Yamaha 1981 LB50 PH Chappy resurrection

[my67xr]

I am surprised that previous post showed up?
My 10 yo PC has been playing games for the last few day's, i can't get it to run now.
Link's etc won't work on my phone, and the small screen make's it hard to see what i've written too.


You should be able to change the tyre size in the Gearing Commander i posted back a couple of post's, that'll give you an accurate speed.
Once you work out the speedo, then you might be able to use a speedo drive gear out of another bike that run's bigger wheel's/similar height to correct the reading at your speedo head.
So by fitting taller wheel/tyre's, you have changed your factory gear to be quite tall too, good for pulling high top speed's!
Might be worth looking into finding a smaller front sprocket (2 or 3 teeth smaller) so you don't burn out the clutch's in your gearbox.

The indicator bulb's in the speedo head might just be a bad earth in the headlight bucket?
They could also just be blown due to age, or from being overpowered with the tail light being out etc.
Iirc they are 1.2w bulb's?
Do you have a multimeter you can check it out with?

 

[twosmoke]

Hi 67, I was jus curious bout the indicator lites in the speedo, I didn't see em on when the bulb blew, but that was in the daytime, & I didn't see em @ nite either, but I'm sure they're blown 2. I found a few 25 watt headlite bulbs on amazon that I mite get, I'm not sure what wattage the 1 I ordered is tho, I don't have another speedo gear, jus gonna get a cheap bicycle speedo & ty-rap it on, should b pretty accurate 2. well I guess that xplains the slow acceleration in 2nd gear, the taller tires made the gear higher, would goin down a few teeth on the front sprocket make it much slower? I'll check out the ratio calculator ya posted earlier, do I hafta use both tire sizes or jus the rear? Thanks a bunch 67-------twosmoke

 

[my67xr]

The rear tyre is the one that change's the speed/gearing

 

[twosmoke]

OK, thanks 67, I figured that, the sprocket ratio converter ya posted doesn't go as low as an 11,12 or 13 front sprocket & the lowest frt sprocket I could find on ebay was a 12 tooth, I'll keep lookin tho. would it really make much diff? would the engine get in2 the pwrband quicker in 2nd gear w/a smaller frt sprocket? I knw it would be a lil slower, but I need it 2 accelerate a lil faster in traffic, & BTW, I'm still tryin 2 figure out how 2 send ya that vid of me screamin down the ave wide open! I have it in my downloads but it asks 4 a url when I hit the ''insert video'' icon. thanks so much 67,-------twosmoke

 

[my67xr]

You need to put it on your google account, or open a youtube or photobucket account


The sprocket ratio convertor will go down to a 1 tooth front sprocket,
Just select the smallest one it list's then click on the arrow next to it again and you can chose smaller etc

The gearing commander will let you change the rear tyre size too, just enter the tyre size in the current/ second row of bow's down from the top

It show's the difference from a 10" rear tyre to a 14" rear tyre the same width is-
10" top speed is 46.8mph, and 14"top speed is 72mph at he same 6500rpm's

 

[twosmoke]

Ok 67, thanks, I'll get it rite over 2 ya, lemme know whatcha think, ok?-------twosmoke

 

[my67xr]

Here you go, look's pretty quick there, sound's pretty sweet too
How is you spark plug looking ?
Have you had a chance to do a plug chop ?
click on the pic below to watch the flying Chappy.

 

[twosmoke]

Hi 67, thanks, yeah it does! I had the speedo touchin 40 MPH, but aint sure how accurate it is, It felt like I was doin 60! hahaha, I think I'm gonna go to the bike shop 2day & check out a digital bike speedo, they're pretty accurate & cheap 2! I was thinkin of getting a 37 tooth rear sprocket 2, stead of a smaller frt, its the same thing,aint it? would it get off the line a lil quicker? I know I will lose a lil top end, but gain a lil power, the plug is a sweet chocolate brown, but not black like b4, should I move the clip down a notch 2 get a lil more fuel in @ top end? theres a #75 main in it rite now like ya said, should I go a lil higher? it runs gr8 the way it is! thanks mate,-------twosmoke

 

[my67xr]

Was that video of it in 1st gear ?
What is the tyre size on the rear of it now ?

