BWS 100 / Scooter / Yamaha- High speed question (mechanical)

Life Cars & Motorcycles
1

Ok so I got my 1997 BWS 100.

Bored 4mm over, +1mm stroke, 22mm carb with manual choke, Maxxis 6029 120/90-10 front, 130/90-10 rear street performance tires, NCY gold forks, 220mm full floater rotor disc, Wakawa over sized opposed 2 pot caliper, high temp brake pads (not too grippy at first but after a few good pulls they get stronger), kevlar brake line, V8 performance 2-stroke exhaust, after market Taiwan made HV coil, upgraded clutch and variator, new rollers, race rear shock. This thing hauls butt and pulls the front wheel off the ground from a 10 km/hr rolling start. Still using oil injection- full synthetic, high performnce, no-smoke oil only. I run 50/50 95-98 octance with fuel booster every 2 tanks. The big luggage rack on the back makes it look like a plain jane run-around scoot until the throttle is cracked open.

So the problem:

I am going through the tunnel to Neihu from Shilin side chasing down a 250cc hornet, and passing him (yes he pushing his bike…hehe), so at 110~115 km/hr the scooter cuts out (was pulling hard until it cut out) 1/4 way through the tunnel. No sputter no hesitation just dies, no electrics no nothing, but the fuel gage stays up so I know it isn’t the battery or main fuse. I pull into the connecting exit tunnel give a kick start and it runs up no problem. Plenty of fuel in the filter. O.K. maybe I pushed it too hard, chalk it up to over zealousness.

Same day I am running up Yang De, running again at about 110 km/hr and accellerating up hill, suddenly nothing again, pull over check fuel, kick start it, runs great.

O.k…the question. I have the stock CDI still. Is there a rev limiter / speed limiter from the factory set at around 110-115 km/hr (which would be rpm dependant since the speedo doesn’t electrically interface with the CDI or coil)?

If it was the coil and it over heated, it would miss-fire or sputter? Right.

If the CDI was the issue it would reset once the RPMs were below the threshhold, but without kicking it over it would just kill the spark? right?

It seems like the CDI, but I would like a second (more experienced) opinion.

The lights were out, which only turn on when the motor is running. The fuel gage was still operational with the key in, and was working when the motor cut out.

Lastly, does anybody have a spare tank with no rust in it? I need to buy a new one as I can see a noticeable rust coating but no floaties or loose particulate----YET.

Also if the verdict is the CDI, anyone know where to get a 10.8 K rpm CDI / or adjustable timing curve CDI for this scoot?

Any ideas?

You ask why do I have a BWS beefed up like this…Because the wife wouldn’t let me get the 160cc polini built street legal Aprillia RS 125, so I settled for the next best 2-stroke I could get under her radar. HeHe…

Thank you for any help.

2

you might have scuffed your piston rings against the cylinder. I had a similar incident once on my NSR.
side question :
do you use your bws for any offroading? I’d like to build something like that for some offroad fun.

3

I thought about actual mechanical interference as the cause, but after doing a quick scope inspection down the spark plug hole, there was no indication of any scuffing or piston / ring / cylinder problems. Plus the scoot started right up about 15 - 30 seconds after the turn off and now issues either time.

The BWS is no longer for off road. The front NCY forks are performance road types and the originals had a bit more spongy travel to them. The old rear shock was shot, and bottomed out several times during rides on Cheng De Rd. The new rear shock is firm and not for off-road. The tires are strictly street perfomance (look a lot like Metzler MEZ1 or MEZ2 tires) but only on 10 inch rims.

The bike has a boost bottle (stock), but has nothing in the terms of low end torque as with most 2 strokes. But it screams once it hits around 7k rpm. It would be good for off roading with a bit more of a slippy or high winding clutch assembly since most of the time off road you aren’t topping out, so you want the out of the corner get onto the jump power or off the line power. This BWS doesn’t seem like much off the line but at about 5-10 feet off the line the steering gets light and I have had some head shake (no contact with the ground) when I wasn’t paying attention.

