minimal/race bike wiring

R

regal7point5

Active Member
OK, so after searching some old posts, I am pretty confident I know what wires to give the snips to. Basically all I want is battery to ignition with a switch of some sort in between (and fuse of course). The bike will have a tach, but will likely be the Vapor Trail Tech and (if i understand correctly) will be self powered. I have seen many diagrams and references relating to old bikes with points ignitions. However, I have a 1980 SR250 (yeah, I know, worlds slowest race bike) that has a CDI box.

I will obviously need to retain this, but if I understand the wiring diagram correctly, I can still remove the regulator/rectifier, stator, rotor, etc, right? Or am I totally nuts? What gives the signal to the CDI to fire? Measure twice, cut once...

 
After studying a little more it seems I can get rid of the charging system and everything related (rectifier/regulator), but still need to send crank signal to the CDI. Does part of the generator do that? Still confused on that.
 
If anyone cares, I studied the actual harness/bike against the schematics for a while and figured out what to do. Unfortunately, I can't pull the "flywheel" since it has the magnetic pickup for the CDI on it. I can still take the generator coils out to help cut down on parasitic loss, but must keep the flywheel/rotor.

Basically, for the CDI, ground the black and sky blue wire, orange goes to coil, red/white goes to coil. The white/red and white/green coming go to the magnetic pickup. Wire in a relay and key switch between the coil and we are good to go.
 
regal7point5 said:
Oh, and the bike is down to the frame, or else I would just disconnect the item in question to see if it would still work.
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And call it a day. Really? Sell the bike, you're done. Take the bus.
Yamaha is not my speciality but with Honda's its simple.
Make sure the red or black wire connects to the coil and you're good to go.
 
Bert Jan said:
And call it a day. Really? Sell the bike, you're done. Take the bus.
Yamaha is not my speciality but with Honda's its simple.
Make sure the red or black wire connects to the coil and you're good to go.
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Not sure I understand what you mean about selling the bike, taking the bus, etc...

This is a minimal/"race" bike and will likely never be driven on the road. The bike is CDI so it MUST have a crank signal to fire the coil. Not as simple as red to coil unfortunately. That being said, since I found out I can't remove the "flywheel" since it provides the crank signal, I will likely keep the charging system as well to keep ignition voltages above the battery voltage for a little stronger spark.
 
regal7point5 said:
Not sure I understand what you mean about selling the bike, taking the bus, etc...

This is a minimal/"race" bike and will likely never be driven on the road. The bike is CDI so it MUST have a crank signal to fire the coil. Not as simple as red to coil unfortunately. That being said, since I found out I can't remove the "flywheel" since it provides the crank signal, I will likely keep the charging system as well to keep ignition voltages above the battery voltage for a little stronger spark.
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I mean with my previous post that if you choose to just remove electrical parts of a running bike to the point the bike wont stalls, you're a dumbass.

For example, on a running bike, you can remove the starter motor and it's circuit, the starter button and the kickstarter. When the next thing you remove is the coil, the bike will stall and you will never get it to run again. (yeah yeah bumpstart blabla) - i hope you understand where i'm going for.

If you want to do something, it kinda 'helps' to know what you're doing. Just removing parts is just dumb. You can easily damage vital parts and it will only cost you more. CDI's and such are damn expensive ;)

Get a manual and try to understand wich part does what. If you know that, you can safely remove or de-attach some plugs or remove complete units.

--

Now, on topic. Is it not possible to take some weight of the flywheel by putting it in a lathe? Since pick-up is crucial, is there no way to get rid of some unwanted weight? A lightened flywheel does A LOT for throttle-response. Could you make a picture of the flyhweel in question? that might help..
 
Bert Jan said:
I mean with my previous post that if you choose to just remove electrical parts of a running bike to the point the bike wont stalls, you're a dumbass.

For example, on a running bike, you can remove the starter motor and it's circuit, the starter button and the kickstarter. When the next thing you remove is the coil, the bike will stall and you will never get it to run again. (yeah yeah bumpstart blabla) - i hope you understand where i'm going for.

If you want to do something, it kinda 'helps' to know what you're doing. Just removing parts is just dumb. You can easily damage vital parts and it will only cost you more. CDI's and such are damn expensive ;)

Get a manual and try to understand wich part does what. If you know that, you can safely remove or de-attach some plugs or remove complete units.

--

Now, on topic. Is it not possible to take some weight of the flywheel by putting it in a lathe? Since pick-up is crucial, is there no way to get rid of some unwanted weight? A lightened flywheel does A LOT for throttle-response. Could you make a picture of the flyhweel in question? that might help..
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It looks like a previous post of yours was removed or edited, so that is where I might have been missing out...didn't recheck this post until this afternoon.

I do know enough to be dangerous, never claimed to be an expert, that is why I am seeking a little help. I am not just blindly removing components...or so I think. I understand basically the principle of the CDI. It is a protected, transistorized unit that receives 12V directly from the battery without being stepped down, so I don't think I can fry it. Following the wiring diagram, the service manual, and laying the actual loom out has led me to the conclusion that I can remove everything as long as I can send a crank signal to the CDI.

Lightening the rotor/flywheel has crossed my mind, but the positioning of the pickup will make it difficult to take too much out. I could put some lightening holes in the face of it and rebalance it I suppose. I will snap a picture this evening or tomorrow and post up. Thanks for the direction on this!!
 
