2006 FJR only start when jumped

I had this same problem and it turned out to be a defective rectifier/regulator.

Want to know just about everything about your moto charging system/battery?
Buy this little gem of a product and connect it to your cell phone via Bluetooth. It is far better and faster for diagnosing electrical problems than virtually any but the most experienced mechanic. It will pay for itself the first time you use it.

It is small enough to fit in your jacket pocket when not in use. . When connected, you can check your battery charge from about half a block away. It will do voltage, cranking voltage, and charge tests.

https://antigravitybatteries.com/products/accessories/battery/chargers/bluetooth-tracker-lead-acid/

RossKean said:

I suspect that if you had a meter on that battery when it clicked, the voltage would have dropped way down. Sometimes, a battery cell will show "full" voltage when there is no demand but falls flat on its face when you try to draw any current - effectively "open". The only way to tell for sure is a proper load test after fully charging the battery. I would never assume that a new battery is OK but, as you say, further diagnostics are needed - including connections.

Note: The boost wouldn't really help much if the relay was bad...

Click to expand...

My thoughts too

I have seen multiple times and multiple vehicles. Voltage looks good but battery was still bad. Once under load from starting voltage dropped excessively. A proper load test should have revealed this condition. I’d also suggest putting an amp meter on while cranking it as others mentioned the faulty component may be down steam - started , starter relay etc.

I’ll look in the service manual to see if they provide an actual spec for current draw.

VAcracker said:

I’ll look in the service manual to see if they provide an actual spec for current draw.

Click to expand...

I don't think you will find a spec for starting current draw but should be less than 100 amps or so. If you want to measure it, you will need a clamp on DC ammeter - far too high a current for a conventional series-connected ammeter.

RossKean said:

I don't think you will find a spec for starting current draw but should be less than 100 amps or so. If you want to measure it, you will need a clamp on DC ammeter - far too high a current for a conventional series-connected ammeter.

Click to expand...

I did not find a current draw.

I suppose technically a severe voltage drop during a start would also indicate high current draw so I suppose my old school training is just out dated by todays standards. Would still be nice to know if 20-25A = good and or +30A = bad. That’s just random numbers I invented as an example.

VAcracker said:

I did not find a current draw.

I suppose technically a severe voltage drop during a start would also indicate high current draw so I suppose my old school training is just out dated by todays standards. Would still be nice to know if 20-25A = good and or +30A = bad. That’s just random numbers I invented as an example.

Click to expand...

A bad starter will draw 100 amps or more. Voltage drop on cranking MIGHT indicate a bad starter but more likely a bad battery.

The battery on my FJR would only start if jumped as well. Went to O'reilly for a new one, but the only ones they had were too wide. Batteries Plus had the one I needed. When I bought it, they asked me to come back since they had to fill it with acid and fast charge it, so it was brand spanking new.

damcis said:

The battery on my FJR would only start if jumped as well. Went to O'reilly for a new one, but the only ones they had were too wide. Batteries Plus had the one I needed. When I bought it, they asked me to come back since they had to fill it with acid and fast charge it, so it was brand spanking new.

Click to expand...

I like to add the acid myself, give the acid a good long time to fully soak into the mat and then do a SLOW charge (1 amp rate). Slower charge is better for the battery.

Starter load should be 65 to 85 amps in the bike. On a bench, probably 30 to 35 amps.

I had a bad starter that pegged my ammeter's 160-amp scale. Bike would start with a jump but not from the bike's battery, especially when warm. Stone cold, it would start OK most of the time.

I haven't seen anyone post that this was solved, so my 2-cents worth. Loose or corroded contacts at the battery connectors. When jumped, the wires from the other battery have good contact with the bike's wires, resulting in an easy start. Bad battery in the first place, no cranking capacity so voltage drops severely under load; same thing, jumping bypasses the issue. The bike will start with much smaller jump wires than should be used, as they'll carry the extra current needed for the few seconds needed, without bursting into flames. I've jumped mine through the battery tender leads.