Yamaha 1981 LB50 PH Chappy resurrection

[twosmoke]

Hi Guys & Gals, I finally got the ole girl fired yesterday, didn't ride it yet, just started it & tuned the carb a lil, it doesn't take the gas too fast, but revs nice if ya roll it on slow (could be running a lil on the rich side cuz there is a bog when ya blip it) IDK, maybe its lean, like it aint getting fuel fast enough? The clip is set to the middle groove, maybe i'll move it down a tick if it's rich & vice-versa. Another snag (as usual) this 1's for you my67xr, I'm havin a prob w/the directionals, can't get em to work. I put in a brand-new battery, but didn't connect it, they didn't work w/the scoot running, just the head & tail lites. does the battery have to be connected in order for those lites to blink? (I do have the pos side connected w/the in-line fuse, the ground is not) What do any of you electrical geniuses think? I did manage to upload a pic to show ya'll what it looks like now, so ya can tell me whatcha think-------twosmoke

 

[my67xr]

How many turn's out is your mixture screw set at ?

Sound's to me like the main jet isn't big enough?
Try changing the clip on the needle down to the bottom one and see if it's any better.

The indicator's need to have the battery connected to work

 

[twosmoke]

Hi 67, thanks for getting bk so quick! the mixture screw is approx. 1.25 turns out. how can the main jet not be big enuf? its a wayyy bigger carb! it's got a 70 main-30 idle-needle #4f18-needle jet #145650-0 & the slide cutaway is#1.0, would that bog be due to a lean condition? I thought it mighta been a couple ticks too rich? (I've been known to be wrong before!) and does the scoot need to be runnin w/the battery connected? cuz I connected it w/it not runnin and they didn't blink, but both the head & tail lites were on! oh yeah, the carb is a mikuni vm18, it sounds like it's a perfect carb for a 70cc, no? thanks again my67xr-------twosmoke

 

[my67xr]

Your pilot jet is just ok with the mixture screw at 1.25 turn's out.
But i would try the next size up, what's it have now a #20 pilot?


The #1 slide is pretty rich, you could try removing the air filter and see if that help's.
If it goes better then go down 1 or 2 sizes in the main jet


The carby having an 18mm bore also mean's a lot more air can be sucked through it too.
My son's PW50 from memory has around a 65 - 70 main jet in it with the big carby and a foam Uni filter.

 

[twosmoke]

Hi my67xr, the slide slot was @ the 2nd from the top, so I moved it to the bottom position, & choked & kicked it, it fired on the 1st kick! IDK if that's any indication that is a better position or not, didn't rev it as it was pretty late & that point. is the pilot jet the same as the idle jet? if it is, it has a #30 idle jet, if not IDK what size the pilot is. Really don't wanna take out the a/f cuz it is a b@#$h to r&r. It is a stock Yamaha foam a/f lightly oiled w/k&n filter oil so I think it's just fine ,not too restrictive, but the main jet is a 70 which I think is just bout right. gonna take out on the street today & put her thru her paces, polini recommends topping out @ 3/4 throttle & no further to break in the cylinder, piston & rings, so we'll see how that goes. I'll keep ya posted later on today on how it runs. thanks 67.-------twosmoke

 

[my67xr]

Yeah the pilot jet supply's fuel for the idle circuit.


So when it's been warmed up, if you blip rev the throttle is there any hesitation ?
If there is, get a bigger pilot jet, the next size up, so a #32 and fit that.
You'll need to adjust the mixture screw to suit the new pilot too, try turning it out between 1/4 turn and 1/2 turn more than where it was previously set at.


Having the needle clip on the bottom slot mean's it will need the next size up main jet, but you need to dial in your pilot jet first.
May even need to adjust the needle clip position again

 

[twosmoke]

Well, thank you my67xr, sorry to say, I got super side-tracked today & didn't get a chance to take the scoot out on the street , I had to do a complete brake job & a mickey mouse xhaust fix on my temporary ride, a 96 Nissan maxima, a real POS, but it's only for a short time till I get my 80 Z28 tranny rebuilt, then this abortion gets driven off the nearest cliff or bridge. But the day wasn't a total waste, topped it off tonite w/ steak off the barby & a couple of fosters oil cans! G'day, mate, lol. BUT, I will try to spend some time tomorrow following your advice ya told me yesterday w/that carb jetting. thanks my67xr, as usual-------twosmoke

 

[twosmoke]

Hi again, well I followed your advice 67, the engine didn't respond too well w/the clip in the bottom slot, it kept breaking up @ 3/4 throttle ( that's all I can give it per the polini break-in procedure) so I changed the clip to the middle slot, revs much better but has a slight bog, & no breakin up, I think I can live w/it for now till I can open it to full bore. & yes, I have another electrical gremlin (as usual!) I connected the battery, started it, flipped the indicator switch and the blinker didn't lite, both sides! the headlite dimmed and the taillite went out. when I pressed the horn button, the oil indicator lite came on! what could this be? short? bad flasher? the bulbs look good. Can sum1 pleeeaaase figure this mess out? thank you so much in advance-------twosmoke

 

[my67xr]

I would be taking the headlight retaining ring off, taking the head lamp out, and checking if the wire's look connected correctly.
Sound's like they have been mixed up in there, the indicator's should have 2 wire's the same colour joining into one terminal plug , then connect to the same colour socket with one wire running back to the switch.
Also check the earth wire
Horn switch sound's like it is hooked up to the oil light

eg; green to green, orange's to orange, blue's to blue etc



The slight bog as i mentioned before would be the pilot(idle) jet is too small
Get the next size up.
I reckon this ^ is why you are having trouble tuning it.
Once the Pilot is dialed in then the needle clip adjustment will work better, it still may need a new main jet but you wont know till the pilot/idle circuit is sorted.

 

[twosmoke]

Hey my67xr, I'm pretty sure the indicator wires are connected correctly. I did take the blinkers off to paint em, & was sure to connect em back the same way, cuz I marked em,. but I will take the headlite out & double-chk em. The horn did work(not too good tho) when the bike was running w/the bat disconnected. Another thing, like I said, I changed the clip position to the middle slot and the engine revs up better than the lowest clip slot, but when I put in gear, lock up the frt brake it doesn't seem to pull too hard when I give it gas? could this problem be due to the wrong mixture, wrong weight oil in the crankcase (I put in 22ozs. of penzoil 10w30 in when I did the top end) or a slipping clutch? The clutch worked fine before this new carb. & why do you think I need a bigger pilot jet? this engine idles perfect, am I missing something? Sorry for all these questions, but on this board, you're known as Mr Chappy! Thanks a million 67.-------twosmoke

 

[my67xr]

The slight bog when pulling on the throttle, the mixture screw set at 1.25 turn's out, both say the pilot is too small.
And when you dropped the needle clip to the bottom you mentioned it started easier, but didn't want to rev up higher mid-3/4 throttle (too rich?)
But with the needle clip on the bottom notch that would have also helped the pilot mixture's

So i think you need to richen the idle mixture with a bigger pilot jet, then lean off the main jet (fit 1 size smaller maybe 2 ?)


The horn has a small philip's head screw on the back of it near the wiring terminals, adjust it a tiny bit then try it out.
You can sort of tune them

 

[twosmoke]

Thank You 67, like I said, I returned the clip to the middle slot from the bottom slot yesterday cuz it wouldn't rev even on the lowest slot. now it revs up nice, but the mixture screw isn't set @ 1.5 turns, I didn't count the turns this time. you're prob rite bout the pilot jet, gonna see if I can locate and order up a 32 or 32.5 today. like I said, I locked up the front brake, put it in gear & gave it some gas & it didn't seem to pull too hard? could this be due to the pilot jet being too small & not being able to supply enuf fuel from the transition from the idle to the main circuit? it seemed to pull harder w/that other carb (still couldn't figure out the make of it) it came off that mx80, so I guess it was set up for 80cc? I will also try to figure out that weird indicator problem too, could a bad flasher cause them not to work & cause the headlite to dim when I flip the switch rite & left? I don't even know where the flasher is located, lol, but I mite hafta find it soon cuz I'm almost positive I rewired those blinkers rite, but will pull it apart today & double-chk, damn, I really wanna try this scoot out on the street to see what she got and all these probs are killin me! Thanks for your words of wisdom my67xr.-------twosmoke

 

[my67xr]

Flasher can is normally just above the ignition coil, below the oil tank.
Yeah might be faulty, they are a 6v 2 pin type.

 

[twosmoke]

Hi 67, would that be the square plastic box that's on the back of the airbox? -------twosmoke

 

[twosmoke]

Hi 67, just had the scoot out on the street, it doesn't seem to get past half throttle, it bogs & doesn't accelerate into the powerband, could that small pilot jet cause it not to have any pick up? I'm beginning to think so. We lifted up the back wheel & revved it & it got up there no prob. I think the transition from idle to the main circuit is boggin it & not allowing it to rev. I'm gonna order up 2 jets from treat, a 72.5 & a 73, ya think that would correct the boggin prob & allow it to accelerate? I shoulda listened to ya the 1st 3x ya told me to change the jet! IDK why I ever doubted ya, sorry! thanks again,67.-------twosmoke

 

[twosmoke]

Hey 67, ooops sorry, I meant to say a 32.5 pilot & not the 72.5 & the 73, DUH!-------twosmoke

 

[my67xr]

As the new carby is the OEM one for the Chappy, the factory jetting in it might not be suitable for this particular engine combo.

Yeah try a couple of bigger Pilot jet's, and tune the mixture screw so that it rev's sweet and smooth when you blip the throttle.
Fit the #32.5 pilot and start up the bike (should start easy), and let it warm up for a few minute's.
Then raise the idle speed a couple of hundred rpm's, now adjust the mixture screw in till it start's to stall, and back it back out till it just idle's ok.
Then turn the mixture screw out 1/4 turn at a time, then let the engine settle for around 10 second's, now adjust the mixture screw out again, and let it settle again.
Listen to the way the engine is running, you eventually want it adjusted so that the engine is at the smoothest/highest rpm.
Once you are happy it's pretty close, turn the idle speed screw back out so the rev's drop back to a normal speed, give it a couple of blip's to check it come's back to idle speed ok, and it's not set too low.
Turn the bike off, and screw the mixture screw back in till it start's to nip up, count how many turn's it takes
Eg , 1.75 full turn's, 2 full turn's etc
And then turn the mixture screw back out to where it was set at.
Let me know how many turn's out it run's best at, my guess is about 1.75 - 2 full turn's

Take the bike out for a little ride to check that there is no hesitation or stumble off the throttle, it still may need a little tweaking from there to get it spot on, but it'll only need adjustment's of 1/16th turn at a time .

Then once the pilot is dialed in nice you can suss out the needle jet/clip setting and or the main jet for 1/4 throttle to wot.



I just had a look at a Service Manual for a Yamaha Chappy i found.
For the wiring diagram, see page 110 here- http://projectmopedmanual.info/Manuals/Yamaha/Yamaha LB2 Chappy service manual.pdf

The R/H indicator's have an orange w/green stripe wire, they both connect to a dark green wire behind the head light.
I can't tell by the diagram what colour the L/H indicator light's use (diagram say's Ch, blue from memory?), but they connect to the same colour single wire from the msain harness.

There are 2x black w/red stripe wires for the low oil indicator light.
The horn connect's to one of the same black w/red wire's the oil light uses, but on the other side of the horn it has a Pink (P) wire

 

[twosmoke]

Well,67 the carb is not the OEM for the chappy, its a mikuni vm18, brand new, its wayyy bigger than stock! I got a bigger carb for the added displacement, but I'm still waiting for the 73.5 jet to get here from cal, then I'll follow your procedure. as for the indicators, I checked the wiring, the rt has a blk wire (frt) & a blue (rear) going in a double plug connected to a green wire. the left has a blk (frt) & a brn (rear) into a double plug connected to a brn wire. I took out the headlite, (had to) & just for s#%$s & grins, started the bike & & they dimly glowed when I flipped the dir switch. sounds like a bad flasher ( still havn't found the flasher can under the oil tank, just a blk plastic box on the back of the airbox ) Is this it? As for the oil lite & horn, I found the pink wires, but no blk wires w/a red stripe! was that wiring diagram for an 80 chappy? I tried to download it, but the file was too big & was takin 4ever to download! but if I have to, I will! if you can find out nething else, please LMK. thanks, 67,-------twosmoke

 

[twosmoke]

Hi Guys & Gals, Hey my67xr, I installed that 32.5 pilot je today & I think it did the trick! so I reinstalled the carb, started it,( you were right 67, it started on the 1st kick!) so I turned the idle up, tweaked the mixture screw & got it real close to where I liked it, it revs up nice, didn't break up, has a slight bog, if ya wanna call it that (I returned the clip to the middle slot) but it pulls way harder when in gear, so I think it'll be better till I break in the top end for 500km, haha, then I'll mess round w/the clip position again.(sorry67, I didn't count the turns, but will 2moro when I take it out in the st) as for the indicator problem, I located the flasher, removed it, took it apart & guess what? IT WAS RUSTED SOLID! I guess that explains that, cuz my wiring was correct, the indicators came on right & left when I flipped the switch. So I'm gonna take the scoot out 2moro as soon as we get finished replacing that tranny pan on that Nissan POS. but for now, I think I'm gonna drain my 3rd Foster's oil can, Ynot? I deserve it! G'day,Mates!-------twosmoke

 

[twosmoke]

Hi Everybody, I been away from the resurrection for a bit cuz of a string of automotive disasters! but I'm back @ it again, this is takin wayyy longer than expected! Well, I took the scoot out on the st yesterday, started it, warmed it up, revved it up, it revved up nice but w/a little bog if I rolled it on too fast, I just r&r'd the pilot jet from a 30 to a 32.5 & it still seems to run the same! It revs up nice & high in neutral but when I put it in gear & ride it, seems not to wanna rev up & move the bike past 10 mph! I jus can't figure it out! It jus doesn't go like it should! it went faster w/the tiny stock carb! could the clutch be slipping? I don't think so, cuz wouldn't be revving to the moon & not going newhere? could it be getting too much/not enuf fuel? the clip is in the middle slot. but what I did do b4, when finding out that I couldn't open it up past 3/4 throttle, was to put a few washers under the carb slide spring to limit the slide's opening to 75% travel. could this be the problem? I have no idea! does this mess up the idle to main jet transition? could it cause the engine to not rev @ 75% open? could some1 pleeeaaase help cuz I don't have a clue? how bout you my67xr ne educated guesses? thanks every1-------twosmoke