Here are some photos of the rotor/flywheel. It has magnets on the inside attached with screws from the outside and am certain those will be quite a bit of weight. Also, you can see the position of the two ignition pickup "strips" that have gone just past the ignition pickup (ATDC), so there won't be much lathe work that could be done. Given the cup shape of the rotor, I would be nervous to scallop it either for fear of expansion at high RPM and contacting the pickup. I will remove the magnets and charging coils and maybe make some lightening holes in the face. Also note the drilled out balance cuts made by the factory.

I am also looking at slotting the mount points for the ignition pickup to allow some timing adjustments. The factory manual does note there is no adjustment in timing, other than to make sure there is sufficient gap between the "strips" on the flywheel and the pickup. Easier than rephrasing the flywheel for sure!





 
As far is i can see no post was removed or edited. Doesn't matter ;)

The flyhweel is to complicated to lighten on the cheap. If the pickup is only for the CDI, you could look into a hall-effect electronic ignition and remove the complete flyhweel. You'll have to be good on a lathe because you'll need to make a new ring to accomodate the sensor and pick-up. If you succeed, you're golden. It will scream :)

Now, if you choose to go this way, i suggest using a strobe light to determine the exact positon the sensor gives signal. That will give you less headaches along the way once the other unit is installed.
 
I have looked into Hall Effect pickups as well...might be promising. The only thing I am unsure of is if the stock flywheel/rotor is zero-balanced or neutrally balanced. If not, I would have to get the entire rotating assembly rebalanced. The only way to tell is yank it and chuck it up in a wheel balancer or similar fixture.
 
I strongly believe the crank was balanced before put in the case. The flywheel is balanced because it's not by itself due to magnets and such. If you remove the flywheel, im confident nothing will be unbalanced.
 
STOP before you actually do permanent harm.

The rotor can be machined to remove a small amount of weight. Search for Banshee rotors and you will see what they do on that motor and use it as a guide.

Do not remove magnets or scallop the rotor.

You still need the CDI charge coil/s as well as the pickup. If you remove the flywheel you can see a whole series of coils on the stator plate. You could work out which are the CDI charge coils and remove the rest but realistically that will save three fifths of five eighths of sweet f.. all. On that wiring diagram it appears to have all the charge coils wound together which suggests that there are no separate CDI charge coils, so that's a bust.

I just did a quick on line search and it looks like that bike has a really old fashioned twin charge coil system.

Don't bother slotting the pickup unless you have a dyno and a really good dyno operator to develop a new ignition map.

Which brings us to the main question and that's why try to race that bike? Is there a class for it? If not maybe it would be better to sell that one and buy something more suitable.

1980 SR250 would have to be slower than anything else on track and therefore dangerous unless it's in a slow class of some sort. Not trying to dampen your spirits. :-)
 
teazer said:
STOP before you actually do permanent harm.

The rotor can be machined to remove a small amount of weight. Search for Banshee rotors and you will see what they do on that motor and use it as a guide.

Do not remove magnets or scallop the rotor.

You still need the CDI charge coil/s as well as the pickup. If you remove the flywheel you can see a whole series of coils on the stator plate. You could work out which are the CDI charge coils and remove the rest but realistically that will save three fifths of five eighths of sweet f.. all. On that wiring diagram it appears to have all the charge coils wound together which suggests that there are no separate CDI charge coils, so that's a bust.

I just did a quick on line search and it looks like that bike has a really old fashioned twin charge coil system.

Don't bother slotting the pickup unless you have a dyno and a really good dyno operator to develop a new ignition map.

Which brings us to the main question and that's why try to race that bike? Is there a class for it? If not maybe it would be better to sell that one and buy something more suitable.

1980 SR250 would have to be slower than anything else on track and therefore dangerous unless it's in a slow class of some sort. Not trying to dampen your spirits. :-)
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I am failing to see from the wiring diagram why I will need the rectifier and charge coils at all. It appears from the diagram the white wires from the charge coil come out of the loom and go straight to the rectifier circuit. At the plug-in connector the Red and Green from the ignition pickup change to white/red and white/green, but do not appear to be connected to any of the white wires...unless it is a splice. It appears the CDI (even in stock configuration) gets 12V direct from the switched source. I am not second guessing anyone, I just can't make heads or tails of it from the diagram....maybe it is my limited knowledge of how the CDI actually functions.

As far as why to race it...well I love the bike, the simplicity and the potential to improve power. Yes, there are classes for this bike. I am looking at standing-mile races. There are very specific classes for 250CC, four strokes...and some geared towards "vintage" bikes as well. Right now Ninja 250's dominate that class and understandably so...they are much more modern machines. But they are not "vintage"...yet.
 
You could be right. That diagram is a little hard to read.

Usually a CDI like that uses charge coils in the alternator to power the ignition system and different coils to charge the battery. That one looks as if it has one simple pair of coils to charge the battery and the Spark Unit appears to use battery power.

If that's right then you could run without the charge coils or rectifier/regulator or any of the lights and run it as a total loss system and keep a battery charger on hand. .
 
The ducatis are gonna own that class and those guys will out spend the best of us
 
bradj said:
The ducatis are gonna own that class and those guys will out spend the best of us
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Good point, haha. That is just my point, I want to prove to myself (and probably fail at it) that even if I can't outspend, I hope to outwit :)
 
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