Technical How To

The Battery, Lights & their story:

If you run your MB5 without a battery, you will blow out the headlight, taillight and other bulbs. You can get battery eliminator diode that wires in and then stops this from happening. If you did blow the headlight, it is discontinued from Honda, get one from Perk LLC (see links), he has a replaceable bulb headlight from Europe. Replacement bulbs for that headlight can be purchased for him, kind of a special bulb. The cheap battery is only about $10 from a motorcycle shop. Yuasa # is YB2.5L-C, you may see some of the off brands labeled RCB2.5L-C or RB2.5L-C, same thing. There are some AGM or maintenance free models now available, those are a sealed battery and should have a better life. When you turn the key on, the dash lights, turn signals, horn and taillight/brakelight should work, but the headlight doesn't come on until the engine is running. Replacement turn signal and taillight bulbs can be bought from your Honda dealer or an auto parts store. Oh yeah, and don't forget to check the main fuse that comes off the battery. For a wiring diagram, see the Resources Page.

Maintenance Items:

The service manual covers the maintenance schedule as recommended, check page 1-8, download it on the Resource Page

- Change with the spark plug about every 2500 miles, stick with the original NGK plug if it is stock, BR8HS.

- Clean the air filter every 2000 miles, more often if you are in dusty conditions. Use a good motorcycle foam air filter oil, not the gear oil that the service manual says.

- Keeping the chain adjusted and lubed (recommend Bel Ray Super Clean) every 1000 miles will give you the most life out of your chain. Remember the adjust it to specification and aligned properly.

- Now that these MB5s are quite old, you should grease parts of the chassis that may be a little dry. Use a good waterproof grease (I like Maxima or Torco) on your steering head bearings, center stand pivot, rear brake pedal pivot, control lever pivots, wheel bearing seal lips, speedometer drive gear, swing arm pivot, and rear cam pivot for the drum brake. Use a good cable lube, not WD-40, I recommend a dry film lube, on the clutch, throttle, tach and speedo cables. Keep those clutch and throttle cables adjusted too.

- Changing the front fork oil would be recommended, use a good 10wt motorcycle fork oil.

- Check the tire pressure often, (especially because these are small tires), this will give you the best life and handling of your tires.


I personally recommend Motul 600 for use in the stock oil injection, it is a high quality synthetic oil the can be used in oil injectors, if switching oils, I don't recommend you mix synthetic and non-synthetic. So when in doubt drain the tank and bleed the oil pump (check the oil pump adjustment while your there). Oil tank capacity: 1.2 quarts or 1.1 liters

If you have gotten rid of the stock oil injector and you are pre-mixing, use Motul 800, it is even better than the 600, recommended mix is 40:1.

For the transmission: I recommend Motul Transoil, it is a high quality oil that works great! It will use 1.0 quart / 0.9 lit when you change it and 1.1 quarts / 1.0 lit when it is disassembled. Change this oil every 5,000 miles or 9000 km.

There are many good oils out there and you don't have to use a synthetic, these are just my personal recommendations.

So your MB5 doesn't start - well here's were to start

If your MB5 has been sitting for a long time, most liked your carburetor needs some attention. The common stuff is a plugged fuel valve, float valve, and plugged up carburetor jets. Take the carb. apart, clean it (THOROUGHLY) & replace any o-rings/gaskets. Follow the owners manual, don't skimp on the cleaning process.

Your two-stroke motor needs 3 things in the right amounts at the right time to run:

1) Compression, of the engine

Start with compression, it's the easy one if you have a compression tester. Remember, check it with wide open throttle. 110 psi is the minimum on your compression gauge. If you don't have that, at least pull off the head and inspect, you will probably need a top end rebuild or replace. Check the piston, rings, cylinder, etc. 185 psi is the standard compression when it was new. If you don't have a compression tester handy, check the other 2 and see if you can get it to run.

2) Ignition, the spark that makes the fuel go boom!

If compression is good, go to ignition, pull the plug out and get a new one, rest it against the head with it attached to the spark plug boot, you should see a decent size blue spark when you kick it over, (with the key and kill switch on of course) if you don't, you need to check your stator, CDI, coil, wiring, etc. (Check your service manual, but a wiring diagram is available on the Resources Page)

3) Fuel, the boom juice

Fuel needs to get to the cylinder in the proper amounts, first check to see it flows out the fuel valve at the tank, then open the drain plug on the bottom of the carb, if those are good, pull the carb off and check the float level, float valve, clogged jets and clogged passages, worn out jet needle and needle jet. Also remember to check for broken reeds, but that is rare. (Check your service manual for more info)

And if you are reviving a sitting bike, make sure you have fresh oil in the tank, a bled oil pump and fresh transmission oil.

Counter Balancer Alignment

Align the gears as shown in the picture when you are assembling the motor: