HELP! It won't start!!!

Jordarnos

Jordarnos

75 CB125s
Hey Guys,

I've hit a massive wall with my 1975 Honda CB125s. It won't start!

I've been riding it for about 2 weeks and was running perfectly, then I parked it up and went away for 5 days and when I came back.......nothing.

I've checked the spark against the engine and it's sparking strong, I've re-charged the battery AND put new fuel, new spark plugs and a new spark plug cap.

It's getting fuel because after I crank it for awhile it seems to flood and the spark plug gets a fuel smelling moisture on it.

So I'm really confused Fuel + Spark (should) = Run, but all I'm getting is a little puff or a backfire every now and then....

Any help would be greatly appreciated.

Cheers,
J
 
Hmmmm. I was gonna say battery but you checked that. Possibly the timing or the valves, but they shouldn't have changed in 5 days. You checked spark on both plugs, right?

Sounds to me like everything is there, just needs some good kicks.
 
Assuming that no one messed with it, it's probably flooded. Take teh plug out and kick it over as many times as you can without dropping dead from exhaustion. Then fit a clean dry plug, open the throttle wide open, fuel OFF and kick some more and it should fire.

The trick with a flooded motor is wide open throttle. The air coming through at starting speed with a wide throttle cannot pick up any fuel, so it usually works.
 
OK so I'm still stuck.

Kicked it till my leg almost fell of last night, with combinations fo throttle open and closed, choke on and off.

I pulled the carb off and checked there were no blockages, the valves seem to be moving nicely. Not sure on the timing I suppose i should check that tonight. Drained the oil, which looked reasonably clean, new oil, new fuel. Kicked my bloody guts out in the 38 degree (at 8 O'clock at night) heat.

All I'm getting is this weird back-fire, not like a massive BANG coming out the exhaust but like a little pop which seems to come back through the carb???

Could this be the value timing being off? How would that even change when it had been running fine a few weeks ago?

If so how do I adjust?

Any thoughts would be awesome! You guys are always such good help and I appreciate it.

Cheers,
J
 
Well, the valve timing shouldnt be off at all if it was recently running. Unless your cam sprocket, chain tensioner, or crank sprocket is so worn that the chain jumped a tooth.


On the left side of the crank under the side cover are the timing marks - make sure those line up with the spark. The pop thru the carb indicates a lean condition......but that doesn't make much sense with a flooded motor. My next guess is to take it up the biggest hill from your house and try to bump it the whole way home.


Seriously, don't do that.
 
Good thing you said don't do that, I've got a long steep driveway and was contemplating putting it in gear and bumping it the whole way down but it just sounded bad. If it doesn't want to start don't force it yeah?

OK so now I'm just wigging out cause (and let's be honest, I'm no mechanic but I'm trying) the spark gets kinda damp if I kick and kick and kick and kick, which suggests to me flooding but then it gets the lean pings?

Would this be something a mechanic could work out in 5 minutes? I'm kinda considering letting them have a go but also don't want to take it up and get hit with a massive bill, cause well the bike isn't worth much and I bought it to learn.

Cheers,
J
 
I personally wouldn't take it to a mechanic. They probably would charge a bundle.

Have you checked the timing on the end of the crank yet?
 
Have you 'been inside' the motor?
Check valve clearances
Points are under cover on cylinder head, timing marks on flywheel.
Set points 0.014" should 'break' at F mark
Check advancer is working, points cam should move easy about 20~30 degrees and spring back
 
Haven't cracked the motor or done any work inside.

Will check points, valve clearances and timing tonight.

What is the advancer? and where is it located?
 
Working from memory here: it's behind the points plate. It has 2 little spring loaded arms that open up as the camshaft spins faster.
 
The only pictures I have are of a single points conversion for Yamaha XS650.
I used Honda advance unit, your will be similar set up but not exactly the same.
This is what advancer looks like when removed from end of cam
CB93topview.jpg

All you normally see is the points cam and points
XSsinglepoints.jpg
 
Hey Guys,

OK so did timing which was a bit off, checked the advancer and that is working find (gave it a bit a clean whilst at it) checked the valves that were fine.

Started first kick, although it's running a little rough but that's because I've toyed with the carb settings when I was trying to identify the problem (will re-do tomorrow).

So firstly, big thank you for your help as always.

Secondly, although I'd never properly set the timing before on this bike, it was running before. Any thoughts on what would have put the timing off so much that it would prevent the bike starting? Do I have an underlying serious problem here? Anything I should be keeping an eye on or anything?

Cheers,

J
 
Glad to hear it's running, even a little rough.


Maybe the cam chain or the tensioner is wearing out? I don't think it would be so sudden though.
 
More likely the felt pad is dry and points heel and contacts wore down changing gap and changing timing, plus a little wear on cam chain/tensioner
When combined it can 'move' timing 10~15 degrees or more
 
When you say felt pad, you mean that little thing on the point plate that basically cleans the cam rotor? That was in a bit of a bad way so I turned it around to the clean side, what do you "wet" it with? Oil? Does this just clean and let everything run smoothly?

I also, cleaned and gently sanded the point, however would you recommend buying a replacement?

Cheers.
 
Use a couple of spots of engine oil.
Cleaning points is OK as long as you can get a 0.014" gap.
New ones are not terribly expensive though (even genuine Honda from dealer)
 
Too easy, I'll put a drop of fresh oil on it tonight. Might buy some points just to have in my spares for future.

That's what kills me in the end, waiting 3 weeks for parts to be shipped. I just have to look at my bike and cry!

Thanks again for your help!
 
Doesn't Les Barker sell electronic ignitions to replace the points all together? Just a thought.
 
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