R75/5 blowing fuses when starting

[r67boxer]

I recently brought my '71 R75/5 out of storage. Against my better judgment I fitted it with an older battery which resulted in the engine turning over rather slowly. Today, when I tried to start the bike today, it turned over slowly and then stopped. All three indicator were off. Upon examination I determined that I blew a fuse. Once I replaced the fuse (15A) it started. Later in the day I tried to start it again but managed to blow 4 fuses. It seems that if the engine doesn't catch immediately, it blows a fuse. Is the problem the starter drawing too much on the battery or is the battery at fault, or both?

Kevin

[Rob Frankham]

Well, it's unlikely to be the starter itself because current to the starter doesn't go through the fuse, although it could be the starter solenoid.

It's unlikely to be the battery because the battery only supplies the current demanded by the loads connected to it.

So, what is it? more information required.

What actually happens when you try to start the bike... does the fuse blow immediately? Does the engine turn over slowly before the fuse blows? Does the engine appear to turn over normally before the fuse blows? Are there any other anomalies with the electrical system? Any 'upgrades' such as electronic ignition & etc...?

This is going to be caused by one of two things, either there is an intermittent short circuit in a wire or component in the starter circuit or a failing component (such as the starter solenoid, or the starter relay, which is drawing too much current.

Rob

[r67boxer]

Thanks Rob. My answers are as follows:

What actually happens when you try to start the bike... does the fuse blow immediately? No.

Does the engine turn over slowly before the fuse blows? Yes. It turns over, usually for a few seconds, before the fuse blows.

Does the engine appear to turn over normally before the fuse blows? No. It seems slower. First it turns over, then seems to stop, then turns over again but almost with a groan if you catch my drift. Not normal for sure. My R50/5, in comparison, turns over quite quickly.

Are there any other anomalies with the electrical system? Any 'upgrades' such as electronic ignition & etc...? No, nothing has changed. Electrical system is OEM.

Kevin

[r67boxer]

As an update I have checked the ground wires (coil and transmission) and cleaned up same with emery cloth. None were overly corroded. I also used emery cloth on the starter solenoid connection and each spade connector on the starter relay. Same issue when I tried to start it.

[SteveD]

Once I replaced the fuse (15A) it started....

Fuse should be 8A???

[Rob Frankham]

Once I replaced the fuse (15A) it started....

Fuse should be 8A???

Yes, checked with the repair manual (/5 1972) both fuses should be 8 amp. Looks like this may be a problem that has been around for some time and a 15 amp fuse was used to try to get over it. Don't recommend going for an even bigger fuse. That way is a road to bigger issues. The issue needs to be located.

Rob

[r67boxer]

I've sourced 10A fuses and will use those for now. This bike was originally without fuses.

So, what else should I check? I'm at a loss.

Kevin

[Kurt in S.A.]

Use a 12v bulb/wire setup to bridge the contacts for the fuse. If the bulb lights up, then you have a problem. Pull parts of the wiring harness until the the bulb goes out. When that does, you will have started the process to isolate the problem area.

Kurt

[gspd]

First it turns over, then seems to stop, then turns over again but almost with a groan if you catch my drift.

Sounds similar to what happens when the timing is way too advanced.
(but that should not blow a fuse)

How well does it crank over if you disconnect the ignition coil?
Have you checked the timing?
The static timing can be checked with a test light while turning the engine manually.

How well does it crank over with the spark plugs removed?
If the fuse blows with the plugs out (no compression) you have a bad solenoid.

Another suggestion that might help narrow down the problem...
Power the starter solenoid activating terminal directly from the battery with a 8a fused wire, thus by-passing the complete harness and all relays and switches. If the fuse on the jumper blows you have a faulty solenoid.

[r67boxer]

Thanks. Timing was correct and it failed to blow a fuse when the harness was bypassed and when plugs were removed. So, I decided to go back to a poor or bad ground. My good friend and fellow Canadian biker Brett suggested that I replace the ground from the battery to the transmission. After much searching I found one and installed same. Voila, it started without blowing a fuse. Coastal corrosion was likely the culprit. Thanks to all.

Kevin