I am going to take it into a good 2 stroke tuner down on Bade Rd near the DMV to have him rejet the carb though, it seems to be a bit lean at times in the low end and not quite flowing right on the top. It may just be that I expect more from the motor than it has to give. I mean should it really have much of a kick at 100km/hr when I open the throttle the second half-way open? It may be a bit over carbaurated as well.

I could recomend someone to build the engine for you if you like, if it turns out you are going to do it. I think he said some where around 8-9k NTD to go from stock motor to bored and stroked, performance crank, exhaust, reed valve cage, new carb and tuned and installed. I believe he went with all Yamaha and Japanese parts. He originally built this one as a super motard type with 12 inch wheels and long travel front forks and rear shock, but I had him convert back to stock as I wasn’t into the motard thing.

Good luck.

4

I was very interested in the BWS a while back…saw some craaaazy bikes people built for off-roading. NOt much was left of the original BWS but it looked like a lot of fun! That’s fast! I get scared when I go faster than 60!

5

I’m not familiar with this vehicle but I’ll try.

Does your brake light still imuminate with the engine off?
Does it have enough juice to restart, or do you have to kickstart it?

If you have enough power then its fuel starvation or spark.

it has a manual fuel inlet if I am correct, and if so it should splutter as it reaches starvation point, not simply cut out, so I’m going with spark. Ignition coil perhaps.

6

Hello,

Yes the brake light still worked when the engine died, the fuel gage was operating as well.

The battery was good to use the starter but because of the high compression the start has a hard time even when the battery was brand new. Sometimes if the piston is on the compression stroke even the kick start kicks back.

The fuel is vaccum valved so it only flows when the engine is operating, and yes the fuel filter was full. No sputter just instantly dead.

Brand new coil. I ohmed it out, checked the connections and checked the cable and plug (iridium plug). All good.

I know the spark stopped because I had air and fuel, and electrics…but no spark. It fired immediately after dying (within 15 seconds) on the next start.

I was leaning to the CDI as I have heard most BWS’s don’t get past 100 km/hr. So i figured maybe a rev limit in the CDI at an RPM that would equate to 110 km/hr ???

I will be replacing the CDI soon with an NCY motors 10.8k rpm CDI, and then I’ll run it up again and see what happens.

Any additional diagnosing would be very much appreciated.

7

[quote=“dunnman99”]
The battery was good to use the starter but because of the high compression the start has a hard time even when the battery was brand new. Sometimes if the piston is on the compression stroke even the kick start kicks back.
[/quote]As an aside, if you have such high compression you are leaving some high rpm power on the table. Too high a compression ratio prevents a 2-stroke from reaching peak rpm.

[quote=“dunnman99”]
I was leaning to the CDI as I have heard most BWS’s don’t get past 100 km/hr. So i figured maybe a rev limit in the CDI at an RPM that would equate to 110 km/hr ???.[/quote]
I understand your reasoning, but the way that electronic rev and speed limiters work is to kill ignition signal to spark (either every power stroke, or every other) until the revs (or vehicle speed) drop below the set value, where the plugs fire normally again. So, if you backed off the throttle a little then it should run properly again. Somehow I don’t think this is the problem, but changing out the CDI unit will at least tell you if the original has a problem or not.

8

The compression after the rebuild was apparently too high so a thicker head gasket (shim) was used to lower it a bit, and it has less than 200 km on it, so it is still a bit tight.

As far as the throttle thing, I did not back off. The kill was sudden enough that it just died, it took me about 1-2 seconds at speed to realize it was dead the first time, the second time just dead.

I figured since this was built and designed (1997) way before good rev limiters that actually allow the multi cylinder engine to run but at lower rpms (My RC-31 had a rev limiter that just let you bounce off the redline endlessly). Maybe this one has a defective CDI rev limiter, and the internal high speed relay circuit is not allowing the reconnection of the coil during operations.

Thank you for the advice, I will revisit the coil issue, and look into the CDI after that, since it seems the problem is spark, there are only 2 components that have the ability to do what is happening. I was told the Taiwanese built coil was better than the Chinese one I originally chose, but they looked identical. I have no way of running the coil independantly of the bike at around 10k-11k rpm, so changing ou the coil should be the simplest trial.

If anyone else has any ideas, I am open to try them.

  1. change out coil
  2. change out CDI if needed.

Thank you.

9

Ride slower! Check the other thread today about the Ninja 650 bloke who makes videos of riding crazily in Taiwan and who has been the subject of Chinese news reports. Well, today the cop authorities are falling over themselves to promise a SEVERE crackdown on two-wheeled offences in the wake of that clown and his videos. Granted it’ll only last a few weeks, but it’ll be real enough while it lasts.

10

I think your bike just doesn’t like tunnels.

11

No vids from me, and my 60 mph burst last for about 10 seconds on straight aways with very little traffic.

Imagine that 50-60 mph is considered High speed. I remember regular 110 - 120 mph driving on public open roads (no one for miles) in the states without a second thought.

Many of you europeans probably have stories of driving 120 mph plus for miles on end on the autobahn and thinking you were just cruising.

I gues us foriegners really are too fast.

As cutting traffic and weaving, I am the rider on the right, that passes only when the traffic in front of me is below the speed limit and I pass with authority to remain next to the passee for a minimum amount of time, and I almost never pass on the right.

I know us foriegners are too fast, but hopefully when we first get here we tend to obey the traffic laws more than the people who live here. That is why we complain soooo much, because we seem to tbe the targets of the 'bad" driver persona, even though we make up a very small minority of drivers.

A Taiwanese friend of mine said they must be better drivers because less people die in accidents on the road here. I reminded him that when the speed limit is 24-28 mph it is pretty hard to have a 2 vehicle fatality accident unless someone was doing something real stupid ( I told him I had ridden in bumper cars and crashed at higher speed than I see traffic in Taiwan).

When a school zone speed limit in the USA (15mph / 23 km/hr) approaches main city street speed limits 18 mph / 30 km/hr in Taiwan, you feel like you are at a crawl here.

For irony sake, I was on Nanjing (I think) the other day and I saw a big billboard on a bus stop (the one in the middle of the traffic area- brilliant), And in a life size picture it said it is illegal for more than 2 riders on a scooter -in chinese. And showed a picture of 4 people with small children included on a scooter and a big red X on it, and a picture with 2 riding next to it and a green check. And right in front of the sign a scooter cop with a fully laden 5 rider 100 cc scooter between him and the sign…I so much wanted to take a picture but didn’t have the camera. To make it even worse he even looked at them with the sign picture perfect behind them saying they were in violation of the law, and he looked back ahead an rode off when the light turned green.

My wife and I were laughing so hard along with my 3 kids (seat belted in and not jumping around in the back of the car) as we drove off. I have pladged to sit for a day in front of that sign this summer and take pictures of violators as they pass in front and mail the time/date stamped picture to the DMV headquarters…not that it will do any good.

I think my little rant is in the wrong forum, so I will end it now.

Any other BWS advice would be greatly appreciated.

12

It’s the CDI crapping out. I’d bet anything from reading your very detailed posts this far.

The stock BWS CDI has no set limit. It will go as far up there as you can mod the bike to go, that’s why they don’t make performance CDI for this bike.

Made in Taiwan: NT$600

Genuine Yamaha: NT$ 2,400 or so.

The made in Taiwan don’t last, so go with the genuine Yamaha CDI. Problem solved.

marboulette

13

I went through the whole electrical system this weekend and replaced a few Taiwanese spliced wires…yes you all know what that means. Replaced them with solderless connectors and butt connectors and shrink tube.

Ran the scoot out to Fujhi Harbor on Tuesday (100 km round trip), and ended up dieing twice on the way out there. I wasn’t going particularly fast- 80 km at one point, but it was under a load and going up hill.

Died instantly, and then fired right up again.

The CDI is stock Yamaha, but the coil is Taiwanese…I am now leaning toward an over heated coil. But wouldn’t it fail to work right after dieing?

I am going to replace the fuel line with larger tube this weekend, and go with a larger fuel filter just to eliminate the possibility of any fuel problems…but again no sputter no loss of power, just dead.

Thanks for the help, since prior people have said the Yamaha CDI is perfectly good and has no limiter, I am going to stay with it, and replace the coil again.

Thank you,

14

Bike would not crap out if it’s the coil. It would backfire and shit. Wouldn’t restart well, either if it overheated. CDI, you stubborn you. CDI.

marboulette

15

CDI it is then.

I will hit the Yamaha shop up for a new one this week.

Thank you for the confirmation.

16

You’re welcome. My wife and I own two of them. Nowhere near as modified as yours is (mine is a little bit modified), but my experience is that when you run these bikes in the top end all the time(or often), the CDI don’t last as long. Identical symptom as what you described. The bike would just quit at the top end and restart as if nothing happened.

Replaced the coil on both scooters and other bikes over the years, too. The symptoms are more like misfiring causing shuddering at the top end with backfires.

I’m pretty darn sure a new CDI is your ticket. :slight_smile: Let us know if it works for you!

marboulette

[quote=“dunnman99”]CDI it is then.

I will hit the Yamaha shop up for a new one this week.

Thank you for the confirmation.[/quote]

17

To All,

Found a solution and it was a simple one.

First off:

  1. Replaced CDI - No change
  2. Replaced inductive pickup and Alternator (suggestion of mechanic and free)
  3. Cleaned and Rebuilt carb

Solution. Bad unvented gas cap- I punched a pin hole in the top and in the metal surface exposed to the tank making a tiny breathing hole.

I also replaced the clutch, belt, and tuned the variator now, so wheelies from stop light are a bit easier, well as simple as full throttle from a stop…LoL…Heheh.

It seems when I had a full tank and very little air space in the tank, At High speed the cap and vapor vent on the top of the tank was unable to vent “fast enough” to keep up with the modified motor’s fuel flow rates and would die within 1 km, but with an empty to 1/2 tank it would take about 5-6km for me to out flow the vents and cause a vacuum in the tank…stopping just gave the air enough time to vent in and allow fuel to flow again. I punched a small “vent assistance” hole, and whalla, I can ride from Jihnshan to Yangmingshan up the twisties at 80-90Kph, (removing the chicken strips) and throughouly embarrasing the “Taiwanese knee dragging ZX-6” that I passed up hill, as his friends took pics of him trying to drag knee on some beautiful turns.

I would love to see the picture of a full leather equiped, knee puck wearing Green ZX-6 rider in his home videos and pictures with a 12 year old BWS 100 flying past him uphill. OK so maybe those images and video were deleted…LoL

I admit the tires will not last long with my new found fun.

But at least now the sides of my tread will wear out before the center of the tires…LoL

Now for the boost bottle and Japanes tuneable race CDI.

Cheers, and I hope this helps out anyone with a hotted up BWS that was having the same problems.

So if you are in North Taipei or Tien Mu area and a Blue BWS goes screeming past you smelling of Pina Colada (gas drag race additive) manhattanoil.com/fuel-fragrances.php, doesn’t smoke a lick, honks at people cutting him off with the installed 140 db truck horns and the guys is yelling yahoooooo. It might be me…

Have fun and keep the rubber side DOWN !!!

18

[quote=“dunnman99”]Ok so I got my 1997 BWS 100.

Lastly, does anybody have a spare tank with no rust in it? I need to buy a new one as I can see a noticeable rust coating but no floaties or loose particulate----YET.

[/quote]

I thought most “modern” (i.e. not Vespa) scooters had plastic fuel tanks? Since scooters are fairly generic (though the BWS is a bit less so) maybe one from another make would fit.

19

Yup, The BWS has a steel tank.

The USA and Canadian Zuma has the same tank…All 5.3 L in big sizedness…LoL

I may just have to live with it and change the filter more often.

And the BWS is not modern, it is 2-stroked and 1997, 12 years old.

20

glad u found the problem.

i was going to say fuel related issue. my watercooled dio had a 28pwk and there was a speck of debri in it. so small and so hard to see but sure enough on full throttle it would clog the main jet and shut the motor down. once it shut down the debri would fall right out and start after a couple kicks. ran fine all the time just not full throttle near top speed.

run a good air filter, good u got a fuel filter also. take the carb apart and clean it when u can. not shoot carb spray and put the filter back and call it a day lol.