Blue Max Chinese engine made by Jiangdong. It's "modeled" after the Honda GX200 but I'm not sure if it's a full clone. There's an interesting piece below from a go-kart club which races these engines.
Some comments found online at:
http://www.thunderhill-speedway.com/Blue%20OHV%20engine%20rules.html
In an effort to keep Kart Racing fun and affordable, Thunder Hill Speedway is introducing the use of a very affordable and reliable engine. This engine is a 6.5 horsepower copy of a Honda engine. Other tracks across the nation have been using this engine for over a year with great results in reliability, performance and very competitive racing. It is working the best to leave the engine as Box Stock as possible. At Thunder Hill Speedway we will have an adult Flat Kart class just for these engines and we will also allow this engine to be used in our Novice class and Junior Wing/Box Stock Wing Class as per the rules below. These engines are available right now at Harbor Freight Stores for only $159!!! Sometimes on sale for only $129!!!(Example: Harbor Freight in Eau Claire, WI)
There are several sellers of these engines on EBay for 109 to 149 with shipping ranging from about $25-50. I've written to several of the sellers to ask if there are dealers for warranty work and parts around the Boston area. One of the EBay sellers lists that for warranty or parts you have to go back to the distributor. But possibly there are enough matching GX200 parts for standard use replacements. ??
SPECIFICATIONS
Starting: Recoil Pull Start
Fuel Consumption: .51 GPH
General Use Engine Oil: SAE 10W-30 API SJ or SL
Cooling System: Forced Air
PTO Shaft Rotation: Counterclockwise
Ignition System: Transistorized Magneto
Fuel Tank Capacity: .95 Gal
Displacement: 12 Cu-In
Engine Type: Single Cycle, 4 Stroke, OHV
Dimensions: 12"L x 14.3"W x 13.2"H
Crankshaft PTO: 2-7/16" x 3/4 Diameter Tapped 5/16 x 24 UNF
HP Rating: 6.4 HP @ 3600 RPM
Controls: Throttle/Fuel/Choke/On-Off
Engine Oil Capacity: .63Qt
Spark Plug: BP6ES
Idle Speed: 1400 RPM (+200/-150)
Fuel: 86 Octane or Higher Unleaded
Max Torque: 9.76 Ft/Lbs @ 2500 RPM
Shipping Weight: 37 lbs.
HDC Item: 03163
* HORIZONTAL SHAFT
(2-1/2" long x 3/4" diameter with 3/16 inch keyway & threaded end)
* SHAFT ROTATION (COUNTERCLOCKWISE)
* CONTROLS ( THROTTLE / CHOKE / ON-OFF)
* APPROX MOTOR SIZE (L 12.3 x W 14.8 x H 13.2)
* MOUNTING PLATE
( Approx size 7" x 4" total size see pics)
( holes approx 6.25 long way and 3.25 short way apart)