Post by Detasman on Nov 22, 2004 7:48:46 GMT -5
I recently acquired an NP Passport 50 with the 89cc engine from RC Motorsports. I've done a few things I'd like to share. I am no expert on motors, but I do have good common sense, average mechanical skills, and a willingness to experiment. Don't blame me if any of this ruins your otherwise fine machine.
Holes in airbox -- I drilled about 20 holes in the air box. Most are 3/8" in size. I arranged the holes in a pattern along the sides and front of the top of the box. This is nothing new or novel but it has been proven to increase airflow considerably. In my case, it did just that. It also added a new beefier sound to the intake. If you do this be sure to remove the box from the bike and remove the filter from the box before drilling any holes. Also make sure all plastic shavings are cleaned away and that nothing is left inside the box that could be sucked into the engine.
Holes in muffler -- Again, nothing new here. Just good oldfashioned tinkering. I did a couple different things here. I started by running a long 7/16" drill up through the center pipe in the back of the muffler, eliminating what I believe to be three baffles. This gave a perceptable difference in both exhaust flow and sound. I ran the bike like this for a few days. Still unsatisfied, I drilled three holes in the back end of the muffler in the locations that appeared to be spot welds. A standard length drill is all that's needed here. I started with a small pilot drill and enlarged the holes with a 7/16" drill. I did this in hopes of being able to remove the baffling system altogether. No such luck but it did give additional flow and sound. I would say that the three holes in the back of the muffler were much more effective than drilling out the baffles up through the center.
After doing all of this, using the procedure outlined in the owners manual, I readjusted my air/fuel screw to account for the added air flow. The net result has been a slight increase in top speed (1 or 2 mph) accompanied by a definite decrease in the time it takes to get there. Improved acceleration is the real benefit. I also like the louder sound of the exhaust and the beefy sound from the intake. Another side benefit has been the elimination of a slight bog when opening the throttle quickly. Overall I'm very pleased.
If you are interested in increasing your top speed to any great extent you should look into regearing with a 15 tooth front sprocket. These are cheap and easy to come by. This is, again, nothing new to Passport owners.
Holes in airbox -- I drilled about 20 holes in the air box. Most are 3/8" in size. I arranged the holes in a pattern along the sides and front of the top of the box. This is nothing new or novel but it has been proven to increase airflow considerably. In my case, it did just that. It also added a new beefier sound to the intake. If you do this be sure to remove the box from the bike and remove the filter from the box before drilling any holes. Also make sure all plastic shavings are cleaned away and that nothing is left inside the box that could be sucked into the engine.
Holes in muffler -- Again, nothing new here. Just good oldfashioned tinkering. I did a couple different things here. I started by running a long 7/16" drill up through the center pipe in the back of the muffler, eliminating what I believe to be three baffles. This gave a perceptable difference in both exhaust flow and sound. I ran the bike like this for a few days. Still unsatisfied, I drilled three holes in the back end of the muffler in the locations that appeared to be spot welds. A standard length drill is all that's needed here. I started with a small pilot drill and enlarged the holes with a 7/16" drill. I did this in hopes of being able to remove the baffling system altogether. No such luck but it did give additional flow and sound. I would say that the three holes in the back of the muffler were much more effective than drilling out the baffles up through the center.
After doing all of this, using the procedure outlined in the owners manual, I readjusted my air/fuel screw to account for the added air flow. The net result has been a slight increase in top speed (1 or 2 mph) accompanied by a definite decrease in the time it takes to get there. Improved acceleration is the real benefit. I also like the louder sound of the exhaust and the beefy sound from the intake. Another side benefit has been the elimination of a slight bog when opening the throttle quickly. Overall I'm very pleased.
If you are interested in increasing your top speed to any great extent you should look into regearing with a 15 tooth front sprocket. These are cheap and easy to come by. This is, again, nothing new to Passport owners.
