Re: The Official Yamaha Chappy (LB50) Thread!!!

Josiah Radebaugh /
Screenshot2019-10-08at10.36.54AM.png

Would just like to say...

Re: The Official Yamaha Chappy (LB50) Thread!!!

> Jack Rutherford Wrote:

> -------------------------------------------------------

> Btw, the pw50 offset timing key sold at peeweecycle.com should work in

> the Chappy to advance timing 3.6 degrees as it appears the Chappy key is

> the same dimensions as the qt50 key and thus the pw50 key.

> >

Dang . They aren't at all very proud of that little key , are they ?

"3.6 deg offset timing key 22.49"

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

yeah, guess they gotta make their money.

So I rode the Chappy more today. Could that tiny mini-rotor affect shifting from 1st to 2nd gear. When I first started, it would shift to 2nd and pretty much just fall flat - almost like it wasn't in gear at all. Rpms would drop way down - almost to nothing. As it warmed up, it got a little better. There is a flywheel weight that you can add. I wonder if that is the problem or if the timing needs adjusted although it revs out real nice in 1st gear so probably not a timing issue.

I left my petcock on prime all night and found it leaking gas from the exhaust connection to cylinder. But I don't think that would affect shifting especially after it had warmed up and burned off that gas in the pipe. (edited)

Re: The Official Yamaha Chappy (LB50) Thread!!!

> Hunter Skiff Wrote:

> -------------------------------------------------------

> Wow Ken! Just WOW

last weekend i did open the case up again. the primary reason was to replace both crank seals, but while i was in there i pulled out the 1st gear clutch again. when i reassembled i used an unsanded comet spring to get that little bit of extra tension. i also replaced the hub with the lb80 "speed hole" version i got from salvage.

FINALLY got the launch rpms up to 4k5, 5k range!

i also realized that with a bit of work one could flip 2nd gear to a "leading shoe" orientation vs trailing. the idea would be to get a more positive engagement into second. i noticed a tiny bit of bluing to the steel clutch bell on the 2nd gear side. i've also noticed a slower transition into 2nd while riding. i think this is because with the higher tension springs causing the shift points to rise in RPM there's a bigger delta between 1st and second. the sluggish engagement means that delta is creating a lot more heat.

meanwhile i continue to troubleshoot my erratic idle and possible lean condition... thought for sure it was the crank seals, but i swapped both out to no effect. then i pressure tested from intake manifold to exhaust port with 20psi and heard nothing. so next up is disassembling the entire carb, douching it out, resetting the float, and changing the filter.

fuckin mopeds.

Re: The Official Yamaha Chappy (LB50) Thread!!!

good times!

20191023_184630-01.jpeg

Re: The Official Yamaha Chappy (LB50) Thread!!!

meanwhile, a chappy update:

I discovered the etching and scoring on the cylinder was too far gone... compression only tested at 125 vs 150 when healthy. my idle issues were due to blowby in the end. I feel pretty stupid for not doing a comp test in the beginning and of course the end to end leak test didn't reveal anything.

so I ordered a 45.4mm OS piston from treats, borrowing a lisle 16000 small bore rigid hone from a buddy and taking it 0.4mm larger (worth about 1 or 2 ccs). (edited)

Re: The Official Yamaha Chappy (LB50) Thread!!!

Ken I'm sorry for the ticket but seeing a minibike on a traffic cam is hilarious, impressive speed too!

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

Added the flywheel weight to the hpi mini rotor on the lb80. Update coming soon.

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

Almost there with the HPI system on the lb80

Re: The Official Yamaha Chappy (LB50) Thread!!!

nice vid jack. i'm running out of things to do on the chap and the HPI might be the last piece of the puzzle. well that and possibly cracking the case open to check bearings/reseal halves/etc over the winter.

you're 100% right on about the PITA factor of mucking around with the clutch engagement(s)! ;)

ken

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

Thanks, I may pick up another Chappy. IF so, perhaps I'll dig into the clutch some on that one.

Re: The Official Yamaha Chappy (LB50) Thread!!!

well it's been a while since my last updates...

