CB125T need battery charging?

[ish765]

I am new to this forum so hello all.

I have been working in my Honda (cb125t) 1978 and was told by my local dealer when I bought the battery that the bike would start/run without the battery charged. It is not. Could this be the problem?

Thanks.

[extreme3d]

I'm a little unclear as to what you mean. I think you may have missed out the odd word here and there

Am I right in assuming you have bought a new battery? If you have then yes it sounds like that particular battery will need charging.

It should however still have enough power to light up the instrument lights. Does anything come on? Try the indicators?. Also check it's in neutral as most bikes won't allow the engine to be turn on in anything but neutral. If nothing shows any life then check the fuses - the main 30amp fuse should be your first point of call. (assuming bikes that old have a fuse of that rating)

[Kickstart]

Hi

Think the old CB125T will quite happily run without a charged battery (although it might blow bulbs easily, and running with no battery at all might well fry the charging system).

If it isn't running then I would look elsewhere for the problem (unless it has an aftermarket electronic ignition system).

For best battery life a new battery should be charged before use.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[ish765]

Thanks for you replies. The new battery did have some charge yesterday and it did start but would not run for long. The lights were also working a bit. However if I may indulge you …..When I got the bike it was running on one R/H cylinder so I took the carbs of and cleaned them (the bike has been sitting for 10 years). I found that the L/H carb float had beet bent out of shape. Basically it looked like someone had removed the float chamber and just pulled the floats outwards, this allowed the float to hang much lower in float chamber. I just cleaned them at first and reset the height with the proper method. This still meant the float was hanging lower because the proper method only sets the top height. I thought the bottom height didn’t matter so much. After refitting I found that it was now running on the L/H tampered crab???
So last night I also reset the float to match the un-tampered one by bending the bit that stops it from dropping in the chamber. My reasoning was that a lower (more open float) would drag more fuel and prevent the other from working properly.. And this morning Ahhhh… nothing. So I checked the sparks and they defiantly seem weaker and the lights are non existent.

I have new air filters, new sparks and new oil.

Ps.. Im sorry for any mishaps in my writing. I do try my best and spell check and proof my stuff but I am a little dyslexic so please forgive anything I miss.

[Kickstart]

Hi

With the carb upside down, the further the float is from the carb body the less fuel it will allow into the float bowl. Best to clean both carbs out thoroughly and set the float heights according to the manual.

With the spark, difficult to tell. In daylight they will appear dimmer.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[ish765]

Cheers...I assumed that because moving the float away from the body was pulling the needle jet out it was letting in more fuel. I am making rather rash assumptions being a novice.

Unfortunately the bit that sets the furthest distance the float can go from the crab body should not be bent and therefore has no setting in the manual. The only thing I can think is to match it with the good one. The bit that sets the float hight against the needle has been done according to the manual. and i have cleaned all the jets

Thanks for your time....i am learning a lot from doing this. Though its a frustrating in-pass ive reached.

maybe ill be of some use when its done.

[stinkwheel]

Also check your points gap and ignition timing if it has been sat for a long time.

Those bikes do have a habit of firing up on only one cylinder (not always the same one) with the other kicking in 10-20 seconds later. I've seen a few and they all do it.

Keep at it, I think you probably have one of the rapid ones (wire wheels, round headlight, cable operated disc brake?). Should be good for a genuine 80mph if you get it running right.

[Kickstart]

[ish765]

Ok then tappets is next. Ignition timing is already done. Thanks for the encouragement. Ill look forward to at least keeping up with the traffic . My old gp100 never quite had enough on open roads.

[stinkwheel]

What I did with my CB125 superdream when I ran out of patience trying to get the carbs set up was to bolt on a CM125 inlet manifold. The CM uses basically the same engine but only a single carb, the manifold splits to feed each cylinder from the same carb.

You then just bolt the better of the two carbs on and away you go, perfectly in balance. No adjustment required.

Only problem with that being, I don't know if there is enough frame clearance on the twinshock bike to fit a single carb down the middle (the superdream is a monoshock).

[ish765]

mmm so did you use an air filter?
Sounds interesting though... if all else fails I will consider. I’m gona buy a charger tomorrow to rule that one out...I have a feeling the carbs are ok now, maybe not balanced but that should not stop it starting? I have reset the pilot screw to factory spec (I little loser because its cold) throttle stop screws are balanced 6 turns in, which was how they were when it got it. Fuel is going in both. The only other thing I can think is that I have messed with the throttle valve to make sure they close properly and give some play in the handle as the book states. So they will not be balanced but I can still adjust from the grip side. Ill get a vacuum gauge when it’s running…
ill keep this thread updated as it may be useful to others but i'm thinking out loud a bit (not being greedy) unless your interested.
Thanks for the help so far guys

[stinkwheel]

Aye, I used a pod filter now I come to think of it. It was a while ago.

You can balance the throttle valves reasonably easily by adjusting the gap under them to be the same. A drill bit is as good as anything to use as a 'feeler guager'. Slide it under the throttle valve from the air filter end and adjust the height so the drill bit is lightly gripped between the valve and the carb body. Adjust the other one so it is the same and they are more or less balanced. Then just make sure you move both screws the same amount thereafter.

Something else to try. Why not connect the output from the points directly to the coil with a flying lead? This will eliminate any dodgy wires between the two. If it fires up when you do this, you know where the problem is.

EDIT: Actually, scrub that. Just had a thought. Could be the condensers. Try seperating the points with the ignition switched on. If a spark jumps the gap, the condenser is gubbed.

[ish765]

Thanks stinkwheel. That is a good idea about the setting the throttle valves, never thought of it. However my newest update is I give up…for now …

I actually got it started today, on one I think. At least I could only see smoke out of the left hand exhaust.

It started with low revs and then went around 4-5000 for about 1min but died when I closed the choke. Then later on nothing. I checked the NEW plugs and the left hand one had gone? So I replaced with an old one which sparked ok in the HT but can’t get the bike past a splutter now.

I’m at my whit’s end.. I think if I could make the thing disappear I would. Poof gone

If this seems symptomatic of something give us a tip but I realize it may be several things which may mean a garage job so I’m gona Start saving…