leaky carb

I just bought a slow-running Honda Urban Express. I'm new to mopeds but decided to fix and learn. I got the manual, got Fred's guide-- cleaned the carb, exahaust port, burnt out the exhaust pipe...reassembled and crossed my fingers:

If I'm lucky, the engine turns over for about two seconds. After that, the carb's drain pipe leaks pretty consistently.

I checked the drain screw multiple times to no avail. It doesn't really stop the flow. (I don't have a tube attached to the drain spigot, it didn't come with one, not sure if I'm supposed to).

Is this just an assembly order blunder or did I seriously fuck something up? Thanks.

Re: leaky carb

Don Pflueger /

only four things will cause a carb to leak;

worn inlet needle and seat

dirt in between the inlet needle and seat

a leaking float

the float bowl is on backwards and binding up the float

Re: leaky carb

Thanks. I've checked some similar posts also and will investigate.

One thing: I made the mistake of disassembling the bowl without really paying much attention to how much tension the float screw is supposed to place on the float. Is it supposed to be loose and "floaty" or does compression push it down?

Re: leaky carb

Don Pflueger /

i'm not really sure. the best place to ask that is at www.network54.com and then look up expressly mopeds forum on that site.

Re: leaky carb

your float might be sticking. I had that problem on my old batavus.

make sure the float is not sticking open.

Re: leaky carb

I fixed the leak...the float pin was placed incorrectly, although that's probably a hint towards greater problems:

Second try, I kicked the bike into gear, it ROARED to life (muffler still off) with IMMENSE pull...I had to dodge this kid who came out of nowhere to play with my dogs and couldn't tell if I turned the bike off or it stopped by itself. Either way, I can't get it started again. No leak, but no luck.

It should be mentioned that I haven't an air filter, just a cheap, stiff rubber tube. I played around with altering its intake, but again....

Any suggestions appreciated. Thanks.

Re: leaky carb

Sounds like your float needle valve needs replacing. I would also recommend you buy a complete gasket set to rebuild the carb. Lots of little rubber "O" rings on that carb.

Also make sure the you screwed down the float securing screw.

There should be about 0.48 inches or 12.2 mm between the the float and the carb casing + or - 1 mm or .04"

You can order the gasket set at your local MC dealer or http://www.partsfish.com

To set the carb,

turn the air mixture screw in all the way but don't force it. Then back it out 2 full, 360 degree turns.

The air mix screw is the one on the bottom.

Start the bike and let the engine warm up, use the throttle stop screw to keep it at about 1800 rpms or a little less than half throttle.

Then turn the air mix screw in or out to find the highest idle speed

Then use the throttle stop screw to reset the idle.

You may have to fiddle with it a bit to get it to level out and run smoothly.

The NU50 has an autochoke so you have to let it warm up for that to function correctly at idle.

Re: leaky carb

Make sure your throttle valve set is properly aligned into the carb or you will get a run away throttle, as you already found out.

Drain the float bowl and reclean your plug and let it sit for a little bit and it will probably start again

Also while you have the top of the carb off, try to get some lubricant down the throttle cable sheath.

There is a Shop manual online for downloading at Mopedriders.org.

I would recommend you use it as that carb has more hose lines than the Shuttle Orbiter.


Re: leaky carb

Thanks Zippy. I'll try it all. I do have that manual and almost have those hoses down by feel. Obviously not effectively enough.

Since my last post, now the reverse occurs:

Fuel doesn't seem to be reaching the carb at all. When I turn the drain screw, nothing comes out. I disconnected the hose and there was no dribble or evidence of any fuel in the HOSE.

With the hose fully off, though, fuel flows freely to the ground so I know the tank, filter, and valve are okay. I don't quite understand why it would be completely blocked when attached, unless there's some sort of restrictive vacuum effect occuring.

Re: leaky carb

Leon Swarmer /

can you blow through the hose?? hold it to your lips, not in them or use compressed air? sounds like the hose coudl be a big problem too....but hey, they're cheap!

Re: leaky carb

If I remember correctly, I had one doing the same thing and the actual input pipe on the carb that the fuel line was connected to was clogged.

Double check that throttle slide when you put it back in the carb to make sure it is seated properly.

Re: leaky carb

I blew air through the tube, it's okay. Now gas definitely flows up until the carb. Reinserted the throttle cap (slide?) and needle, with groove properly aligned... I pulled off my makeshift air filter and looked into the body- the slide's groove was resting over the tip of the idle screw which I assume is correct.

Still no gas draining when I loosen the screw. Short of disassembling the carb and actually seeing if the gas input is clogged, I poked a piece of soft wire into it and stuck it with a quick pump of aerosol cleaner.

Before I take it apart for the nth time, what is more likely:

1.) Something as dumb as a loose float could block the gas input so maddeningly effectively.

2.) It's just a huge, tenacious wad of dirt doing the above.

2.) There is something wrong with my drainscrew, gas is actually in there, and my sparkplug isn't working now.

Re: leaky carb

Don Pflueger /

take the carb off and disassemble it. use a piece of wire and poke it thru every hole you can find in the carb body and its parts. some holes can be as small as a human hair. after that, blow carb cleaner thru every hole. put it back together and try to start the bike. if you still get the same result, then spray some carb cleaner into the carb throat and try to start the bike. if it starts, you definetly have a fuel problem. if it does nothing, you have an ignition or compression problem.

does this bike have a vacuum line coming off the intake and running up to the petcock? if so, check it. it may not be opening the petcock and allowing fuel to flow.

Re: leaky carb

Leon Swarmer /

does it have the auto choke?

Re: leaky carb

50, it does have an autochoke.

Re: leaky carb

Thanks donp, I'll get right to it.

As far as I know it doesn't have a vacuum tube. Only one connecting to the petcock and that's clearly the main fuel line.

Re: leaky carb

Don Pflueger /

ok.i just wondered if it had a setup like a honda spree has or not. can find a ton of info on this bike at www.network54.com. once you go there, look for expressly mopeds forum thru their search engine. those guys know this bike inside and out. especially george a.k.a. themopedwhiz. this bike is his specialty.

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