New here! 50cc build

[Greg58]

In the ten years I've been building these I've watched the 48cc fade away, I haven't seen any new upgrades for them. I've also heard of people ordering the 48 and received a 66 or 69. Most carburators are jetted too rich, probably the same #71 drill as the 66, I had to solder and drill jets for both 48's, I'm at 900 feet above sea level.

 

[Atvrunner2]

The bcd for the 48cc being a 40mm bore is not the same and there are no aftermarket cnc heads for it, there used to be a pancake style head but few still sell it, though most 50cc scooter heads are adaptable.

Good to know, I will have to see whats adaptable.

 

[Atvrunner2]

I run two 48cc bikes, the only head I have found with a squish band is the grubee gt2b head, my avatar bike engine is from bgf on ebay. That engine came with a head without the squish band. Stock 25 mph was all the grubee would do, the bgf engine was a turd, about 20-21 was all it had. After widening the ports and all the other things learned here and the other forum I get 32mph from both. The grubee engine is the fastest, it's in a 24" tire bike, I did much more to it tho, both are over 10 years old.

Very nice, I honestly figured 25mph stock and if I did mods hoped for 30mph. Great info, exactly the stuff I am looking for. Thank you

 

[Greg58]

A lot of people don't like grubee, they have been good for me. Comparing the two engines on a tear down the grubee is better. What you have may be of better quality, my ebay engine had poor machine work and needed a lot of cleaning up.

 

[Greg58]

The 48cc likes lower gears, I run a 44 tooth on 26" wheels and 41 on 24" wheels. I once changed to a 41 on the 26" wheel bike and lost top speed, the rpm feel below the power band of the pipe.

 

[Karl Snarl]

Good to know, thank you. I know it is said to run 87, I would have no problem running 95 octane or more. This is not a commuter bike. But definitely wanted to know the limits, which I may eventually push it and the rebuild it. For now I will probably go with your suggestion around that .7-.8mm.
Has anyone tried to taper bore the stock carburetor? Unfortunately I have the 'speed' one, but I will buy an NT one a bit later. Was just thinking to try that since it works well on every other 2 stroke I have done. Then a better pipe. See what that nets in power.
Typically in the case reed PB motors the 40mm stays cooler with the extra cylinder meat, over the 44mm engines. Not sure if that is the case with these bicycle engines.

Saw carb this bad boy, you won't regret it. I use the rwj-4b for performance builds, and the hs254b for mild builds. @DieselTech also uses saw carbs, and some other guys. You would have to ask them what their go to carbs are. No need to buy jets, and super easy to tune. The ones I use are because I can find them for cheap as dirt, and they are performers.

With all engines, the bigger one puts out more heat. Gotta watch the tuning, and set the a/f mix a little richer, an you shouldn't have heat issues with these engines.

 

[Atvrunner2]

The 48cc likes lower gears, I run a 44 tooth on 26" wheels and 41 on 24" wheels. I once changed to a 41 on the 26" wheel bike and lost top speed, the rpm feel below the power band of the pipe.

I believe the gear that came with is 44. I will stick with that. Thanks

 

[DieselTech]

Yes I'm a saw carb lover thanks to the support of the forum. Love my saw carbs

 

[Atvrunner2]

Saw carb this bad boy, you won't regret it. I use the rwj-4b for performance builds, and the hs254b for mild builds. @DieselTech also uses saw carbs, and some other guys. You would have to ask them what their go to carbs are. No need to buy jets, and super easy to tune. The ones I use are because I can find them for cheap as dirt, and they are performers.

With all engines, the bigger one puts out more heat. Gotta watch the tuning, and set the a/f mix a little richer, an you shouldn't have heat issues with these engines.

Well I use a lot of wt668 clones among others between 12 and 16mm for gopeds and 43-49cc pocket bikes. So I am very familiar. So to be adapted, what intake is used?? My favorite part isnt the tunability as much as it doesn't matter if they are at any degree possible and will still run flawlessly.
Maybe after I modify this carb I will jump straight to , as I call, a pumper carb. Or saw carb. Lol

 

[Atvrunner2]

Yes I'm a saw carb lover thanks to the support of the forum. Love my saw carbs

Which model do you use??