PDA

View Full Version : 1981 Honda Express-SR a.k.a. NX50


Smithers
12-01-2008, 06:39 PM
I've had the wonderful experience to rejuvenate a Honda Express this past couple weeks. I don't know what Honda was thinking (profit I'm sure!) when they made these things as they just do not to more than 25mph. Why not just ride a bicycle? These things just scream college student all over them.

Nevertheless it's a bike worthy of cruising around anyone's neighborhood and it must be brought back to life!

The Beast lurks under there...
http://www.fourwheelperformance.com/honda/honda_express_sr_02.jpg

Smithers
12-01-2008, 11:35 PM
So here is a shot list of things to do in order for this little bike to be back in running order This is not optional stuff as the scooter has been sitting for a long time and there is just no way the carb will run properly no matter what bike your working on. If you want a smooth running bike that you can depend on just break yourself down and buy a proper carb kit and do it right.


Get new battery on order
Get a carb kit on order
Check spark plug
Replace battery connectors
Remove carb for a cleaning
Completely drain fuel tank
Check for fuel filter to clean (not stock item)
Pump tires and check for leaks

Here is your big enemy... dirty carb monster.
http://www.fourwheelperformance.com/honda/honda_express_sr_03.jpg

So once you have your gasket kit in hand just sit right down on your stool with some coffee and start scraping sediment out of the carb.
http://www.fourwheelperformance.com/honda/honda_express_sr_04.jpg

Smithers
12-01-2008, 11:42 PM
I didn't take a picture of the carb before I started cleaning as I can just say it was just dirty. The main bowl gasket was completely rock hard as well as the gaskets on the throttle screw and the mixture screw. The gasket for mounting the carb on the engine was chewed up from a previous installation so every gasket was failing in every way.

Here is a look down the mainjet and also the needle which is rubber coated at the point. It's still in great shape so I'm happy here as you can tell. :p There is still plenty of sediment to be removed and I spent a few minutes scraping in order to prep it for some chem dip to really clean things out. Yeap that's right, you are in luck. I'll show you the only way to clean carbs as far as I'm concearned.

I used a few drill bits to turn down into the seat. I just use my fingers and spin the bit with light pressure in order to spin away any curst that might be down in the hole that the needle was pulled out of.

http://www.fourwheelperformance.com/honda/honda_express_sr_05.jpg

Smithers
12-01-2008, 11:49 PM
I just scrape about everything I can reach with my favorite scraping tools before I put it in the dip. Here you can see the idle adjust screw on the top and the mixture screw on the bottom. FYI they go in the carb in the same order from top to bottom.

http://www.fourwheelperformance.com/honda/honda_express_sr_06.jpg

Smithers
12-02-2008, 12:00 AM
Now here is the stuff. It's Yamaha carb dip and nowadays it's not as toxic but it still works great. They used to call this stuff the green slime back in the day... so I hear. I was shocked to see it still no the shelf of my local motorsports dealer. It wasn't more than $12 too! Sweeet.

So what's up with the Oxy Clean? Well I HIGHLY recommend that you put this solution in a sealable container so you can re-use the solution. You mix it with water per-the instructions so make sure to read the bottle. YOU MUST mix with water. The solution can be used a few times before it becomes too contaminated so if you can seal up your container you can save it. This little one is just big enough for small carbs and other bits.

http://www.fourwheelperformance.com/honda/honda_express_sr_10.jpg

Smithers
12-02-2008, 12:03 AM
This is just dip just after I removed the 50 carb from it. On the bottle of the dip it recommends that you agitate the solution as the carb sits inside it. Just shake it from time to time. Now the important part: the dip will eat away at the carb if you leave it in there for too long of a time. I left this particular carb in the dip for almost 40 minutes which I consider max time to do so. If you are dipping a rare carb or one that is much more expensive or hard to come by I highly recommend 15 minutes max and then removing it for inspection before leaving it in there for more time.