1) i can safely say that the rebore w/rigid hone worked a treat, and i was able to save my worked-over polini 63cc cylinder. i used the lisle 16000 small bore rigid hone with the included 160 grit medium stones. after a lot of research i honed dry vs oiled. during the honing process it became pretty clear that the bore was decently out of round as it sat. granted it had seen a couple of seizes and hundreds of heat cycles, but it does give credence to the old adage of a "seasoned" block being a better starting point for machine work. the 160 stones gave a nice cross hatch with the final strokes. this method of overboring works best with access to top and bottom of cylinder. rings are still seating as i haven't been riding as much, but it feels very strong, stronger than ever (likely a contributor to #3 below).

2) while out for a weekend trip to the bank i pulled out of a parking lot and suddenly felt a lot of drag, like a brake was locked on, and heard a rubbing noise. i quickly pulled over and discovered my entire luggage rack was suspended by the rear light wire harness, and nothing else. the rubbing was the license plate folding over against the rear tire. ALL FOUR m6 mounting bolts had worked themselves loose. only one remained which i used to reattach the rack, and i used some strong twine to shore it up for the short trip home. could have been a disaster at 40+mph. PSA: check your rack bolts!!!

3) my parts (vm20, ported MLM intake manifold, 8 pedal stage6 block, heavily ported+oversized polini, shaved OEM head, MLM people's pipe) are starting to come together as a system. now that my top end is running better than ever i am seeing a different limitation in the form of detonation at high (9k+) RPM and full load. static compression is tested at ~10:1 and prior to now detonation hasn't been an issue at all, but i think under dynamic conditions as the pipe comes up and volumetric efficiency comes with it i'm getting marbles in the chamber. running any richer at peak power just 4 strokes.

to test my theory i doubled up on the head gasket to take off a little CR, and it did help the situation, although it was not eliminated. at this point i have four potential solutions to the knock: add octane, reprofile the combustion chamber adding a little volume, attempt to retard timing on the OEM ignition, or go CDI for a timing curve.

add octane: more $$ per gallon. would use an MMT concentrate such as torco. about $10 per 5g will give 102 octane. no direct change in torque, in fact may be able to go back to one head gasket which would increase torque. MMT leaves deposits in chamber, not such a concern on 2 strokes where we have more frequent/easier top end maintenance. will not change chamber heat per se but if CR is increased that will increase chamber heat.

reprofile/lower CR: free, labor only. will give up a small amount of low end torque. will reduce chamber heat at high rpm. would eliminate the double head gasket, and improve/reshape chamber squish characteristics.

OEM retard: free, labor only. will give up a small amount of low end torque. will reduce chamber heat at high rpm. not sure best way to accomplish other than slotting mounting holes.

CDI upgrade: one of the single most expensive upgrades you can do. would not give up low end torque. will reduce chamber heat at high rpm. also gets 12v system for easier bulb selection, etc.

i'd love to just whip out the visa and order the HPI kit, but at this point i'm probably going for the slight head reprofile and look into retarding the oem ignition...

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

yeah that HPI price sticker is a tough one to get past but you could probably sell your stock flywheel, stator, etc., and recoup most of the cost.

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

My buddy killed it!

4 speed Chappy!

Damn!

Re: The Official Yamaha Chappy (LB50) Thread!!!

4 speed! Lucky bastard hahaha

Re: The Official Yamaha Chappy (LB50) Thread!!!

Dirty30 Dillon /

Pretty rare in the states indeed, rare elsewhere too.

I would be surprised if it was truely an LB80/4, and not the LB50/4, but they did indeed make a four-speed manual shift 80.

Re: The Official Yamaha Chappy (LB50) Thread!!!

it might sound strange, but im actually more interested in the 3 speed auto... keep the pedals!

Re: The Official Yamaha Chappy (LB50) Thread!!!

update: shaved a little bit of dome off the OEM head this weekend, smoothed it in with 500grit. concentrated around spark plug area. retained second head gasket for now. did not retest CR yet. knock nearly gone despite 30* ambient temps. still lusting after HPI CDI kit...

going to gear a bit taller by going from 14/32 to 15/32. also going to drain tranny fluid and go to something thinner & grippier, maybe an oil/ATF/MMO blend, since my summertime fluid is basically sludge at low temps.

Re: The Official Yamaha Chappy (LB50) Thread!!!

> ken gilbert Wrote:

> -------------------------------------------------------

> . still lusting after HPI CDI

> kit...

>

welp, thanks to treats black Friday sale, that's on its way...

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

Sweet!

Re: The Official Yamaha Chappy (LB50) Thread!!!

had a crazy idea--anyone (besides me, ha) ever consider using an lb80 crank in a 50 as part of a stroker build? rods and spacers would have to be worked out and could be an issue... still have to do more research.

meanwhile, cdi should be arriving today. when im going to get a pass to fuck around in the garage is another story.

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /
IMG_6601.PNG

Ok now I've seen it all

Re: The Official Yamaha Chappy (LB50) Thread!!!

Dirty30 Dillon /

Wow, that's news

Re: The Official Yamaha Chappy (LB50) Thread!!!

Cheap for that neat little granny rig .

35000.00 PHP = 688.98 USD

Re: The Official Yamaha Chappy (LB50) Thread!!!

so I still haven't installed the hpi cdi. im working out the electrical system due to 6v --> 12v upgrade.

to ease the transition pain, I ordered one of these:

Voltage Reducer, DROK DC-DC Buck Converter DC 8-35V to DC 1.5-24V 5A Power Supply Step Down Regulator Module 24V 12V 5V Volt Transformer Stabilizer

https://www.amazon.com/dp/B07KWX33X5/

these little buck converters can drop rail voltage without burning it off as a lot of heat and lost power (efficiency).

my plan is to use a full wave bridge off the lighting coil, then filter with a cap. this will be unregged 12vdc, the final value tbd.

then the adjustable bucker will feed off that rail, be dialled to provide ~6.3vdc, and plumbed back in where the oem R/R used to be, basically replacing it with a more stable version. I'll leave the OEM 6v battery in place.

the total current capacity of the bucker is 5a. im already running led signals and tail, so those draw nothing. I plan to rig the front headlight to use the 6v dc rail, so it'll be a nice steady brightness regardless of rpm. the bulb is 25w so that should draw about 4a.

someday the headlight will burn out and I'll revisit how im going to wire its replacement, which will almost certainly be 12v led.

unfortunately the bucker won't be here for a few more days, and I'm not going to rip apart the coils/ ignition until I have it, but this is my plan to get from point a to point b with minimal bs.

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

alright Ken, time for an update on that HPI set up and btw

looks like this one is coming back to me as the owner hasn't done anything with it. It needed a stator. I used mine to get it running. Now that I have the HPI in my other one, I've got a free stator to put back in this one.

(edited)

Re: The Official Yamaha Chappy (LB50) Thread!!!

got the HPI CDI installed and running well. i was hoping to document with pics and took a few but they're scattered around at the moment. plus jack is calling me out!

first thing i did to the HPI was float the lighting coil. easy to desolder the existing strap to ground, pulled another conductor (stripped extension cable 14awg) through the sheath and soldered to coil.

rigged up a quick 7a bolt-mount full wave diode bridge that i scavenged a decade (or two) ago and fed that into a simple single stage cap input filter. cap was another part i had hanging around (50v 6800uF) and sufficed.

