Speedway bike ignition blues

[Maido]

Hey folks,
After someone who has had dealings with speedway throw togethers before, specifically someone who has run a total loss points ignition system in an SL125 or similar.

What is happening:
bike will start and run but will not take throttle without coughing and spluttering (much like a rich condition). (obviously choke isn't stuck on!!). The issue here is not carburetion, it is ignition (we have tried the carburettion path it leads nowhere!)

Bike history:
We have what appears to be an SL125 engine (good condition internally, timing is correct etc), fed by a keihen carb (looks like it is off an XR100 or similar).
Someone has wired in a total loss points ignition, the points themselves are new, the wiring is fine, the capacitor has been replaced, the coil is not the original but tests ok.

What I am wondering if anyone here has run an AC ignition off an sl or similar, without a battery, I was under the impression that you would still need to maintain the battery to get the bike to run correctly.
I thought that the phrase total loss referred to when you weren't running a charging coil to keep the battery charged, not not running a battery at all?

cheers for any help
Has anyone got a similar bike or know of someone i can get hold of to sort this out?

[Kwaka14]

You could try Gary Harris in Glen Eden, he has built a large number of 1/4 midgets which run the ignition system you're looking for and he should be able to point you in the right direction....

[Maido]

Super, thanks heaps +Rep for you!!

[dickytoo]

I had lots of fun trying to get a buddy's SL125 working. it didn't have any power above 3k. I checked the points, replaced the condensor. checked and rechecked valve clearances, checked compression and even valve timing. pulled the carbie apart a million times, checked the float level, cleaned the jets etc.

it would start perfectly and run normally until you tired to rev it beyond 3K rpm. then it would bog quite badly.

One of the guys at atomic wreckers (quite awhile back) figured it out and had great pleasure telling me as i had pretty much scratched a pretty deep furrow on my head.

There are two coils in the ignition system and the secondary one requires about 9v on it. i think the sl125 has a 6 volt battery as standard so the rest must come from the a combination of the charging system and the battery.
without power on the secondary coil, the bike just wouldn't rev past 3k rmp.


hope this helps

[bungbung]

I've got a wiring diagram somewhere, please hold...

You don't need battery for the ignition portion

[bungbung]

I got it from here:

http://oldmanhonda.com/MC/WiringDiag...ring.php#class

[dickytoo]

I've got a wiring diagram somewhere, please hold...

You don't need battery for the ignition portion

that's what i thought, having owned a couple of dirt bikes with a magneto type ignition. and that's why the guy from atomic took great pleasure in rubbing my face in it when he found out what the problem was!

[Maido]

Thanks heaps fellas!!! + rep for everyone!!

[Maido]

Just got the tart running earlier to day.
Turns out you don't need the battery, I firstly tried bridging a battery into the system, which didn't do anything to bike performance. Secondly, I rewired the entire bike as some of the wiring looked like it could use a help! I pulled on the exciter coil wire a little hard and the connector came undone from in behind the sprocket cover, I removed gear lever and cover to find some muppet thought it would be neat to soldier the the exciter coil wire without heat shrink or electrical tape, hence the coil wire was shorting/arcing against the crankcase. I feel a bit silly I didn't look here first!!

Isn't it funny how electrical problems always look so simple when you are finished!!

Anyways, thanks everyone for their input.