http://www.fourwheelperformance.com/honda/honda_express_sr_08.jpg

http://www.fourwheelperformance.com/honda/honda_express_sr_11.jpg

Smithers
12-02-2008, 12:05 AM
This picture shows some of the grey alloy coming off on my fingers! This means that the carb is ripe and it's being worked over by the chem dip a little too much. A quick wire brushing off after wards, some brake clean and a little air compressor and just about any carb will be working and looking like new.

http://www.fourwheelperformance.com/honda/honda_express_sr_09.jpg

Smithers
12-02-2008, 12:15 AM
It would be a shame to forget to check the mainjet. Just grab a brand new screwdriver or risk stripping the head of it... then you will REALLY by up a creek.

http://www.fourwheelperformance.com/honda/honda_express_sr_12.jpg

Clean the float really well and remove the steel alloy rod that it hinges on. Use a razor blade or something to scrape off any residue to that it hinges nice and free.

http://www.fourwheelperformance.com/honda/honda_express_sr_13.jpg

Smithers
12-02-2008, 12:18 AM
A cordless Dremel would be idea here with a steel brush cup bit to clean up some of the deep grooves inside the carb. Unfortunately mine is worthless because the battery just gave up after a couple hours of use.. what a POS. Anyhow this is getting ready to replace the float and needle after the dip. If I worked any harder at removing anymore residue I would probably damage something or wear out the details in the casting. This is nice and adequate.

http://www.fourwheelperformance.com/honda/honda_express_sr_14.jpg

Smithers
12-02-2008, 12:20 AM
Time to get out the gasket set. I placed mine on a white plastic sheet so I could keep track of every tiny little seal and rubber o-ring.

http://www.fourwheelperformance.com/honda/honda_express_sr_15.jpg

Smithers
12-02-2008, 12:30 AM
Getting down to the screw seal replacement: Make sure you remove the washer and the seal underneath it. These little guys are HARD to see and might look like part of you carb and not a seal at all. The new o-ring you see is exactly what you want to use to replace the flat, leaking one. Much better.

http://www.fourwheelperformance.com/honda/honda_express_sr_16.jpg

Here is the trick I used! Think smarter not harder.
http://www.fourwheelperformance.com/honda/honda_express_sr_17.jpg

Smithers
12-02-2008, 12:37 AM
Here is the little ol o-ring and the washer installed on the jet ready to go back in. And then below I'm replacing the float bowl drain seal. This is the screw down on the bottom of the Honda carbs that NO ONE every uses but they should. It simply drains the fuel out for storage... but no one drains the fuel ever and guys like me have to fix them years later. :D

http://www.fourwheelperformance.com/honda/honda_express_sr_18.jpg

http://www.fourwheelperformance.com/honda/honda_express_sr_19.jpg

Smithers
12-02-2008, 12:43 AM
Seals coated with synthetic grease and all ready to go back together for the last time.
http://www.fourwheelperformance.com/honda/honda_express_sr_21.jpg

And all together now.
http://www.fourwheelperformance.com/honda/honda_express_sr_20.jpg

Smithers
12-02-2008, 12:48 AM
It's amazing! We're all done after all that carb cleaning. The fun part is putting the clean parts all back together again.

http://www.fourwheelperformance.com/honda/honda_express_sr_22.jpg

http://www.fourwheelperformance.com/honda/honda_express_sr_23.jpg

The fuel shutoff was installed by a previous owner who opted to manually shut off the fuel instead of fixing the leaky gasket and seals. Not that I blame him at all. It's a good idea to have the off valve on there anyhow.

Smithers
12-02-2008, 01:13 AM
And 10 minutes later I had ignition after a couple cranks of the starter. Now the manual states that the screw adjustments are as follows:



Upper Idle Screw - 1.592 rotations from all the way in
Lower Mixture Screw - 2.187 rotations from all the way in

You notice how exact and how much I care about these calculations. I'll explain:

Upper Screw: The more the screw is turned out (counter clockwise) the lower the throttle slide is dropped which decreases the throttle. It's not going to hurt the engine in any way to have the screw backed out 1 turn or 3. Start at 1 turn out so that when the bike starts up it will keep running. The bike has probably been sitting forever and it will need a good helping of throttle to feed the dry engine to keep it going. Once this particular engine starter up it went dry of fuel after 30 seconds unless I revved the engine a good amount.

Once I jumped on it and rode it around for 10 minutes it kept running at idle. But until you run the engine up through the RPMs for a few minutes there is no way that this little 2 stroke will stay running at idle. 2strokes are made to run at full throttle all the time. You know your weekwacker? Those things never break until the owner screws up and doesn't mix the oil and fuel properly. 2 Strokes might wear out from use but you won't wear out this engine for a long long time as long as it's getting oil in the fuel.

Lower Screw: This one is a little more tricky... just a little. Ok having this screw turned IN (clockwise) all the way shuts down the oil from being mixed in with the fuel. As you turn it out a couple turns it is richening up the fuel. 2 turns from all the way in is NOT enough. I seriously doubt anyones Honda 50 engine will run to it's top speed potential at 2 turns out. I used the factory recommended 2 and 1/8 out. It revved really slow and kept dying. So I backed the mixture screw out to 2 and 1/2 out and took off down the street.

Adjusting The Screws: I rode the little 50 around the block and it moved ok but it started running a lot better after 5 minutes of use. I don't recommend just revving the engine on the kickstand and adjust the screws. Carry your screwdriver with you and hit the road. If you aren't smelling 2stroke oil within the first half of a minute of the engine starting up you had better check your oil pump and check to see that it's working. You don't just want to go riding around without oil or your engine will be cooked really soon!

So ride the bike and get it nice and warm riding around at a medium pace. A slow pace will just load up the engine with oil and maybe foul out your sparkplug. A higher RPM pace is recommended after another 5-10 minutes of operation if your engine hasn't been run in a few years. The engine needs to be run at a good and warm temperature to shake the cobwebs out of it and to make sure the oil is flowing through it.

Here is a video of the first engine start up of the NX50 Honda Express:
u2Qtg8akwkc

Smithers
12-02-2008, 01:21 AM
Upper Screw Adjustment (after engine warm up):
Once it's nice and warm after some riding around you can adjust the idle down when you come to a stop by turning the upper screw out (counter clockwise) a little at a time while listening to how the engine responds by slowing down. Don't let the engine idle too slow because then it will take forever for the RPMS to build up for the bike to take off from a stop sign. I like mine kind of high because you don't want to be caught with your pants down out in the streets with soccer moms breathing down your neck!


Lower Screw Adjustment (after engine warm up):
Now that the bike is burning oil properly with a nice hot spark plug you can judge how well the mixture of oil and fuel is. The factory recommends 2 and 1/8 turns out but I found this to be too lean (not enough oil mixing). How can I tell? Well the top speed was only pulling up to 20mpg and then the engine would sputter and run really rough. The fuel was burning off too quickly and not pushing the complete stroke of the combustion cycle... just take my work for this if you aren't up on your combustion engine science.

So with my trusty screwdriver on a country road I backed out the screw a half a turn and hit the straightaway again! This time it ran better but STILL sputtered and spit. It sounds like the difference between a little weed wacker running at half speed compared to full throttle. You know, the wacker is sounding funky and sputtering like it wants to be given full throttle to take off. Well that's just how the 50 was running. Then I adjusted out the screw another half of a turn and the top speed increase by a few MPH as the engine sang it's note to full RPMs. I rode the Honda Express around some more roads and hills listening to the engine and making sure it sounded and ran like a good little 2 stroke. The air mixture screw is now out to around 3 turns out and it pulls 25 MPH consistantly.

Smithers
12-02-2008, 01:23 AM
Here is a TOP SPEED run on the Honda Express-SR 50. This is one mean little bike! Notice the throttle technique needed to get the engine RPMs right where I needed them in order to set the Honda 50cc world record. The wind was brutal at this speed.

http://www.youtube.com/watch?v=oG2gIganWYw

It's a good thing we had the roads shut down by the local law enforcement for this event.

THE HONDA WILL possible run a little more rich with oil once the air filter is placed back on the carburetor. For this top speed timed run the bike in the video was running an illegal unrestricted air configuration. Your adjustments might vary from the setup on this bike once you install your own air filter. I recommend a UNI foam filter that you can guy at just about any motorcycle shop. They make displays with universal filters hanging on them for sale and you should be able to find one to fit your carb without any problem.

