Carb isuues with 78 NC50

Having a small issue with this carb. When I turn the petcock (new one) "on" gas flows and 2 seconds later its out the overflow at a steady pace. When I shut the gas off and unscrew the drain screw on carb the bowl is empty. What I have done:

-Cleaned carb including needle seat w/toothpaste and Q-tip

-Replaced gaskets

-Re-installed float and needle then put a tube on the gas inlet and blew while slowly raising the float and it stops (this why I am confused)

The needle looks mint and there is no holes in float. Now, there is a little "button" on top of the float needle and was wondering what that does, mine springs back when pushed down.

Before this it would start and run with throttle going at all times, throttle screw pretty much all the way out or it would die but would start up a minute or two later. The idle was wacky so I sprayed (carb cleaner) checking for air leaks and when I did the bowl the idle shot down and it died out. That's when I bought the gasket kit. Now, I have this issue....flooding ugh! I must be missing or not checking something so that's why am asking for help. (edited)

Re: Carb isuues with 78 NC50

The only thing that comes to mind is either the bowl drain is not completely shutting off or the overflow pipe has a hole/not sealed at the base.?....Or the float is hanginging up along the way and not closing?...Thats all I got.

Re: Carb isuues with 78 NC50

Noah Reinhart /

check and see if that float needle tip is hardened. Iv had them do that before on different bikes. if its hard youll needa new one.

Re: Carb isuues with 78 NC50

Does yours have and adjustable float or not? Black float will be an adjustable float. tan or light brown will be non-adjustable. Very early 78's had the adjustable floats.

The little "button" on the float needle is supposed to spring back like that.

Sounds to me like your idle before was off due to a plugged idle circuit tube. As this is almost always the problem with the Express carbs.

From what you are saying about the fuel overflowing and then the bowl being empty right away, I'm not sure...

That really makes no sense. Because it a correctly working carb, the bowl will fill with fuel before it comes out the overflow, and when you unscrew the bowl drain screw fuel will come out untill the bowl is empty. Unless your drain screw is not actually opening up to the bowl, meaning it's blocked.

Anyway, your biggest thing right now is the overflowing fuel. Either your needle needs replaced or the float is bad/out of adjustment. As this is the internal valve that shuts off fuel flow to the carb.

Re: Carb isuues with 78 NC50

Yes, its non adjustable float. Now, the needle is supposed to be soft at the tip? Mine is hard, like its solid metal from the top to the tip.

I tried pulling the idle out but its in there pretty well. Any suggestions to loosen it, spray with some PB? The bike has 1010 miles on it and I would say that I am the first to open this carb. As for the drain screw it was rusted in there and am not sure that passage was cleaned but, that's a small issue.

Re: Carb isuues with 78 NC50

If the drain screw was rusted, it might have distorted the sealing face in the bowl. Even though its shut all the way it still wont seal right. Dont pull the idle tube out if it wont come out easily, One of the big problems with that idle circut is it clogging bad. To clean it out good you get a nice steel spring out of a pen, unwind it and keep shoving it down the tube until you can see light thru the tube and out the idle air/mix screw hole. It has to be a really thin strong spring though. Check that drain for sure, if it is messed up go to the hardware store and get a little o-ring that will go around the screw and at the same time seal up the bowl portion. Good luck and keep us posted.

Re: Carb isuues with 78 NC50

Noah Reinhart /

in my experience, usually not with mopeds however but motorcycles, if the tip isnt supple at all it will not creat a seal when the float raises it. making the fuel pass arround the valve. I would replace it and see if it fixes the problem. while your at it make sure the carb is good and clean before the reinstall.

Re: Carb isuues with 78 NC50

Ok, so I pulled it off and what I did was close the bowl to the body turned gas on and separated it while it was filling and I found that the bowl is not filling and emptying out a small hole/tunnel at the bottom for the drain screw and overflow. Does it make sense? I can't see if they are supposed to be separate channels or if this "test" is even valid. Look at it here: (edited)

Re: Carb isuues with 78 NC50

That would appear to me as the drain boss/hole is so corroded it goes right by the drain and out the channel.

Re: Carb isuues with 78 NC50

Well when you mentioned a small o ring for the screw I realized that I did have a smaller one than the one I put on there so I changed it out, screwed it in tight, and BAM! it stopped flowing out! I tried starting but engine is still flooded so I removed plug for it to dry. I will try it tomorrow but its still "burping" out gas when I try starting it.

Re: Carb isuues with 78 NC50

Did it over flow again? or no. If no, then, you really should do the idle circut cleaning like I described before, check for spark, and the thing should run like nobodys business.

Re: Carb isuues with 78 NC50

your better off getting a week-ends intake and a new carb.

Re: Carb isuues with 78 NC50

I totally agree with Kl.

Your float might be sticking ''downward'' the small needle point stays open...always demanding gas to keep the bowl filled...and it then it escapes by the small overflow copper tube.

Same principle as a common bathroom

Yes, check for needle point tightness and float free-play.

One trick I found is to tilt the bike on the right side...the carb starts leaking. (at least on my 1981 Nc50)

If you tilt it on the left supposed to stop.

A question of float angle.

In any case, I'm feed up with my old Honda carb.

Getting a Mikuni.


Re: Carb isuues with 78 NC50

So I had to take the idle out (wasn't in there that bad) and I watched the u-tube video (uses a newer carb w/auto choke). I am supposed to see straight through it right (I can't)? My end is eathier really clogged or there is a Honda engineer in there. No matter what I put in there I cannot get it through.

Re: Carb isuues with 78 NC50

Dennis, I'm guessing you watched my video?

The carb I used was from an 82 urban. but still basically the same. Am I reading it right that you pulled the idle tube from the carb body? If so you should be able to see a tiny bit of light through it. Yours will not have the little holes at the top where it goes into the carb body like the 82 urban carb did, but you should still be able to see light through the tube the long ways.

I use a bristle from a wire brush to clean the tube. It's stiff enough to push through and thin enough. May take a bit of time if yours is really clogged. Also with the tube out of the carb you should be able to see light through the carb where the tube was.

Re: Carb isuues with 78 NC50

Well, after an hour and a half I finally got the idle circuit clear, thank you for the advice! But I still have the overflow issue, it has to do with the drain screw not sealing off the overflow channel, even with an o-ring. The overflow and the drain channels flow into each other. Now, I need to seal off the drain "entrance" at the bottom of the bowl. Any ideas, JB weld? (edited)

Re: Carb isuues with 78 NC50

matt boda1nz /

i always plug those up with jb weld or another epoxy.. they are worthless..

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