Yamaha 1981 LB50 PH Chappy resurrection

[my67xr]

Hey,
Try lowering the needle clip 1 notch and try it again, this will richen the 1/4 - 3/4 throttle and should get rid of the bog
If it's better but still not quite 100% try it on the bottom notch


You mentioned before that the carby intake tube is hard to remove, or the filter was hard to get off.
If you can remove the filter or tube off the carb and try riding it, and the bike pull's better it will prove that the main jetting is too rich


The bog at 3/4 throttle and up would be too big on the main jet, i would try 2 size's down from what is currently in there as a start.
Can you use the pilot jet from the old carby, same type, size dimension's ?

 

[twosmoke]

Hi 67, thanks 4 getting back so quick! yeah, it's a pita to take off that intake tube, but if I hafta, I will. yeah, it does sound 2 rich 2 me 2. No, the other carb was tiny compared 2 this 18mm, I doubt the jets r the same size, the needle is way smaller, & the pilot is smaller 2. I'm gonna move the clip @ the top slot & take off the intake tube & see if that works. I really don't wanna order a couple of smaller mains, they take a wk 2 get here, hahaha, but again, if I hafta, I will. Do you think that my ''75% governor'' has nething 2 do w/it tho? I wouldn't think so but I've been known 2 be wrong b4! Thanks 67-------twosmoke

 

[my67xr]

Is this the Mikuni carby a VM18 - 144 ?
Supplied with a #30 pilot and #70 main jet's

VM22/210 Pilot jet's -

VM4/042 Main jet's -

The needle control's mainly 1/4 to 3/4 throttle mixture's,
so moving the clip down to the 4th or 5th notch down will richen it a little and should solve the slight bog.
May still need a bigger pilot?
But see how it goes for now


With your stock main jet in it now, you could try restricting it if you want.
You need to find a single strand of copper wire .5mm diameter, cut a bit from an old bit of car wiring harness etc, then slice the insulation and remove 1 strand.
Cut it approx 5mm longer than the jet, then bend one end at 90°
Thread it through the jet and then bend the other end over at 90° as best as possible.
You may need to trim off any excess, the bend's at either end should stop it from coming out the jet and dropping into your fuel bowl.
This will reduce the bore of the jet down close to a #65 main jet
Might be another way to temporarily see if a leaner main will work better.
I have used this method quite a few time's with success



Contact these guy's for jet's etc, i have bought Mikuni part's from them before, usually cheaper than any where else, and received the part's in Australia in 7 day's
VM4/042 Large Hex Main Jets
The other option is to use the detail's up the top of this post and contact a few scooter shop's, or motorcycle tuning shop's near you.
They may have something in stock, saving you a wait for postage
Or search amazon with the part number VM4/042 and a 65 (jet size) after it, you might find some one local with one
http://www.amazon.com/s/ref=nb_sb_n...jet+mikuni&rh=n:15684181,k:VM4/042+jet+mikuni
http://www.newbostoncrane.com/mikuni-genuine-mikuni-vm22210-pilot-jets-detail.htm?productid=7941193
EBC BRAKES MIKUNI VM22/210 STYLE PILOT JETS from Western Power Sports ATV
http://www.motorcyclesboston.com/Mi...22210-PILOT-JETS-detail.htm?productId=8172979
http://www.momsouth.com/mikuni-genuine-mikuni-vm22210-pilot-jets-detail.htm?productid=8668954

With your washer/governor trick, that it just not allowing the throttle to open past 3/4 and reach the over rich mixture's from the #70 main jet

 

[twosmoke]

Hi 67, yeah, that's carb I have, same xact 1. If I move the clip to the bottom slot, wouldn't that richen it even more & cause it to bog more? shouldn't I move it to the top to lean it out? if you say the main jet is too big, wouldn't moving it up allow more fuel in @ 3/4 to wot? I'm so confused! Do you think I should take out the washers in the carb? would that make a difference @ 3/4-wot? IDK. I'm still gonna try takin the intake tube off & see if that helps & if worse comes to worst, I'll hafta see if a smaller main jet works. I just can't understand it, it went from a 50 to a 70cc, & I figured a lil bigger carb & a hi- perf xhaust would require a couple ticks more fuel, It shouldn't be brain surgery! It revs nice w/no load on the engine. I'm sure you can sort it out! thanks buddy-------twosmoke

 

[my67xr]

Tuning a 2 stroke can be a little different to tuning a 4 stroke.

When setting up a new carby that wasn't originally for the bike you need to start by working out which pilot jet it need's,
then move onto the needle/needle clip if it has a bog or stutter at 1/4 to 3/4 throttle, then finally onto the main jet.
If you try setting them up in any other order than that, it can throw thing's out in the transition's from pilot / needle / main circuit's
You then have to try compensating for it by losing some ridability in other throttle position's.
Eg; higher idle speed to keep it idling, which mean's it start's running on the needle/needle jet circuit and then the main's.
It make's it really hard to tune.


With lowering the needle clip, it will richen the 1/4 to 3/4 throttle position and hopefully get rid of the slight bog you have off idle.

How many turn's out is your mixture screw at now with the 32.5 Pilot jet ?
You've tuned it and adjusted the mixture screw and idle speed to suit the new pilot jet yeah ?


A free flowing exhaust/ more efficient expansion chamber need's a leaner main jet because it can let a lot more exhaust out.
So this ^ will make the carby suck more air, and this also mean's it will draw more fuel through.
Which then make's your jetting richer.

At 3/4 - WOT the carby run's mainly off the main jet, so fitting a smaller jet will hopefully sort out the mixture's up top



The earlier Mikuni VM18 (SS) was also used on the mid 70's - mid 80's Kawasaki 80cc 2 stroke's.
The factory jetting in them had a #25 pilot jet, and the main was a #65.
They also listed other jet's for tuning it including a #62.5, #65, #67.5
But if you fitted a better flowing expansion chamber/silencer the jetting would need to be even smaller

 

[twosmoke]

Hi 67, well I put the clip on the top slot & its still the same, it won't take the throttle unless I roll it on very slowly, then it revs up nice, I also took out the ''governor'', that just allowed it to open up to full bore. the bog isn't from 3/4 to WOT, its down low @ closed to bout 1/2 open, so I think the pilot is all rite. It seems to bog & not rev down low to bout 1/2 open & in gear & doesn't pull too hard, but if I put in gear, raise the rear wheel & rev it, it picks rite up & revs to WOT w/no boggin? so what main jet size(s) should I get? (there's a # 70 in it now) 2 of those dealers are located rite here in Ma, so they won't take too long to get here & they're just $2.95 ea, so the price is rite too! Thanks again, my67xr, I'm gonna get this thing figured out sooner or later, like I said It's a challenge now!-------twosmoke

 

[my67xr]

Move the needle clip to the 2nd notch from the bottom of the clip, you keep mentioning the other way around !

Like the needle on the right here

I'd try a #65 main and see what it does

 

[twosmoke]

Hi All, Hey 67, I followed your directions, moved the clip to the bottom groove, took off the intake tube, & started the scoot, well it was a lil better, still bogged when I opened the throttle , but revved nice if I opened the throttle slowly & if I opened it fast & not let off, it would die. I messed w/the mixture screw, but all it did was make it a lil better. I put it in gear & it still don't seem to pull too hard & doesn't seem to rev past approx. 1/4-1/2 throttle. I just cant understand it! If I lift the back wheel off the ground & rev it, it spins up to WOT! I throw my arms up! I'm completely baffled! could it be an ignition problem? could all that compression be blowin out the spark? I didn't replace the plug, I jus cleaned it on the wire wheel & regapped it to .030. It does have a puch hi-comp head installed. IDK, I thought I'd jus throw that out there. @ this point I feel I'm grasping @ straws! Does nebody have a clue WTF is goin on inside this scoot's head? Thanks every1 in advance-------twosmoke

 

[my67xr]

So how many turn's out is the mixture screw now ?

