Tech Tips

Up Manual Get it Running History Tech Tips

First, you should know that I am no mechanic.  I like to tinker, but most of what I know about small engines comes from experience with radio control airplane motors.  I have never cracked the case on my Honda Passport's engine, and I hope I never have to.

That said, this bike is very easy to work on.  Once you get past the step of removing all of the plastic bodywork, everything is right here for you to handle.  The C70 comes from a large family of Honda motorcycles with identical power plants.  The only differences between them are bodywork, suspension, electrical systems and concealed drive chains.  There are many manuals available covering tear down and maintenance of these.

Gas - Use Sta-bil.   In any small engine, this junk will keep it from gumming up in the months when you don't run the scooter.  Sta-bil is great stuff.  Gasoline changes as it sits, which is why every old lawnmower you see runs like garbage.  If you don't use Sta-bil, you're going to be using gumout in the spring.  Did I mention to use Sta-bil?

Plugs - I run NGK C7HSA plugs, which are the closest thing I can find to a match for what it requires.  Once I got the timing set right, it stopped burning them out.

Tires - be careful - I had 1 supplier send me a 2-ply rated front tire.  Scary over 35 mph.  Got rid of it, and quick.  But, Kenda still makes a front tire that fits, and Bridgestone still makes a rear.  They are not the same, make sure you're getting the right ones.  

Parts - I'm getting replacement parts from a guy on Ebay who seems to get up in the morning, pull a couple of parts off, put them online, and go finish his coffee.  The only damaged parts on mine are the number plate and the footpegs, which Chris P bent on his first foray into motorcycling.  Another great source is Banzai Motorsports, in Libertyville, Illinois - (847)362-7110, ask for Jason in Parts.

Battery - Be careful - up until 1981 these are 6-volt.   Later ones are 12-volt.  Outside the US this may vary.  The 6-volt is available at Pep Boys.  I run an Interstate battery now, works fine 

Carburetor needle -- on about the 15th attempt to clean out carburetor, I lost track of how many turns it took to set the needle at the factory setting.  Honda cleverly put a wing on the side of the needle, to preclude turning it more than three-quarters of the turn away from this setting.  The only way to go past this is to remove the bottom half of the carburetor.  After about five rounds of this, I took out my Dremel grinder and buzzed off the wing..  I can now remove and replace the needle without disassembling the carburetor. 

Rusty Gas Tank - Of course, the reason for the frequent carburetor rebuilds was a rusting gas tank.  You can cure it by scraping off the big pieces from the inside, accomplished by any number of means.  Filling the gas tank with gravel, and shaking it around, or others.  Honda doesn't have NOS tanks any more, so I took mine to a radiator shop, had them sandblast it, and used a product called Kreem that I got from a Harley dealer to seal it.  Seems to work.  I guess Harley owners are more prone to restoring motorcycles, and a lot of interesting parts are available there.

Dying Engine - 

Make sure the vents aren't blocked on your gas cap.  If they are, which often happens after using Kreem, then you'll start up fine, and die in a few minutes.  When you check to see if you have gas, the bike will start up again.

Irrelevant sidenote -- my old friend Bob (see the writings section) taught me how to get dents out of motorcycle gas tanks.  This doesn't apply to the Passport, since you have to be in a very bad wreck to dent the internal gas tank.  But it works for almost anything else.  Seal the fuel line attachment, fill the tank with water, and put it in the freezer.  Check it frequently.  The expansion of the water will force out the dent, but it could conceivably split the gas tank.

Vibration - These things vibrate a lot, and are full of resonances at different engine speeds.  I got rid of some of them by squirting silicone caulk on the turn signal lenses and then remounting them.  

Gas Puddle - The drain screw on the float bowl leaks sometimes, and is worth either tightening down or replacing.  Also make sure the float isn't stuck on the carb.  Otherwise you'll be using kitty litter on the garage floor. 

Headlight - This is an expensive little booger, and Honda still has some, but I don't know for how long.  It's probably DOT-Illegal, but if I blew another one, I'd consider fitting something else.  In any case, make sure your entire wiring harness is tight, or you'll blow several before finding it as well.

  1. Make sure your battery is charged, puts out 6V or 12V (depending on model year) and is installed tightly. 
  2. Check all the harness connectors in the middle of the bike (under the gas tank) are tight. Not a bad idea to pull the gas tank anyhow, and put in new gas lines. Stick a filter on each line while you're at it.
  3. Before you put that $30 bulb in, test the circuit with a cheaper bulb- get some test leads (or better yet a junk taillight) and put a 6V (again, or 12V if it's a later bike) bulb in the circuit and see if it'll blow. Run around the block a few times so the engine gets to operating speed.

Note, the headlight appears to be powered by AC, not DC like the rest of the bike. It's driven directly by the magneto, but the damping that comes from the battery takes the peak out of the voltage.

When mine were blowing out, the voltage on the headlight, with the engine running at road speed, went through the ceiling! After I found the bad connection, it went to a nice stable 6-8V. But at idle, it tested OK.  Then, and only then, put the actual, solid gold, mail-order-only bulb in.

Timing - Burning out spark plugs?  Check your timing - mine had slipped.  You can adjust it with a simple continuity tester and a little patience.

Manuals - Most of the important pages are on this site