DC-DC bucker idea described in earlier posts did not work due to insufficient voltage at low rpms. after some testing i ended up taking the output of the cap filter and wiring it directly to where the oem coils used to go. one coil went as AC to the headlight circuit, the other went to the acc/batt circuits. i crimped on spade connecter terminals and did not disurb the oem molex plug.

i also replaced the battery in its original location with original electrical connections (including fuse).

so with a minimal amount of modification i am running my 6v chappy on an unregulated 12vdc. there is a good deal of sag at idle but due to the retention of the battery turn signals still work, horn still works (a bit softer). while spinning along headlight is very bright but reaches a max which looks exactly as bright as on the oem magneto. i suspect that the oem voltage regulator is a simple shunt type (zener to ground) and since my entire electrical system is in parallel this clamps output voltage to oem value.

the 60w accesssory coil on the HPI is not stiff. expecting multiple amps at 12vdc indefinitely at idle will not work. the original 6vdc loads, along with the battery, work well. to really see what's going on in the rail i really need an oscilloscope as there is a heavy ac component, but i can't argue with results. my old tek scope died years ago sadly.

switching to an LED headlight would make a profound difference, enough i believe to remove the oem "one wire" voltage reg, replace with a 12v unit, and switch to 12v accessories.. currently i have LED tail and rear turns which help a bit, but the headlight draws 35w which is 6a@6v (but the beam pattern is nice, and plenty bright while moving). i can't run the headlight on ac and everything else on dc unless i abandon chassis ground for one of them.

what most folks don't realize is that switching to cap input filter does two basic things:

1. with no load, the output voltage will rise to a max equal to the peak ac voltage. this is 1.4x the ac "rms" or heating/lighting voltage for a sinusoidal waveform. given a 12vac rms input, the no load voltage will be 16.8vdc.

2. there's no free lunch. peak current will also be multiplied by 1.4x. my 35w headlight draws 6a @ 6vac. that current load will be "felt" by the coil like 8.4a of ac load.

this is why so many oems like to run the headlight on AC--perfectly fine if you want to half wave rectify, since the AC coil stays grounded on one side and you just tap off for the DC load.

for the near future, i snagged some 10a schottky diodes off amazon and plan on replacing the bridge. switching to schottkys cuts your diode junction voltage drop in half. in a full wave bridge you've got two drops, so you'll get about 0.7v more voltage. the smaller drop means less power is lost as heat; at 7a current load 0.7v is just shy of 5 "free" watts.

ignition wise i did not seem to have any of the shorting issues that plagued jack. in fact i paid no attention whatsoever to just bolting the mounting plate on to the crankcase with oem flat head machine fasteners. i did watch carefully my lead dress and made sure i didn't pinch anything on the way back together. i slit the oem rubber double shoulder bushing and put it on the HPI sheath as that area is not only easy to pinch but also exposed to chain wash.

i set timing to 2mm btdc which ends up setting peak advance to 25*. i have not verified with a timing light. due to a high CR i hear just a hint of knock here and there so if anything i would retard it a bit.

i ran with the unit as ordered for about three days, then i ordered the 300g flywheel (btw treats absolutely honors their price match guarantee) and have to agree with popular consensus that it just is a way better configuration. what sealed the deal for me is the possible (probable?) improvement in longitudinal crankshaft rotational inertia balance, and by extension crank/bearing lifespan. idle is also more stable and any sluggishness in throttle response is barely perceptible. for all intents and purposes there is no downside performance-wise, however it does make adjusting timing without taking off the chappy side housing impossible (you can't get clearance to the bolts by taking off the flywheel cover plate, and it won't fit out the flywheel cover hole). (edited)

Re: The Official Yamaha Chappy (LB50) Thread!!!

also refreshing all engine seals. for future reference, part numbers appear below:

20200122_180530.jpg

I snagged these all from boats.net for just under $50 shipped.

Re: The Official Yamaha Chappy (LB50) Thread!!!

Jack Rutherford /

I'm still digesting your penultimate post

Re: The Official Yamaha Chappy (LB50) Thread!!!

tried flipping 1st gear clutch to see what kind of difference between leading and trailing shoe (stock).

the leading shoe lowered clutch engagement by a LOT (2-3k rpms). unfortunately it ruined the drivability due to making the launch stall speed basically stock (vs. the 5-6k it was with my mods), so back it went to trailing shoe.

1st can be flipped in a matter of a few minutes. due to the nature of 2nd gear, flipping it requires a teardown (ie, removal of spring) and rebuild. i do have a spare set of clutches and may prep one to swap in for a quick test. even with practice i still hate dealing with those heavy comet springs...

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