96 Sport : Engine dies after starting

[WaiNYC]

My 1996 Skorpion Sport keeps giving me headache: It has a hard time starting, but once it did, dies within seconds.

The issue is way above my paygrade. I need the community's help again. To follow is the sequence of events:

- Over the past weekend: I installed a louder 12V horn that has a 5 amp draw <-- this may or may not be related to the issue.
- Trickled charged the battery.
- On Sunday, Rode bike. First 2 mi (I was the rider) no problem. Then a friend rode it, and the engine died at 5 mi out. He told me that the bike was sputtering -- he's a new rider and I think he meant a lack of power.
- Pulled bike aside. Let bike cooled. Started engine, rode for about 1/2 mile. Engine died again. Towed it home.

- On Monday, hooked it with same battery (fully trickle charged). Bike starts right up. Throttle-RPM response feels normal. Voltmeter V goes up as RPM goes up. I turn off the engine after one or two minutes.
- About hour later, want to go for a test ride. Bike starts but there is clearly a lack of power coming from the throttle. It dies within 10, 15 secs. Try again, but now, the battery feels as if not enough power and won't turn over engine.
- Thought maybe battery was defective - it's 5 year old, been sitting around 1 year plus, without trickled charged. So I hook up the MZ with what I know to be a good battery: The engine sounds like it is dragging, starts, then dies within seconds, same feeble response from the throttle.

- Today: I use that good battery (fully trickle charged) on the MZ again. Like yesterday, the engine has a hard time turning over. It does eventually start but the engine sounds not only feeble but abnormal (not sure how to describe...), and dies within seconds. Then it won't start again at all, as if battery had no power. Video:

https://photos.app.goo.gl/gjWYrL5razi86oBWA

(let me know if the link does not work)

- But then I hook up the same battery with my other bike (an airhead) and it starts right up, so I know it's not the battery.
- (somewhere in this sequence of events, the 15 A fuse got melted (but fuse wire not broken) during one of the tests...
Pic:

Fuse wire is intact, but housing is somewhat melted

The problem has got me scratching my head. I can eliminate a few possibilities:
- it's not the battery. The same battery that won't start the MZ would start the airhead.
- the stator appears to be fine. on Monday, it clearly was delivering more current when tach goes up

- what is strange is that the bike appears to be performing progressively worse. When the issue first surfaced on Sunday, it could at least start and be ridden for like 1/2 mile. On Monday, it could at least start and engine didn't sound abnormal. But today, not only did engine had hard time starting, it sounded strange, and then it wouldnt start again.

Any ideas where the problem might lie? A big thank you in advance for all the help.

I am both frustrated with the bike and feel challenge by it. The latter bec I want to learn how to maintain and fix bikes, and the MZ does not lack lessons to give

[droy]

Not sure if this is going to help but I'd do the following:

Replace the 6 year old battery with a new one (their cheap)

Make sure your side stand switch is deleted

Full tank of gas?

Drain the carbs

disconnect your new horn

Replace all the fuses

If there is still a problem after that to look for a short, bad ground or other electrical issues.

[lavrentyuk]

Fuel cap breather. Water in the petrol tank as a result of a blocked drain hole? Water/crap in the carb float bowl

These are the main reasons I get for an unexpected stop.

[WaiNYC]

Not sure if this is going to help but I'd do the following:

Replace the 6 year old battery with a new one (their cheap)
Make sure your side stand switch is deleted
Full tank of gas?
Drain the carbs
disconnect your new horn
Replace all the fuses

If there is still a problem after that to look for a short, bad ground or other electrical issues.

Thanks @droy, for the suggestions. I'm afraid though that they are not related... I did not try a new battery, but did use a very good battery and it's still the same. The video was of that very good , and just recharged battery.

I don't think its the others either; It was not the horn, cuz it's been disconnected -- in fact, the test that I recorded the video for, I had even disconnected the front lamp to reduce power draw.

Except for that "melted" 15A, which had been replaced, all the three fuses (3, 7.5, 15A) were fine as well.

