We have a lot of experience with tuning and modifying 900 cc engines.
First of all we replace the steel flywheel to a light one made from alloy. The quiet running remains full thereby.
Further Dynojet kits affect also the quiet running positively. Stage 1 does not increase hp but stage 2 gives approx. 2-3 hp and 5 nm.
Consistent solution of the quiet running and the responsing mode is naturally the Keihin carburetor kit in 39 or 41mm. A razor-sharp responsing mode without delay paired with the increase in hp and, which is naturally still more important: the torque!
Keihin carburetors do not have a starter cable and are a little bit funny to start. Three-five times the gas grasp must be operated before starting. Then the accelerator pump is injecting and the mixture is rich enough for the cold weather starting.
Keihins raise performance approx. 5 hp and approx. 10 nm. Price/performance relationship is outstanding. Most effective tuning without dividing the engine.

Afterwards follows stages with cylinder head porting. The valves become reworked on 44-39, 45-39 or 44-38 and/or. 45-38. Depending upon character desire of the engine. 45-39 and 44-39 is used for SS types with broadband character and 45-38 and/or. 44-38 for monsters types with more torques desires.

These stages are the actual condition for achievement, which is as well known with each 4-stroke engines in the heads. Depending upon stage the horsepower increases from 6 to 20 hp with the appropriate carburetors and/or exhaust systems.

Tuning continues with cam shafts which should be selected depending upon need and/or character desires.

Starting from an output of 90 hp the use of Carrillo piston rods is recommended cause of higher rpm. The crankshaft must be balanced then! Also a double ignition should be installed. This leads also to a limited thermal discharge and a softer engine run.

The 944 cc kit is a "bolt on" kit without machining the housing. It can be installed without changes. If the 985 cc kit should be installed the housing must be up-spindled. During capacity increase on 944 or 985 cc an adaptation of the exhaust system is necessary cause of higher temperature values!

Here is an example with 944 ccm bolt on kit, 45-39 Race ported heads and special
cams combinated with 41mm Keihin carbs and an Akrapovic exhaust system.