Wrong battery preventing bike starting?

[chinny]

So i picked up an old Yamaha YB125E (70's or 80's) which is 2 stoke, 12V with both electric and kick start. Last owner couldn't get it working. I am only using the kickstarter to try and get it going.
It has compression, fuel/oil and air. Spark seems weak though - sometimes its a dim blue but most of the time its orange. This is when the plug is out of the cylinder btw.

I heard for these old Yamahas you need a decent battery to get it going, which is reinforced by the fact that mine won't spark if the battery is taken out.
The service manual says battery should be 12V 10Ah (12N10), but its currently got a 12V 5Ah (a Besco 12N5 3B).

Question then, is the 5Ah battery the culprit?

I should mention that i got it going one time (ran for for like 2 seconds) which happened after i cleaned the carb float bowl out. Died when i opened the throttle. But hasn't started since, even tho i've since unblocked some jets and done more carb cleaning...

My thoughts are the battery is too weak to create sufficient spark inside the cylinder under compression cos its only 5Ah but my electrical knowledge isn't flash...
Any thoughts?

[FJRider]

Try a plug you KNOW is good and compare the spark. Even if it wont fit in the hole.

And go from there ... and hows the air filter .. ???

[chinny]

Try a plug you KNOW is good and compare the spark. Even if it wont fit in the hole.

And go from there ... and hows the air filter .. ???

Need to buy a new spark plug then - no biggie but would like to eliminate the undersize battery before other things. Was thinking of new plug but inconsistency in spark made me think it wasn't the plug. Will buy new plug soon and try it.

Air filter is old and crumbly - haven't had a good look, but i've tried kicking it with filter out too.

Thanks for the suggestions.

[Brian d marge]

From memory the insulation in the generator of those old things goes funny or something like that ,,,and they do have problems making sparks
Really can't remember the details but its something a long those lines
A 12 v battery is just a 12v battery , how long it makes the 12v is another story
Make sure every part of that electrical system is in good and clean nick with a good earth
Some one can correct or elaborate on this as I'm not near my desk

Stephen

[FJRider]

Need to buy a new spark plug then - no biggie but would like to eliminate the undersize battery before other things. Was thinking of new plug but inconsistency in spark made me think it wasn't the plug. Will buy new plug soon and try it.

Air filter is old and crumbly - haven't had a good look, but i've tried kicking it with filter out too.

Thanks for the suggestions.

A weak battery may not spin a motor over fast enough to start it (typical of low compression) ... but that also takes power that the plug needs. Kicking it over does not have that drain on the power ... just as a push start doesn't have a drain on power. (Or a BIG HILL)

A shot of easy start in the carb throat may get it to fire up. If that doesn't fire it up it may not be a fuel/carb issue. With a good plug ... it should fire.

CDI or points .. ??

[chinny]

From memory the insulation in the generator of those old things goes funny or something like that ,,,and they do have problems making sparks
Really can't remember the details but its something a long those lines
A 12 v battery is just a 12v battery , how long it makes the 12v is another story
Make sure every part of that electrical system is in good and clean nick with a good earth
Some one can correct or elaborate on this as I'm not near my desk

Stephen

Was afraid someone would say that...i dread electrical fault finding (a wire's a wire, right?) as its all electrons, current and unseen stuff. But yea, thanks for the headsup - will attempt to check through the electrical systems starting with the insulation.

A weak battery may not spin a motor over fast enough to start it (typical of low compression) ... but that also takes power that the plug needs. Kicking it over does not have that drain on the power ... just as a push start doesn't have a drain on power. (Or a BIG HILL)

A shot of easy start in the carb throat may get it to fire up. If that doesn't fire it up it may not be a fuel/carb issue. With a good plug ... it should fire.

CDI or points .. ??

How would a weak battery hinder the motor spinning if its kick-starting we're talking about? or am i missing something here...My understanding was that most bikes are wired so that they can start w/out a battery (kick or bump start), however some bikes (e.g. mine) require the battery regardless.

Ok might give easy start a try if i run out of ideas.
Forgot to mention - when i got the bike and kicked it over the plug was always dry. After cleaning the carb the plug is now wet. Seems to be both oil and fuel in there...

CDI or points? No idea, my guess is points given what Brian said in his post?

Tomorrows shopping list - multimeter, spark plug, carb starter (if its cheap)

[FJRider]

How would a weak battery hinder the motor spinning if its kick-starting we're talking about? or am i missing something here...My understanding was that most bikes are wired so that they can start w/out a battery (kick or bump start), however some bikes (e.g. mine) require the battery regardless.

Because as it turns the motor over ... it hogs ALL the power. Thus weak spark. Kick it over and the sparkplug gets ALL available power. In MOST cases ... it will start (by kicking it over) with a flat battery. But usually needs to be wired to start without a battery in the ignition circuit.

Ok might give easy start a try if i run out of ideas.
Forgot to mention - when i got the bike and kicked it over the plug was always dry. After cleaning the carb the plug is now wet. Seems to be both oil and fuel in there...

THAT is a start. Progress even ...

CDI or points? No idea, my guess is points given what Brian said in his post?

Find them then ... look for (usually) a small round cover on the side of the engine. (not sure which side) Clean them up and set the gap. It wont be far out if it gives spark to the plug now.

Tomorrows shopping list - multimeter, spark plug, carb starter (if its cheap)

Just a plug first .... and install at the right (or near) gap. Clean and Set the points. Try again. Dont spend money if you dont need to.

[Skiwi]

To answer your original question:
Hook up a car battery to it with some jumper leads, if it starts the answer was yes, if it doesn't the answer was no.

[chinny]

To answer your original question:
Hook up a car battery to it with some jumper leads, if it starts the answer was yes, if it doesn't the answer was no.

Great news - finally started today!
At first i thought hooking up the car battery was a joke, but turns out no harm done to bike (i hope)..
Anyway, the car battery alone didn't work, so went out and bought a new plug and presto!
FJ, thanks for the suggestion. I thought the current plug looked ok and sparked, but i guess it wasnt.

Without the car battery connected the bike starts using the kicker but takes a few tries (3 last time i tried) but it goes.
Managed to ride it down the street and back
Idle is fine, but chokes when i open the throttle - probably carb issue, but also might be battery not performing.
I'll try opening the throttle with it connected to car battery to see if it solves the problem - if not then it will probably be carb related.

Thanks for the help guys - owe you one!

[Skiwi]

Unless the battery and charging system on the bike are totally goosed i would put my money on the carby.

Does it start on the kick start with the battery in?
If you have a volt meter, test the battery with the bike off, then test it when running.
It should be about 12.8 without engine running and about 13.8 when the bike is running.

If it is markedly different with engine off it will probably be the battery. That's likely if it has been sitting a shed somewhere for ages without any loving.

If it doesn't go over 13 With the engine running (give a bit of a rev) it is likely to be the charging system on the bike.

(FYI The difference between a 5ah and 10ah battery is in how long you can crank for, not how intense it is. 5ah= five amp hours, which means it can supply one amp for 5 hours or two for 2.5 hours etc before it is totally flat)

PS: Just had a thought - you are using fresh petrol?

[Edbear]

I love seeing battery threads.

But you are obviously on a tight budget...

[chinny]

Unless the battery and charging system on the bike are totally goosed i would put my money on the carby.

Does it start on the kick start with the battery in?
If you have a volt meter, test the battery with the bike off, then test it when running.
It should be about 12.8 without engine running and about 13.8 when the bike is running.

If it is markedly different with engine off it will probably be the battery. That's likely if it has been sitting a shed somewhere for ages without any loving.

If it doesn't go over 13 With the engine running (give a bit of a rev) it is likely to be the charging system on the bike.

(FYI The difference between a 5ah and 10ah battery is in how long you can crank for, not how intense it is. 5ah= five amp hours, which means it can supply one amp for 5 hours or two for 2.5 hours etc before it is totally flat)

PS: Just had a thought - you are using fresh petrol?

No - as i said in my original post it doesn't spark unless the battery is connected.
Didn't end up buying a multimeter, but will look at borrowing one and doing the tests - thanks for the figures.
I tried revving the engine with the car battery connected, but it still stutters once the throttle gets to ~30%. So my guess is carb.
Yea the battery has probably been sitting for ages. At least 1 year - that's how long the previous owner had it.

Oh ok - thanks for the explanation on amp hours.
FYI - its starts first time using electric starter (or kick) with the car battery. Without car battery the electric start won't start it (it really struggles) and kick starting takes about 3-4 kicks.

Yep - fresh petrol and oil.

I love seeing battery threads.

But you are obviously on a tight budget...

My budget isn't super tight, but a new motobatt will cost me $110 from a local dealer. If its really needed yes i'll get one, but $110 is a lot to spend if i wasn't sure it was the problem.
I've looked briefly a getting a Yuasa, but haven't got any real info for pricing that i could find online.. (12N10, 10Ah).
I've read a few posts where people love the motobatts, while others seem to have bad experiences with them.

Will jam a screwdriver into the carb soon and see what happens

[Canis G.]

For what its worth, sounds like your battery is either flat and needs a good charge up or it is buggered and won't hold a charge. You really need to take some voltage readings:
1. before you start the bike.
2. when the bike is running.
3.charge the battery then take a reading soon as you take it off the charger, then 2 hours later, then about 12 hours later and then about 24 hours from when you took it iff charge. Report your results back here and we can probably give you a good steer as to the problem.

Hope it helps.

[unstuck]

Get that bit of shit out of the carby, buy a new battery and away you go. Talk to ED about a new battery, He,s a good bugger, and will give you a good deal, right ed?

[Skiwi]

For what its worth, sounds like your battery is either flat and needs a good charge up or it is buggered and won't hold a charge. You really need to take some voltage readings:
1. before you start the bike.
2. when the bike is running.
3.charge the battery then take a reading soon as you take it off the charger, then 2 hours later, then about 12 hours later and then about 24 hours from when you took it iff charge. Report your results back here and we can probably give you a good steer as to the problem.

Hope it helps.

+1 = good advice