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paso
11-12-2010, 11:37 AM
i'm lookin to install a modern (2 stroke) :peace:125cc mx motor in my RS 50. what motor is the best fit ? HONDA CR, SUZUKI RM ,OR KAWASAKI KX ? i want to use a motor that will accept a aftermarket lighting coil.(the yamaha YZ motor does not have light coil availiable ) .

cafe750
11-15-2010, 10:27 AM
using a 2003 kx 125 in my rs with lighting coil from moose racing

RS_Patrick
11-16-2010, 09:34 AM
Dont you think its more fun to Tune the Stock Engine up?

cafe750
11-16-2010, 11:37 AM
yeah, it was fun doing the whole rs50 upgrade route, but thought it would be fun going with the 125 engine too...btw parts for a kx125 are alot cheaper too

one thing for sure, the rs50 kitted was alot more road worthy, the kx125 engine may have tons more hp but thats not always the best for street riding but get her on the track and WOW!!!!

paso
11-16-2010, 12:40 PM
well i figgered that i could spend $$$ on the 50cc ,(which can only be increased to 67=70cc ) or go ahead and 125 it and have a street legal (appearing) 2-stroke 125 curve buster .as far as i'm concerned the 50 is not a good city bike in it's present form , u-no 7-8 thou. rpm launches EVERY time i have to come to a complete stop . cafe750-- why is the MX motor less street friendly than the 50 ? thanks .

cafe750
11-16-2010, 12:51 PM
in my area an unlicensed '50' is considered a moped, hence 38mph limit and the kx doesn't like the slow speeds, thats the only reason......if you are able to ride faster its great on the street, but as you know all the power is between 85k and 13k and at 38mph i only hit 6k which makes the bike feel like its waiting for me to crank the throttle, which i do plenty of times to keep it happy:)

it does feel like you have a true gp bike under you when you get to gas it....tons of fun

RS_Patrick
11-16-2010, 02:13 PM
well i figgered that i could spend $$$ on the 50cc ,(which can only be increased to 67=70cc ) or go ahead and 125 it and have a street legal (appearing) 2-stroke 125 curve buster .as far as i'm concerned the 50 is not a good city bike in it's present form , u-no 7-8 thou. rpm launches EVERY time i have to come to a complete stop . cafe750-- why is the MX motor less street friendly than the 50 ? thanks .


With a 125 engine it wont be legal anywhere, if you tune the stock engine up with a nice big bore kit etc, its still legal in some states as a Moped as long as its less than 80cc.

And i have no idea where you get the idea from that you can only increase the AM6 to 70cc...

50mm bore is the biggest that will fit straight on wich wil give it 76cc displacment.
You can also buy Kits that come with a Longer Stroke Crankshaft wich will give you up to 90cc Displacment.

Some of the 76cc kits already pump out nearly 20HP with the adviced setup/tuning done (look in the install manual that comes with these kits for that)

paso
11-17-2010, 07:16 PM
i have a title for the U.S. , so after i install a 125 motor i feel that i should license it so that i won't have to constantly be looking over my shoulder ! (staying below 35 mph sux ).

RS_Patrick
11-17-2010, 09:19 PM
You cant licence the bike as road legal with a 125 engine in there mate.
Its designed and licenced as a 50cc, your lucky if your states lets you licence it as a RS 75~80cc, but never as a 125 mate, because that exeeds wel over the constructional capabilities of the bikes frame, so your DMV will never give off a road legal status for it.
Nice for Track Use a 125 engine, but only if its tuned up, or a wel tuned RS 76cc can still beat it.

paso
11-18-2010, 12:29 AM
who besides ME is gonna know its a 125 mate ? in va. there are no motor inspections . frame #s , license plates , and insurance is all thats needed to ride on the street .

RS_Patrick
11-18-2010, 09:06 AM
Dont understand your previous post than, you want tpo licence it so you dont constandly need to look over your shoulder.

