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ANSWERED Starter Mystery

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This morning when I went to start my red-framed beauty I was greeted by a snap upon pressing the start button.

 

The 15A fuse had blown. After replacing the fuse, I tried again and observed. Starter relay clicked, but no starter activity. After a few seconds of depressing the starter button the fuse blew again.

 

Replace the fuse again. Remove the spade terminal from solenoid. Start. No fuse blown this time. Seemed to me that I have a starter problem. A multimeter did show 12V at the solenoid as well as a voltage drop while the start button was depressed.

 

Not wanting to admit defeat quite yet, I removed and cleaned all connections at the starter and battery. I scrapped off oxidation on terminal ends, retightened connections, and vasolined them up. This time the bike roared to life triumphantly.

 

Sounds like a happy story, but I'm unsure. Given my limited electrical knowledge, this doesn't make sense to me. Shouldn't a loose or high-resistance connection have caused a drop in current instead of a rise that blows the 15A fuse? Did I get lucky and the starter decide to work again (i.e., it is on borrowed time?). Am I simply misunderstanding the mechanics of the solenoid action, and a bad connection does make sense as the culprit?

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When voltage decreases amperage increases. Right?

Does it? I'm thinking of Ohm's law V=IR, so if resistance is higher shouldn't current be lower?

 

Perhaps Ohm's law is not relevant to the situation... it has been some years since my last physics course.

 

 

I'd say job well done!

Thanks! At any rate I am glad to not have to buy another replacement starter.

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When you get the "clack", but no rotation, if you hold the starter button, it will eventually blow the 15A fuse.  The solenoid draws a high initial current until the starter is rotating.  Kiwi Roy may have a better expl. on this one.  But I've seen it on my V11.  Just try not to hold the button more than 1 second when attempting a start when you get no initial cranking.  Wif, when this happens to me, I will repeatedly hit the button, until it does crank. 

 

And I'm not sure if this is the same thing as "Startus-interrupus".  Maybe Mr. Roy can answer that question, too.

 

Note that there is also the CLACK where the starter will never rotate.  This is where the field magnets become un-glued on the stator, and crash into the armature.  Not a lovely sight, when you open up the starter to investigate.

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The real starter circuit is nothing like it shows in the manual, there are two coils in the solenoid

One lets call it the Holding Coil that measures 1.05 Ohms between the spade terminal and chassis. Apply Ohms law to that, 12Volts / 1.05Ohms = 11.4Amps

But there's another coil I call the Pull In coil measuring just 0.25 Ohms wired between the spade terminal and the starter motor if you apply Ohms law to that 12Volts / 0.25ohms = 48Amps (the motor itself is close to zero)

 

The instant you press the start button the start relay applies 12 Volts to the spade terminal and you get a combined current of 45 - 50 Amps (this is providing the wiring is up to snuff)

Less than 0.1 seconds later the solenoid pulls in closing the main contacts and putting the same Voltage on both ends of the 0.25 Ohm coil so it's current drops to zero and just the Holding Coil is holding the solenoid in place at ~ 11 Amps. At the same instant 150 - 170 Amps charges through the starter motor spinning it up to speed.

 

If the main battery cable is not making good contact when the solenoid contact closes there is no Voltage to pull the Pull In coil to 12 Volts so it continues to try and spin the starter through the 15 Amp fuse and Start Relay

 

I did a test on mine, I left the main wire loose to simulate a bad connection, sure enough the fuse popped in les than a second. This is what happened to yours.
Scrape the terminals and smear on a little Vaseline and it won't happen again.

 

BTW, you may have heard the term Startus Interuptus , this is an affliction Luigi passed on to almost every Guzzi by wiring the Start relay through the ignition switch. The cure is to bypass the switch.


 

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^^^^ what KR says, of course.. but if the starter solenoid fails and hangs up, it'll blow the fuse too. Mark at MGClassics had a box of failed starters from warranty replacements when the Mighty Scura's acted up. They were either loose magnets or failed soleniods. I took one apart that had loose magnets and replaced my solenoid. It's been fine ever since. 

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When you take your finger off start button the current runs backwards through the Pull In coil and the Holding coil in series. there should be no current through the fuse in this case because the relay is open.

The 2 coils are supposed to cancel each other out letting the solenoid go (contact open) but I have seen one brand new solenoid on a Bosch starter hang up every time causing the starter to run until the battery could be disconnected.

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So THAT'S why it's fixed. :luigi:

 

Very interesting stuff. Thanks so much for the elucidating replies. 

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I have the same problem on my 2002 LeMans. So Roy the problem is not in the start. You say it is in the wiring. I have replaced the starter ones and no more problems for two years now the problem is back. So I will look into the wiring. This happens mainly when the bike is hot.

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I have the same problem on my 2002 LeMans. So Roy the problem is not in the start. You say it is in the wiring. I have replaced the starter ones and no more problems for two years now the problem is back. So I will look into the wiring. This happens mainly when the bike is hot.

2002 begins the wiring that lets the Position#1 Relay be Livin' Easy :rasta: , but taxes the Ignition Switch :wacko: ?

 

Once you've cleaned and serviced all of the starter  and battery connections, the Ignition Switch might benefit from service.

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As Docc says try cleaning the ignition switch, just remove the two Phillips screws from below to release the switch block

Remove the back and tilt out the white plate, wipe all the old grease from the contacts and replace it with fresh Vaseline.

When you put the switch back together try to fasten the cable to the back cover so the wires are unable to twist inside or they will break off.


To test just the starter run a temporary wire from the spade connector on the solenoid and touch it on battery Positive

Make sure the bike is in Neutral and hold the clutch in for good measure or you will launch it.

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Kiwi_Roy has also taught us to inspect the soldered connections inside the Ignition Switch for breakage. :thumbsup::luigi:

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I have the same problem with my 02 Scura.  Tried to commute to work this morning and no start.  At first the starter was working but then eventually even the starter stopped making any noise.  Then eventually I held the start button for more than 4 seconds and the 15A fuse blew.  So the fix is to disconnect the battery and clean the terminals and also disconnect the starter and clean those terminals?  Will give it a shot.

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Plexi - do you have original relays or have you upgraded to the Omrons or similar? My LeMans had some weak starts and occasionally had to hold the button in for a bit before the starter engaged. New relays - and ensuring snug fit in the relay bases - has cured the problem.

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Plexi - do you have original relays or have you upgraded to the Omrons or similar? My LeMans had some weak starts and occasionally had to hold the button in for a bit before the starter engaged. New relays - and ensuring snug fit in the relay bases - has cured the problem.

Will check and replace if they are original. The first time I had this problem the fuse blew before anything else so after replacing the fuse everything was fine but now it is happening again so seems like a bigger problem.  Will check relays and clean the connections and add vaseline.  Thanks.

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