Up Manual Get it Running History Tech Tips

Getting an old Honda running again - the basics

If it's been sitting for 10 years in somebody's garage, there are a bunch of things you'll need to do, but first of all do these.


Change it NOW before you start the engine.  There's not much oil in these things, so it really matters.

Buy a plastic oil pan and enough of the right oil. 
Check to make sure there's oil in the engine, then run it for a few minutes to get things warm. 
Turn it off, slide the oil catch pan under it. 
Loosen the oil cap on top. Take off the oil plug on the bottom with a wrench - not vise-grips, a wrench that's the right size.  The plug will fall into the pan.  Get a paper towel. 
Let everything drip out.  Pick the plug up from the pan and put it back in with your fingers, so you can make sure it's not cross-threaded. Then tighten with the wrench - don't really honk on it, just make it solid. 
Add oil, run for 2 minutes
Check the level, add more as needed to get it at the right level.


If it's been sitting, then the headlight's probably OK.  If your nephew got it running once or twice in the intervening time, with a dried-out battery, the headlight's probably shot.  Sorry.  So...

Before you do anything, disconnect the headlight.  If you forget, you'll trash the headlight the first time you get the bike running.  Wouldn't want to destroy that happy moment, would you?  A blown headlight means no legal street riding until you get a new one, and that can take a while.

Get a new battery, and put it in.  The old ones die even if they aren't used for anything - that's life.

Get a handful of all the bulbs you'll need, long as you're at the store.  

Good, clean fuel 

  1. First, make sure the fuel valve is in the OFF position so that all the gunk that gets loosened up doesn't go into your carb.
  2. Then, put a bunch of Gumout in the tank, then slosh it around and let it sit overnight. Stabil is good for this too.
  3. Next day - get something to catch the gas (it holds a gallon) and have it ready. Remove the fuel tank cap or this next step will take a while. Then pull the fuel line off the little nipple that leads to the RES line. (There may be a clip holding it on) and drain into the can.
  4. Then remove the ON-OFF-RES valve from the carb by loosening two screws that hold it on, and clean the screen that's behind it.
  5. Using a flashlight, look inside the tank. Does it need more cleaning? Is it rusty? Make sure that it's pretty clean before you put things back together, or you'll be doing steps 1-5 again and again for weeks to come. 
  6. If it's very rusty, At this point, you may as well pull the fuel tank from the bike - flip up the seat, and remove the bolt and screw that hold the tank in place. If the tank wiggles, you've got both of 'em. Now wiggle the tank and you can persuade it to come out of the hole that holds it. You'll think you have to take more junk off the tank, but you don't - the whole mess can be taken out of the hole. I'd go to a cycle dealer and buy some KREEM Fuel Tank Liner. Then take the tank to a radiator shop and have them sandblast the inside. Then go home and KREEM the inside of the tank. Just follow the instructions. Then put it all back together.  Important - have the Kreem ready before the blasting, and don't delay afterward or it'll rust before you put the Kreem on.  Also If you use the gas cap when you slosh the stuff around, make sure afterward that you clear the vent hole in the gas cap. Otherwise gas'll dribble out the carb whenever it gets hot. Next time, I'd probably use something else to cover the tank hole.
  7. If you're lucky, you can put it all back together, put fresh fuel in the tank, and start the bike. If it runs OK, enjoy. If not, you're probably looking at cleaning the carburetor, which is discussed in detail in other threads in this group. One source for the gaskets and bits you'll need is www.siriusconinc.com
  8. Since the thing hasn't run in a while, INSTALL A NEW BATTERY BEFORE YOU START IT. Otherwise you might blow out the headlight (which costs as much as the battery that you are going to have to buy anyhow.)

While you're at it, consider replacing the fuel lines.  They're really cheap, they'll get messed up when you pull the tank off, and they're a frequent cause of trouble.


Look at 'em.  Be honest, they're old, and there's only two of them.  When you buy replacements, make sure they're not just the right size, but the right PLY RATING - there's more than one layer to these things.  Lots of people make tires that'll fit, but are too thin.  Bad news.  Get the tubes too.

