'81 KZ 750 - HEADLIGHT replacement to save the bike from dying

Hi guys -

I'm no mechanic, but it seems by 81' kz750 keeps dying because the headlight is always on, and is a huge power draw. I imagine you've experienced the same.

Looking at my options, and wanted to ask you guys for input. Can I just change the bulb to an LED and be done with it? Do I need some adaptor/something else to be able to do that simple change?

Or should I try to buy a whole new headlight assembly thing? I've seen some posts related, but was hoping we could get some fresh eyes/clear answers regarding the issue above.

Thanks so much guys!

How did you come to that conclusion? If it's the original headlight for the bike I don't see how it would draw too much unless there is a different issue. Nothing against changing to LED's or anything, but it sounds like a band-aid for a different issue. I think after 74 all headlights on motorcycles are required to be on when the motorcycle is running.

M_a_t_t wrote: ............... I think after 74 all headlights on motorcycles are required to be on when the motorcycle is running.

Not so. I believe that requirement started in 1978. My 1977 KZ650 came with an ON/OFF headlight switch. Ed

The stock H4 headlight shouldn't be a problem. The battery may need replacing or the charging system isn't keeping the battery charged. There could be a drain on the battery when the engine is off.

650ed wrote:

M_a_t_t wrote: ............... I think after 74 all headlights on motorcycles are required to be on when the motorcycle is running.

Not so. I believe that requirement started in 1978. My 1977 KZ650 came with an ON/OFF headlight switch. Ed

My old '82 KZ750-LTD did not have a headlight on/off switch. It was always on. It has the same right hand side control part number as t he '81 model. So I don't think he can turn it off.

In California, a law was passed in 1978 that motorcycles must be equipped with at least 1 and not more than 2 head-lamps that turn on automatically when the engine is started and remain lighted while the engine is running. What this means is that it is illegal in California for the lights to be able to be turned off if the motorcycle is from 1978 or later. I would suggest this is why your '77 and his and my early '80s KZ750s don't have that ability.

While yes it's California, and California isn't everywhere, it's cheaper to to just make them all the same way, especially given that most states at the time (if not all) already required the light to be turned on at all times, even in the day time.

That said, I'm riding around on a bike from 10 years later that has the ability to switch off the headlights... but it's also a bike that was made exclusively for police... and the headlight being on all the time would make running a speed trap a bit harder.

All of that said... an '81 KZ750 should have more than enough juice to spare to run any H4 bulb, seeing as how just being stock it has a 60+ watt halogen H4 bulb. Seriously, if removing the headlight bulb makes the bike run and putting it in makes it not run, you have something seriously wrong with the electrical system on the bike and buying an LED is like putting a bandaid on a hemophiliac with a severed artery. You're running on time bomb regardless of what bulb you use. Be smart and figure out where the problem in your electrical system is.

At that age, I wouldn't be surprised if it's a voltage regulator issue. Doubly so if you put a lithium ion battery in it... I did that to my KZ1000P and now I'm having electrical issues a couple months later due to the voltage regulator burning out...

Setton wrote:

650ed wrote:

M_a_t_t wrote: ............... I think after 74 all headlights on motorcycles are required to be on when the motorcycle is running.

Not so. I believe that requirement started in 1978. My 1977 KZ650 came with an ON/OFF headlight switch. Ed

My old '82 KZ750-LTD did not have a headlight on/off switch. It was always on. It has the same right hand side control part number as t he '81 model. So I don't think he can turn it off.

All of that said... an '81 KZ750 should have more than enough juice to spare to run any H4 bulb, seeing as how just being stock it has a 60+ watt halogen H4 bulb. Seriously, if removing the headlight bulb makes the bike run and putting it in makes it not run, you have something seriously wrong with the electrical system on the bike and buying an LED is like putting a bandaid on a hemophiliac with a severed artery. You're running on time bomb regardless of what bulb you use. Be smart and figure out where the problem in your electrical system is.

At that age, I wouldn't be surprised if it's a voltage regulator issue. Doubly so if you put a lithium ion battery in it... I did that to my KZ1000P and now I'm having electrical issues a couple months later due to the voltage regulator burning out...

That was my point. It is designed to run with the light on all the time.

Hey guys!

Thank you for all of your thoughts/opinions. My Uncle is a Harley mechanic by trade for over 20 years (started with Japanese Bikes in the 80's), and he was the one that suggested it was an issue due to simply the un-optimized design.

The bikes' starter clutch went out, and we rebuild it from the ground up with new gaskets, and new dynatech, as well as a number of other components. Everything seemed fine, until it just started to drain the bike way to much. We've checked the battery, and regulator. Both seem g2g.....

After thinking it through Uncle was stumped, and just knew with these bikes that yes, due to the law, and the efficiencies of building all bikes the same...THIS BIKE WAS KNOWN to have issues at idle and he suggested considering a headlight that didn't pull as much, and if I didn't fix it it was just something one had to live to deal with.

I'm hearing that you guys disagree, and thats fine....but now I've opposing viewpoints on what the problem is, and am now.....well still up shits creek!

Thank you all though

What tests did you perform on the battery? Simply checking the voltage doesn't tell you a ton; it's much better to check it after letting it sit for 6 or more hours (a day would be best). That way you know the issue isn't a parasitic drain and that it's not temporarily hanging onto the charge that it had when you took it off the charger.

A lot of classic japanese bikes don't really charge the battery up at idle, but there shouldn't be any drain. If you're seeing some, then there's some kind of fault somewhere. Have you checked your stator windings?

Rather than trying to change headlights or do other guesswork why don't you simply test the various charging system components to ensure that they are all working properly? These tests are described in the Kawasaki Service Manual. Believe me, the bike's charging system worked fine when the bike was new or the first owner would have taken it back to the dealer while it was under warranty. So if the battery is not staying charged while the engine is running there is a problem that can be corrected. Ed

Put a DC Volt meter across the battery with the engine running then rev up the engine to 5000 rpm. You should see a minimum of 14 volts otherwise your charging system is botched. This test requires a good battery that properly charged. Ideal voltage is 14.5 VDC. That's what I get on my 750 after replacing the stator and R/R anyway.

Oh, and my 1981 KZ750E idles perfectly with the headlamp on.

The energy drawing of the headlamp is not a problem. I'll be cynical; a stock headlamp on hi beam, is 60 watts. That robs the engine of exactly 0.00804 HP for legal and safety issues during the day..

hugo wrote: The energy drawing of the headlamp is not a problem. I'll be cynical; a stock headlamp on hi beam, is 60 watts. That robs the engine of exactly 0.00804 HP for legal and safety issues during the day..

If the power demands of the bike are greater than what the alternator can provide....it's a problem.

Have you added anything that increased the power draw? Phone charger? Heated grips? Anything that might increase the demand? That may be the reason your battery isn't charging at idle. As for the headlight...yes you can switch to an LED. Many people have done it. I don't know if it's as simple as switching the bulb though...you should do some research.