Interesting: Starter button "boost"

[frankenduck]

Was looking at some of Don Eilenberger's dyno runs over at IBMWR:

1 - The run plotted in red (#21) was a base run. No changes or modifications to the engine/bike.

2 - The run plotted in green (#22)was done with the starter button held in. Holding the starter button in on an L-Jetronic bike results in enriching the mixture by approximately 10% as it activates the start-enrichment circuit. The L-Jetronic brain prevents the starter motor from operating since it knows the engine is already running.

3 - The run plotted in blue (#23) was done with a different L-Jetronic brain in place (Thanks to Brian Curry). The additional power may also have been a result of a full warmup of the engine at this point (the cooling fan was now cycling). This brain remained in place for the remainder of the runs.

[Lawrence]

Lesson being the system is too lean at high rpms?

[frankenduck]

My guess would be that since it's an analog device that they optimized the design for a "normal" RPM range when riding. Maybe fuel economy too?

[BobZ(IL)]

Starter button=passing gear.

[BexarWolf]

So, what we're saying here is it's safe to press the starter button while the engine is running? That doesn't engage the starter, shearing off teeth like it does in a car?

[wmax351]

Some of it is likely for emissions. 14.7:1 is best for emissions, slightly leaner for MPG, and slightly richer for power. I am tuning my bike to run at about 13:1 for WOT, and it provides significantly more power at mid to high rpm and high load.

[WayneDW]

So, what we're saying here is it's safe to press the starter button while the engine is running? That doesn't engage the starter, shearing off teeth like it does in a car?

No, don't do that, only partially depress the starter switch and it'll squirt some more go juice into the works.  (some models?)

[wmax351]

So, what we're saying here is it's safe to press the starter button while the engine is running? That doesn't engage the starter, shearing off teeth like it does in a car?

No, don't do that, only partially depress the starter switch and it'll squirt some more go juice into the works.  (some models?)

For the K bikes, the starter button only tells the ignition controller that the button is pressed. It stops running the starter once it hits 300 rpm or so. From there, it just enriches the mixture.

In any case, most bikes (notably excluding airheads and Guzzi's) use a sprag clutch type starter, which is a one-way drive system. You could hit the starter at redline, and nothing would happen, as it would just freewheel.

In the case of Airheads and Moto-Guzzis, an automotive, bendix type starter is used. The solenoid slams the bendix mechanism, which includes a one way clutch, into the flywheel gear.

[frankenduck]

partially depress the starter switch

The L-Jet knows if the bike is already running and cuts the ground to the 85 terminal of the relay trigger.  The starter button is binary -  it's either making an electrical connection or it isn't.  There's no "partially" about it.

[WayneDW]

Thanks for the clarification.  Obviously I didn't know what I was talking about.  :dunno2:

[frankenduck]

Thanks for the clarification.  Obviously I didn't know what I was talking about.  :dunno2:

I don't either. I just pretend on The Internet.

Feel free to PM me if you need some legal advice. I'm an Internet Ninja lawyer as my second job.

[TimTyler]

It is possible for the starter to run while the engine is running if the starter relay gets stuck, as can happen if you start the bike successfully on a low battery.

This happened to me last year and fortunately I stopped to fuel-up just a mile or so into my journey. I hit the bike's kill switch and turned the key off at the gas station pump and the starter continued to keep the engine running. It really caught me off guard. I had to put the bike in neutral, put it on the center stand, and disconnect the battery terminals to stop the starter.

Tapping the starter relay with a tool was enough to un-stick the connection. I started and stopped the bike a few times successfully in the gas station before driving off onto the highway.

[wmax351]

It is possible for the starter to run while the engine is running if the starter relay gets stuck, as can happen if you start the bike successfully on a low battery.

This happened to me last year and fortunately I stopped to fuel-up just a mile or so into my journey. I hit the bike's kill switch and turned the key off at the gas station pump and the starter continued to keep the engine running. It really caught me off guard. I had to put the bike in neutral, put it on the center stand, and disconnect the battery terminals to stop the starter.

Tapping the starter relay with a tool was enough to un-stick the connection. I started and stopped the bike a few times successfully in the gas station before driving off onto the highway.

And thankfully, the starter motor uses little current when running unloaded. It doesn't heat up much because of that.

[gavthirtyseven]

Interesting data, but other than riding with my thumb on the starter is there another way I can get this benefit all the time? Replace the starter button with a toggle type switch? Any other ideas?

[gavthirtyseven]

Anyone know if the later 16v bikes would get the same "starter boost"? I'm always keen for cheap horsepower so the toggle switch starter may be the way.... :hmm:

[frankenduck]

Anyone know if the later 16v bikes would get the same "starter boost"? I'm always keen for cheap horsepower so the toggle switch starter may be the way.... :hmm:

One way to find out - try it.  As has been pointed out the one-way sprag is not going to catch up with an engine running at RPMS.  It's not like a solenoid on a car that will grind things.

[pallum]

And thankfully, the starter motor uses little current when running unloaded. It doesn't heat up much because of that.

Thankfully is an understatement. When I fused a starter relay 90 miles after leaving a friend's house, I just rode right back. Only inconvenience was the load shed relay being active the whole time disabling headlights and blinkers (possibly brake light too but I never bothered to check). Better than being stranded out in the rain and it did no damage to the battery  :loopy: