Wednesday, October 21, 2009

How To Clean a 1978 Honda Express Moped NC50 Carburetor...

I am going to outline some suggested steps in order to remove and clean a 1978 Honda Express nc moped carburetor, and they reinstall it. I hopefully will include photos I have taken to document the process. I find the photos are good demonstration tools to help others follow along or correctly put things back together if you forgot how you took it apart on a '78 Express motor bike.

  1. Shut Off Fuel - Turn the fuel value to OFF that is attached to the moped's petcock.

  2. Put Container Under Moped - I happened to have a large plastic sheet that I put under my express moped to protect and collect any fuel that spilled when doing maintenance. You could use card board, plastic tub, newspapers, whatever to catch any spills.

  3. Stay Away From Flames - Do do your honda moped maintenance near flames or anything that could ignite the gasoline fumes. Don't DIE working on your moped.

  4. Remove Air Cleaner Covering, Foam Air Filter, Filter Unit - See pictures below. Also, note that there is no foam 1978 nc50 Honda Express Air Filter/Cleaner on the table. That was because the previous owner never put it back on!

  5. Remove Throttle, Choke Attachment, and Fuel Line - Carefully unwind the plastic honda express throttle cord attachment. The nc50 choke cord attachment to carburetor will require a adjustable wrench to remove. Finally uncrimp the little tensioner ring around the rubber fuel line that is attached to the moped carburetor. You will find out quickly if you forgot to shut off the fuel, because gasoline will come spilling out everywhere. Granted, you will get some gasoline spilling out because there is still fuel in rubber line.

  6. Remove Carburetor Itself - There are three bolts holding the Express Honda carburetor in place. Once the bolts are removed, it should freely be taken out. Gasoline fuel will continue to spill out that is left in carburetor.

  7. Clean The Carburetor - BE CAREFUL NOT TO LOOSE YOUR HONDA EXPRESS NC 50 FLOAT PIN. The part is very small and will cost you if you loose it! I used "STP Carburetor Cleaner" to clean the moped carb. You can find the product at many local PepBoys or AutoZone.

  8. Inspect The Components - Take care to inspect the moped's plastic float, rubber honda moped gasket ring, express float pin, and honda express carb main jet. Take care to use a can of compressed air and blow out the valves and make sure they are not obstructed. When the carburetor is put back together you don't want any water left in it. Get it dry as a bone. You could remove and clean the throttle stop screw and/or the moped air screw, but I didn't. I figured they were set properly before and I didn't need the hassle of re-calibrating it.

  9. Reassemble Carb Components - Should only take a few minutes once they are cleaned and dried. Just reverse the steps taken to remove it. Once I reinstalled the carburetor onto the Honda moped express frame and connected the fuel line, I opened the drain screw in the float bowl. When I turned the fuel lever to ON this allowed the fuel to fill the float blow and "bleed" out the air. Probably didn't need to do that, but I did and it worked.

18 noped comments:

Unknown said...

JFK, I'm fixing my Dad's old honda express(78), all it needs at this point is a petcock. Do you have any you would be willing to part with? Email me if you can help out.
Thanks, Rob

jfk said...

Hey, rob! Sorry... I don't have any extra. I would totally give you one.

Here are some sites you can get a Honda Express Petcock (call or ask them to make sure your purchase will fit):

Also, talk to "mattschmitz" on this Moped Army post:

Hope that all helps!!


Unknown said...

Hey there, I know nothing about small engines or carbs but I tackled this tonight with my 78 express. Everything is cleaned and dry but the gasket for the carb is a tad stretched now that I try to put it back on, won't fit quite right. Any suggestions? Also, do I need to put some sort of grease on the gasket? Seems like I should. Thanks!

Anonymous said...

does anyone know what the float level is and where to measure from on a '80 express II NA50? perhaps what page it is in the 79-91 honda NA50 shop manual. thanks

jfk said...


Page 8-3 of the nc50 shop manual says- Float Height: 10mm (0.394 in.) - Check the float level height measured from flange with float valve just touching float arm tang. Use float gauge to check.

It could be the same on the express II na50. Don't know why they would change it up.

Thanks for posting!

Unknown said...

I am restoring a 1983 Honda Express. I have cleaned out the gas tank, air filter, and carb. I got it to start but it will only run on choke. When i take it off it dies. It also has a bunch of white smoke coming out of the exhaust. I tried adjusting the air flow screw on the carb but it didn't help much. Any suggestions?

Unknown said...

i have a question i have a nc50 79 honda express and i get it going i ride it but during the ride if i let go of the throttle the bike still goes but if i turn the throttle again to keep going it dies out i do not understand why? any suggestions?

Unknown said...

i own a honda express nc50 year around 1978 i believe...what are the settings for the 2 other words how much do i screw each one in or out? fred

jfk said...

look at the workshop manual, I believe it tells you in there:

Tony said...

Hi, I noticed sort of an "extra" piece to one of my carburetors. It looks like some sort of input or output metal tube (~1cm length) connected to a ~1cm brass looking box. It's next to the fuel line. Actually you can see it in the top picture pretty well. What is this piece? Should I be plugging any hose into it? My other carburetor does not have this piece, and I can't figure it out! Thanks

jfk said...


I'm not sure about the extra metal tube. I have two identical express carbs and the other one doesn't have it. Just cap it. No need to hook it up or worry.

camhsl said...

Hey, I have a 82 express NU50m that was running great in the morning, and then in the evening, after work, It wouldn't start up. I had the carb professionally cleaned a couple months ago, and it's been running great since. Changed the spark plug, and checked the gas line... not clogged. It turns over, but won't fire up unless I have the throttle wide open. And even then, it just kinda boggs out. almost like it's not getting enough air or gas or something. Any Ideas?

jakeaaeeyy said...

I know the exact piece you're talking about, the same one fell off my carburetor. It hooks up to the outside of the carburetor, changes the direction 90 degrees, and connects to a hose. I don't have it in front of me so I'm not sure what hole and what hose though...

jfk, i just got a 1978 express for parts, i was cleaning the carburetor and i think the main jet fell out, it looks like the top left picture in the manual:
I'm not sure where exactly to put it back, or what direction to put it in. Please help!

Bhrbergman said...

HI all First off i love this website just bought a 1980 Honda Express in iowa, so not sure if it is NC50I or just the regular NC50 but i have a question regarding the air intake box. JFK I have watched your carb clean video and noticed that the black seal that hooks the air box to the carb is completely different than mine. Yours is part number 4 at this link

While on the 1980 mine is part 4 at this link

It seems as mine limits air, i do not want to cut it down to size without getting an opinion. Im no expert but smaller hole= less fluid movement through said opening... please help.

Unknown said...

I'm having a problem with my non adjustable float on my 78 nc50. How can I adjust it? I melted the little tang where the needle goes and I had it right,but fuel was coming out of overflow tube, so we tried again and ruined the float. got another one and didn't mess with it and it runs great until you hammer down on it and it wants to bog like it's not getting enough gas and when it is running good, it won't run but about 23 mph.Going up hills it runs fine wide open, on flat ground at wide open,bogs or on flat ground,bogs at wide open. does anyone know what I can do?

artistsincharge said...

Are the 1977 honda express carburetors the same as the 1978?

Unknown said...

Will a 1980 Express Pet Cock fit on the tank of a 1981 Express do you think?

jfk said...


I am pretty certain it will. I think they are fairely generic and you could even buy a nonamed brand online that would fit. has one:

The comments someone left are really helpful:

"Correct thread size for the NU50 Urban Express. Output fitting comes out the back instead of the side, and is larger (8mm) than stock. You'll need to use a reducer for the fuel line to get it to match up to the smaller stock fuel line."

Good luck!


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