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Post by katt on Jul 22, 2018 17:36:50 GMT -5
Considering installing cheap 47mm (72cc) bore kit from ebay for $30.
Will it let me accelerate faster and by how much more top speed will i gain, my current GPS verified is 32mph at 8000RPM? Any other PROs?
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PirateLabs
Scoot Enthusiast
Posts: 296
Location: Bowling Green, KY
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Post by PirateLabs on Jul 22, 2018 17:50:29 GMT -5
I would not turn 8,000 rpm with a big bore kit as it is a big strain on the stock crank. I have no idea what the redline should be for that size BBK but others here can tell you. (maybe I am wrong?) I know that size is the better choice rather than the 50 mm kit as that places even more stress on that tiny, stock crank. I am considering, sometime in the future, going to the 63 cc sized BBK. I figure it is safer because some scoots actually came with this size stock from the factory. Some guys on here will tell you they never had any problems with their BBK's and that is good. Some others will tell you the crank let go not too long after they installed the BBK. I am getting old and do not want to sacrifice dependability/longevity for another H.P. or two. If you are hitting 8,000 rpm then a BBK will not increase your speed much unless you upgear. Maybe you have the wrong belt size or sliders/roller weights? You should be running about 37+ or more stock. I hit 43 mph (gps verified) on my scoot which is still 49cc with a few mods. That happens at about 8,150 rpm with this current set-up.
Yes, acceleration will improve a lot, I have heard from the fellows on here that have done this. You will have more power so, yes it will take off better. Good luck whatever you decide to do.
Bill
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Post by acvw74 on Jul 22, 2018 17:50:45 GMT -5
It will really help your accelerations, but you may need to work on your transmission to get the most top speed out of it.
For the best longevity, try to find a BBK with rings from Japan or Taiwain and don't forget to upjet your carb to supply fuel to the newly added cc's
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Post by eclark5483 on Jul 22, 2018 18:29:29 GMT -5
BBK's do not give you a better top speed. They just make getting to that top speed go alot quicker. You'll want to focus on the CVT to increase your top speed. Even without CVT tuning, a BBK is well worth it.
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Post by katt on Jul 22, 2018 18:37:26 GMT -5
You should be running about 37+ or more stock. I hit 43 mph (gps verified) on my scoot which is still 49cc with a few mods. Bill All 50cc rated max 30MPH, what mods do you have on yours?
I don't see what difference sport variator or weights will have on top speed, if stock variator pushes belt all way up what difference will it be with new variator.
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Post by acvw74 on Jul 22, 2018 18:45:41 GMT -5
If you are looking for max speed, check out the Speed list - usually a full description of the mods made to the scoot to achieve the speed.
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PirateLabs
Scoot Enthusiast
Posts: 296
Location: Bowling Green, KY
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Post by PirateLabs on Jul 22, 2018 18:49:08 GMT -5
You should be running about 37+ or more stock. I hit 43 mph (gps verified) on my scoot which is still 49cc with a few mods. Bill All 50cc rated max 30MPH, what mods do you have on yours? Tires pumped up to max. cold pressure...cone air filter, glass pack exhaust, and carb. jetted for the mods with a 32 pilot and 85 main. High performance Variator and, my scoot takes a weird belt size that helps speed...681 x 17.7 x 30. That's really about it. I weigh 200 pounds at the moment and carry a bunch of tools and spare parts with me at all times. Most 49cc 4T scoots are limited to 35 mph but, mine has no restrictions as it is old so I didn't really have to remove any. Bill
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Post by katt on Jul 22, 2018 19:15:02 GMT -5
I am not fan of putting engine in red zone, but it was necessity before to even get 33mph.
Just checked my speed with GPS after i changed the belt (perhaps old belt was stretched and narrowed on the sides) and scraping carbon buildup from piston. Results are impressive i hit GPS 38mph on 8000rpm mark now and 35mph around on 7300RPM. Pretty sure with few mods i can make it hit 40mph on 7000RPM Guess i am keeping this scooter after all, my plan originally was to sell this slow 30mph scooter and get 150cc to be able to hit 40mph mark, since i can do it without any mods will just keep 49cc.