Stuck Transmission

Gears won't shift?  Group member Don from Ohio suggests:

"Drain out any oil that's in there and refill the crankcase SLIGHTLY more than normal with 1/3 kerosene and 2/3 motor oil.Start it up and run it at a slightly high idle for 2 minutes and then try to shift it thru all the gears and back to neutral while you're sitting on it and giving it some throttle. Then
before a total of 5 minutes has elapsed,shut it off.If it didn't shift better, let it cool for an hour and try the same thing one more time. If it isn't better and doesn't shift,drain the oil out and tear it down. This trick can sometimes free-up crusted parts with burnt oil deposits on them.  don-ohio  (:"

But remember don't do it more than twice and not more than five minutes one hour apart. The reason for this is that the kerosene will also cut a certrain amount of gunk loose inside the engine and could possibly plug your centrifugal filter. So clean your filter afterwards too. Hope it works for ya'! 
don-ohio  (:^)"

Editor's Note - DON'T DRIVE THE THING WITH KEROSENE IN IT.  JUST IDLE IT.  Did I say not to drive it?

No Spark

If you've replaced the plug and still don't get any spark, Don suggests:

"Sitting that long,it's probably just the points are not making good contact. Take off the cover and pass a file thru the points a coupla times and then an emery board or cloth. Then put some carb cleaner or brake parts cleaner(NOT starting fluid...it has lubricants) on a lint-free cloth and pass it thru the points. Now check the gap and if they are opening and closing correctly, you'll probably get a good spark.    Nine out of ten times on a stored bike with no spark,it's the points. Also, always replace the plug too.  don-ohio  (:^)"

Confused by the Carb?

Thanks to Club Member Mike G for this explanation:

The carb on a C70 should have a total of four hoses and two cables  attached to it.

The two cables are obvious - the throttle at the very top of the body  and the choke on the side.

Two of the four hoses are the main and reserve fuel supply lines.  They they are twice the size of the others and attach to the fuel  petcock with either spring clips or hose clamps. The original rubber  hoses come from the factory 'polarized' - the main line has a smooth  surface on the outside and draws fuel from a tube raised off the  bottom of the tank (so it runs dry a little before the tank is  completely empty) and the reserve hose that comes off the very bottom  of the tank has longitudinal 'ribs' on the outside to distinguish it  from the main line.

The other two are half the size of the fuel supply hoses, are  attached at only one end (the carb) and handle only manual fuel  drainage and venting.

The one that comes from the top half of the carb is the float bowl  overflow vent hose. It's attached to a small aluminum pipe that is  always above the split line in the carb between the body and float bowl and usually right above the idle adjustment screw. It's source  is the hole in carb body that's on the roof of the float bowl cavity, and it provides venting for proper fuel flow into the bowl and   overflow protection should your float valve stick open while your  petcock is open. The open end of this hose is usually routed toward  the back of the bike, over the top of the starter motor and into the  main frame cavity. From there it allows air to get into the float  bowl from above the highest possible place water can get in, and also  drains raw fuel overflow safely on the ground, away from sources of  spark.

The one that comes off the very bottom of the carb is the manual  float bowl drain valve hose. It's attached to a brass fitting on the bottom of the float bowl and has a brass adjustment screw immediately next to it. The screw is the manual float bowl drain valve, which with the petcock turned OFF allows you to empty the float bowl before maintenance or storage - and with the petcock ON offers you a simple way to 'prime' the fuel system - the vents are open, lines are clear
  and the float valve is working properly if gas runs fast and free for long enough to be more than just the capacity of the bowl (maybe 10-20 seconds). This hose is usually routed down from the carb,beside the cylinder fins to a clip in front of crankcase where it raw fuel can drain safely away from sources of spark, and the fuel can be drained into a catch tank of some kind if you are doing planned maintenance.

There are photos of the proper routing of these hoses on page 5-2 of the online manual at this link: http://autos.groups.yahoo.com/group/Honda-Super-Cubs/files/shopmanual%20C70%2080-82/055.jpg

Have fun.
Mike G."

> My 81 C70 runs strong at open throttle, but surges and backs off >immediately when running at any lower RPM. Maybe it is the Maine >weather. Fuel is fresh and clean. Carb was opened and semi-cleaned >(I blew on it).

Low to mid range is controlled by the main jet, the throttle slide and slide needle. You appear to have a lean situation - a flat spot in the mid range and surging at partial throttle.

The main jet or it's holder may have any crud in them. Take the main jet and holder out and clean all the small passages in the brass unit.

Another source of lean running is if the needle is set too low.

If your needle has multiple rings on the end, if the locating clip is not in the bottom slot, move it there (raising the needle in the slide - makes the bike run richer at partial throttle).

If this doesn't cure the problem, get a main jet one size larger.

>I do question whether the needle sitting on the end >of the throttle cable should wiggle. Where the needle attaches to >the cable with some sort of clamp and trap, the needle itself seems >to easily wiggle.

Wiggle is OK. Travel up and down in the slide is not.

Locating clip sets needle position, "W" spring holds the clip on the needle down and the coiled spring holds the "W" spring.