noob - 7hp briggs motorcycle build - drivetrain and ride-ability Q's

#1
clutch or cvt?
looking for a top speed ~ 70mph, gear ratio of 5-1?
rear tire diameter will be ~ 26"
flathead engine will have governor removed, mikuni carb and header - not trying to break 5k rpm's
will be used for fun commuting and country road cruising

because this will be driven on public roads i dont want to be a burden to traffic at stops (acceleration) or hills. with the mods listed for the engine what seems like the best option? will a cvt be necessary for enough power to ride safely? the cvt complicates the build as there is little space in the frame and the power will exceed the recommended limit of the lower end cvt units with the bolt on backplates; from what i have read anyway.

i am used to riding modified 2 stroke mopeds and those commonly have 1 or 2 internal gears and can reach 50mph+; although slow off the line. the variated mopeds are much preferred for acceleration. i just dont know how to compare this motors performance to real world conditions.

thanks in advance
 
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#3
it is a motorcycle :wink:

merriam-webster:

Simple Definition of motorcycle
: a vehicle with two wheels that is powered by a motor and that can carry one or two people
Source: Merriam-Webster's Learner's Dictionary

Full Definition of motorcycle
: an automotive vehicle with two in-line wheels

but in all seriousness it is a titled motorcycle. but what fun would it be to simply mount in a modern motor when building a throwback, vintage, wannabe board tracker?
 
#5
I am just not too sure what would be the better direction to take. a 2 speed jackshaft may be more reliable, idk; thats why i am asking questions first.
 

fistfullabar

Well-Known Member
#6
If you make it modular you could swap um out. The bigger the wheels its best to use the belt drive but if you spend $$$ on a "race clutch" it will work too.
 
#7
I tried to build something like that in my younger days. I used a honda 200 3 wheeler engine. Ended up parting it out after I finally came to my senses and figured out I had almost enough in it as a good used motorcycle would cost and wouldn't had to fight with the DMV about getting it street legal.
 
#8
neo, i hear that. exactly why i have avoided building another moped; you get tired of being bothered by police for just going the speed limit (but still faster than legally allowable) :laugh:

i am lucky in that i have enough spare parts laying around and friends with welding skills to assist. this project will need a very minimal budget.
 
#9
can you share some pics of the motorcycle frame setup?
and first thought comes to mind is will 7hp be enough??
how heavy is your chassis?

another thought,if you look at the chinese 4 wheelers they use a cvt clutch setup system that looks adaptable for other builds?
most of those are good for parts only anyways so should be cheap.
last 2 we got were free get them outtas here types.
 
#10
not being familiar with modifying flathead motors i dont know what to expect as far as performance after modifications.. 11-12hp?
I started this project thinking i was going to use a predator 212cc but happened upon this 7hp briggs flathead for cheap.

from using online calculators, factoring wind resistance and drag into the equation, the minimum hp needed to go 70mph on a motorcycle weighing in at 350 pounds (including rider) is ~16 hp.

9hp with 5.41 gearing 1/4 mile calc came to 17.9 seconds / 71.55 mph

i even went as far as calculating rough mpg's.

as of right now the bike is stock and i havnt begun the build. i am gathering all of the necessary data first. it is a 60's benelli fireball; originally a 50cc 2 stroke 4 speed. the bike is very small with only a 74" wheelbase, axle to axle.

i'll look at the atv's. other than using the series 40 cvt pulleys i havnt came across any other budget minded options.
 
#11
i should add that the sportsman flyer 200 bikes have a honda 200cc motor and can cruise at speeds over 50mph. other than by looking at images provided i cant tell if any mods have been made other than a carb and exhaust. also, they utilize a single clutch on all their models up to 250cc. the diameter of their wheels is well over 26 inches; so its interesting.

sportsmanflyer.com/product-category/motorcycles/
 
#12
Trail or sport model? Too far gone to restore? Seems a shame to hermaphrodize a sweet little vintage hotrod, especially with a lump with limited performance parts despite low initial cost.
 
#14
ludicrous, thats the bike. what i have available is only the frame and a very tired one at that. if my bike looked like the linked, complete bike, modifying it would be off the table.
 
#15
okay it kinda resembles an artic cat engine cradle so lets roll on that thought.
you should be able to fit a honda gc 190 or 212 = 6.0 horse and with the usual mods be at 7hp.
air filter open the jet and add header.
i rec that motor because its very lightweight and a real honda will last.
also that particular engine design is Straight-up/down like our older tecs and briggs.
Unlike the predators,clones,and so forth,which have their heads angled back into the frame tube.

im sorta leaning towards a jackshaft setup,because of space.
this will compromise top speed tho...

a tav would give all speed,but space is going to be tight.
still might be able to custom grind it or check out other tav backing plates.

edit: just remembered this,muchos importante~
when you do your mockup,ie,
engine with tav assembled on it,
make Sure that your Chain gear on the tav is angled or set at almost Exactly the Same spot as the Original motor/trans has its chain gear set at !!!!
( og picture in link.)
otherwise,you gonna have some issues with chain slack/it looks to be about an inch and a half Higher than the frame so your engine plate will have to be setup for this additional height.<<<<

its an interesting bike you are building please keep sharing :thumbsup:
 
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#18
Cuda, that idea not off the table yet. my early concerns were that the clutch(s) would wear quickly but a 2 speed would resolve the necessary slip from a stop.

to power the lighting i have been thinking about how to have a constantly driven pulley or belt for an alternator since i havnt had much luck looking for a flywheel and stator setup for this engine. trying to run without battery.
 
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