Kawasaki F11 250cc History & Performance modifications
Below is information, video & history on the Kawasaki F11 250cc. This page also contains KMC service pages for modifications to the F11 250cc to increase performance for racing or endurance applications.
My Kawasaki F11 as seen in the video
The above video is a brief history and review of the Kawasaki F11 250. It takes a look at Kawasaki's early years and history in building motorcycles and leads into the development of the F11. It also features the direct competition the bike had at launch and how it fit within the market. It is an interesting story on a bike that was "the odd one out" in Kawasaki's 1972 lineup.
Kawasaki F11 performance page 1
Kawasaki F11 Motocross reference 72-013 Page 1
dated 10-11-1972
Immediately Following the release of the F11, the Service Pept. at KMC has been deluged with phone calls concerning the specs necessary for converting the F11 for Moto-X (motocross).
In an effort to furnish this information, we have been involved in a concentrated research program and have developed some very useful specifications.
All the information was tested on a dyno and raced on the track. It works very well but it is by no means the absolute limit; it's just a good solid foundation for you to start with. Our main problem was developing an exhaust system that would give good power in a useful range. The specs were developed are the result of man, many experiments, ideas, theories and many exhaust pipe tests. For some reason , it is very critical on the F11 engine and this reason we suggest that you follow the exhaust pipe specs very closely.
We sincerely hope that this information is of benefit to you and we would appreciate any suggestions that you have to improvements.
dated 10-11-1972
Immediately Following the release of the F11, the Service Pept. at KMC has been deluged with phone calls concerning the specs necessary for converting the F11 for Moto-X (motocross).
In an effort to furnish this information, we have been involved in a concentrated research program and have developed some very useful specifications.
All the information was tested on a dyno and raced on the track. It works very well but it is by no means the absolute limit; it's just a good solid foundation for you to start with. Our main problem was developing an exhaust system that would give good power in a useful range. The specs were developed are the result of man, many experiments, ideas, theories and many exhaust pipe tests. For some reason , it is very critical on the F11 engine and this reason we suggest that you follow the exhaust pipe specs very closely.
We sincerely hope that this information is of benefit to you and we would appreciate any suggestions that you have to improvements.
Cylinder Head: Std (standard no modification)
Cylinder Timing:
Exhaust 172-174 deg (raise exhaust port 2mm)
Transfer ports 102 deg (std timing)
Intake 154-155 deg (cut 4mm off rear piston skirt)
Carburetor: VM34 (34mm Yamaha road race type)
Main jet 300
Needle jet 0-6/8
Needle 6f5-3
Cutaway 3.0
Pilot Jet 60
You can use the std. carburetor manifold and cut or grind the ID to 34mm and match the cylinder to the manifold.
In my Barn Fresh restoration series I show some of these performance techniques in practice.
Cylinder Timing:
Exhaust 172-174 deg (raise exhaust port 2mm)
Transfer ports 102 deg (std timing)
Intake 154-155 deg (cut 4mm off rear piston skirt)
Carburetor: VM34 (34mm Yamaha road race type)
Main jet 300
Needle jet 0-6/8
Needle 6f5-3
Cutaway 3.0
Pilot Jet 60
You can use the std. carburetor manifold and cut or grind the ID to 34mm and match the cylinder to the manifold.
In my Barn Fresh restoration series I show some of these performance techniques in practice.
Kawasaki F11 performance page 2
Page 2 includes the drawing with all the specs needed to build the perfect expansion chamber exhaust for the F11.
Air Filter (find a POD that fits from UNI-Filter or K&N Part# 2R-801)
Magneto F81M
Ignition timing 22 deg (3mm) BTDC
(this is the "button mag" which is difficult to find today, consider lightening the stock flywheel at a machinist)
*See drawing for expansion chamber exhaust for the F11*
However Bassani and Hooker did make a very good expansion chamber that if you look hard enough on Ebay you might find one. However the photo to the left will let you build one if you are good at metal fab.
As stated in my Kawasaki F9 performance project there is more to motorcycle performance than just engine modifications. Suspension modifications are a must with these bikes as the stock suspension is lacking. If you have a set of Boge Mulholland shocks here is a page that has the breakdown of parts and a how to of sorts to rebuilding them.
Air Filter (find a POD that fits from UNI-Filter or K&N Part# 2R-801)
Magneto F81M
Ignition timing 22 deg (3mm) BTDC
(this is the "button mag" which is difficult to find today, consider lightening the stock flywheel at a machinist)
*See drawing for expansion chamber exhaust for the F11*
However Bassani and Hooker did make a very good expansion chamber that if you look hard enough on Ebay you might find one. However the photo to the left will let you build one if you are good at metal fab.
As stated in my Kawasaki F9 performance project there is more to motorcycle performance than just engine modifications. Suspension modifications are a must with these bikes as the stock suspension is lacking. If you have a set of Boge Mulholland shocks here is a page that has the breakdown of parts and a how to of sorts to rebuilding them.
See my performance secrets and tips in my "F9 Project" video series Check out the Video at the bottom of the page for some vintage footage of me riding my Kawasaki F11 250cc around a motocross track.
F11 wiring diagram
Kawasaki F11 250 vintage advertisment