Have fun and watch out for John Law and his radar gun.

Dobber
04-14-2010, 09:51 AM
Hello, I am wondering if you can send me more pictures of how the carb. is supposed to be hooked up. I just bought a nx50 and the guy who had it before me had it all messed up and I am having a little trouble figuring out what goes where. Any Pictures or info. would be greatly appreciated!
Thanks, Chris

you can e-mail me if it is easier
[email protected]

Smithers
04-14-2010, 01:10 PM
I'll be visiting my friends place who has the bike this week. I'll do my best to get a couple good pictures of the carb and the hoses.

Dobber
04-15-2010, 04:37 AM
Hey Thanks I appreciate it, but after I replied on here I actually got it figured out from the pics. on here! Thanks!

electrohacker
11-08-2010, 07:21 PM
I just bought a used 82 nx50 and cant seem to get any help anywhere.

thanks for the picture showing the vacuum bypass, mine was also missing the airbox

I have no idea why mine isnt starting though. I tried every thing you've said and even sprayed some ether in the carb with no luck.

I know I'm getting compression as the starter is strained and turns over easier when the spark plug is removed. I also verified spark.

the only thing I can figure is I didnt disassemble and clean the choke

I'm out of ideas...

Smithers
11-08-2010, 10:37 PM
Hmm that's a bummer. I'm wondering HOW much compression it's getting though. How many miles does it have on it? The rings could be bad even though it feels like it has compression. :-\ And you're trying to start it without an airbox right? That would make sure that it's getting air. Basically the carb controls everything. You really have to be thorough when cleaning them out and disassemble every single thing.

I've seen TONS of bikes thrown away simply because of a dirty carb. It costs big bucks to have a mechanic get them going again! I'm working on some really complicated carbs at the moment. The bike was basically trash simply cause the carbs were completely neglected and in really bad shape. I'm just wondering how many miles are on your cylinder. 2 strokes don't last all that long.. but then again it's a Honda and they are the highest quality 2 stroke mopeds out there.

electrohacker
11-09-2010, 02:29 AM
it is rather high mileage (part of why it was so cheap) over 2000 miles. but I'm not afraid of re ringing the cylinder, infact I might just save up and upgrade the cylinder at the same time

electrohacker
11-09-2010, 02:30 PM
I'm going to check the head gasket tonight as I saw fuel leaking from the forward part of the engine. a head leak would explain the fuel leak and the low compression issue. I can also check the cylinder walls and rings while im there

Smithers
11-09-2010, 02:52 PM
Very good. That would be great if it was just a leaking head gasket. Here is a place to order parts that has been recommended to me by a good friend. He insists that they offer the best prices/quick shipping. http://servicehonda.com/

My local dealer really goes out of his way to give me the best prices on OEM parts so I haven't tried Service Honda yet but I'm sure I will in the near future. I've known the owner of my dealership since I was a kid so I support his business. With times being hard supporting local shops and businesses that do a good job is important. The only problem is that the dealership is an hour away so yesterday I just called in some tiny carb parts to have them sent to me from a place that only sells carb parts. I just needed some simple o-rings sent to me so I ordered them from a carb part specialty business http://carbparts.com/

I looked at a few carb parts websites for the tiny little parts that I needed for my friends ZX-7R carbs (http://www.fourwheelforum.com/forum/showthread.php?t=1103) and I just couldn't tell exactly what I would need to order. So I just called them up and literally within a minute I told them exactly which part it was and they knew exactly what to send me. The only thing they asked me was how many and what type of card will I be using. The parts were cheap and they are on the way.

Let me know what you find when you get into the engine some more.

electrohacker
01-16-2011, 09:13 AM
sorry I havent posted updates, I found that the rings and piston were just plain wore out. it was going to cost me over $110 to have it hones and get a new piston and rings so I opted to get a 70cc big bore kit from 1977 mopeds. parts just dropped on and other than a vacuum choke issue I had she started right up and I;ve been running it around in the snow covered detroit like a fool (got it regestered and all the lighting repaired) now I just have to track down a fuel leak, when I fill the tank I come back the next day to an empty tank...

