Performance Tuning a Suzuki
Q-How fast should my Suzuki go?
- A-Stock the FA50 should reach 28-30mph. Stock the FZ50 should reach 30-34mph A correctly adjusted carburetor and Muffler cleaning are the two most important factors in reaching the stock speeds.
Q-Why won't my Suzuki start or idle well?
- A-Common problems are idle speed and mixture adjustments, clogged idle jet, and rusted fuel bowl floats.
Q-How do I make my Suzuki faster?
- A-It's important to start with a bike that at reaches the stock speeds. If you can't reach near these speeds something is wrong and all future adjustments will be off. Tuning a FA50 to hit 28 mph is cheaper, easier than tuning to break 32 mph. Start with Fred's Guide.
Increasing power, and top end performance.
One of the fastest and virtually free improvements is increasing compression by milling or shaving down the head. Raising compression boosts power across all ranges. The original motors had low 6.5:1 compression. It's possible to remove at least 2 millimeters from the head, bringing the mating surface even with the cooling fins, and remove the head gasket while still using 87 octane without issue. At least 2mm more can be removed, compare head gasket diameter to combustion chamber diameter for a gauge of piston clearances.
The stock air filter is restrictive. It is possible to drill a few holes to increase airflow. Other easy options for the FA50 include removing the plastic airbox and reusing the rubber elbow connecting it to the carb. Various "performance" auto parts store valve cover breathers will fit this elbow. The FZ50 air filter bolts on to the carb with 2 screws. New filter housing can be either screwed to bracket or a rubber hose can be fitted to the carb throat to adapt other filters.
One of the few performance parts available for the 49cc Suzuki motor was the Simonini Expansion chamber. Powerband is a little high, it kicks in at about 22mph. There is some loss of low end power but worth the major increase in top end power. Expect to increase your carburetor jetting to prevent a lean condition and to maximize top end power. The lost low end can be regained by increasing the compression if not already done.
FA50 tire size is restricted by the minimal clearance to the rear mounted carburetor. Low tire pressure can add significant drag, up to a 5 mph loss. Inflate to 35 psi or higher for less resistance. FZ50 rear tire size can be increased from a 12x3" tire to 12x4" with minimal changes. This adds about 2" in tire height which will increase gearing and top end. A 12x3.5" tire should fit with out any changes. The 12x4" requires filing a bump off the transmission and off setting the 2 wheel pieces by 1/4" with washers.
The FA50 service manual recommends running 500ml 20w-40 multi-weight oil. Changing to Mobil 1 0w-30 synthetic is worth a 2-4mph increase. Another common problem is an overfilled transmission. More than 500ml will add excessive drag on the drivetrain. Its only necessary to fill the transmission 300ml.
The FZ50 has a 2 speed automatic transmission. The 2nd speed clutch works by centrifugal force dictated by rpm. Typically they shift between 10-12 mph. The service manual recommends 900ml of 10w-40. The most common ways to raise the shift point on similar clutches are running thicker oil, lightening the clutch shoes, or changing to stronger springs. Oil designated for motorcycles will give greater protection for clutches and transmissions.
An engine kit is generally a an oversized piston and cylinder designed to increase engine displacement. There are a few engine kits available. The most common increases the piston bore from 40mm to 45mm yielding 58cc displacement. NC-Motorsports out of Denmark sells a 45mm kit for Suzuki FZ50/FY50/FS50 as ebay item#250556009383 currently less than $120 with free shipping.
Increasing engine size will increase low and mid range power but probably won't increase your top end speed without porting. This is because the biggest limit on stock motors it the amount of air available to flow through the engine. Increasing engine size with the same airflow restrictions should actually lower total available rpms.
Once properly tuned the biggest restriction on top end and speed becomes airflow. Porting the transitions between the carburetor through the entire motor can sigificantly increase rpm and top speed. On the FZ50 the transition between the intake and the reed block has a 3mm difference between the two. Removing the intake and reed block is only 4 bolts more than removing the carburetor. Using a file or a dremel tool to match these parts will help the engine's powerband and raise max rpm. It is possible change how the motor breathes by porting the cylinder's windows. Smitty's_Cylinder_Porting_Guide. The Suzuki 50cc intake port is small and could be improved by enlarging and squaring. Stock piston skirt covers a large portion of the transfer ports. Spinning the piston 180 degrees, with arrow facing up towards the intake could make a significant improvement.
Both motors use oil injection. The suzuki oil injection is quite reliable. The injection mixes with the ratio of 40:1. The FA50's oil injection tends to cover the spark plug making it difficult to read plug chops. Bypassing the oil pump and switching to 50:1 premix can increase the amount of gas entering the engine.
Fa50 and FZ50 standard plug is a NGK BP4HA, crosses with Nippon Denso W14FP-UL. Its recommended to run a cooler plug especially if raising the compression. Cooler plugs would be the NGK BP5HA and BP6HA.
How to Index a spark plug. Mark the location of the electrode on the spark plug's porcelain. When installing make sure the electrode is opposite the exhaust port. In other words not in the way of the ignited fuel and the exhaust port.