Kymco and Derbi Atlantis confusion

[astrubinger]

Hey gang,
I'm working on a used scooter my sister recently purchased. Before I start asking technical questions about the machine I need some help  figuring out what exactly we have here. The title shows it's a 2007 Kymco (50cc) but the decals on the scooter seem to indicate it's a Derbi Red Bullet. The VIN plate shows the "model" as a "Derbi Atlantis" and the year of manufacture shows 2006ish (it's hard to read). I'm a motorhead from way back but my expertise is in early 70s through late 90s cars and trucks. I'm new to scooters. I'm trying to tune the carb but before I get into that I need to know exactly what I'm working on. Is this a Kymco machine?

Once I figure this out then I can start asking about the carb adjustment.

Thanks!
~ Alan

[Vivo]

If the VIN plate shows Derbi Atlantis, then it might be a Derbi Atlantis.  The earlier model is just the Derbi Atlantis with boring colors. Then the newer models were painted with racy colors and graphics and called the Derbi Atlantis Red Bullet. However, the difference between the two are just aesthetics. I don't know about the Kymco title... can you post pictures?

[zombie]

LOADS of scoots have mis matched titles. The reasons are as varied as the amount. Derbi is Not Kymco. We can still help you here in fixing it up. A scoot is a scoot!

[astrubinger]

Hey gang,
Thanks for the info. So it looks as though I have a 2006 50cc Derbi. That helps. I've attached a few photos... as requested. Here's what I've been working on. I've been wanting to tune the carburetor. I found the idle speed screw and the air/fuel mixture screw. All the documentation seems to indicate that I should screw the air/fuel mixture screw in all the way, then back out the screw 1 3/4 to 2 turns out. THEN, start adjusting 1/4 turn in either direction until the highest RPM is achieved (then 1/8th turn clockwise to rich-en the mixture just a bit).

Well, first of all the bike has always run a little rough since I've had it (a month). That's why I wanted to do the tune-up. So today I got out my screw driver and attempted to screw in the mixture screw. Imagine my surprise when the mixture screw was already in as far as it would go. Besides it always smelling like gas and running rough, it's basically been running ok... especially at full throttle. Now, after I adjusted the mixture to where it SHOULD be (1-7/8 turns) it idles much smoother. However, sometimes at about half throttle it'll lag a little until I back off the throttle a bit. At full throttle it actually starts slowing down.

What did I do wrong? Should I have left the mixture screw turned in all the way? That do ya think gang?

~ Alan

[zombie]

You did good. Your needle inside the carb slide will fix the mid range bog. Try lowering the needle by raising the clip one notch. If it improves try one more. If it gets worse go the other direction till you nail it. The slide is the bit attached to the end of the cable.

[astrubinger]

Thanks Zombie. I just finished adjusting the needle valve (I think that's what it's called)... I tested it on every single setting and the setting that seems the best is the bottom notch (most rich). It still seems to bog down a bit but not like it did. I also had to re-adjust the air/fuel screw and the idle speed and everything seems pretty good now. I don't like that the needle is on the lowest notch so I may take it up a notch tomorrow and adjust the air/fuel mixture again... just to make sure the needle really belongs set so rich. My next option is to check the float but I have NO idea how to get into that.

[zombie]

Actually you need to go 1 size bigger on the main jet so you will find the float at the same time. Take the carb off the bike, and remove the bottom bowl of the carb. Do this carefully so you dont trash the gasket. Your jet will have its size stamped into it. They usually go up in 5 increments...90-95-100. When you go up to the next size it will allow you to lower the needle. That is the EXACT right way to do this... Adjusting the idle/needle/jet each time till it's right. What brand carb is on there.