 

[twosmoke]

IDK, I had it in & out so many times, so I didn't count em, cuz I couldn't get it to run rite, so I'd say approx. 1.5-2 turns, but I'm thinkin bout orderin up the next 3 smaller main jet sizes tho, sumthin's gotta give!-------twosmoke

 

[my67xr]

Have you rung any scooter place's near you and asked what jet's they keep ?

I have been trying to find someone with a similar set up to your's on the net, to see what jet's they run.
I have found a couple using an #80 main, and an #85 main jet too

Also has your new exhaust still got the restrictor washer in it where it bolt's to the cylinder ?

 

[twosmoke]

Hi 67, no I haven't called ne of em yet till I knw WTF I'm tlkin bout! yeah, that was the 1st thing to come outta that pipe, mistake?

 

[my67xr]

You could either just ask them if they have any Mikuni jets VM4/042 type and if they do pick up a #80 and try it out, if it's better but still not 100% get a #85
Maybe take your jet as a sample

Or tell them what you've done to the Chappy, explain you fitted a bigger bore/piston , high comp head, VM18 etc and see what they suggest
But they might tell you to book it in and they'll fix it, then you could end up spending another $300 + on it


The only other thing i can think of is the manifold i/d would still be a restriction, and the reed's are old.
Could be worth replacing the reed's with some Boyesen reed's, and fitting a matching size to your carby intake manifold

 

[twosmoke]

Hi Kids, Hey 67, weren't ya tellin me to replace that #70 main w/a few progressively smaller? what would a bigger jet do? it's still only a 70! Now I'm 110% confused! what bout the plug? would that cause it to bog & only run @ half throttle when I ride it? I'm really runnin outta options here! -------twosmoke

 

[my67xr]

Well tuning wise as i've mentioned before there isn't really a standard type jet for them as the carby's can suit all different model bike's.

What you need is an assortment of jet's both bigger and smaller than what you have in it now.
But jet's can be expensive, and can take a while for shop's to get in too sometime's.
Buying them from a local scooter shop might be easier for you as they may keep the jet's in stock.
That's why i mentioned trying to restrict the main jet in it now with a strand of wire in a post before.
This will give you an idea if a smaller jet will help your bike at not cost to you.
If the smaller jet make's the problem worse then you'll need to try a bigger than standard main jet

 

[twosmoke]

Hi 67, got yet another question 4 ya, could I try the other main jet from the stock carb? will it fit the vm18? or maybe the other main from that mystery carb? If not, that link that ya posted 4 the jets is the next town over from where I work, so if neither of those jets fit, Imma scoop the nxt 3 smaller & the nxt 3 bigger jets for that carb, they're only $2.95 ea, so it aint gonna break the bank! another thing, I ran it 4 awile 2day & pulled the plug, & it looks like it's on it's way 2 becoming black, another condition of an overly rich mixture, so I guess ur right again, as usual, could ya please check ur chappy carb $ lmk what size jet is in it? that is if ya have a carb lyin round? I wouldn't want ya 2 tear ur bike apart jus 4 a jet! thanks again,-------twosmoke

 

[my67xr]

Sorry i don't have a complete carby off the bike, and the bike is not easily accessable atm.
You could try the other carbys' jet's, i'd think the Mikuni jet's would be the same at least?