[WaiNYC]

Fuel cap breather. Water in the petrol tank as a result of a blocked drain hole? Water/crap in the carb float bowl

These are the main reasons I get for an unexpected stop.

Hi @lavrentyuk, thanks for the input... I don't think that was it. Since reviving the bike about a month ago (see my old msgs), I had ridden it for the distance of a full tank of gas. And I'd checked the float bowl, and it was clean

[DAVID THOMPSON]

was riding my traveller one day and it got ratty and i got lucky

i stopped and was trying to get it parked and just happened to SEE
the hot wire 12v to coil had dropped off the spade on the coil
via a very small gap between tank and frame it was a miracle i found it that easy

the only reason was if i had had to push it was about 50 feet and coast all the way home

the spade had lost its tension and would not stay there when i plugged it back in
tightened it a bit with pliers and went back home and soldered a new one on the wire

if that hit the frame a fuse may blow or get very hot
dave

[Puffs]

It appears to me you have 2 different issues: the engine running poor & stalling, and an electrical issue.

Yes, the video shows that once it's running, the voltage even climbs to 13.93V, just before it cuts out. Presuming that is the voltage as measured on the poles of the battery, that is high, and that voltage is seen to vary quite quickly: are you sure this battery is good? As for the poor starting I think either your battery has lost it's capacity, or there is a problem with the starter motor, or a drain along the lines Dave described. If your battery is fine and of the right capacity, I'd definitely also have a look at the starter motor.

As to the poor running: all the usual suspects: carb fouled, fuel supply inadequate, ignition issue, compression inadequate, valves too tight, ...

Good luck!

[WaiNYC]

Thank you @David , @Puffs... Looks like I've the work cut out for me. It's raining here in NYC this weekend, but I'll get to it as soon as possible and report back to you all. Thank you again for the help so far.

[WaiNYC]

It appears to me you have 2 different issues: the engine running poor & stalling, and an electrical issue.

Yes, the video shows that once it's running, the voltage even climbs to 13.93V, just before it cuts out. Presuming that is the voltage as measured on the poles of the battery, that is high, and that voltage is seen to vary quite quickly: are you sure this battery is good? As for the poor starting I think either your battery has lost it's capacity, or there is a problem with the starter motor, or a drain along the lines Dave described. If your battery is fine and of the right capacity, I'd definitely also have a look at the starter motor.

As to the poor running: all the usual suspects: carb fouled, fuel supply inadequate, ignition issue, compression inadequate, valves too tight, ...

Good luck!

I am a poor student of electrical stuff..... What does having a high V, like 14V mean? What would cause the voltage to be so high? I thought if the V output is too high, the regulator kicks in to stop the current from going to the battery... Is that what you meant by "voltage as measured on the poles"?

Thanks for the lessons.

[breakwellmz]

Hi.

14v is what i would expect to see as a charging voltage for a 12v battery - https://www.powerstream.com/SLA.htm#:~: ... r%20damage.

When you had the carbs apart did you find the`hidden`filter? - viewtopic.php?f=3&t=10435&hilit=+hidden+filter

[Puffs]

V is the abbreviation for Volt, the unit of electrical tension (aka voltage), https://en.wikipedia.org/wiki/Volt.

On the battery (https://en.wikipedia.org/wiki/Automotive_battery, and https://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery) there are 2 poles, usually lead or copper, a + pole and a - pole. If you measure the voltage across those 2 poles you have least losses due to voltage drops caused by high currents (as occur during starting) flowing through resistive cabling.

From memory, your video showed the voltage to drop to (or below?) 9V while starting, and then quickly rise to 14V while running. Yes BreakwellMZ is correct in saying that 14V is a rather normal voltage while charging, but IMO it is an upper limit, and I think to see it go from 9V to 14V in a matter of seconds, as measured on the poles, is an indication that the battery is poor. Yes I know others often give 14.5V as the upper limit. Lithium batteries may die almost immediately if exposed to voltages above 14.6V. The lower limit for a normal charge system is around 13V.
IMO & IME voltages above 14V will, on the long term, cause too high charge currents in the battery and slowly destroy it; the regulator should limit the voltage & hence the charge current. Also it will cause incandescent bulbs to blow.

The plastic molten on your fuse might be caused by poor contact, giving resistivity at that contact which may, on the longer term, heat the fuse up. Poor contact causes resistivity and drop of voltage, when a current flows through it. See https://en.wikipedia.org/wiki/Ohm%27s_law on resistivity and on electrical power I²R see https://en.wikipedia.org/wiki/Power_(physics) or https://en.wikipedia.org/wiki/Watt.

[WaiNYC]

Thanks all for the guidance and particularly to @Puffs for the detail explanation.

In the video, I had connected the battery to the MZ via a 8 gauge jumping cable. This is the battery for my Airhead and is of a difference size. And the voltmeter was hooked up at the bike end of the jumping cable, not the battery end. I am not sure if this helps so explain the jump for 9V to 14V during starting.

In any case... Yesterday, I try to check all the relays and the coil that @David mentioned. Everything I found was clean and lugs well connected.

Then I took out the spark plugs for inspection. it was quite clean, and the gap was good, though some oil on the threads:

So I wipe off the oil, and reinstalled the spark plug.

I thought what the heck, I'll try starting the bike. And guess what, it fired up and got started. Unlike in previous trials, when it might start but would die in secs, this time the engine just kept going as if normal. And I just took a test ride for a few minutes and it felt ok (more on this in the next msg).

Could that be it???

For the entire time, I'd thought that it was an electrical problem (recall that I'd installed a 5 Amp horn) that had somehow affected the ignition system. All indicators of the problem seemed to have pointed to a electrical issue, or so I'd thought: Engine losing power and eventually dying ; inability to turn the engine ; the sound of the engine being cranked over was that of a weak battery (or weak electricity transmission) ; a good battery was able to start the bike, but a less good one could not ; the engine would fizzle out and die after starting...

Could it actually be a spark plug / combustion issue ? I am glad I got the bike started (I still need to give it a good 10 mile run to be sure), but I don't understand it.

Any thoughts to help me understand this mystery?

Ps. I did not touch the carb.

[WaiNYC]

And I just took a test ride for a few minutes and it felt ok (more on this in the next msg).

As said, the MZ starts now and I just took it out for a 2 minute test ride. But it sounds differently: it sounds as if there's something rattling inside the engine block, a distinctive tic tic tic that goes with every explosion cycle.

https://photos.app.goo.gl/1owevGp3jTenWzun7

I'd checked for lose fixtures, and I am quite sure that's not it.

In fact if you compare the engine sound of this video, vs the one in the first post of this thread, I think you can tell that there's a difference in the engine noise.

Am I being overly sensitive? Or somehow something has changed or, even got damaged ??? This is quite mysterious

[breakwellmz]

Sounds like tappets to me, have you done the valve clearances?

[Puffs]

I see, you hooked up another battery via jump cables and then measured on the bike end of the jump cables. Yes, that explains the quickly varying voltage very well: it is due to losses over that jump start cable and it's connections.

When checking all the connections (and finding everything fine), you probably touched & moved some connection, thereby fixing an issue? The bike has done less than 5k miles, so it has been standing for a while. That mileage makes it very desirable...

Oil on the threads of the plug is not the cause. I often put some copper slip there, on these small plugs.

Good it now keeps running, but we may never be certain of the cause. One possibility is that the valves were too tight, particularly the exhaust. And then when it ran for a few seconds, that exhaust valve heated up (as they do), hence the stem expanded and the valve stopped closing properly. Then you loose compression and the thing stalls. (And if you were continue to ride it you might burn the valves and/or seats.) I suggested 'valves too tight' earlier because of the total absence of any valve noise in your earlier video. It is common to hear a bit of valve noise in a big single.

I suspect the bike has not been used for many years, 4.7k miles in 24 years is not what you would call 'intense use'. I don't know, maybe something was stuck? I think too that it's the valves you hear in your 2nd video. So whatever it was, it has now become unstuck.

Check the valves, do a full service. Then ride & enjoy the bike.