SG50 Sting
Contents
Yamaha Sting SG50
YAMAHA STING SG50 34N
Year of manufacture: 1984 to 1985 (though some were made in 1983 and sold as 1984 models)
Specifications*:
Engine size: 49cc
Cylinders: 1
hp/kW: 1
Engine idle speed: 1650-1850 U/MIN
Carburettor air screw: 1,5-2 AUSDREHUNGEN
Tyre pressure (front): 2,3 BAR - 33psi
Tyre pressure (rear): 2,3 BAR - 33psi
Spark plug 1: NGK BPR6HS Spark plug 2: NGK BPR6HIX
Electrode gap: 0,7 MM - 0.027 inches
Battery: YUEM225LC (Batteries Plus part number) or Yuasa YB2.5L-C - 12V 2.5AH 19CCA FLOODED
Fork tube diam.: 1 inch
Fork length: bottom of tree to wheel mount bolt - 18 inches, overall length 26 inches
Head size: 25mm
Head tube length: 7 inches
Grey Market
The Sting was never imported into the U.S. All Stings that are here were privately imported. Many come from Germany. According to reports, there are less than 20 in the U.S.
Most do not have pedals, making them not a true moped. However, pedals were an option, as seen in the picture of the white Sting. So, pedals make them a moped...
They have been called a "dirt ped" since they have a definite dirt bike styling influence.
Engine is a 50cc with a driveshaft and differential setup mounted on a swing arm, similar to the Yamaha QT series. Many parts are interchangeable, though the Sting does have a significantly longer driveshaft.
Yamaha Sting Sales Brochure
Brochure is in German.
Yamaha Sting User Manual
User manual was in English, German and Dutch. Only the English section is included.
Maintenance and Repair
Repair Manual
The following is for an MJ Towny, but similar engine and wiring:
http://www.mopedarmy.com/forums/file.php/6/60111/1280009876_yamaha_towny_mj50_manual.pdf
The following is for a QT50, but also similar engine and wiring:
http://projectmopedmanual.info/Manuals/Yamaha/Yamaha%20QT50%20shop%20manual.pdf
Parts Manual
European parts manual that shows all parts and part numbers in English:
http://knallertforum.dk/download/yamaha/reservedelskataloger/Sting_sg50%20katalog.pdf
Modifications
Engine Performance
Cylinder kits for the QT50, YT60, MJ50 and SG50 all are basically interchangeable for the engine. That means you can keep the stock 50cc, or upgrade to 60cc using factory Yamaha cylinders. There are also a few 70cc kits as well.
Both Stings pictured have the Malossi 70cc kits.
Malossi makes a 70cc cylinder kit specifically for the Sting:
https://www.treatland.tv/yamaha-QT50-YT60-malossi-70cc-kit-p/malossi-qt50-kit-318007.Htm
Motion Left makes a bolt on intake for the Mikuni VM18:
https://www.treatland.tv/MLM-QT50-vm18-clamp-style-intake-p/motion-left-qt50-intake-558.htm
Boyesen makes reeds:
Exhausts for the QT50 do exist. Motion Left makes one, as well as Jemco. These can be adapted to the Sting with some work. It is also rumored that Tomos A35 exhausts work with modification as well.
The white Sting has a MLM sidebleed exhaust made for a QT50. The red Sting has a custom exhaust using a Giannelli expansion chamber.
Cylinder head theory varies about what to use, and what yields too high of compression. Puch heads are a popular choice. The red Sting is running a Puch Gillardoni (Gila) head. The white Sting is running an A55 Tomos cylinder head (same bolt spacing as Puch).
This thread gives some theory:
http://www.mopedarmy.com/forums/read.php?7,2108771,2108771
These threads relate to Sting performance:
http://www.mopedarmy.com/forums/read.php?7,3525767,page=1
http://www.mopedarmy.com/forums/read.php?7,2086762,page=1
Ignition and Electrical
The stock Sting CDI box appears to be a fixed timing CDI - meaning that it does not change timing and has no timing curve to speak of. This may cause cylinder and head temps to climb higher than wanted, especially on long, high rpm blasts.
A common modification among the QT50 crowd is the Yamaha Jog/Zuma 5 wire CDI box. It has a high rpm retarding feature that keeps the temps down by retarding the ignition timing as the rpms increase. However, this 5 wire box DOES NOT work for the Sting. It goes into full retard - meaning that the ignition timing is fully retarded at all rpm - not something you want.
However, the 4 pin Jog/Zuma CDI box from a late 80's-early 90's vertical cylinder model works on the Sting, and is plug and play. It appears to have a retarding curve as well.
Forks
The front forks are substantial, with very thick tubes and stiff springs. They are easily disassembled by removing a circliip at the top of the "strut" assembly and removing the insides. Shortening the tubes is easily done. The red Sting pictured has 4 inches cut out of the tubes, allowing full suspension travel while providing the lowered look.
The factory uses loose ball bearings in the headset. However, the Puch 26mm caged headset bearings work almost perfectly as a replacement and upgrade.
Suspension
Some Stings came with a rear mono shock mounted to the driveshaft side of the swing arm. Others came with 2 rear shocks. The mounting points are said to be there regardless of model.
Shock length is 11 inches. There are decent quality replacements available on eBay for under $80/pair. Otherwise, it appears as if 10 inch will work as well, providing less off-road appearance and still allowing proper clearance at the rear tire.
Wheels and Tires
The front rims are 17 inches, the rears are 16 inches.
A 16x2.75 tire fits the rear with plenty of room to spare. A 17x2.75 inch will fit the front with good clearance.
Gears
PW50 gears can be interchanged to alter the acceleration and top speed.
About the Author
This wiki page is written and updated by Cynical1
Both Stings pictured are currently mine. So, I guess I'm the only guy in America with 2 of them...
The red one has been around and changed hands a few times before I purchased it. The white one had been under the same owner for the past 4 years before I purchased it.
I am slowly modifying them, learning about them, and updating. Feel free to correct me if any info is wrong.
--Cynical1 10:04, 23 October 2014 (EDT)
