1980 Yamaha Chappy clutch dilemma

[twosmoke]

Hi Geniuses, I am pretty new to the club & have a few questions bout my scoot. I was given a 1980 Yamaha chappy lb50 awile ago & finally got it runnin, not too good @ 1st, but runnin. after a polini 70cc big bore kit, a giannelli pipe, a mikuni vm18, a puch high-comp 'o' ring head & numerous jetting changes, got it to rev up nice w/out the bog that plagued me from day 1. Question is, the scoot gets off the line slow, takes awile to wind up to 2nd gear ( its a dual range, 2 speed auto-trans) & when it grabs 2nd, it doesn't seem to wanna accelerate too fast, seems like its stuck @ a low rpm & doesn't go ne higher? w/all the mods done shouldn't it be a lot better than that? I'm thinkin the clutch is not grabbing? do ne of you guys know offhand what the clutch pad thickness specs are? there are 2 clutch hubs in that carrier, & the rear 1 looks a lil thicker than the front. I already took the engine case apart & am just waiting for the dimensions so If I need to replace that front clutch I will! (if I can find 1!) & oh yeah, there's 4500 mi on the clock! & don't know how long a stock clutch should last! Thanks guys.-------twosmoke

 

[my67xr]

I just found this service manual, it's not a good scan but has the service limit's for the clutch etc
http://projectmopedmanual.info/Manuals/Yamaha/Yamaha LB2 Chappy service manual.pdf

I still think your main jetting is a bit rich
I would try fitting the 75 or 80 main and start it up, hold it at wot for 10-15 second's and see if it clean's up the way it's revving.

Have you checked the spark plug, the colour on the porcelain near the electrode ?
Is it spitting any spooge (black watery/oily looking stuff) out the exhaust when you're trying to rev it in top gear ?
Maybe even post a video of it the way it's running now so we can hear what it sound's like when it's wot in 2nd gear

If your clutch wasn't engaging then it'd be revving really fast.


Another thought, sorry i can't remember if i've asked already,
when you fitted the piston is the intake hole on the bottom half of the piston facing upward's ?

 

[twosmoke]

Hi 67, thanks 4 the quick response, I thought ya had enuf of my chappy questions since I didn't hear from ya instantly as per your usual! I have a 85 main & a 40 idle jet in it rite now, seems 2 run ok but the mix screw is bout .75-1 turn out & barely idles! the plug is a lite coffee color, not 2 dark, & not sooty black, so I think I'm ok there. I thought the same thing bout the clutch 2, revving 2 the moon & not movin. I think I put that piston in like the old 1 came out, I think the ports r facing the xhaust, but not 2 sure, it was awile ago, but I'll pull out the reeds & look, but if I put the piston in wrong, it wouldn't run @ all, rite? & I don't think I can shoot a vid, all I have is a galaxy, & the file would be too big 2 send, bsides, I need both hands on the bars 2 control the scoot on these torn up boston streets, hahaha, thanks again,-------twosmoke

 

[twosmoke]

Hey 67, I jus pulled the reeds out to check the ports on the bottom half of the piston & I didn't see ne ports on the intake side, so I guess I fitted the piston w/the ports facing the xhaust side, but if I did, wouldn't it not run @ all since there would be no ports to let the fuel/air in? now I'm really confused! I thought I installed it the same way it came apart! The plot thickens! thanks buddy-------twosmoke