Question about Derbi Motorcycles

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I own a derbi drd pro sm 50 (2 stroke), it's completely standered apart from the back sprocket has been changed from a 53 to a 48 so it's hits 50mph, running the standered 12 t on the front... I brought a brand new full arrow pipe and I want to know what main jet size I will need to make it run how it should... The standered jet is a 80... I have tried the exhaust before and it doesn't go past 4k, so clearly it needs upjetting which Is obvious, any help on what jet size would be great, Thankyou, the bike is a 60 plate.

Posted by Anonymous on

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  • Derbi Master
  • 59,701 Answers

Hi, Anonymous if you have changed your fuel delivery system, air filter size or flow rate, mufflers or exhaust system or a significant change in altitude your carburetors need re-tuning and if your fuel system (gas tank, filters, fuel valve and carburetor) is contaminated with ethanol sludge, varnish, rust, dirt, water etc. or your bike has been sitting for months or years without running these components must be "PROPERLY" cleaned and reassembled "CORRECTLY" before any adjustments can be made. Tuning your carburetor is fairly simple once you understand the basic principals. You engine is a simple airbox sucking air in and blowing it out, it is finely tuned at the factory for maximum performance once you upset that delicate balance by changing air filters, camshafts or exhaust systems your performance may go down the and the engine may run poorly, you need to compensate the air-fuel mixture in the carburetor in order for the engine to run smoothly and at peak performance. If you are running multi carburetors you need to sync them first and make sure your air cleaner element is clean and dry for paper elements or lightly oiled for foam and meshed elements and properly installed. Here is how and where you compensate trouble: "TIP" if your engine "BOGS" your not getting enough fuel.
1. Closed to 1/8 throttle is managed by the air screw and pilot/slow jet.
2. 1/8 to 1/4 throttle is managed by the air-screw, pilot/slow jet, and throttle slide.
3. 1/4 to 1/2 throttle is managed by the throttle slide and jet needle.
4. 1/2 to 3/4 throttle is managed by the jet needle, needle jet, main jet, and air jet.
5. 3/4 to wide open throttle is managed by the main jet and air jet.
6. Wide open throttle is managed by the main jet.
If you are running lean, spark plug electrode color is white, engine runs hot and feels like it is starving for fuel you need to go up on the jet size or move the c-clip down one notch. If you are running rich, spark plug color is black or dark gray, engine runs cool, and bogs down when accelerating you need to go down on jet size or move the c-clip up one notch. When your carburetor is properly tuned for maximum performance your spark plug electrode will be a light tan color like coffee with cream. If you prefer fuel economy over performance you can go down on main jet sizes until a satisfactory level of lower performance is acceptable versus MPH, your spark plug color will be whiter and your engine will run warmer. These tuning adjustments will only make improvements if your intake and exhaust system have no air leaks or sealing issues and the entire electrical system is in proper working order and you have no mechanical issues. For more information about your issue and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day.
Carburator Theory and Tuning
My tuning Derbi DRD PRO SM 50
https://scootergrisen.dk/scooterhjemmeside/download/derbi_50cc_6speed_servicemanual.pdf
https://www.oemmotorparts.com/oem2.asp?M=derbi
Derbi SENDA SM DRD PRO 50 Owner Manual

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/gregg_c0ec1df182c7330e

Posted on May 14, 2017

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Hi there,
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Posted on Jan 02, 2017

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Anonymous

  • 66 Answers

SOURCE: i just bought a 2009 ktm 450exc new from dealer

First KTM's are great bikes and are reliable.
Second don't adjust the carb unless you know what your doing.
Third it's a thumper....ie big single cylinder and is also a dirt bike.

So with that being said, if your riding it on the street it's going to overheat and if your riding in tight woods is will overheat as well. The puke hose goes to the frame between the radiators and is a messy location in the event of coolant loss. Most riders make the mistake adjusting thiers carbs when that is usually Not the problem. Unless you've installed an exhaust system or live at high altitude you do not need to adjust anything on the carb Except maybe the IDLE stop screw.

For overheating: KTM has a great add on electric fan kit that will help greatly. Also use Engine Ice or at least Water Wetter for better cooling performance. This costs more but is my favorite....buy some Evans NPG coolant and never boil over again!

Lastly, I'm a huge Husky fan but buying that next is like moving sideways, it's still a 4-stroke. Note... KTM's and Husaberg's (the original husqvarna) are made in the SAME Factory.

Posted on Oct 06, 2009

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