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In this video, I talk a little bit about jetting for a hi-flow air filter such as the K&N on this Honda Express. When I was working on this Express, I discovered by accident that I could swap many of the parts from the Honda Aero 50 carb with the carb for the Honda Express. All Honda Express nopeds are not created equal. Fortunately for me, this 1981 NC50 has a removable main jet. I believe the stock main jet is 75 on the NC50 and the stock main jet on the Aero is 80. So I swapped main jets because my Express was running lean with that huge air filter. The float, float needle, float pin, float pin screw, many of the gaskets and perhaps even the float bowl are interchangeable between the 1981 NC50 and the 1986 Aero. This is wonderful because eBay sellers charge a fortune for NC50 carb parts and used carburetors. I’ve seen used carburetors on eBay going for $100-150. I’m not aware of any new, aftermarket carbs that are knock-offs of the stock carb for the NC50 either. You can always upgrade the intake and go with a different, bigger carb.
You can get a new Honda Aero carb (aftermarket) for $19. Take out the carb parts you need and swap them with your old NC50 parts.
On my Express, I also raised the needle jet (under the throttle cable at the top of the carb) to its richest position. In the video, it often seems like my NC50 isn’t running quite right when I take off from a standstill. I think it is still running a bit lean although sometimes it is hard to tell (9:16 in the video, for example). Usually, if they run too rich, they will stutter and pop. If they are running lean, you’ll get a low bog. I think it is running lean at take-off. I can’t do much except maybe make sure the idle jet is clean and maybe go to a bit larger main jet. Watch the video and let me know what you think. Part of the problem may be the aftermarket petcock I installed. It sits at an odd angle and, as a result, may not deliver fuel as well as the stock petcock.
Despite adding a new speedometer cable, my speedo is a bit erratic. It will go a long fine and then when you hit 28mph or so, it kind of does its own thing. I manage to hit 30 mph at about 9:00 in the video. I was doing 26 mph up hill a bit before that (around 6:00 in the video).
Here’s a short/long list of what I did to this one:
New speedo cable;
new headlight with replaceable bulb as opposed to sealed beam on original;
had to go through wiring inside headlight and get it right;
new ignition cylinder and key;
added hi beam indicator light (originally missing);
replaced all instrument lights that needed replaced;
New piston rings, head and base gasket;
bigger main jet, needle jet on richest setting, added float needle and float pin;
new hi flo air filter;
correct spark plug;
new petcock, fuel filter and fuel line as well as oil line;
fuel tank leaks into oil tank so went to premix;
fixed wiring in rear for proper functioning of blinkers and tail light; new battery;
changed transmission oil;
replaced broken spoke on rear wheel;
added new hardware in various spots;
added exhaust shield;
added drain hose and overflow hose to carb;
replaced missing rear fender;
tightened up handlebar nut;
and perhaps more that I’ve since forgotten.
Here’s a follow up video talking a little more about the K&N Air filter.
2/7/16 – I’ve since changed my mind and feel that it’s running a tad rich as it is hard to start after riding. I’ve backed off the needle jet to the 4th setting. We’ll see what happens.
2/28/16 – I think I have gas leaking out the air filter when I ride. I’m guessing this is because of the increased amount of air rushing into the carburetor and pushing the gas out. I’m going to try to fit on some extension to the carb and then mount the air filter to that. PVC pipe or radiator hose might do the trick. Update – gas was actually leaking from the oil sight on the side of the gas tank so I had to go to a new gas tank.
5/22/16 – Here’s my latest carburetor adventure on the Express. I found a cheap aftermarket carb on eBay that will work with the Express. I had to drill out the idle jet to 0.55mm. I think 0.50mm would’ve worked better. But it starts right up with the help of the choke lever. Right now, it is four-stroking a bit so I’ll have to make some adjustments. I’m using a 28mm K&N filter which works perfectly with this carb. One solution would be to dry out some of the oil in the air filter. I think I may just adjust the needle jet clip a notch leaner.