Yeah smaller front sprocket will do the same as a bigger front sprocket, make it take off quicker.
Going 1 tooth smaller on the front sprocket equal's adding about 3 teeth to the rear sprocket.
How much chain adjustment do you have with it adjusted at the moment?
With a 38 tooth rear sprocket, it'll need another 6 link's in your chain, so your adjuster would want to be backed right off atm with the axle sitting as far forward as it can.

I'd be leaving the jetting as it is for the moment.
Then see how it look's after doing a wot run in top gear, plug chop once you have swapped the lower geared sprocket on

 

[twosmoke]

Hi 67, that was WOT in 2nd gear, hi-range. the rear tire is 14'', the chain is 1 line from from all the way rearward, if I put a smaller sprocket up frt, then I would prob hafta take 1 or 2 links outta the chain, so I think imam gonna put a bigger 1 on the back, it looks a lil worn 2 me, how big should I go? it has a 32 tooth on it rite now. I'm not gonna touch the jetting, it runs good & starts on the 1st kick, even w/the k/s pedal broken off! Thanks 67,-------twosmoke

 

[my67xr]

A standard LB50 Chappy chain has 92 link's (pin's) count your chain to make sure.
I use DID heavy duty chain's on my bike's,i know there is a 106 link 420 pitch chain available from most motorbike shop's for around $20 (about $25-$30 here)

JT sprocket model number's and measurement's are pretty much an industry standard in sprocket's.
Most motorcycle shop's can cross reference part number's to match them up.
The Chappy's use a JTF546-14 for the front, eg a 14T front sprocket is a JTF546-14
For the rear sprocket the Chappy's use a JTR832-32, a 32 Tooth as you know
Front sprocket's wear at 3-4 time's the rate of the rear sprocket's, so double check you don't need a front one too.
About 75% of sprocket's will also fit other model's Yamaha's, Suzuki's etc etc too


Here are 44x JT rear sprocket's to suit a Chappy- Amazon.com: JTR832 sprocket: Automotive
And 52x JT front sprocket's to suit a Chappy- Amazon.com: JTF546 sprocket: Automotive



I haven't heard your bike take off from a standing start, to hear whether it's labouring or not, or how bad it is.
You didn't mention the rear tyre size ^^, is it something like a 90/80/14 or close ?
But i'm guessing a sprocket that lower's the ratio about 20% would work fine, maybe a 37t or 38t, even a 39t.

 

[twosmoke]

Hi 67, yeah, I did do some hunting 4 a rear sprocket, I found 1 on boats.net, from a 77 Yamaha dt100. the part # is 122-25436-10-00, its a36 tooth. I think that would be big enuf to solve the acceleration prob in 2nd gear. I didn't check the frt sprocket, tho I will, if I need 1, I'll get a 31 tooth which will lower the gearing down more & prob wont hafta add links 2 the chain, the rear tire size is 14x3.50. the scoot doesn't really labor off the line, but the lower gear will really help, but I think a higher than 36 tooth would really kill the top end but give it mountains of torque. I also found a speedo gear from a 80cc Yamaha w/the same size frt wheel 2, do I need 2 replace both parts, the str8 gear & the worm gear as a set? cuz I used the original chappy hub w/the smaller wheels? I have my GPS all set up 4 another rip maybe later on 2nite, I'll keep ya posted on my timeslip. thanks buddy-------twosmoke

 

[twosmoke]

Hi 67, well, I'm drawin a blank on the sprocket, either the bolt spacing is off or the tooth count is, do you know where I can get 1? I tried JT sprockets, but they don't seem 2 have the correct 1 either! I'm not leavin the 32 on there! my headlite came 2day, guess what? the lens is 2 small 2 fit in2 the hsg, it goes rite thru! the stocker is a 5'' dia & the new 1 is 4&1/2''! the ad didn't even say how big it was, so I Mcgivered it 2 work, I stuffed the whole hsg in2 the chappy hsg, it didn't go all the way in tite, so I put a few lumps of J-B weld on the outer ring & clamped it down w/a small pr of visegrips, I think it mite jus work, hahaha. I have 3 wires comin off the receptacle, a ground, a blue w/a white stripe & a white w/a blk stripe. the stock plug is marked grnd, pass & drive, what does this mean? how would I connect these 2 make sure the hi/lo beams r wired correctly? ne ideas guys? thanks-------twosmoke

 

[my67xr]

Don't quote me on it as i'm not 100%,
but earth is easy enough, blue w/white is high beam (pass) and white w/black is low beam (drive)


Does this sprocket have the same dimension's as your's
If it does then maybe the Australian one's use a different one ?

 

[twosmoke]

Thank you 67, ok, I wont quote ya on the wiring, but I'm not gonna doubt ya either! if worse comes 2 worst, my hi beam indicator will come on when the low beam is on! nbd, I'll jus swap the wires, that's all. my bolt spacing is 60mm diag , & the bore is 45mm, IDK why I'm havin such a ***** of a time locating 1, BTW, how many teeth is that 1? thanks a lot,-------twosmoke

 

[my67xr]

Now i realise why the sprocket's above wont fit, you have different wheel's on it :11doh:
What are they off again, an MX80 ?

There's lot's of 32t or 39t and bigger on ebay


But look at what i found for you !!!
What measurement is your's between bolt's ?
New 00 03 Yamaha TTR90 LeMans Rear Sprocket 35T 109 25435 10 | eBay

 

[twosmoke]

Hi 67, yeah, that last sprocket ya posted is the rite 1! same dimensions, bolt spacing & center diameter, the 1 I found 4 a 77 lb80 was similar, but the part # had the same 25436 in the middle but 3 different letters/#'s 4 the 1st 3 digits. maybe this 1 will fit, but I aint spendin 95$ 4 a sprocket! I will chk those Yamaha part sites & see if they have the part # ya gave me in stock, they're like 18$. the funny part is that when I swapped sprockets, (the mx80 was a 41 tooth) I used the mx80 hub & the chappy 32 tooth bolted rite on, so a mx80 sprocket will fit but I don't want a 41 tho. gonna install my Mcgivered headlite 2day (the J-B worked) & put the taillite bulb in 2, I'm still waiting 4 the cheap flasher & speedo indicator bulbs 2 get here frm amazon (yeah, 3 of em blew 2) maybe I'll take it out later 2nite 4 a rip down the ave @ full bore! mite even shoot another vid w/the GPS strapped on 4 an accurate speed reading! as always, thanks 67-------twosmoke

 

[twosmoke]

Hi 67, I spent most of the day yesterday hunting down that sprocket from a bunch of shops & even called JT, but they only sell 2 distributors & not the gen public, so I called sum distributors & they would hafta special order it & it would take 2-4 wks 2 get it, so as a last resort, I chkd amazon, they had it in stock, so I ordered up 1, It was 16$ w/free shipping! its a JTR 832.37, same xact dimensions as the last 1 ya posted w/37 teeth, so gonna put that on & see how she rips. had the scoot out last nite 4 a blast w/the GPS on it & got it up to 46 MPH! IDK how accurate it is, but I was flyin! 1 problem tho, after awile, the headlite lo beam blew then the taillite went! IDK what the problem is, they worked good 4 awile, maybe It was revving 2 high? would a higher wattage bulb do the trick? there is a 25w bulb in it now, would a 35w bulb drag more power 2 drop the voltage down so the rest of em don't blow? I chkd the plug & it was coffee colored, jus a touch dark, looked clean & not oily @ all, I was thinkin of putting a #80 or 85 main in it 2 get a lil more top end 2 compensate 4 the lower gearing? it has a #75 main in it now. Now I gotta order more bulbs frm amazon, here we go again, jus when ya think ya got it all figured out, Murphy's law rears it's ugly head, haha. thanks 67-------twosmoke

 

[twosmoke]

well guys, I think I got my lite prob all figured out! I'm simply gonna put a 12V automotive brake/taillite bulb in it, it'll be a lil dimmer but it can be seen, & it will pull sum voltage from the headlite so it don't blow @ high RPM, whatcha think gang?-------twosmoke

 

[my67xr]

Well the other 12v bulb will fit, but it's just a bandaid fix.
Have you had a multimeter across you battery terminal's when it's running to test the voltage there?