubee GT5. SBP expansion, 2 boost bottles, CNS carb stock jet 3rd notch, 44t on an Ozone 500 Canyon, 183lb +/- 3 (stood on scale and carried bike, i'm 139lbs) : 37mph.

 

[atombomb232610]

OPTI-2 OPTI-2 OPTI-2 OPTI-2 RUN THIS OIL AT WHATEVER MIX YOUR COMFORTABLE WITH! I run my bike at 70:1 mix at full rpm almost the whole life of the engine (426 mi so far) My break in consisted of a 50:1 Mix, three 20 minute temp cycles and 4 blocks at part throttle. And then 100 mi of varied RPMs and never full speed for any long period of time. Mid range riding speed while cracking the throttle all the way open (with the clutch engaged) this will dump extra gas/oil into the engine by way of low air speed but full needle/main opening. This way of driving will oil a plug quickly and you should always check your plug during break in. Full rpm all the time will kill your magneto.(resolder and rtv it. if your talented or have alot of patience rewind yours.)

MORE TO COME LATER.......

 

[atombomb232610]

I dont know why everyone has such trouble getting top speed out of these bikes. growing up we frequently built go carts and minibikes that topped out at 50 and 55 mph while everyone else is at 40-45mph. (MANCO dingo with a 5.5hp honda and a small frame minibike with the same.)

It is all in the build.


NOTHING IS EVER PERFECT,but i bet all of us here can get pretty close.

 

[GasMonkey]

i understand that a boost bottle doesn't lend a hand at producing top speed, but they're not completely useless. it smooths idle and gives better throttle response at low speeds and lesser throttle openings.

 

[rustycase]

What a fun thread!
I'll be working toward a racer over this winter... straight line...
Any idea how FD would work?
Best
rc