63cc BBK?

[PirateLabs]

I have seen kits around for this size and, knowing that some 49cc 4T scoots used to be imported as "secret 63's" I wonder if this is a worthwhile upgrade that will not over stress the crankshaft while turning high rpm's? (8,000)  I thought about the 72cc kits and maybe machining the piston to make it as light as possible.  Brent posted a few years ago about a BBK (Airsal I think?) that was 80cc but had an aluminum piston that weighed the same as a stock piston.  Ring any bells out there?  Now if they, or someone, made a 72cc piston that was as light, or lighter than stock I might go that route when the time comes.

Just sort of spitballing here to see what you guys think?  Maybe doing a BBK at 63cc is not worth the effort compared to the stock 50cc?  I have almost 6,000 miles on my engine and all is well at the moment but...if/when it begins to burn oil or have any other serious issues,  before getting a new engine I might go for a BBK even though the bottom end is still stock.

Bill

[golfmech]

Do the 47mm/72cc kit it's a massive improvement and you can run the stock head I got mine for less than $40 on eBay at least a third faster all around

[humanshield]

I have an Airsal 50mm piston. haven't installed it yet. My 50mm BBK is just running too good to tear it down. Might build an extra motor tho. I had the same thoughts. Lighten up the bigger piston.

Remember the golden rule to power.......

There is no replacement........for displacement

[scooterpimp]

Im a fan of the 72/80 cc while using stock head. Healthy compression helps with the get up & go.

[Moat]

Hey Bill - I've got a 63cc BBK ($29 Glixal from Amazon) with about 700 miles so far - I like it. Nice little boost in acceleration and hill climbing ability. Went from about 39 mph stock to 41-42 (GPS). I do run it conservatively, though, and cruise at about the same speed as before (32-34 mph) - and never WOT continuously. But it'll hold that cruise easily at 1/3 throttle - wind or no - whereas it was 2/3 to 3/4 throttle before. Uses essentialy no oil, but does vibrate a little more (not at all bad, though) and strains the starter a bit more, too. Premium fuel, then, just to be safe.

Like you, I considered the stories of stock "Secret 63's" and am more interested in reliability/longevity than outright performance - as I often find myself 30-40 miles from home, out in the boonies. Only replaced due to the previous owner having apparently left the scoot out in the rain too often, causing watermarking (rust) of the original bore and thus a bit of oil use/carbon-fouled valves.

Good kit, fit and finish was just fine. I'm happy with it.

Bob

[PirateLabs]

Thanks for the replies guys. I am still leaning toward the 63 as it will be a lot less strain on the stock crank. I know me...I will eventually be running it W.O.T. no matter what I end up using so I need something that will not risk the crank too much...especially at around 8,000 rpm. I most likely will not make any change for a while as it has been pretty dependable in stock form for me but, I must admit, a little more oomph would be very welcome.

Thanks,

Bill

[KSR Moto]

Jul 19, 2018 9:19:07 GMT -5 PirateLabs said:

Thanks for the replies guys. I am still leaning toward the 63 as it will be a lot less strain on the stock crank. I know me...I will eventually be running it W.O.T. no matter what I end up using so I need something that will not risk the crank too much...especially at around 8,000 rpm. I most likely will not make any change for a while as it has been pretty dependable in stock form for me but, I must admit, a little more oomph would be very welcome.

Thanks,

Bill

I have installed 44mm BBK as well, had some minor issues but managed to get it runing perfect, I can definitely recomend that you install one,your electric starter will be able to start it too and my scoot niw has over 12 000 miles total

[KSR Moto]

And I forgot to mention that it runs better than some of the 47mm that I had, it also does not sound like it is going to fall apart at high rpms, it tops out at about 43mph, I am riding it everyday now, best BBK that I have ever installed

[Sir Scoots-A-Lot]

I am thinking of putting in a Big bore kit 44 47 or 50mm. Main reasons are hill climb and getting an extra 5-10mph top speed above the 39moh it eventually goes on a long flat in ideal conditions.

I just wonder if I can get a decent performance gain with just the basic cylinder & piston kit with the aftermarket air filter I already have and making sure my exhaust is derestricted? Or would I also need a new carb, head, performance a9 cam and expensive exhaust to get anything noticeable in acceleration and at least a 5mph top speed gain.? Would I need to switch out the final drive gear with a bbk to get a 5mph or more top speed gain? .

[KSR Moto]

Jul 20, 2018 21:53:43 GMT -5 Sir Scoots-A-Lot said:

I am thinking of putting in a Big bore kit 44 47 or 50mm. Main reasons are hill climb and getting an extra 5-10mph top speed above the 39moh it eventually goes on a long flat in ideal conditions.

I just wonder if I can get a decent performance gain with just the basic cylinder & piston kit with the aftermarket air filter I already have and making sure my exhaust is derestricted? Or would I also need a new carb, head, performance a9 cam and expensive exhaust to get anything noticeable in acceleration and at least a 5mph top speed gain.? Would I need to switch out the final drive gear with a bbk to get a 5mph or more top speed gain? .

It is very hard to tune stock bore to climb hills or to go 40mph

[Sir Scoots-A-Lot]

Jul 21, 2018 0:11:57 GMT -5 KSR Moto said:

Jul 20, 2018 21:53:43 GMT -5 Sir Scoots-A-Lot said:

I am thinking of putting in a Big bore kit 44 47 or 50mm. Main reasons are hill climb and getting an extra 5-10mph top speed above the 39moh it eventually goes on a long flat in ideal conditions.

I just wonder if I can get a decent performance gain with just the basic cylinder & piston kit with the aftermarket air filter I already have and making sure my exhaust is derestricted? Or would I also need a new carb, head, performance a9 cam and expensive exhaust to get anything noticeable in acceleration and at least a 5mph top speed gain.? Would I need to switch out the final drive gear with a bbk to get a 5mph or more top speed gain? .

It is very hard to tune stock bore to climb hills or to go 40mph

Thanks. I appreciate the reply, but I think perhaps you misunderstood me. Maybe I was unclear.

What I meant to say is: my scooter which I think is stock 50cc long case 139qmb with 12" wheels gets up to between 35-40ish flat ground. If I get a basic Big Bore Kit with just the 47 or 50mm cylinder, piston, wrist pin and circlips and not changing anything else can I expect very much better hill climb ability and at least a 5mph top speed gain?

Side note: I already have a short cone screen air filter and plan to make sure my stock exhaust is as derestricted as I can make it. I also want to scour the forum for the best 4 stroke exhaust design and figure out whether the best 4t is just free flow or is something similar to the technigas/ Leo Vince TT for 2t that they also sell looking the same for 4t better?

[scooterpimp]

If you put a bbk on otherwise stock scoot (carb. jetting will be nesesary ) you will increase take off/ climbing abilities & will gain higher speed. Every bbk i added was on stock engine with increased main jet.& made a big difference over stock, then i go cvt tuning.

[Sir Scoots-A-Lot]

Jul 18, 2018 21:08:16 GMT -5 scooterpimp said:

Im a fan of the 72/80 cc while using stock head. Healthy compression helps with the get up & go.

Scooterpimp-- you mention rejetting for the 47mm bbk. Can I use stock carb? If yes, what size jet(s) do you reccomend on a 47mm bbk? Just change main or all? Or of i get a new carb what size/ is a bigger carb plug n play or rejet also? And does a bigger carb= needing a bigger intake boot?

[scooterpimp]

Jetting kinda depends on your location , & what works best for you. In my area north eastern (usa) i usually just use a stock carb that has a removable float bowl (screws) & im usually around #78 on main(stock usually #75) jet.on bbk with stock airbox & exaust.

[Sir Scoots-A-Lot]

Jul 22, 2018 19:13:07 GMT -5 scooterpimp said:

Jetting kinda depends on your location , & what works best for you. In my area north eastern (usa) i usually just use a stock carb that has a removable float bowl (screws) & im usually around #78 on main(stock usually #75) jet.on bbk with stock airbox & exaust.

I live maybe a couple hundred feet above sea level also in the NE USA Hartford County Connecticut. So I think I will try that if I can open my carb. (previous owner 50% stripped the top screws on my carb just by taking a very cursory look. They also recommended I get a new carb if I wanted to "go fast" when I bought the scooter. What they really meant is get a new carb air filter fuel lines and add oil cuz it's dry lol.) Otherwise maybe I will drill out the A/F mixture screw and turning that up or get a new 18 or so. Thanks for the reply and if you're ever in CT I will race you once I get this kit on next month