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Discussion Starter · #1 ·
My buddy and I have decided to tear into our stockers... I'll bring my scientific education to the table and him, his backyard mechaninc mentality... He is a certified technition. I want to stay on pump fuel. The only rules are:



Nothing over 50cc

------------------------------------



I'm interested in what head is a good choice while keeping stock bore x stroke?



I plan:

ceramic bearings internally, and in rear wheel with a billet rear wheel...1lbs lighter than stock for less rotational mass.



High comp. piston, cam, valves, headwork....



any other ideas?
 

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If you want a 50cc wringer, this is what you do:



Powroll Piston

Porkchop and thin the crankshaft ways

Run an xr70 head with a TB camshaft, springs, and clean the ports

VM20 carb

Ceramic bearings

Coat the tranny gears

Inner Rotor

Takegawa Special Clutch

Then you'll have a 5.5 hp wild ride for your $1500 investment



OR



Buy an 88 kit stamped 49cc and a cam and carb for about $200 and you'll make more power.
 

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Discussion Starter · #3 ·
fatcaaat said:
If you want a 50cc wringer, this is what you do:



Powroll Piston

Porkchop and thin the crankshaft ways

Run an xr70 head with a TB camshaft, springs, and clean the ports

VM20 carb

Ceramic bearings

Coat the tranny gears

Inner Rotor

Takegawa Special Clutch

Then you'll have a 5.5 hp wild ride for your $1500 investment



OR



Buy an 88 kit stamped 49cc and a cam and carb for about $200 and you'll make more power.


lol... I know..



What do you mean coat the tranny gears? and is the Takagawa special clutch a manual clutch... I don't want a manual clutch... Could I just run a 70 bottom end to get fourth gear with the drum inserted?
 

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There is no 4th gear drum insert on a CRF/XR70...

You have to split the cases to insert a 4-speed in the 12V Honda cases
 

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fatcaaat said:
If you want a 50cc wringer, this is what you do:



Powroll Piston

Porkchop and thin the crankshaft ways

Run an xr70 head with a TB camshaft, springs, and clean the ports

VM20 carb

Ceramic bearings

Coat the tranny gears

Inner Rotor

Takegawa Special Clutch

Then you'll have a 5.5 hp wild ride for your $1500 investment



OR



Buy an 88 kit stamped 49cc and a cam and carb for about $200 and you'll make more power.


As said above - plus:



Select correct piston to match head

Lighten balance and knife-edge the crank

Use titanium valve caps

Lighten the rockers

Lighten primary drive gear.

Machine down matching gear.

Drop in a 4 speed box and use the rovaza 4th gear

Use light-weight everything you can get your hands on..titanium bolts and fitments

Engine breather system - just vent to atmoshpere - from above crank and top rocker cover.

Carbon BMX bars

Plastic filler cap..billet looks "bling" but weighs more ;);)

Machine sparkplug spotface so spark is directed to centre of barrel

Set carb and ignition up properly and accurately

Machine sprockets so you can run a 415 chain/sprockets set up



There are probably more things - but they are straight of the top of my head. ;)



Personally I would use a Takegawa +R head and matching piston and reduce the stroke on the crank...so you get a high-reving 49cc motor ;);) - but hey what do I know about building engines!!
 

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+R head would be a hugely wrong choice...



Fatz 70 head idea, or an e22, milled to get the chamber chamfer gone(about 1-1.5mm) 82-87 piston. Critical to get the squish tight. Light oil, and not too much of it. Remove any gear not used if it's a dyno shootout, or a close ratio trans if they're gonna be ridden. Coat the piston and crank too. Fancy fuel, or even alcohol if you can get the compression up enough. Lightest wheel/tire combo you can find. Maybe even 35 chain, can be done;)
 

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What fatcaaat said:



fatcaaat said:
Buy an 88 kit stamped 49cc and a cam and carb for about $200 and you'll make more power...
What fatcaaat meant:



fatcaaat said:
...Buy an 85 kit stamped 49cc and a 51mm stroker crank and a cam and a carb for about $375 and you'll make a ton of power. Wait for your buddy at the finish line, and if he says one word to you, stomp the snot outta him...
 

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yea it could be nothing that looks over 50cc haha. fatcaats setup sounds good tho.



you could get the powroll 15:1 piston, get the shiit ported out of the stock head, get a cam, get a big carb and a UNI filter. knife edge the crank and get it balanced. get a 4 speed tranny. get an HD auto clutch of some sort. get an IRK. some Ti clutch weights. the head breather kit. a choke plug for the carb. an exhaust (fast50s).

then get all the light parts you can and go for it. run that shiit with no plastics and helium in the tires lol
 

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Discussion Starter · #13 ·
if I go with a crf70 head... port/polished.... what do you guys think size carb could i run?? 18mm? 20mm?
 

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Use a stock XR/CRF70 carb (17mm) with a UNI air filter, it looks close enough like a stock 50 carb to pass for one, and keep the whole 50 stocker hoax going...
 

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Discussion Starter · #15 ·
dirtbkr188 said:
Use a stock XR/CRF70 carb (17mm) with a UNI air filter, it looks close enough like a stock 50 carb to pass for one, and keep the whole 50 stocker hoax going...


thats a great Idea to mask it like that... but would I be able to run bbr's 18mm carb set up with more efficiency?
 

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burch753 said:
My buddy and I have decided to tear into our stockers... I'll bring my scientific education to the table and him, his backyard mechaninc mentality... He is a certified technition. I want to stay on pump fuel. The only rules are:



Nothing over 50cc

------------------------------------



I'm interested in what head is a good choice while keeping stock bore x stroke?



I plan:

ceramic bearings internally, and in rear wheel with a billet rear wheel...1lbs lighter than stock for less rotational mass.



High comp. piston, cam, valves, headwork....



any other ideas?




head work and stuff would be great. put on a fmf 4.1 or pro circuit t-4. get bbr sp-5 forks and a rear shock
 

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If the BBR carb looks like the XR50 or 70 carb, sure, go ahead and use it. If it mounts inline like the 50 or 70 carb, that's even better, it still looks like a stock carb. I'm sure you can match port the stock manifold to help you a little, too.
 

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Discussion Starter · #18 ·
already have i-shock and many extras... you think the procircut pipe is better than bbr?.... thats what I have.
 
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