I added an inline petcock like your previous owner did and this revealed that my leak is at the stock vacuum petcock, probably where it joins the tank. I'll tear down the tank and figure it out.

electrohacker
01-16-2011, 09:14 AM
oh and so far I'm 1/4 or so through my break in, and I'm up to 33mph, not bad considering I'm running stock exhaust with no porting and stock intake with an aftermarket filter

electrohacker
01-16-2011, 09:26 AM
videos
http://www.youtube.com/watch?v=H9bpDJekuzw first start up
http://www.youtube.com/watch?v=KgvpdhYZJE0 first drive
http://www.youtube.com/watch?v=Nv_yP2rC8D8 top speed run around the veledrome

Smithers
02-21-2011, 08:26 AM
What the heck? Are you getting your bike ready for the scooter races there or something? I was looking at other vids of that park and it seems like they have some pretty sweet races there. Ah that looks like so much fun. Wow almost 35 mph out of that thing is a substantial improvement. It sounds like it has some balls now. I bet you can't wait for the weather to warm up!

aidynphenix
07-09-2011, 02:10 PM
hello guys, this is my first post here at 4wforum, and im excited, i got one of these little honda scooters the other day from sombody on craigslist..
it works pretty good and on a level surface i reach about 28mph.

there is a few things i still need to get working before i can drive it legally like i need to.
first my tail light and headlight are blown, and i think its because i have no battery.
im going to see if i can find a 12v battery for farm/lawn use today that will fit.
i am going to replace the taillight, but dont have the replacement headlight for the front, so i think i will have to improvise for now., planning on cutting the back of of the light off with a dremil and puting my own light in the houseing..

i also, have a problem with they keys. i cant take the key out and have it turn off. it doesent work, it can even be started and driven without the key, and i dont like that.
i can no longer lock the handlebars in place with the key, i cant push it in and turn to the left at all.

and lastly, i dont know what kind of oil i should be putting in it, and also where i can buy it, the guy i bought mine from said he put, Honda GN-2 auto oil in it..

if these questions can be answered in the user manual or some troubbleshooting guide could you guys point me in the right direction, i would really like a pdf manual on the bike to help me get these problems worked out.

im needing this bike for my transpotation at the moment, i will be putting about 15 miles on it per day on my way to and from work.

aidynphenix
07-09-2011, 07:17 PM
i went to the store and bought a few parts. Battery, bulbs, generic front headlight.

ok hooked up all lights, have the front light and rear lights functioning, i now hear a click when the turn signals flash. and correctly now.

but...

the taillight never turns off. dispite me turning and takeing out the key, it stays on. with the engine off and the red knob in the off position, it wont ever turn off.

i believe something is wrong with the part where i insert the key.

i cannot lock my front wheel, i cannot kill the engine by taking out the key and turning it to the off position, i cannot turn off tailight either.

i dont even need the key to fire it up and start driving.

i know this is simply a electrical problem somewhere. but could anybody give me any clues where to look so i dont have to dissasemble the entire bike and follow all the wires?

thanks.

aidynphenix
07-10-2011, 08:20 AM
the ignition switch, was broke. the inside is made of plastic and it eventually wore out.
there is a 2 position switch inside, and it was stuck in the ON/RUN position. so even if the key was turned the switch wouldent move. basically a square metal tab was ment to fit into a plastic fitting to move the switch, but the plastic fitting was wore out.
it is a 2 way switch, 4 wires. 2 of them are to let the electricity and lights work.
and the other two are a kill switch.

so what i did is, i ordered a 4 wire ignition switch. it probably wont arrive for a few weeks. but i need to use the scooter it now. so i wired up a switch so that i can still use it. i hid the switch on the bottom of the scooter where it will be unseen, and put the old ignition switch back so that i can still lock the front wheel in position. so as long as nobody knows about the switch on the bottom, nobody will be able to start it up. and when i flip the switch in the other direction, all the electrical turns on.