1200 sport blowing starter fuse despite wiring mod

After my 1200 sport suffered from starter fuses blowing I did the well known mod of providing a direct fused supply to the starter relay. This appeared to be successful for the last 18 months but now the 20 amp starter fuse is blowing sometimes when starting from cold. I’ve stripped and lubed the starter solenoid, greased the pinion gear on the end of the starter and changed the starter relay, but the fuse still blows sometimes. So far putting a new 20 amp fuse in has proved successful. It even started fine when I had ran out of the correct rated fuse and I used a 15 amp one instead !
Has anyone any suggestions what I should try next?

Don’t know but I got through 3 fuses on mine today. It doesn’t like being re-started soon after being stopped. Initially I thought it did not like being hot started, but it did it cold as well. Was a hot day today so don’t know if that has a bearing?

It was a 15 amp fuse that went. Now has a 20 amp in it as that is all I had left on the bike.

Don’t know about the mod but I am sure there is something about it around here somewhere.
Where,s the best place to get the fuses? Tried Unipart so far but they don’t do them

Hmm - no problems like this in theist 7 years with mine?

Brian Le C was always good for the magic lecy stuff, you can get him on guzziriders.org

Make sure the starter is bolted on tight to the engine.Check both battery connections are good.Never a bad thing to run an earth lead from one of the starter bolts to battery negative.20a seems high to me btw.

Thanks. Will do some checks.

Managed to get fuses from a small automotive distributer in Avonmouth called Poolec. £5 ish for 20 fuses. Fowlers list at £1.97 each, and don’t have them in stock

Thanks for the suggestions, I’ll double check all electrical connections. My guess is that its caused by something electrical because its an intermittent problem rather than a mechanical cause at the solenoid or starter. I’ve noticed that I stated the wrong fuse ratings in the original post. It’s 15A fuses(blue) that are blowing but it has started OK with 10 amp fuses substituted! I purchased a pack of cheap 15A spare fuses (from Ebay )that I now carry with me on the bike. I may get some more expensive fuses in the hope they may perhaps be more durable.

This has come up before hasn’t it but can’t remember the details. Was it siezing up pivot for the pinion lever? This would put power on the solenoid engagement winding for too long and as its resistance is negligible it would certainly blow a fuse. What normally prevents that happening is the reactive impedance of the winding, and the solenoid is supposed to close quicker than this impedance can fall to zero.

The vagaries of this behaviour would also explain why it blows a fuse only at random times.

Hope that makes sense.


Thanks for suggestion. But today I dismantled the starter solenoid again, cleaned, re-oiled, checked free movement of pivot/lever and starter pinion gear. Dismantled and cleaned all electric connections on relay, solenoid, starter, battery and re-assembled. I squeezed male spade connector on solenoid supply a little tighter as it felt slightly loose. Checked for resistance on supply lead from relay to solenoid -appeared okay.
Tried to start bike - I did not hear engine turn and 15A fuse blew. Removed blown fuse, substituted another 15A fuse, pressed starter again and engine fired immediately !
Took the bike for a run, stopping twice, engine re-started fine both times. Although, the problem is intermittent, its only happened when starting from cold. I’m running out of ideas and I’m tempted to try a stronger 20A fuse.

Have you checked the battery if voltage is low amperage will increase once run for a while battery voltage should be higher, Battery’s on CARC bikes are prone to early failure Just a thought
Regards Keith

Yes, it’s all coming back, I remember doing this in a computer simulation, if battery Voltage drops too low when trying to start, there’s a point where there’s not enough Voltage to work the solenoid BUT (perversely) loads of current can go through, enough to blow the fuse.

This could equally be a bit of resistance in a connection somewhere.

Are battery terminal connector absolutely clean and good and tight, also battery earth points. On mine I put the battery earth strap onto the back of the gearbox, not to frame. Just by the way. Original frame connection point was nasty and rusty.


I was thinking that this morning as I tried to start the bike. First go it would not turn over, but the solenoid did click, and seemed to click back when I turned the ignition off. Tried again and it did the same. Third time it started fine. I have still got the 20 A fuse in there so it did not blow this time. I was warned about the battery on these and advised to keep them on an optimate all the time. Strange thing is I have been using it quite a bit, whereas after I bought the bike it was not touched for 5 weeks and still started first press.

I am going to check the starter motor mountings as Ian suggested, and then put it on an optimate to see if that helps (I did buy one but have not got round to connecting it yet). Will revert to 15 A fuse and see how I get on. It definitely felt like a weak battery to me this morning, hope I don’t have to buy another one. Weak batteries cause all sorts of crap problems though.

Still do the connection checks though. I once found a battery cable eyelet was loose!

Yep. Once had this problem on my Le Mans. Was having problems starting and then noticed a whisp of smoke from under the seat. Checked the connection which was very loose. Amazing how much better it started with a tight connection!

I will check battery voltage but the batteries not old, connections are very clean/tight and it was connected up to an optimate just before blowing the fuse.

I know that you’ve had the starter out a few times, but problems with my B1100 were caused by a loose and ill-fitting connector on the starter solenoid. I also found the earth to the engine was loose, early on.

The small positive supply connector to the starter did seem a bit loose and I tried to squeeze the spade connector together to make it tighter- I’d describe it as reasonably firm to connect but it can still be rocked a little side to side when in place. The earth connections to gearbox and starter solenoid, battery are tight and clean.
One thing I find slightly puzzling but can probably be explained those that fully understand ‘electrickery’ is why the negative supply to the starter solenoid is a heavy gauge wire and the positive supply is relatively small and weedy in comparison. Would the bike benefit from running a heavier gauge positive supply wire between the relay and solenoid?

The solenoid is a switch which only needs a small current to trigger it. When it trips, it allows the full current to flow from the battery to the starter through that big bastard red wire and out through the big bastard black wire.

Mackers2014-07-23 03:40:25

The solenoid actually has two windings in parallel, of both thick and thin wires.

The thick wire is the energising winding.

The thin wire is the holding winding.

The energising winding takes the max. power that’s needed to pull the solenoid pole piece. When complete, and pinion is engaged, the other end of the core closes a high power switch connecting battery across the actual motor. Note this same switch also shorts out the energising winding, whose negative end is earthed through the motor, leaving just the holding winding.

The holding winding is much lower power (hence thinner wire) which is all that’s required to hold the pole piece in the closed position.

The energising winding has a DC resistance of about 0.1 Ohms (I measured mine, Bosch starter). Making a wild guess that its inductance is say in the region of 1 - 2 Henries, not a lot, its impedance will drop to the DC resistance value within say half a second. If that happens it will definitely blow a fuse because 0.1 Ohms is practically a dead short. (Without a fuse, wiring will catch fire.) Ergo solenoid must close in less than this time and it’s probably normally a couple of tenths of a second.


PS: the negative end of the holding winding is most likely connected internally to the solenoid casing so is not obvious. The negative end of the energising winding connects to the lower of the two threaded studs (motor side).