Yamaha 1981 LB50 PH Chappy resurrection

[twosmoke]

Hi Guys & gals, hey 67, I jus ordered up sum main jets from treatland @ $3/shot. I got #'s 60,65,75,80,85,90&95. It's all trial & error from here on out, I'll be sure & keep ya'll posted who the lucky gal is!-------twosmoke

 

[twosmoke]

Hi my67xr, well those jets will be here on mon, 7/6. I was jus wondering which jet to try 1st based on the way the engine is running. I wanna try to get it rite the 1st time jus to avoid taking that carb off & on & draining it repeatedly. Could you please point me in the rite direction, or @ least put me in the ballpark as to which jet to try 1st? I got 7 of em & really don't wanna r&r it 6x! Thanks in advance.-------twosmoke

 

[my67xr]

Maybe try the #80 first going by the scooter forum's ?
See what it does then, if it's a lot worse then you know to go back the other way.

 

[twosmoke]

Hi Guys & gals, Hey my67xr, I'm bout 2 tear that carb apart, got the jets yest. 1 question, should I put the #30 pilot jet back in it? remember I swapped in a #32.5? would that make much of a difference when I put the #80 main in? 2day could be the day! Thanks mate-------twosmoke

 

[twosmoke]

Hey Crew, well I'm sorry 2 say, none of the gals were lucky! I tried the #80 1st, seemed a lil better, but not 100%, still a bog, I had 2 screw the mix screw pretty far in 2 get it down 2 a slight bog. but it wouldn't idle in that far, so I tried the #90, sumwhat the same thing, then the #95 & that didn't cut it either. so I put the old pilot jet back in it, (a #30, took the #32.5 out) still a marginal difference, I even put the air tube back on thinkin that would pull in more fuel 2 no avail! then I put the #60 main in & that was def not letting enuf fuel in! @ this point, I don't know WTF is goin on! ne of you guys have ne hats w/rabbits in em? how bout you, my67xr, ne leftover magic? Thanks Gang-------twosmoke

 

[my67xr]

The carby need's to be tuned to suit the intake tube and filter.
when i suggested that you take it off before was to see if the jetting was too rich.
If it was over rich, then it would have run a bit better with no filter/tube

When you are blip revving it, is there a hesitation ?
Does it still happen if you open the throttle slower ?

The only restriction i can think of is the intake, do you know what the i/d is of the original?

What about posting a question on the Treatland site about jetting, put it on the review's like other's have
i would ask it on the Yamaha 70cc kit's area

I am wondering about the pilot jet too
Thinking it might be too rich, might be worth trying a 25 and a 27.5 ?
Then again my sons PW50 seems happy with à 40 atm.
I have been making up a new expansion chamber for it over the last few days so wont have a final jet sizing till it's done and tuned.

Maybe you should get the next 2 size pilot jets up and down for your pilot to?

 

[twosmoke]

Hi 67, the I/D is bout 15mm, I don't think that's the prob tho, when I blip the throttle, there is a slight hesitation, but it catches up, when I gradually give it gas, it revs up gr8. the pilot jet is a #30, I swapped it 4 the #32.5 that I got frm treat. ya really think I need a smaller pilot? could it also be the oil injection system? would 2 much oil b fkin the mixture up? whatcha think? thanks again,-------twosmoke

 

[my67xr]

Not sure i you have seen it, but i edited that post above not long ago.
Sorry i'm still waking up, lol.

Nah the oil/fuel ratio should be fine.
If you drop back the oil in the fuel mix it means there is more fuel, so it'l be a richer mix


When you fitted the bigger Pilot jet, it improved it a little didn't it ?
So next 2 or 3 pilot jet's up might be the go ?

 

[twosmoke]

Hi 67, no, don't think I saw your edit, what was it? actually, it did run a lil better w/the 32.5 pilot, but not 2 much, it seems 2 run better w/the bigger mains tho. I left the #90 in it & called it a day. doesn't the pilot control the idle ckt? I didn't think it had 2 much 2 do w/1/2-WOT? maybe I,ll order up sum bigger pilots if I cant get get this figured out w/what I got. maybe I'll post sumthin on treat's board as a last resort tho. thanks, 67-------twosmoke

 

[my67xr]

Pilot control's idle and up to 1/4 throttle.
If it's too lean still it'll bog and wont allow a smooth progression to the next circuit.
If it start to rev better if you slowly open the throttle then the bigger pilot should help


That edit above, i mentioned my son's PW50 Mikuni had a 40 pilot in it (stock)
But i wont know what the final jetting will be till i make up the new exhaust and tune it to suit.

 

[twosmoke]

Oh, ok 67, so a bigger pilot will allow it 2 rev quick? well, that sounds like the ticket! That lil 50 had a 40 in it? well I guess those lil mx bikes hafta get 2 the powerband quick! would I hafta change the main 2 a lower # too if I put in a bigger pilot? jus curious, wouldn't it b overjetted w/a bigger pilot & a #90 main? what size is your kid's carb? what size(s) would you suggest I order? so far, I have a #30 & a 32.5, but I put the 30 back in it when I started w/the smaller mains. I'm gonna check out treat's site 2 see what they got. maybe I shoulda got a few when I ordered the 32.5! Thanks a bunch, 67-------twosmoke

 

[my67xr]

I'd be trying the 80/85/90's with the 32.5 pilot, with the air filter and tube on.
You need to find the perfect jet for the pilot to get rid of that bog before you can worry about the main jet

If you get a 35, 37.5 and a 40 pilot, i reckon it should be close ?

 

[twosmoke]

Hey 67, I put the 32.5 pilot jet back in it awhile ago, there's a 90 main jet in it now, it seemed to run better w/that jet in it w/the 32.5. I will order those jets you recommended rite now from Treat, hope it all works out, will that larger pilot allow that mixture screw 2 b adjusted more than 1 turn out w/that bigger pilot? cuz it doesn't idle w/the screw that far in but doesn't bog as much when I blip the throttle. thanks, as usual,-------twosmoke

 

[my67xr]

Yeah the next size up pilot will allow the mixture screw to come out between 1/4 and 1/2 a turn, same again with the next size pilot up.

 

[twosmoke]

Well my67xr, I ordered up those 3 pilots from Treat late last nite, a #35,37.5 & a 40, but now I gotta wait another wk 2 get em! what should I try 1st? smaller pilot w/a bigger main, bigger pilot w/a smaller main? I already had the carb apart & 2gether @least 8x! I'd like 2 keep the r&r 2 a minimum! w/all these jets, the possibilities r endless! Thanks,-------twosmoke

 

[my67xr]

What is the mixture screw set at now, is it 1 turn out ?
If so try the 37.5, and have the mixture screw at about 1.75 full turn's out.
I reckon main jet i'd try an 80 in it

 

[twosmoke]

Hi 67, I don't know where the mix screw is @, I've turned it in & out so many times, I didn't even bother 2 count! but there's a 90 in it now & I'm gonna try that 1st w/the 37.5 pilot, that 80 doesn't look 2 much bigger than the stock 70, so I'm gonna try the 90, but if it seems 2 flood, I'll try the 80 & count the turns of the mix screw, if that doesn't fly, I'll try the #40 pilot w/a smaller main. Do ya think I should try the #35 1st? like I said, the possibilities r endless! but @ ne rate, I'll keep ya posted, but gonna hafta wait a wk 1st, its the waiting game that I hate! Thanks again my67xr-------twosmoke

 

[twosmoke]

Hi Gang, Well I got those new pilot jets yesterday. I took out the 32.5 & tried the 35 w/a 90 main. the engine seemed to have a slight bog off idle, but I had to turn the mix screw in almost all the way in to get rid of it, then the engine wouldn't idle, even w/the idle screw almost all the way in! so I tried the 37.5 idle jet & jus bout the same thing, then I put the 40 jet in,& took out the 90 main & put the 85 jet in, Mistake? it seemed to run better but that mixture screw still was bout 1 turn out in in order 4 it to idle! the scoot seems 2 be slow off the line but revs up 2 the top, it takes awile 2 grab 2nd gear(in hi range) then doesn't seem 2 wanna accelerate 2 well! but gets goin after awile. shouldn't it do better after all the mods that were made? I'm starting 2 think its the clutch? Hey 67, do you happen 2 know what the shoe thicknesses are 4 the clutch in order for it to engage & hold @ those rpms? I already drained the crankcase oil & am gonna take the case apart 2 have a look, boats.net has a clutch carrier in stock if the shoes r 2 thin & outta spec. I will order 1 if I need 1, but I wanna b sure b4 I do that, maybe its something else? Thanks Gang-------twosmoke

 

[my67xr]

Just try changing 1 thing at a time so you can tell the difference.

When you're tuning it each time after changing the pilot jet, do you start it let it warm for a bit, then raise the idle speed a couple of hundred rpm's
Then adjust the mixture screw 1/4 turn at a time, then let it settle for 10 second's or so, then adjust it again 1/4 turn and let it settle etc etc, till it reaches the highest smoothest rpm's
Once you are happy it's there, turn the idle speed screw back out to lower the idle speed back to normal.
Then try blipping the throttle to listen for the bog.

I would think the main jet will need to be closer on a 70, but you wont know till the pilot jet is tuned first

 

[twosmoke]

Hi my67xr, Yes, I followed your tuning instructions 2 the letter, turning, listening, swappin jets, turning, listening, swappin jets.... so far I have #'s 30,32.5,35,37.5 & 40 for the idle jets & #'s 55,60,65,70,75,80,85,90 & 95 for the mains, it seems to run the best w/the #40 idle & # 90 main. where should I start? is this combo ok? maybe there's a better 1? I got the bog outta it, but the mixture screw is bout 1-1.5 turns out, jus barely idling, if I turn it out ne further, it idles gr8, but the bog returns! like I said, the possibilities r endless! could this carb be a cheap, pos, Chinese copy? could you suggest a good ballpark idle/main dynamic duo? as for the clutch, I got the case apart, found there to be 2 clutches in there, the front lining seems to be thinner than the back clutch lining, is that part of the acceleration prob in 2nd gear? do you know offhand what that thickness should be? ne & all help is greatly appreciated! thanks for letting me pick your brain!-------twosmoke