What causes the occasional Chuff sound?

[beemer]

I get this sometimes when starting the bike,also,does anyone know the value/type of diodes fitted on the diode board,and how many of them are there,i might consider changing them,thanks,Julian.

[Bob_Roller]

I wondered about that for a while, it's really a troubleshooting item for the ignition system .

When you turn the key to the on position, the ignition system gets energized, and the spark plugs fire, if you have a valve open, and there is enough fuel/air mixture in the cylinder to ignite, you get that 'chuffing' sound .

"They all do that' !!!!!!

[Justin B.]

Bob, I've read that other places as well but for the life of me I have never heard this!  Go figure...

[beemer]

Well that's good to know they all do that!thanks,i did think it was something like Bob explained,but wasn't 100% sure,now i know,i'm chuffed!!!

[MrRiden]

I have had that too and it took me a little by surprise. I've even heard of this starting the engine in some vertical twins but suspect it was more bragging about the fine state of tune by owners than truth.

[Bob_Roller]

As far as the diodes go, I don't think I would bother replacing individual diodes, there is a heavy duty aftermarket diode board available, goes by the name 'Thunderchild', average price in the US is around $75US .

http://www.thunderchild-design.com/

They have automotive size components, and a heavy duty finned aluminum heat-sink as well .

Motorrad Elektrik has an upgrade heavy duty 'Omega' diode board on their website as well, for about $90US .

http://www.motoelekt.com/newomega.htm

[beemer]

As far as the diodes go, I don't think I would bother replacing individual diodes, there is a heavy duty aftermarket diode board available, goes by the name 'Thunderchild', average price in the US is around $75US .

http://www.thunderchild-design.com/

They have automotive size components, and a heavy duty finned aluminum heat-sink as well .

Motorrad Elektrik has an upgrade heavy duty 'Omega' diode board on their website as well, for about $90US .

http://www.motoelekt.com/newomega.htm

Thanks for that,very interesting,mine seems fine at the moment,but you always have these things in mind,just incase!Julian.

[Bob_Roller]

The last time I had a look at my diode board, the area around the diodes was charred black  for about .5 inches (12mm), so I know it's not long for this world, especially for the fact that I run two PIAA 40 55w driving lights as well, so I'm running the charging system probably close to it's output limit .

[drewboid]

Rob - when the diode board does give up the ghost look into the Enduralast 400W alternator system. No diode board, lots more watts at a much lower RPM. I too run running lights and a heated vest if it is cold enough. Just a satisfied user.

[Bob_Roller]

I've checked out the Omega charging system from Motorrad Elektrik, it's been upgraded to 450 watts, and the same troubleshooting procedures from the stock Bosch system apply to it as well .

But it is about $75US more than the Enduralast system .

[Ed Miller]

I like the simplicity of the Enduralast system, but I'm paranoid that, unless you're always using most of that amperage output, that system will eat up the voltage regulator units like crazy.  I think the Bosch system is crazy complicated, but at least it's not producing current unless you need it.  So far I haven't heard much bad news about the Enduralast though.

[Bob_Roller]

The only thing that I have seen in print, was on Snowbums website, he did a comparison of the Enduralast and Omega systems, the maximum output that he achieved on the Enduralast system, was 339 watts, not much more than the stock system, kinda not worth spending close to $500 for that, the 400 watt Omega system tested at 415 watts at maximum output, the latest Omega system is rated at 450 watts .

[montmil]

I wondered about that for a while, it's really a troubleshooting item for the ignition system .

When you turn the key to the on position, the ignition system gets energized, and the spark plugs fire, if you have a valve open, and there is enough fuel/air mixture in the cylinder to ignite, you get that 'chuffing' sound .

"They all do that' !!!!!!

Since no one else has mentioned it, I thought I'd share a little Beemer minutae. You can often get the bike to "chuff" on command. Yes, you can! Place the right-hand kill switch in the Off position. Then, with the ignition switch turned On, toggle the kill switch to the Run position. You'll likely hear one cylinder go "chuff."

Here's the interesting part. Should you be experiencing a loss of spark ignition problem, this technique is also a diagnostic tool! If you can get a chuff sound, it means the ICU is functional. Probable no-spark cause is likely the Hall sensor in the bean can.

About a year ago, this little trick helped me to pinpoint the 81's loss of spark.

Monte

[Ed Miller]

Thanks, Monty.  Now if I could just remember that stuff when I'm panicking at the gas station on my way to work.  

Bob, even 339 watts would leave over two hundred watts for the voltage regulator to bleed off (as heat?) most of the time, for me.  I just don't know how long they hold up to that.  The v.r. on my Triumph is, to say the least, understressed.  

[Bob_Roller]

Ed,  

It's stated in the installation instructions for the Enduralast, that the voltage regulator/rectifier, must be placed in the airflow, or overheating will occur .

When I do need to replace the charging system on the '81, it's going to be the Omega 450 watt system .

Monte,

I found out about the ignition system firing when you turn the key on, by accident .

I have gotten into the habit of removing the spark plug leads from the plugs after I change the oil, and I spin the engine with the starter until the low oil pressure light goes out .

The first time I did it, I was holding one plug onto the cylinder fins, as I turned the key to the 'ON' position, and I got 'bit' real good from the ignition system .