Now i will check compression next to make sure my engine is working at its max capacity now and this will be a deciding moment for getting 47mm bore kit or not.
But from what i see right my next mod is to convert rear brake to disk for sure.
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Post by Happypancake! on Jul 22, 2018 19:29:02 GMT -5
50mph is doable w/ 49cc. A lot of tuning trials and patience is needed. It’s a hobby. Check my build links.
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Post by katt on Jul 22, 2018 19:32:38 GMT -5
50mph is doable w/ 49cc. A lot of tuning trials and patience is needed. It’s a hobby. Check my build links. At what RPM and what your top speed at 8000rpm? And you have original Honda GY6 not Chinese version right?
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Post by scooterpimp on Jul 22, 2018 20:04:13 GMT -5
It takes some tuning , but 50 mph is possible. Bbk , properly jeted , cvt tune & a tailwind. Built a couple that hit 50 mph..(gps app) ..took some fiddling , used stock exaust & aircleaners on both...then i bought a 2t that went faster with mild tuning...but i sold them like an idiot & im starting from scratch.. (again)
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Post by Happypancake! on Jul 23, 2018 18:51:46 GMT -5
It takes some tuning , but 50 mph is possible. Bbk , properly jeted , cvt tune & a tailwind. Built a couple that hit 50 mph..(gps app) ..took some fiddling , used stock exaust & aircleaners on both...then i bought a 2t that went faster with mild tuning...but i sold them like an idiot & im starting from scratch.. (again) 9500-9800 rpm 58 mph
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Post by katt on Jul 23, 2018 20:40:46 GMT -5
Some will argue should never go above 8000rpm (red zone) with Chinese GY6 at least, whats your speed at 8000rpm? I have seen Chinese scooter dash with tachometer reads up to 12,000rpm, however red zone still starts at 8000, not sure if this dash for 49cc or 150cc gy6.
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Post by scooterpimp on Jul 23, 2018 21:09:46 GMT -5
Usually anything prolonged over 8k , means your picking up engine pieces on the side of the road (eventually ) ..a good 2t is just starting to get happy at that rpm..lol.
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Post by 90GTVert on Jul 24, 2018 9:41:38 GMT -5
Pancake has a GET engine, not a 139QMB.
Also may help to define 50MPH. For example, according to Pancake's old linked specs in his build thread the 58MPH run was "moderate downhill". I must assume tail wind may be involved. My 49cc TaoTao did about 50MPH near stock (ign timing, carb & CVT tuning). Problem was it was with a tail wind and a decline as tucked as a big fat guy can get. Day to day it goes 30-35MPH in mostly neutral conditions on flat road with me sitting up.
You surely can do 50MPH with a 49cc... if you want it bad enough. Most of us don't. If you just want to do it to say you did it, then find a hill. If you want something that cruises at 50MPH, get out your wallet and get as much education as you can and free up a lot of time in your future to work on it.... or just get a BBK and so on.
It's hard to beat big displacement. You generally need more displacement or more RPM to make significantly more power. Power adders (boost/nitrous) would be an exception, but those get quite complicated and impractical for the average person. You can work on improving volumetric efficiency the best you can and dialing in all aspects of the tune, but most of us won't actually turn a 139QMB at 49cc into something that does 50MPH reliably that way.
My TaoTao routinely cruises over 8,000RPM. I've seen near 10,000RPM, but only hills and tailwinds or when the belt was thin. That poor scooter probably doesn't realize it can go at less than WOT because it's so slow otherwise. So far 5,000 miles that way. I'd rather replace the engine than ride around at 25MPH because I'm keeping revs down though. High RPM is not good for your engine, but I don't think it becomes a huge issue till you move up to heavier pistons. Good news is you can get away with lower RPMs with the bigger bores. You can also run them at high revs if you'd like. I ran my 50mm bore at 9,000-10,000RPM to finally reach 50MPH with stock gears long ago (there were no upgears back then). With a brand new crank that went in with the BBK, it left me stranded from a crank failure at 2,003 miles. Normal cruising around 40MPH was much lower RPM, but the high revs for any time seems to take a toll on the big end bearing with bigger bores.
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