You wont get much of an idea of how rich/lean it is with the bike idling
You need to do a plug chop
So start and warm up the bike, and take it out for a ride.
You need a slight incline and hold it at WOT in top gear for 20 second's or so, switch it off and bring the bike to a stop.
Pull the spark plug out and check the colour then.
You need a fresh plug to get a good colour indication too

 

[twosmoke]

Hi 67, I 4got 2 mention, I did install a new B6HS NGK spark plug the other day.the ground strap seems 2 be turning a dry black & the porcelain is turning lite brown, I didn't take it out on the st, but I had it runnin 4 bout a hf hr, w/varying engine speeds w/no load. another thing is, the plug I got has a shorter center electrode than the other plug.( I took the wrong plug 2 the a/p store) Does this make much difference? I think it must b a colder/hotter plug? I also changed the clip 2 the middle slot, didn't seem to do a whole lot tho, guess my next step is 2 order up an asst. of main jets from that shop in Marlborough, we're slowly getting there 1 baby step @ a time! I think this is starting 2 look like a Foster's oil can day! G'day & thanks mate!-------twosmoke

 

[my67xr]

The Spark plug chart's i have seen list the B6HS as the standard Chappy LB50/LB80 spark plug.
A lot of the high comp head's need that same shorter spark plug, eg NGK B5HS, B6HS, B7HS, B8HS, B9HS and B10HS
The B6HS is a standard heat range spark plug, but you might want to run a slightly colder plug once you sort out the way it run's, colder like a B7hs or maybe even a B8HS?
You won't know for sure till it is rideable over a long range, different conditions and temperature's etc

Reading the colour of a plug if it's been idled or used without a load won't give you an accurate reading, it will be semi fouled.
You need to do a plug chop like i mentioned above, running it like that will get the spark plug up to the correct 'self clean' temperature (450°C-870°C) and only then can you use the colour to see how it's running.


Lol with all the Foster's comment's too, do you really drink that stuff ?
Not a lot of people drink it here, we end up sending it O/S lol, just joking
Personally i rarely drink (think i had 1 Jack's and coke last year?), i gave up drinking beer when i was 18, but used to drink West End Draught.
The high carbohydrate content doesn't agree with my Diabete's either.
Victoria Bitter and Carton Draught and Crown Lager(from Melbourne Victoria, over the border from me) are popular here with some of my mate's.


Here's an old West End beer commercial, and the stereo-typical Aussie's, lol

[video=youtube;EzzX5vc74fg]https://www.youtube.com/watch?v=EzzX5vc74fg[/video]


And one for you, old Foster's commercial's
[video=youtube;MzJVODm25kk]https://www.youtube.com/watch?v=MzJVODm25kk[/video]

 

[twosmoke]

G'Day Mates, hey 67, I did go 2 the a/p store yesterday & brought the rite plug w/me this time. the guy cross-referenced it w/a NGK BP7HS, a lil longer electrode, so I ran the scoot the same as b4 w/the same results & color. I understand that in order 2 get an accurate reading is to ride the bike @ a sustained RPM & load 4 a short time then kill the engine & coast 2 a stop, then take it out & look @ it. well, I haven't gotten 2 that point yet as the bike wont rev up high enuf to get 2 full throttle. Rite now, the plug is the least of my concerns till I get the jetting figured out. I'm gonna go 2 the bike shop on my way bk from work & get those 6 main jets I mentioned & go frm there, & of course, I'll keep ya posted on what happens. As 4 the Foster's, they usta be brewed in aussie yrs ago, then in Canada, now they're made in Georgia & Texas! I started drinkin em a long time ago when the store ran outta Michelob, & I tasted the difference rite away, but I was a pup back then. Now I jus drink em occasionally 2 save me a few trips 2 the fridge! hahaha. I'm a microbrew guy, I like all the different varieties they're comin up/w. jus last nite, I had a Shipyard Mellonhead, a beer w/a slight watermelon flavor, it was pretty good. as 4 ur aussie humor, gotta love it! I plan on putting Australia on my bucket list 2 visit sum day, I hear its beautiful, a ratio of 7 women 2 1 man, & I jus love ur accent! so when I get rich & famous, ya jus mite see me there! Thanks again, 67-------twosmoke