QuestionHi, I have some little questions about my honda cb125j (monocilinder) from the mid 70's.
I searched after what gasoline to use but couldn't find anything. Here in Europe you can chose between euro 95 en super 98, with the later having a higher level of octane then the first. I've just started riding and I used 98, but then I heard this might be bad for these old bikes.
Second, the adjustement for a non standard carburetor from Mikuni. The bike runs well when he is cold but when he gets warm he performs well in the higher rpm but shuts out in the low rpm. I checked the spark plus and it seemed black and dry. So I assume it needs more air, but now i seem to have messed up the whole settings of the carb and it won't even start as easy as before. Any hints on how to readjust them?
and the last one. I gotta change the sprockets and brakes (drums) on the back wheel. But I'm a little scared because of the bearings that might come loose and especially of the wheel-alignement. I don't know if the alignement really is that important and can cause rapid detoration of the chain/sprockets when not done properly?
AnswerWietse, Hondas run okay on 87 octane fuel in the US, although I tend to use higher grades just to be on the safe side. If there is no signs of overheating or knocking/pinging in the engine under load, then lower grades of fuels are fine. Unleaded is okay, as well.
I have no idea of what Mikuni you put on the bike (or someone else put on it). If the bike starts without a choke and runs okay for the first couple of minutes, then the idle circuits are too rich. Mid-range acceleration is to do with the taper of the needle and the position of the clip on the needle, which will allow for adjustments of the mid-range mixture to a degree. Mid-range to top speed is metered by the main jet. Hopefully the carburetor wasn't designed for a 2-stroke!
Black and dry is too much fuel, not a lack of air, unless the air metering circuits are blocked in the carburetor. Make sure that the needle jet is still in place.
There are alignment marks on the swing arm and the chain adjusters. Just make sure that the marks match from left to right and that the chain slack is at least 3/4" at the tightest spot in the chain. If you are changing sprockets, I trust you are changing the drive chain, as well. Put all of it in new, at the same time...
You can sight down the drive chain to see if it is turning one way or the other, due to rear wheel misalignment.
Bill Silver
