stuff i found researching the 1980 suzuki jr50

« Reply #5 on: March 11, 2012, 04:14:57 pm »

TIMING
=====
24 degrees BTDC @ 3000rpm.  NGK BPR4HS – gap 0.6mm (0.025 in)
Points gap should be set to 0.3mm (0.012 in)
if hard to start but will start and run HARD if clutched, you have the timing wrong!
i.e. reset the points gap – closer. You are opening too early and the maximum is 0.4mm (0.16 in)
If possible, get a dial gauge and meter and ensure it opens exactly when the mark aligns with the notch on the cover.
Timing light shining on the mark will show if you are out.
If always hard to start and everything else is spot on, replace points. If still no good, replace condenser.
If all is correct, you should be able to walk up to a cold machine, flip the choke on, touch NOTHING and kick it.
It will start first or second kick.

CLUTCH adjustment
============
Take the clutch cover off – note engine oil dripping onto your feet.
Loosen locknut. Run the centre screw in until it just hits the pushrod (you will feel it)
Tighten locknut. Too loose and it will not turn the engine over.
Too tight and the kick-starter will not return.
Idle @ 1400rpm, engages @ 2500rpm,  fully locked @ 3000rpm.
Do minor adjustments to suit your little person.
Adjustment of the clutch is recommended so that the bike rolls freely in gear.
This lets the motor gain a few revs before engagement and makes the shift into gear smoother.
Add oil to engine again…
Test by starting up, letting it idle and pushing into 2nd.
It should NOT move off until the throttle is turned.

CARBURETTOR
=========
Mikuni VM12SC, float height 25mm, air screw 1-1/4 turns out
Make sure you fit a fuel filter! They did not come with one.
if fuel is coming out of the overflow pipe too much, you have float setting too low, e.g. 23mm instead of 25mm.
Yes it has two tiny little pilot jets, not one!. Blow out the tiny jets, blow out the main, blow out the other two holes.
Also, adjust the throttle cable up at the handlebars to remove any slack.

OIL
==
Today’s 10W/30 (SAE80W) motor oils are ideal.
There is a bolt in the side of the r/h case. Remove; fill until it comes out of the bolt hole.

The CCI injection container is for boring normal 2-stroke oil.
Fuel should be plain high-octane unleaded. NOT premixed.

LOW POWER
========
Clean out the exhaust – it gets blocked with crud with age.
Compression test should be circa 100PSI.
There may be restrictor plates between carburettor and head.
Also in head to exhaust – remove them.
Give it a new plug and fresh fuel.

1st GEAR
======
Transmission is 2nd-neutral-1st (down-is-second, middle is neutral, up-is-first)
However 1st is blanked-off normally. 1st is a very low gear.
Pull the right side cover off. With the cover off you can look at the shift lever.
The flat arm has a rectangular slot that is only half-width, rather than full-width.
You’ll see where the section has been blanked off.
It’s got an oblong cut one way. Make a second oblong space the other way and now you have 1st gear available.
1st is very, very low, but will pull up mountains.

« Last Edit: March 13, 2012, 07:59:39 pm by lukeb1961 »

https://forum.ozvmx.com/index.php?topic=21605.0

Thanks Vic – I did the mod last night and it works great. The first gear is awesome – before it would hardly pull me – now I can do wheelies. My boy hasn’t riden it yet but he will be very happy ( just hope he doesn’t learn to get the front wheel up when mom is watching ! ).
I would offer some guidance to others doing the mod :
1) Remove the foot peg/sidestand assembly as this blocks access to the shift mechanism. It’s easy to do and makes the job easier.
2) Undo the nut and pull the rear brake lever off its post as well – just more room to work.
3) Mark the kickstart lever/shaft relationship to make sure the kickstart is correctly loaded on reassembly.
4) Remove kickstart lever and oil feed pipe banjo bolt. Drain oil.
5) Remove clutch cover.
6) Remove engine casing. Note order for clutch parts.
7) Remove spring and clip plate from selector.
8) Grind away the material. I put paper towels all round the area and behind the selector to catch the grindings. Put the spring and clip plate back on temporarily to check that the selector goes into the new gear, and sits in the notch in the clip plate. ( By using the normal gear lever )
9) Clean up well, I rinsed with WD40.
10) Remove kickstart stop bolt.
11) Put clutch together and engine case on ( lining up the clutch mechanism ). It may help to turn the engine over with the kick lever to get the oil pump gear to mate. Put clutch cover. Line up kickstart lever with the marks you made earlier and fit clamp bolt, push down and put in stop bolt. Bolt on the clutch cover and other bits ( don’t forget the oil pump feed line). Put in oil. Ride. I’m going to change the oil again just in case I got some filings in there.

It is very easy – it took me a couple hours, but only because I tried to do it without removing the pegs etc.

https://dirtrider.net/forums3/threads/jr-50-1st-gear-activation.104498

ok heres is a list of mods that will make the jr50 a pw50 killer

first take out the 2nd pilot jet.

buy the fmf fatty pipe and power core silencer for it on ebay or somewhere,

drill 4- 1/4 holes in the end of the airbox cover around the 3/4 OEM hole, buy a 12 tooth aluminum front sprocket sunline makes one so does moose and a 28 tooth aluminum moose rear sprocket (less rotating mass really makes a big difference in these bikes

next buy honda crf50 aftermarket aluminum rims and have buchanon spokes make spokes for em (again less rotating mass over heavy steel rims, ) ebay you can win a set for 40 to 60 bucks

activate 1st gear

++++ mill the head take off the entire lip on the head you can do this yourself with a belt sander or have it machined this will up the compression to around 10-1,+++

next do a port job on the intake and exhuast do yourself with a dremel ruffing up the intake

and smooth the exhuast

go EBC brake pads lighter than OEM

i also modified crf50 handlebars to fit on the oem triple clamp by drilling 2 new holes i used the OEM honda throttle assembly better and quicker throttle response

lightened the flywheel

use pirelli tires they are lighter and sticky but wear out twice as fast as dunlops

run 91 octane gas with a little octane boost in it about a 1/4 bottle for every 5 gallons

run amsoil interceptor oil

take out the 2 shorter front springs and replace with 2 longer front springs( each tube has 1 short one long spring keep the 2 old long ones and add 2 new long ones but note you will have 2 extra short ones because you buy both together, this works good for jumping

you can also just drill out the stock rear sprocket for less weight

take off the chain guard and kickstand and everything else you dont need horsepower to weight ratio is the most critical things on these bikes

works connection makes footpeg extenders and they just need to be tack welded onto the existing pegs for wider pegs you can even shave the plastics a little to help with weight.

you can also buy a 20 mill carb that will wake them up

you can take off the oil pump and bottle and run pre mix but i dont recommend it on this bike,

you can easily shave 20 lbs and more off this bike and that will make it rip and out run and modded pw50 even with a QT shaft.

also use a wiseco piston and you can bore 2mm over to turn it into a 55cc motor but i would only go 1mm over after 2mm you can not rebore

i also have been thinking of modding one to accept crf50 triple clamps and forks by welding the downtube onto a jr frame and using kids mountain bike adjustable shocks to the rear

ill let you know if i do as soon as i find a decent deal on

crf50 front end

https://www.thumpertalk.com/forums/topic/570971-suzuki-jr-50-increase-power/#comments

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