Thumper Club Forum
Technical => Bike Problems/Questions => Topic started by: Propellor on July 28, 2013, 05:20:03 PM
-
Hi
My bro is restoring/customising a 1988 model xbr500 and we are on with fully re wiring the bike. It no longer has the electric starter motor or the standard clocks. He wants to eliminate as much of the std loom as possible.
We have a problem that we can't get a spark at the spark plug and wonder if we've eliminated something in the circuit associated with the electric start safety features, which is now preventing a spark?
Not much to go on, but any tips anyone?
Thanks.
-
Probably not going to be much help but I will have a try. I used to have an XBR and can't remember if it was too old to have a clutch switch. This is usually a small micro switch operated by the clutch lever that prevents the bike being started in gear unless the clutch lever is pulled in. Also check the kill switch, some work by connecting the wires others by earthing them so check your switch is allowing the engine electrics to operate.
Failing that ask the elctrickery pushing pixies to push harder.
-
If I were you I would rule out a faulty coil first. If my very basic knowledge of electrickery serves me correctly, you should have roughly the same volts at the coil as you have across the battery. This is how I would check it. Disconnect the two wires at the back of the coil, turn on the ignition and use a multimeter to check for voltage. Red lead to wire, black to a frame earth. One of these disconnected wires should show voltage, which proves you are getting power to the coil. Plug this wire back on, and check across that terminal to the other, unwired terminal. You should have voltage here too, which proves you have power through the coil. No power=bad coil.
If this checks out, the lead, cap or plug could all be at fault. To check for spark, lay the plug somewhere on the head - it has to be physically in contact with something, not just hanging there.
If you found no voltage at the coil you can systematically follow the wiring back to find the fault (I think!).
As I say, I'm no expert but this is how I would do it. If there is an electricity guru out there who can suggest a better way, I won't be offended to be corrected!
-
Thanks guys. We're going to check how the kill switch is wired. On my old Beemer it was simply a break in continuity, so easy to fathom. The x beast r may be different.
The info on coil checking is appreciated. We'll get right onto it!
I wondered if, by removing a lot of the circuit associated with the starter motor, we'd inadvertently left something to do with the safety gadgets permanently earthing out the ignition. There are wires going into the cdi unit to do with this and we're not sure if we need to connect them up?
Also, anyone know what the little black object in the neutral light circuit is? The wiring diagram shows it as a diode or transistor I think?
Thanks again.
-
What is the recommended method of checking the ignition pulse unit? The pulse unit is only a positional device? So we should get a spark, even if it is mis timed. How about checking the cdi?
Cheers
-
We now have a spark. Albeit a weakish looking one. We only have a kick start on this bike, but the battery is fully charged and checks out ok on the optimate. We have a second xbr in the garage which we know runs fine and that too has a fairly feeble looking spark.
What is confusing is that, although we have a spark, we aren't showing hardly any voltage at the connector which goes onto the coil (not the earth side). We checked the other bike and the same applies to that. This is slightly mystifying.
When I worked on rewiring my old Beemer, that showed 12 volts at the coil. But then it doesn't have cdi ignition.
Any ideas?
-
What did you do to get the spark back? I have pretty much the same problem with my XBR which has stood for 18 months and I'm struggling. The resistance readings I'm getting are different to the manual ( may be my multimeter) and I don't seem to have any voltage going into the HT coil. I'm slowly working my way through so any hints would be much appreciated!!
-
The BMW has battery ignition; the XBR should get its spark entirely from a coil in the alternator. If it runs at all, it should run without the battery. The spark is a bit weak when you kick it over because, of course, the voltage is just barely enough to make a spark. Once it fies, it should get more volts.
-
The BMW has battery ignition; the XBR should get its spark entirely from a coil in the alternator. If it runs at all, it should run without the battery. The spark is a bit weak when you kick it over because, of course, the voltage is just barely enough to make a spark. Once it fies, it should get more volts.
Ah, that makes sense then. Thank you very much for reply. It is helpful and appreciated.
Since the bike is kick start only and has a high compression piston in there, is there any electrical mod which can be made to make it a better starter? Like a switch to switch over from a battery fed coil to the standard supply once the engine is running?
-
What did you do to get the spark back? I have pretty much the same problem with my XBR which has stood for 18 months and I'm struggling. The resistance readings I'm getting are different to the manual ( may be my multimeter) and I don't seem to have any voltage going into the HT coil. I'm slowly working my way through so any hints would be much appreciated!!
The answer is simple. We think we always had one! We just weren't kicking hard enough! Plus the spark is "thin" so not easy to see, especially against the aluminium head and the fact that each kick moves the bike a lot.
Basically we started undoing every bit of sheathing on the original loom and started to build our own very much simplified loom. When we got enough wires in place to theoretically provide an ignition switch, fuses and an ignition circuit we tried for a spark. Because we thought we weren't getting one we tested for voltage at the coil and found virtually nothing so assumed that by leaving out all the circuit for the starter motor and all the various "safety" devices, that we'd inadvertently shorted the coil or something.
My bro has another xbr in standard ish trim, with a starter motor, so we tested that for a spark using the starter motor. We got a spark albeit a slightly "thin" looking one. We then tried the kick start and at first the spark seemed to have gone AWOL. But as we'd had a spark by the starter motor only minutes earlier we looked more closely. And realised there was a weakish looking one after all.
We then disconnected all the connectors associated with the bits we don't want on his (my bro's) cafe racer bike to prove that the ignition will still operate. It did. So we realised that all along we'd probably just not been looking hard enough. At this stage the lack of "static" voltage at the coil was still a mystery.
We took our home brewed, half finished loom off the project bike and transferred the loom from the standard bike. We soon were able to produce a spark.
We then tried to actually start the project bike, but to no avail. We gave up after an hour or so of trying, both kicking and bumping. The best we got got was a couple of backfires in the exhaust.
Now that I have a bit more info on how the spark is produced, we can explore further. The carb is a new mikuni slide jobbie so I need to check that is set up right. Then we'll have to check the timing as the engine was sent to a professional builder, who specialises in motocross. We need to satisfy ourselves that the timing is ok and not somehow completely out of sync. We have a spark, but we don't know if it is produced at the right time!
If we can provide anymore info Steve, just ask and I'll try my best! Likewise if you have a eureka moment, please let us know!
Best of luck.
-
I was obviously way off!!
Although in my defence my '87 Srx is the newest bike I've ever had! Don't get these new-fangled CDI thingies on 50 year old Brit twins!
Please keep us updated - I'm learning something here!
Martin
-
I was obviously way off!!
Although in my defence my '87 Srx is the newest bike I've ever had! Don't get these new-fangled CDI thingies on 50 year old Brit twins!
Please keep us updated - I'm learning something here!
Martin
Hee Hee. If I'd a quid for every time I'd said that.....
No worries. I appreciate the input anyway. The fact that you're thinking is good. It beats watching soaps any day.
Cheers.
-
My 1985 had a 'boost' switch connected to the starter button, if yours has that then it might be worth wiring that up to give a little extra when starting. I did experiment with this on my racer but the coil saturates at something like 2000RPM so it wasn't any good for a racing bump start.
-
My 1985 had a 'boost' switch connected to the starter button, if yours has that then it might be worth wiring that up to give a little extra when starting. I did experiment with this on my racer but the coil saturates at something like 2000RPM so it wasn't any good for a racing bump start.
Thanks for that info. Looking at the spec of your bike you are SERIOUS about your xbr's!
When you say booster "switch" I assume you mean some device which is switched in automatically and not manually? And that once we've determined that it is on our machine, we arrange to switch it in and out manually as needed?
Next (and predictable) question. Where will it be? What are we looking for? What is the symbol for it?
We tried bump starting the bike several times, with a bit of a gradient to help. We had the engine pumping several times but still no go! This is what makes me thin there is something perhaps more fundamentally amiss. Like the timing for example. We have two of everything; coil, cdi, rectifier etc and one set was known to work fine, so that helps.
I don't suppose it is possible to have the pulse generator 360 degrees out because we have a four stroke and I assume every other pulse is "wasted"? Then again you wouldn't want to employ the wasted spark principle surely, as this would halve the response time for the capacitor? Have I got that right?
-
My 1985 had a 'boost' switch connected to the starter button, if yours has that then it might be worth wiring that up to give a little extra when starting. I did experiment with this on my racer but the coil saturates at something like 2000RPM so it wasn't any good for a racing bump start.
Thanks for that info. Looking at the spec of your bike you are SERIOUS about your xbr's!
When you say booster "switch" I assume you mean some device which is switched in automatically and not manually? And that once we've determined that it is on our machine, we arrange to switch it in and out manually as needed?
Next (and predictable) question. Where will it be? What are we looking for? What is the symbol for it?
We tried bump starting the bike several times, with a bit of a gradient to help. We had the engine pumping several times but still no go! This is what makes me think there is something perhaps more fundamentally amiss. Like the timing for example. We have two of everything; coil, cdi, rectifier etc and one set was known to work fine, so that helps.
I don't suppose it is possible to have the pulse generator 360 degrees out because we have a four stroke and I assume every other pulse is "wasted"? Then again you wouldn't want to employ the wasted spark principle surely, as this would halve the response time for the capacitor? Have I got that right?
-
It is wasted spark. The 'booster' is part of the CDI, there is a wire that goes up to the starter switch, I don't have a wiring diagram here, the XBR, along with lots of other stuff, is in storage while I build a new garage. Mine ran ton 8500RPM so recharging the capacitor shouldn't be a problem.
When I first modified mine it wouldn't start, we ended up taking it to the biggest hill we knew and bumping it down that. What plug have you got in it? is it properly gapped? is the decompressor adjusted properly?
-
Thanks.
Thinking about it, they probably developed the system on the earlier 360deg twins, which revved higher I seem to recall.
We disconnected the decompressor cable after a while, to eliminate that from our worry list. We still managed to get the engine pumping during bump starting after a bit of practice.
Gap looked ok if maybe a teeny bit close. Plug was new. Can't remember grade, but I'll let you know next time we get to work on it. We tried the old plug too.
So it doesn't sound like it is easy to get the ignition timing wrong?
-
Can I pick your brains please chaps - I have the same problem as propellor -. The XBR was fine when it was laid up a year ago now no spark at all.
I have power to the ignition switch
All the lights and starter work
I've disconnected the 2 multipin connectors from the CDI unit - the 2 pin I assume is the pick up from the pulse generator.
With the ignition on and the black probe of the multimeter earthed, am I right in thinking I should be getting a 12v reading from one of pins in the 4 pin connector? ( live feed into the CDI?) cos at the moment I'm not ???
Sorry if it's a stupid question but Bike electrickery was never my strong point.
-
The xbr does not have a 12 volt dc feed.It is powered by an ac feed from the alternator.The bike should spark even if the battery is disconnected.
-
Right, so if I have no spark I'm looking at either duff CDI or alternator then?
-
Just a thought. Given that the spark seems so thin and therefore difficult to see, especially kick starting, would an in line connected strobe light help to confirm that something is actually happening? Connected in line with the HT lead.
-
Definately no spark. I've just tested the exciter coil from the alternator and resistance seems to be within manual specs. I also tested the resistance on the wires coming from the pulse generator and they seem all over the place so it's looking like it may be that....the search continues...
( already tried different CDI/HT coil combinations and nothing doing)
-
We still managed to get the engine pumping during bump starting after a bit of practice.
So it doesn't sound like it is easy to get the ignition timing wrong?
Bump starting is an acquired art, you need to push it backwards in gear (use 1st) until it comes up against TDC, then give it a damn good push and jump on. A lot of people make the mistake of trying to start it in second - you can push it all day long without it starting. When I first started racing it was bump starts off the line, I didn't have a kick or electric starter on the bike so I got lots of practice.
Ignition timing is fixed, the trigger is splined so it should be good to go. The air gap needs to be set but it doesn't go out of adjustment.
-
Bump starting is an acquired art, you need to push it backwards in gear (use 1st) until it comes up against TDC, then give it a damn good push and jump on. A lot of people make the mistake of trying to start it in second - you can push it all day long without it starting. When I first started racing it was bump starts off the line, I didn't have a kick or electric starter on the bike so I got lots of practice.
Ignition timing is fixed, the trigger is splined so it should be good to go. The air gap needs to be set but it doesn't go out of adjustment.
Invaluable advice and info. Thanks very much.
We were bumping in second! Didn't know of the pulling backwards thang either. Would you say we should reconnect the decomp cable?
Re trigger. As the engine has been rebuilt by someone else, I suppose the gap could be wrong? Having said that, we are seeing a spark of sorts. Besides, the rebuilder is a professional and has a decent reputation so there is no real reason to suspect anything untowards. But then, we all make mistakes.....
My guess is we need to persist and try your recommended starting technique. Maybe look at set up of the new mikuni. And report back on plug grade. Would a grade out prevent it starting?
Thanks again.
-
Would you say we should reconnect the decomp cable?
Maybe look at set up of the new mikuni
Would a grade out prevent it starting?
I never had the decomp cable fitted but, properly setup, it should make kickstarting easier.
The carb adds a big unknown into the equation but mine would start when it was some way out, on a 40mm Amal we had to increase the throttle slide cut away cut a bit to compensate for a HRC cam.
A grade too hard won't help, I mainly ran an NGK platinum as they are a bit more tolerant but it would still fire up on a 10 grade R plug.
-
[quote author=Rhinoman
I never had the decomp cable fitted but, properly setup, it should make kickstarting easier.
The carb adds a big unknown into the equation but mine would start when it was some way out, on a 40mm Amal we had to increase the throttle slide cut away cut a bit to compensate for a HRC cam.
A grade too hard won't help, I mainly ran an NGK platinum as they are a bit more tolerant but it would still fire up on a 10 grade R plug.
[/quote]
Thanks once again.
A general question, to anyone in the know, to satisfy my curiosity only. Do the Amal carbs with their "tuneable" slide cutaways do away with the need for an emulsion tube and air bleed? Not talking the needle jet itself but really just the air bleed and associated bleed holes in the emulsion tube.
Just a thought!
-
Out of curiosity I tried bump starting my xbr a couple of times,downhill in third.The back wheel just skidded.I didn't know about pulling it back against compression.
-
She runs!
-
A general question, to anyone in the know, to satisfy my curiosity only. Do the Amal carbs with their "tuneable" slide cutaways do away with the need for an emulsion tube and air bleed? Not talking the needle jet itself but really just the air bleed and associated bleed
Not as I recall, the cutaway mainly affects fuelling as you come off idle, I swapped to a Dellorto around 1988 when the Amal got sticky.
-
She runs!
Good to hear, what did you do?
-
She runs!
Good to hear, what did you do?
We didn't change anything! We found a steeper hill!
I think the crux though was understanding a bit more about how CDI ignition works. We just realised that the crank rpm when kicking or bumping is vital to get a decent spark. Once we got it going, it started much easier on the kick start.
It sounds gorgeous.
Thanks.