1981 Honda Express-SR a.k.a. NX50
 

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...
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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.
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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.
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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Here is the trick I used! Think smarter not harder.
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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

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Seals coated with synthetic grease and all ready to go back together for the last time.
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And all together now.
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It's amazing! We're all done after all that carb cleaning. The fun part is putting the clean parts all back together again.

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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.

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:

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