Yamaha 1981 LB50 PH Chappy resurrection

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Did your original piston have a port in it like the Polini ?
Yamaha changed to the ported style piston in 1980, earlier model's had a scallop in the skirt.
The Polini piston didn't have an arrow on the crown did it ?
If it did the arrow need's to point to the exhaust

chappy-polini-piston-204.0280-2T.jpg




You would still get fuel in, if it was the wrong way around but it wouldn't run to it's potential.
The piston ring dowel's in the piston would have the ring end gap's overlapping in your exhaust maybe though Check there's no scarring on your bore.
 
Hi 67, No, the pollini piston didn't have an arrow on the crown, but the stock Yamaha piston did. the stock piston has 2 vertical, oval ports in it, w/the arrow pointed in the opposite direction, 2 the side w/out the ports! if the stocker's arrow should be pointing 2 the xhaust, that would put the ports facing the intake side, wouldn't it? I have the ports facing the xhaust, I'm pretty sure that's the way it came apart! did I fit the piston ass backwards? w/the stocker ports facing the xhaust, the ring end gaps would be @ 5 & 7 o'clock above the ports, w/the ports centered below them, but the rings are stopped @ the dowell pins, so I don't think I scarred the bore. thanks,-------twosmoke
 
Hey 67, oh yeah, I 4got to ask ya, I downloaded that manual, the clutch specs r, 4 a new clutch, the lining thickness is 2.5mm & the wear limit is 2mm. what does this mean? they can wear down to .5 mm? the thickness of the shoes is a tick over 2mm on the front & the back is a lil thicker. & why r there 2 clutches neway? thanks 67,-------twosmoke
 
Yeah i was thinking of reason's it wouldn't be running right, and thought about the piston being turned 180°

I'm not 100% on the clutch set up, but iirc i read somewhere that one was for the low gear and the second clutch for high
And yeah, it only need's .5mm of friction material minimum there to work.
 
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ok, thanks 67, I knew I fitted that piston correct! I was thinkin the same thing bout the clutch 2, 1 4 hi gear & the other 4 low, but do ya know which is which? I'd bet the 1 w/the thinner shoes is 4 low gear. ok, so I guess I'll put the engine case back 2gether 2day & start over knowin that the piston is in correct & the clutch is in spec.so I guess its back 2 jet o rama & musical jets! or maybe not 2day, it's 90 degs w/79% humidity up here in Red Sox Nation! hahaha, thanks again, 67-------twosmoke
 
If your port's on the Polini piston are facing down then it's the wrong way around.
I think someone has had a play around with your engine before you got it and fitted the original piston back in upside down


Another thing to check,
When i had my clutch cover off i noticed that there was some play in the Primary driven gear
The gear is rivet to a hub, and internally there are rubber buffer's to take some of the shock out of the drive line.
Mine must have a little wear in the rubber's and it's allowed a bit of movement between the gear and hub.
It will need replacing if i ever want to register my Chappy and use it on the road for a while.
Otherwise it it goes it'll cause a bit of damage inside the cases.
Part number #18 here
 
Thank you so much 67, so, I have the piston in 180* out? maybe sum1 did have a screw round w/it! so, those piston ports should be facing the intake side, correct? if so, that would xplain the game of musical jets! & the splooge drippin from thepipe @ the xhaust flange, & also maybe that's why it doesn't accelerate 2 good in 2nd gear when it finally grabs it? if I r&r the piston, how much of a difference should it make? noticeable? I was thinkin also bout putting in sum thinner oil in the c/c, maybe like a 5w-30? Please advise! thanks mate,-------twosmoke
 
Spooge is a sign that the main jetting is too rich.

I would just leave the SAE 10W40 type SE motor oil or GL gear oil in there, it was designed to use with it.
 
Hi 67, I guess the main jet is 2 rich, w/that piston in bkwards, it must really hafta pull more fuel w/no intake port! I have 10w30 in it rite now, that's what the manual specifies, so i'll leave it, I jus thought that a lil thinner oil would make the clutch grab better. I will turn the piston round 2day & reassemble the top end & see what happns, I bet the jetting will be closer to stock afterwards. what should I xpect performance-wise after I correct the piston? will it be noticeable? thanks 67,-------twosmoke
 
Oh yeah. 1 more thing 67, what combo of jets should I try 1st after I correct the piston prob? I have pilots from 30-40 & mains from 55-95, what would be my best 1st attempt, could ya make a good guestimate? thanks again,-------twosmoke
 
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I think i'd leave the Pilot jet as it is for the moment, but the Main jet i'd drop it back to a #75 and see what it does with that.
Make sure you post up your finding's
 
OK 67, I'll leave the #40 pilot in & drop the 90 main 2 a #75, but it wont b 4 awile till after I put that top end back 2gether, could b later on this afternoon, its another steamer up here in Beantown! but I will b sure 2 post the results as soon as I fire it. thanks 67,-------twosmoke
 
Hi 67, Well, I got the top end all put back 2gether yesterday, there was no scoring in the cylinder @ all, guess I got lucky this time, still cant believe I put that piston in bkwards! I also put the engine case back on, filled it w/10w30 & replaced the leakin oil drain plug. I rejetted the carb, but I took out the #90 jet, & instead of the #75 you suggested, I put in a #80 & left the #40 pilot in it. should I run it it w/out the air filter tube connected @ 1st jus 2 see where I'm @? or connect it? but b4 all this drama happns, I gotta heat & bend that backup k/s, I stripped the splines of that pos I got from Thailand, I guess ya get what ya pay 4! I'll b sure & update ya when I get it fired & tuned in w/the correct piston position! & should I xpect ne better performance from it w/all those mods I made? Thanks mate.-------twosmoke
 
Yeah you'll need the tube on the carby, no point running it without a filter if you aren't riding it without a filter

It should go a lot better with the mod's you've done.
Just need to suss it to find which jet's you need in the carby by trial and error.

I have just fitted a new expansion chamber and silencer to my son's PW50.
I had to rejet the carby, it ended up running a #15 pilot and a #60 main ! original Mikuni VM12 carby jetting was #40 Pilot and #70 main
I won't know if this is the ideal jetting till i can take it out for a decent ride though, but it rev's pretty hard now.
 
Well67, I don't have a pilot that small, but it is an 18mm carb, I have pilots 30,32.5,35,37.5 & 40 & mains 60,65,70,75,80,85,90 & 95. hopefully I get it rite the 1st time & don't hafta play musical jets again! Will that giannelli pipe really decrease the pilot that much? I feel that having the piston installed w/the ports in the rite place will allow more fuel in2 the cylinder makin for a decrease in main jet size, no? Thanks again 67-------twosmoke
 
My lad's PW is still a 50cc, so smaller jetting, the pipe isn't tuned like your's either.

Yeah #40 pilot, #75 main is my guess, but try the 80 if you want
Bog off idle pilot to small, stutter off idle pilot to big
 
ok 67, will try that combo, I think it should be ok, bsides I don't have a bigger pilot jet, #40 is the biggest I've got! maybe the #80 main will be jus rite. @ ne rate, I'll keep ya on top of it. oh almost 4got, the speedometer is funky, when I took it out the other time, it didn't even get uo 2 10 mph & I was goin a lot faster than that! its weird, when I spin the cable by hand, it registers higher than 10 mph, & when I spin the front wheel, it doesn't move @ all! do you have ne xplainations 4 that 1? cuz I certainly don't! the drive gear seems 2 b spinnin when I spin the wheel but doesn't seem 2 make the speedo needle move, jus another snag in this resurrection, I wouldn't xpect nething less! thanks 67.-------twosmoke
 
You might be able to find a universal replacement inner cable for it from an auto part's store, or a complete new one would be under $20
 
Well bad news, boys & girls! looks like yet another snag in this neverending quest 4 resurrection success, as I posted earlier, I had 2 heat & bend that backup k/s, well the heating part went flawless, but the bending part didn't! got the shaft 2 almost cherry-red (hot enuf 2 bend it) so I put the small stillson on the top where the kick lever attaches, STUPID,STUPID,STUPID MOVE! the very end snapped off between the lever & shaft like a dry twig! so I said F#@K! I cant believe I jus did this, my a%& is still sore from me kickin it! I looked @ the metal where it snapped off (it was a clean,flat break) & the metal was black, not the color of steel! WTF? it looked like they cast it wrong &/or quenched it wrong after comin outta the mold. so I emailed the ebay seller bout the defective pos & he said he would send another 1 free of charge! I said WHAT? he said that he always stands behind what he sells & was sorry 2 hear that! I still cant believe people like that are still round, specially on ebay! what else can possibly happen 2 this build? I think I've seen jus bout everything that can/will go haywire! please xcuse me 4 this rant, but I figured I'd jus had enuf & had 2 vent! thanks guys & gals,-------twosmoke
 
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