150cc GY6 scooter lost top speed - Page 3

Battercake · Today, 03:46 AM

I've ended up with three carbs: The original one from the factory, plus two I bought online trying to fix the problem. Going back to where this all began, the diaphragm in the original carb went bad back in January. I swapped out the carb with a new one, which made it run again but things were never 100% after that. I don't remember what all transpired after that, but I ended up buying a third carb and at some point started swapping parts around trying to make it run right. Somehow I ended up with the original carb back in the scooter with the diaphragm out of another carb. But last night I took a notion to swap things out again. The first carb I tried wouldn't work at all. It just filled with fuel and smoked out the tailpipe with every cycle trying to start. So I tried the other one and suddenly this thing started running better than it has since January! These are all the cheap $35 carbs like the one that came from the factory (but with working IAM screws unlike the original). I might consider upgrading the carb now?

sc00ter · Today, 08:56 AM

Are all 3 carbs the same size (inlet size, like 20mm for example) and same jet sizes? Even if you order a "factory" carb it never hurts to check the jetting is the same as the original carb. Even aftermarket carbs can have different jetting even though they are "the same" carbs. Production runs can very for many reasons.

Another fun thing we've run into. My friend and I were getting so flustered tuning a Yamaha Zuma 2-stroke. Luckily my build was close enough to his build at the time and we'd swap my carb over and his scoot ran pretty good. Put his new carb on and it ran weird. Put his new carb on my Zuma and it ran weird. The main jet, pilot jet, needle size and clip height all set the same but his new carb just ran weird. After breaking it down it turns out his carb had a 4-stroke atomizer in it, and mine had the correct 2-stroke atomizer! Ordered the correct atomizer and his scoot ran great. Now we verify what atomizer is in a new carb.

The only reason you'd consider a "performance" carb is if you want more fuel, that will equal more power. BUT, if you do a bigger carb you'll need to provide more air, and that means a different air filter. Then you have to tune it correctly so everything gets along and it runs good. Tuning Matters website has a good How-To on their page that goes in steps.

Another thing to consider, get a brand name carb. A Dellotro or Mikuni are the 2 main players and sometimes do runs under other names, like Stage6 and Polini.

If you are happy with stock then keep it stock, just fine tune everything and make it perfect. The bonus is it will stay reliable. That's what I'm doing with my Buddy 125.If I want something faster I'll just buy a bigger scoot. Keeway Sixties 300i is a dream scoot for me.

Today, 08:56 AM	#32
sc00ter Join Date: May 2017 Location: Norfolk, VA Posts: 572	Are all 3 carbs the same size (inlet size, like 20mm for example) and same jet sizes? Even if you order a "factory" carb it never hurts to check the jetting is the same as the original carb. Even aftermarket carbs can have different jetting even though they are "the same" carbs. Production runs can very for many reasons. Another fun thing we've run into. My friend and I were getting so flustered tuning a Yamaha Zuma 2-stroke. Luckily my build was close enough to his build at the time and we'd swap my carb over and his scoot ran pretty good. Put his new carb on and it ran weird. Put his new carb on my Zuma and it ran weird. The main jet, pilot jet, needle size and clip height all set the same but his new carb just ran weird. After breaking it down it turns out his carb had a 4-stroke atomizer in it, and mine had the correct 2-stroke atomizer! Ordered the correct atomizer and his scoot ran great. Now we verify what atomizer is in a new carb. The only reason you'd consider a "performance" carb is if you want more fuel, that will equal more power. BUT, if you do a bigger carb you'll need to provide more air, and that means a different air filter. Then you have to tune it correctly so everything gets along and it runs good. Tuning Matters website has a good How-To on their page that goes in steps. Another thing to consider, get a brand name carb. A Dellotro or Mikuni are the 2 main players and sometimes do runs under other names, like Stage6 and Polini. If you are happy with stock then keep it stock, just fine tune everything and make it perfect. The bonus is it will stay reliable. That's what I'm doing with my Buddy 125.If I want something faster I'll just buy a bigger scoot. Keeway Sixties 300i is a dream scoot for me.
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