Can you drive faster with a 50cc than in VA wen you licence it?

Keep in mind than that wen you cause an accident with it you wont be insured, and in the USA its not unlikly that the other person will sue you for more money and costs made, in wich case you could be really screwed.

If your alouwed to fit up to 80cc in VA i would go for that option, you can than pick a 76cc (50mm bore) and go for that, wich in that case would be fully legal and easly gets you to 60~70Mph and more if you set it up right.

paso
11-18-2010, 11:17 AM
Has anyone tried a cr 125 or rm 125 motor ? heck i'm even open to modifying the current 50 cc motor , but i dont see that its possible to attain 125cc performance & RELIABILITY from a motor that started out as a 50cc (without spending a small fortune).modern used MX bike =$1,000 - $1,500 , pieces- parts $200 - $500 , then i can part out the remains of the MX bike . so realistically i should be able to do the swap for $1,000-$1,500 .

RS_Patrick
11-18-2010, 01:15 PM
Pink Top Performances will be able to beat a 125 Stock bike with the right setup but throuble is there are no Top Performances parts anymore available in the USA it seems.

rthings you would need to keep in mind to keep it reliable enough is:
Always fit a Race Crank thats been Reinforced on the Flywheel side (Doppler ER1 is the cheapest option than)
Replace all engine bearings with C3 versions and use good quality seals and gaskets.
Always use the Stock Airbox or a Go-Kart Filterbox.
Upgrade The Clutch Plates + Springs.
Get an Upgrade CDI unit (stock ones can fail wen you run at more than 9k for a while)
Always Add Extra Oil (Premix fully synth.) to the Feultank, 1:100 should be fine, this means you just add 100ml to every 10 liters of feul, wich basicly means everytime you need to fill up after switching to reserve you just add 100ml to the tank.
Use 10W-40 Fully Syntetic Motorcycle Gearboxoil for use with a Wet Clutch.
Tank Premium Feul like Shell Advance or V-Power only.
Always use Premix Cooland suitable for Alumium engines.
Use the Right Sparkplug, you probably find you would need a B10EGV Race Plug.
And buy good quality chain and sprockets (its also advicable to replace the Rear Wheel Bearings right away while its off to fit a new sprocket)
Also DOT 5.1 brake fluid and quality brake pads will help your stopping power a lot especaily going down hill.

Naturaly you need the right reeds for your Setup but in some cases they come with the BBK in the packadge.

Sadly like i said, in the USA there isnt much choice in parts, so have a look around and see what your options are, maybe some overseas shop is willing to ship parts to you.

See what it costs compaired to rebuilding it to a 125 engine.

Crim
11-22-2010, 01:52 PM
I went with a 91 KX125 engine, still waiting on some parts to come in from Kawasaki before I can get it on the road and see what she's like. If its anything like Cafe750 says, should be a blast.

I enjoy riding bikes, but I think I enjoy tinkering in my garage a bit more, so for me putting this thing together has been tons of fun. Getting to play with it on the street will just be the icing on the cake so to speak.

paso
11-23-2010, 12:15 PM
crim , let us know how she turns out ,should be a hoot ! so far it looks like the KX 125 motor is the most popular swap . i wonder why .

Crim
11-23-2010, 01:03 PM
so far it looks like the KX 125 motor is the most popular swap . i wonder why .

My guess is price. I picked up my KX125 (granted an older one..1991) for $700 in perfectly running shape. Newer KX125's can be had for not much more. You ever priced out a YZ125? Those things hold their value like no other!

cafe750
11-23-2010, 11:01 PM
got mine for 500 a few years ago and just finished fabbing this spring, 2003 model, vforce reeds and modified rs125 pipe, crim got the other one. using a br8 plug and mixing 32 to 1

cheaper to go with the 125 engine than to rebuild an rs with a bbk, but i did it both ways and both ways are plenty fast, a bbk build will run a grand to do it all right, check with podperformance.com too