Very strange misfire on Mk III with Tri Spark.

Hello there.
I am new to the Forum.
Live in Perth Western Australia and have a Commando IIA and a Mark III.
IIA runs like a dream.
Mark III is giving me heartburn. It has Tri-spark, relatively new Trispark coils, leads and plug caps, 34mm Mikuni, new alternator, good battery.
Starts OK and idles perfectly. Then as soon as I start to ride it farts, burps, backfires and eventually cuts out. Loses power all the time.

At advice of Tri-spark I hot-wired the yellow and black wire on the Tri-spark direct to the -Ve terminal on the battery. Bingo - bike runs like a dream, better and with more power than since I owned it. So Trispark is good, carby is good,
So I know what the problem is ( I assume it is a break down in the wiring somewhere) but not where it is!!
Today I chased, cleaned, re-crimped every wire, clip, join - you name it - on the ignition circuit.
Checked all the clips were well connected to the ignition, all earths were good, pulled down and cleaned the "Kill" switch and basically checked the whole system (I thought).
Took off the "Hot-wire" and re-instated the original set up. Went out for a ride. No change!! Burp fart no power etc!!!

Help?? Where else do I look to find the electrical fault or how else do I do it?
Or is it time for a full frame re-wire?
Kind Rgds
Dickyboy.
Perth

The Mk3 has a larger wiring loom than the earlier models and uses a lot of connectors with small pins which are somewhat prone to dry joints and quite fiddly to check. I'd suspect the junction blocks under the fuel tank. Do you lose the warning lights when it pops and bangs (ie main feed to the ignition switch - brown / blue) or are you losing just the ignition, in which case the white / yellow from the kill switch may be the problem. Both of these are in the same connector block.

If the loom is old then you may find it easier to cut out the nylon blocks and wire them individualy which makes future checking a little easier.

Hi 79X100
Thanks for your fast reply.
I don't seem to lose any warning or instrument lights at all when it happens. All headlights, horn, indicators etc etc all work.
I did pull those blocks apart today but I think your idea of taking them out all together and just using single connectors is a good idea.
Oh well....back to the crimping tool!!
Thanks for your input.
Rgds

You could simply bypass all that suspicious wiring where the problem could be anywhere, and splice in to the live and switched wires coming directly off the ignition key switch positions of "on" and "on with lights".

This would be pretty easy, and would involve taking some wire and running it from each key position terminal back a couple inches to come together and then from there direct to the trispark with a fuse in the line.

I have done so with my pre Mark3 down on the left side ignition switch terminals direct to trispark.

RIght now you have essentially done the same thing by going directly from the battery, only problem is that wire is always live and slightly draining battery because it cannot be switched off, unless you put a clever toggle switch in the that wire.

This seems to work in practice, perhaps someone will tell us now why it won't work in theory?


edit: on second thought why not just put a toggle switch between your direct line from the neg battery terminal to the trispark? That way you know for sure you are bypassing all the built in wiring, and with a toggle the wire to the trispark would not be constantly live. Yes, it would add one extra step of turning the toggle switch in addition to turning on your normal ignition but at at least you can forget about trying to find the bad connection in your wiring loom. Ok, so not the elegant solution of sorting through all your wiring but this would insure a strong live lead to the trispark without all that chasing hassle!

Dickyboy said:

Hi 79X100
Thanks for your fast reply.
I don't seem to lose any warning or instrument lights at all when it happens. All headlights, horn, indicators etc etc all work.
I did pull those blocks apart today but I think your idea of taking them out all together and just using single connectors is a good idea.
Oh well....back to the crimping tool!!
Thanks for your input.
Rgds

Click to expand...

Have you removed or bypassed the ballast resistor? If you are getting your ignition power supply from the wire that originally went to the coils then the ballast resistor may still be in-line and will reduce the voltage to the electronic ignition and cause problems. Jim

Dickyboy said:

pulled down and cleaned the "Kill" switch

Click to expand...

Did you also dismantle the ignition switch?

Worn or corroded internal ignition switch contacts can cause the sort of problems you are experiencing.

To test:
Disconnect the brown/blue [NU] and white [W] wires from the switch and connect them together with a temporary jumper wire (also add the brown/green [NG] and blue/yellow [UY] wires if you also want lights ON) and see if that cures the problem? If so then the fault is likely to be inside the ign. switch.

L.A.B. said:

Dickyboy said:

pulled down and cleaned the "Kill" switch

Click to expand...

Did you also dismantle the ignition switch?

Worn or corroded internal ignition switch contacts can cause the sort of problems you are experiencing.

To test:
Disconnect the brown/blue [NU] and white [W] wires from the switch and connect them together with a temporary jumper wire (also add the brown/green [NG] and blue/yellow [UY] wires if you also want lights ON) and see if that cures the problem? If so then the fault is likely to be inside the ign. switch.

Click to expand...

+1 on LAB's suggestion

had similar thing happen - by passed ignition and was cured so installed an aftermarket ignition like this below (i tried the sparx lucas copy and they were junk(like most of there stuff!) )

http://www.lowbrowcustoms.com/index.php ... tail&p=342

Check carb fasteners, bowl to manifold? Maybe have a needle that jumped its groove or clip, idle enricher/lever may not be fully shutting it off or have it flipped the wrong way so riding on choke like richness that don't burn well. Electrically trigger wires must aways be first suspects on misifire with increased engine vibration throttle. I have had same thing with a ground strap shorting out in brake light area, would start and idle but but soon as I got over ldle on the roll, spit bang pow and dead. Took a while to find with some emotional and self doubts I was qualified to even own a Commando.

1up3down said:

You could simply bypass all that suspicious wiring where the problem could be anywhere, and splice in to the live and switched wires coming directly off the ignition key switch positions of "on" and "on with lights".

This would be pretty easy, and would involve taking some wire and running it from each key position terminal back a couple inches to come together and then from there direct to the trispark with a fuse in the line.

Click to expand...

Won't this turn your three position switch (off/on/on with lights) into a two-position switch (off/on with lights)?

Thanks everybody.
That is all great advice.
I am going to try the ignition switch bypass first as I reckon this could be the problem. The by-pass approach is a great way to test it.
If that doesn't work I think I need to bypass the Kill switch and will work out how to do that.
If it still farts and burps I will attack the wiring blocks under the tank and join the key wires with single connectors.
As I have to still work to pay for these crazy, wonderful bikes and the TLC they require, I will not be able to do this before the next weekend (which starts about 12 hours before most of your weekend!!)
I will put a post here to let you know the outcome and hopefully provide more learnings to us all.
Thanks again.

The feed to the ignition generally goes through the kill switch, which is simply a make or break switch, these get corroded and you will be lucky to get 6 to 8 volts to the ignition if it has to go through a high resistance circuit (typical after many decades) I always use the kill switch simply to operate an on/off relay which delivers 12 volts directly to the ignition from a main feed under the tank.

On Ms Peel I relayed power to the Boyer so only trickle current needed through the key and kill switch. Run a hot wire direct from battery to ignition bypassing key and kill to test on the roll and measure the volts reaching each component. But don't forget the motto if it acts like electrical think fueling first.