Honda Express Troubleshooting

I purchased one of these floats for my 1980 NC50 a while back. It’s finally nice enough to go for some rides and the express starts and idles mint! No choke needed for starting! However once I hit 25mph the engine gets loud and bogs, it doesn’t maintain that nice high pitch 2 stroke sound.

I am not sure if it did this before the new float as the float was needed to get it running good.

I did cut open the muffler and made it “free flowing” and that didn’t help, my service manual says to check timing/points. Do you have any other ideas or could the float be a tad high and it’s starving for fuel at high speed/rpm?


Joe, Thanks for the question. What you have described are the classic symptoms of four-stroking. At full throttle, the carb is actually supplying the engine with too much gas. If you have the oil injection installed and working, the engine may also be getting too much oil. The carburetor is supplying the engine with more fuel than it can burn and the rough running and lower pitched sounds that you are hearing from the engine is the engine struggling to keep up with the fuel.

How can you test this to be sure you are getting too much gas and not too little gas? Simple, ride up a small incline or hill. If the engine doesn’t four stroke or four strokes much less and runs strong up the hill, the bigger load on the engine (fighting gravity going uphill) is allowing the engine to burn all or most of the extra gas. Often times, your Express will come close to matching its top speed even though you are going up a small hill. That’s because, it is finally able to use the extra fuel being shot into its cylinder.

Now ride back down the same small incline you just went up. It should four stroke like crazy. Why? Because there’s hardly any load on the engine and it can’t burn all that extra fuel.

What can you do about?

1. Let off the throttle slightly when it starts four stroking.

2. Stop using the oil injector and premix your gas and 2 stroke oil at a 40:1 ratio. If it still four strokes, try 50:1. Maybe even 60:1. On most of these 2 stroke bikes, the manufacturer erred on the side of caution and set the oil injector to pump in too much oil. The injector is controlled by the throttle. The more throttle you give it, the more oil it gets. Too much oil is even worse than too much fuel and makes it four stroke even more. Also look in the manual, you may be able to adjust the oil injector so that it pumps out less oil. If you do stop using your oil injector, make sure during the change over that the engine never gets straight gas.

3. Install a slightly smaller main jet. I believe the stock main jet is a 75 on the express. You can get one here. Try a 70 or a 74. A smaller jet delivers less fuel. Don’t go too small or your engine will overheat.

4. If you are using the stock air box, then try a less restrictive air filter. This will add more air to the air/fuel mixture and lean out the mixture. You’ll need a 25mm diameter air filter. Search on ebay for a cone, mesh air filter of that size.

5. Try a hotter spark plug like a NGK BP4HS if that’s not what you already have.

6. Lean up your air mixture screw some. Try my carb adjustment procedures (written for QT50 but applicable to almost all 2 stroke biked).

There are some tips to help you out. If I think of more, I’ll add them later. I’ve even had an Express start to four stroke just because I put on a new back tire. Why? It rolled so much better on the new tire that there was less load on the engine. Crazy, huh?

I think I have some footage of a 1980 Express four stroking here.

I have a 1980 Honda express NC50 with blinkers and when the blinkers are on the taillight blinks too. Is this normal? I had another 1980 express II NA50 and it did the same…. is this the way Honda made them?

What’s probably happening is as the blinkers flash, the tail light is turning off. And then as the blinkers go off, the tail light comes back on. The tail light, brake light, blinkers and horn are all powered by the battery. Chances are that the battery is not fully charged and can’t power the turn signals and tail light simultaneously. Try hooking a trickle charger to your battery and fully charging it; that might solve the problem. While you are at it, make sure your battery is filled to the proper level with distilled water and clean off the terminal wires, if necessary. Or you may even want to try a new battery. Another culprit may be your charge coil. Perhaps it needs replacing.

Here is a very helpful video on how to test your charging system on your Honda Express: