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Discussion Starter #1
After installing Mitch's hub (amazing product&workmanship) along with new plugs, an aftermarket air cleaner, and the metal fuel connector conversion I went for a test drive. Night time, edge of town, unlit road.

After the initial test runs and I made about six hard/WOT acceleration runs. Each time the headlight would go dark leaving a me blind to the road (instrument and marker lights were operating). Slowing down and moderate acceleration was no problem. The events occurred in 3rd and 4th from 6k to 8k+ (it's a public road). I'd initially thought I was on high beam but the next tests dispute that.

The next day I removed the headlight, checked the connection to it as well as the sockets connecting to the bulbs. Every thing was tight and bulbs secure. Arriving at my test site, I made six runs on low beam and the headlight failed every time in the same range, ...at or near WOT accelerations in 3rd and 4th gear from 6K to over 8K.
I made the same runs on high beam with no failures.

After reading multiple threads on low beam replacement frequency and failures,...with one stating a support inside that bulb broke, I'm wondering if the problem is worldwide on that particular bulb i.e. it's nots hardened for heavy duty use (no glass tube encapsulating the filament and/or extra isolated supports securing it).

Though I have not done G loading tests on the bulb(s) on a shaker table or in a centrifuge, I suspect high loads are shorting and/or breaking the filaments.

Has anyone found a heavy duty rated bulb that stands up to MV acceleration/use?
 

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Discussion Starter #3
Thank you for the input.

Can you narrow the direction a bit as to exactly which aspect of the reported SPU problems you are referring?
Only several hundred replies on the 50 threads mentioning SPU & headlight, however all those I've read report continuous issues with no respect to speed and they usually site multiple issues/failures except one mentioning blinking/blanking of light with a microtec installed. All of the problems I've read about are occurring in static or quasi static operating conditions.

And at this point I've yet to find one thread denoting failure of only the low beam during hard acceleration with no other issues normally attributed to noted SPU issues. Any specific information that can be provided is greatly appreciated.

A quick look at the schematic shows individual fuses so a buss bar issue in an SPU seems unlikely however I have not disassembled or x-rayed the SPU for fault analysis....yet. And I have not yet subjected an SPU to g-loads in the lab to assess performance under acceleration. All possible if a grant can be secured.

Per several threads on SPU problems, and part numbers, my SPU is of the newer model number so replacing it with the same part seems like an expensive shotgun approach.

Indeed taking a voltage logger along for the ride and monitoring the power lead from the SPU could eliminate that component from the diagnostic regime. This might be a next step followed by G-load testing on the relays.

Since many reports of low beam failure and frequent replacement are being reported, I was hoping this thread might get others to 1) do the same tests I did and report results, 2) look very carefully at blown bulbs, note where the filament or supports are breaking & report back and 3) find a source of hardened bulbs.

Thanks again
 

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Discussion Starter #5
Thanks for sharing the thread info Red.

The connectors/connections, bulbs, & fuses were the first things checked both before and after the designated test session.

If anyone with the 1st series Brutale has the time to do a 6 to 8K WOT acceleration in 3rd and 4th gear at night (or in daylight where someone can see/watch the headlight operation) and has the low beam go out only while accelerating, please let me know.
Thank you
 

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Discussion Starter #6
Thanks for sharing the thread info Red.

The connectors/connections, bulbs, & fuses were the first things checked both before and after the designated test session.

If anyone with the 1st series Brutale has the time to do a 6 to 8K WOT acceleration in 3rd and 4th gear at night (or in daylight where someone can see/watch the headlight operation) and has the low beam go out only while accelerating, please let me know.:popcorn:

Thank you
 

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May Have the Same Issue...

SlowRide,

Did you ever find a cause or solution to your issue?

This has been happening to me as well. I've done the connection check, ground check, fuse check and followed most of the wiring and found no issues. The bulb has been replaced a few times, just in case. It does occur in higher gears as well. The engine speed seems to be the only common factor there.

I did have an ignition coil fail recently. It would have been nice had it just been a symptom of that.

If you're still around, I'd love to hear what you found.

Cheers...
 

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If you guys are talking about Brutales with this failure, then the low beam headlight headlight relay is probably the culprit.

If I knew the year and model of your specific bike, I could give you more specific information.

That relay is probably in your SPU.
 

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I have experienced this intermittently in the past on my 910R and at first was alarmed...but the bike ran perfectly, and the light cam right back on, just a brief flicker off.

And then one night realized my glove was contacting the high beam flash button, and under hard acceleration my grip on the bars tightening would occasionally slightly depress that button...which caused the low beam to go out !!!!

So I quit worrying.
 

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I suppose it could be the SPU, but mine is relatively new and is of the updated variety. My bike is in my profile, but doesn't show; it's a 2004 S model.

Looking at the wiring diagram, it does seem that this is handled by that SPU box.

Cheers...


If you guys are talking about Brutales with this failure, then the low beam headlight headlight relay is probably the culprit.

If I knew the year and model of your specific bike, I could give you more specific information.

That relay is probably in your SPU.
 

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That was one of the first things I thought might be happening since the first few times I encountered it I was wearing winter gloves. However, I have been very attentive to that left hand and I am certain that it is not me that is causing this behavior.

Thank you!

I have experienced this intermittently in the past on my 910R and at first was alarmed...but the bike ran perfectly, and the light cam right back on, just a brief flicker off.

And then one night realized my glove was contacting the high beam flash button, and under hard acceleration my grip on the bars tightening would occasionally slightly depress that button...which caused the low beam to go out !!!!

So I quit worrying.
 

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@quixotic_1: Since the culprit seems to be vibration induced failure at a specific RPM, it might follow that the relays in the SPU don't like that vibration spectrum. It is also possible that the SPU box itself is not mounted well enough to prevent vibration induced effects. I would at least start there.

To put your bike into a visible place on your posts, add it to your signature line.

TOOLS>USER CP>EDIT SIGNATURE>SAVE SIGNATURE
 

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I've experienced it. The SPU was at fault. At high revs, the low beam would cut out. It became very consistent and at lower and lower revs. To test, I put a voltmeter to the socket, revved the engine and the voltage cut out. The low beam relay is part of the SPU. I ended up rewiring the low beam through a relay. The SPU lasted another year until my bike wouldn't even start. After I replaced my SPU, I restored the original low beam wiring and it works like normal.
 

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I am certain that the SPU and its associated wiring are all solidly mounted and connected. I only know this because I have checked, re-checked and then did some work and then checked again.

Given the replies, it looks more and more likely it is the SPU. Fortunately, I have a known good second unit that I can swap in at some point and test. Unfortunately, time does not permit that anytime soon (about to have reconstructive surgery on my rotator cuff, and there are some other priorities: fork re-build, new tires, new chain, etc.). It only happens to me at the high end - never on roads under 50 MPH where I also don't use excessive acceleration - so I can use my high beam while there (no one around here notices motorcycles, anyway, so that helps).

Thank you!

@quixotic_1: Since the culprit seems to be vibration induced failure at a specific RPM, it might follow that the relays in the SPU don't like that vibration spectrum. It is also possible that the SPU box itself is not mounted well enough to prevent vibration induced effects. I would at least start there.

To put your bike into a visible place on your posts, add it to your signature line.

TOOLS>USER CP>EDIT SIGNATURE>SAVE SIGNATURE
 

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Thank you for providing your experience. It does look more and more that the SPU is at fault. Fortunately, this is my second SPU (the updated version) and I have another known good unit to test with. Once I get some time to do it, I'll do the swap and see what happens. (Of course, should the SPU fail before that, well, I guess I'll be testing it even sooner!)

Also, thanks for the tip on the second relay.

Cheers!

I've experienced it. The SPU was at fault. At high revs, the low beam would cut out. It became very consistent and at lower and lower revs. To test, I put a voltmeter to the socket, revved the engine and the voltage cut out. The low beam relay is part of the SPU. I ended up rewiring the low beam through a relay. The SPU lasted another year until my bike wouldn't even start. After I replaced my SPU, I restored the original low beam wiring and it works like normal.
 
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