[Hillyard]

I bought an '03 Suzuki Jr 50 to mess around and stunt with when im bored. I know there is a lower gear in the gearbox and was wondering if anyone could post up a diagram or post pics of the mod. I need the extra torque for stunts and just crusing around the yard. Thankyou so much

[JAMRACING21]

it is very easy, you will see on the shift shaft and the shift fork where it can only turn one way down and neutral up grind the shaft so it can turn the opposite way and go up into 1st gear, very easy to do, but very time consuming a small dremel or grinder will do the job just fine, but there are alot better ways to get power out of the jr50 and 1st is so low geared that you will neve ruse it, it will only go 5mph tops in 1st gear, so its kinda a waste of time unless you mod everything else and go to a higher gear ratio then it becomes worth it, let me know if you really want to mod this bike out, i can help you make it one of the fastest jr's around like i did for my son, alot of it can be done cheap

[Hillyard]

Well thankyou, im going to stunt it out. So low end power is great (circle wheelies and such) I have pegs, 12 bar and big bars for it. But if you have a link to cheap mods or a diagram for the shift fork that would help out a lot. I've been lookin all over and this is the only site I found. I havent seen any mods or aftermarket parts for it at all.

[JAMRACING21]

get the weight down is the biggest thing HP to weight ratio is the biggest factor, first mod lighten it up buy 28 tooth moose racing aluminum rear sprocket, get a sunstar 12 tooth front, and get a regina gold chain also sold under the MSR brand, all these are lighter than stock and less rotating mass means more power to the wheels, next get honda crf50 aluminum aftermarket rims like blue or red green etc buy cheap on ebay then have buchanon spokes make you custom spokes to lace your stock hubs to, again less rotating mass means more power to the wheels next take out the 2nd pilot jet, there are 2 of them stacked on top of each other, take that first one you see out and throw it away, next take a dremel and take the intake manifold and take out any of the big burrs and then lightly ruff it all up you do NOT want it smooth but ruff with no spurs or burrs, next take the exhaust port and dremal that out making it very very smooth with a fine dremel bit, you can also buy a FMF gold series fatty pipe for it and a power core 2 or turbine core 2 silencer for it (get the power core 2) you can find these on EBAY! use a ngk spark plug and spark plug cap and wire, in the front forks there are 2 springs in each fork 1 short 1 long replace both short springs with a OEM long spring that way you have 2 long springs in each fork this may decrease the travel a hair but will prevent the hard bottoming out, we used honda crf50
handlebars that made it really tall and worked great! you can take off the oil bottle and make it pre-mix, run amsoil or klotz a high end synthetic if you do this, next you can take the head off, and hold it on a regular belt sander with 420 or so grit and sand the lip off that mates to the cylinder this will up the compression if you take the lip all the way off it will go from a stock 5-1 to 10-1 a machine shop can also do this for you, if you do it with a belt sander, DONT PRESS HARD let the weight of the head do the sanding it takes longer but it will come out str8 that way, you can check it after will a flat piece of marble.
take the kickstand and chain guard off since they are just extra weight, take you stock airbox and drill 4- 1/4in holes around the stock 3/4in hole, and then drill 4 - 1/8in holes
on the bottom of the cover next to the already existing 1/8in drain hole drilling more holes or bigger holes than this will not add anymore power just let more dirt in,
sorry i dont have a DIA. of the jr50 but bike bandit.com does, it will not show you where to grind etc. but it is a NO brainer once you get in there it will make sense, if not ill help you out, after you do these mods i can help you with a few more,

[Hillyard]

Alright sounds good. Im going to start with the 1st gear mod. The other ones sound great. I realy need to stiffen the front end for it bottoms out easily. Thanks and i'll keep you posted.

[Hillyard]

Can anyone tell me where the stock restrictors are? And how to remove them. Thanks

[JAMRACING21]

i bet you 10 bucks your restrictors have already been pulled out, 99.99% have, there is one at the cylinder and exhuast port between the exhaust and cylinder its just a washer with a small hole in it, the nest one is between the carb and the intake manifold,
but like i said your bike wont have them in it, :prof:

[LotsaDirtBikes]

I found the 2mm over bore piston for the JR50 through Wiseco, but is there a kit for the head or an all inclusive kit to bore the top end out? I have seen the all inclusive kit for the PW50 to tune them up to a 60cc, but nothing for the JR50.

After this season my son will be too big for his JR50 so I plan to experiment with the bike since I got it for only $350! First, I plan to do the gear mod just for fun. Second, the engine runs good, but is all dogged out, it is a 1991 and I don't think it has almost any compression left!! So I want to bore it out to the 2mm over piston/ring kit that Wiseco sells for it. I imagine that I could just take the cyclinder to the machine shop and have it honed/bored out to fit the new 2mm larger cylinder? The other thing that I imagine would need to be done is to have the head machined to fit the new piston?? Anybody done this yet, just looking for some advice so I don't have to re-invent the wheel here.

Also, with the increase to the larger piston and such I imagine the carb will need to be adjusted? Or will I have to get something bigger for the new larger displacement? I saw a reference to a 20 mil carb replacement, what size is the stock carb?

Travis

[JAMRACING21]

aas far as the 2mm piston i would only go 1mm 2 mm makes it a 55cc 1 mm makes it a 52.5 cc no difference in power output, but if you go 2mm and score the cylinder at all you are toast no more fixing it at all, you will have to buy a new cylinder,

you will have to take it to a machine shop to have it bored as there is no all inclusive kit for the jr50, but a modded jr50 will outrun a modded pw50 anyday of the week.

asfar as the head goes you dont have to have to get it machined to match the cylinder you can shave it yourself as i described above, alot of machine shops use the same method for small 50cc bikes to shave a cylinder they never even set them up on a jig or mill, which in my case was a big disapointment to pay 160 dollars for someone to hold it on a belt sander to shave it (something i can do myself)
they can set-up the quish of the head but often it is not done by alot of machine shops, if you do take your head in to have it shaved make sure you and the machine shop is clear on what they will do to it, and how they do it.

i made a mistake the 20mm carb was for a ktm, the suzuki mod is a 18mm the stock carb size is 12mm.
the carb i found was off of a chinese 50cc scooter that i used on the jr50 so i am unable to give you a brand name.
also port and polish will make a big diff. and take out the 2nd pilot jet,

the stock compression is 5.6:1 when shaving the head you can get 10.1:1.
the first gear mod in my opinion is a waste of time, it is way to low to use top speed about 3 to 5 mph
i would use a 12 t front sprocket that will help alot and combined with other mods will make it a fast tuff little bike.

if you have any other ??? about the jr50 let me know thanks

welcome to the TT mini forum by the way!

[LotsaDirtBikes]

Do you happen to have pictures of the shaving down of the head? I can't picture it in my mind, it may be real obvious when I take it apart. Is it just a lip that you shave down to level or is it a perscribed amount you take off? Don't want to end up buying a new head!!!!

[JAMRACING21]

the lip is the lip around the 4 mounting holes, it will be obvious when you take it off, you can take the lip all the way off with great results but no more than that,
i would recommend to leave a little of the lip on in case you mess up, that way a machine shop can fi it later.
but really the most important thing is to have it level and even if not you will have a head gasket leak, dont use pressure from you hand simply let the weight of its self due the sanding, it should work fine i did it my first time after having a machine shop due the same thing for 160 and i think i did a better job then they did.

[LotsaDirtBikes]

Do you have an idea of what it will cost me to bore out the cylinder to the either +1mm or +2mm new cylinder size? I've never had to do it so I have no idea and need to budget for the project this winter.

[jpswap]

My 2002 JR 50 starts, runs for awhile, then stalls. Or it may travel for 2 minutes then will bog and eventually stall.
Exhaust restrictor has been removed. New plug, no dirt in float bowl, muffler is clean, spark seems strong.
Previously it ran ok but was always gutless from a standing start.

I removed the upper second pilot jet, soaked the carb body with carb cleaner and blew it out with compressed air.
Now it will cold start using the choke but stalls after about 15- 20 seconds; it does this after each restart. Finally, after several attempts it will barely run if the choke is off and the head is warm. After a minute or so it comes alive and runs fairly well.
However it bogs at wot. Backing off the throttle a little restores some power.
Any suggestions would be appreciated.
Gramps