Xbr500 wiring

[guest564]

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?

[Propellor]

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?

[SteveC#222]

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.

[blew]

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.

[SteveC#222]

Right, so if I have no spark I'm looking at either duff CDI or alternator then?

[Propellor]

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.

[SteveC#222]

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)

[guest564]

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.

[Propellor]

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.

[guest564]

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.

[Propellor]

[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!

[blew]

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.

[Propellor]

She runs!

[guest564]

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.

[guest564]

She runs!

Good to hear, what did you do?