Driving me nuts

I've had a problem now for a couple of weeks that I just can't find the solution to. A few weeks ago, I finally had my CNW starter motor fitted to my MKI 850. What a fabulous product. However, about two weeks ago, the bike started to backfire and lose power until it stopped and wouldn't restart. Now, the bike starts easily, and then it runs well for 10 to 15 seconds and then starts backfiring on the right cylinder and then stops completely. I have changed the following to no avail. Same result. Plugs, plug wires, coil (single Accel coil) ignition unit (Trispark). I have stripped the carb (VM34 Mikuni) and checked fuel flow which was good. I have totally run out of ideas. I have two mates coming over tomorrow for a look. Charged the battery and while it is running, the Smiths gauges start doing slow revolutions, which is usually a sign of low voltage, as is the backfiring. However, the starter seems to have plenty of juice. Any ideas?

Have you looked at your grounds .... something has changed on the electrical system ....

@Fullauto so you run a single Mikuni VM34 and the left cylinder is fine, so that rules out carburetion and leaves us with electrical.

A couple of things that spring to mind:

1. Swap right to left plug leads on your coil - does the problem move from the right cylinder to the left one?
   Don't forget the sparks jump the opposite way on dual tower single coils, so the left and right behaviours are not the same, even though you have a wasted spark ignition in the Tri-Spark
   
   Better still, do you have twin coils that you can stick back on for testing?
   
   
2. Do you have a Podtronics reg/rec?
   Maybe it is worth looking at the Tri-Spark electrical interference issue?
   Tri-Spark misfire link

That the starter spins well and the coil is a dual coil rules out earth issues from engine to battery. So it is more likely to be related to the Trispark and related wiring including its earth especially any shared with the gauges.

It's well documented that trisparks are not compatible with wide wheel rims

Usually, the most complicated symptoms, have the simplest solutions.

In this case, it would seem that increasing temperature is causing 1) a short circuit to earth in the ignition system, or 2) an open circuit in the earth (ground) system.

I once tracked such a heat induced problem (not a motorcycle, but an electronic instrument), by directing a jet of cold gas at various components until the problem instantly resolved itself. I do not recall the source of the cold gas that I used, but compressed CO2 or N2 should work.

Slick

Edit: I suppose one could use a heat gun on a cold engine,to try to force the condition sooner.

I know radio guys use dust-off air in cans to freeze components to see if they will come alive.
Can you pop on another ignition set up just to see if the Tri Spark is wonky?

Onder said:

I know radio guys use dust-off air in cans to freeze components to see if they will come alive.
Can you pop on another ignition set up just to see if the Tri Spark is wonky?

Click to expand...

Don't forget the many among us who use spray ice when making cake sculptures.....as the propellant is normally butane, if all else fails you can set light the the bike ... LOL

Since the Tri Spark gets its ground from the engine case, try adding a jumper wire from that stud to the battery ground and run the bike with the points cover off.

Nothing new, I'm just babbling...

What kind of wiring modifications are required to install the CNW starter? If that is all that was changed, that portion of the wiring harness is where I would start looking for a poor connection.

A failing coil will act like running out of fuel. Backfiring and full stall are symptoms of a failing coil on an old American V8. I'm not sure how it would act on a Norton, but it would probably be similar. Is the ohm rating of that Accel coil compatible with the tri-spark? Electronic ignition is finicky about that kind of thing. If after checking the connections related to the the starter wiring, I would pull the tank and seat and unplug and re-plug every connector on the bike, and loosen and tighten every ground connection. All while checking for worn wire sheathing against the chassis. Then look at the coil.

If none of that make sense, it's because I don't own a Commando and I don't know if there even are connectors on the main harness. My P11 is about as complicated as a lawn mower wiring wise. I did all the wiring, so it's very simple, like the owner.

maylar said:

Since the Tri Spark gets its ground from the engine case, try adding a jumper wire from that stud to the battery ground and run the bike with the points cover off.

Click to expand...

Not recommended with a Starter fitted, if the thick red starter earth cable loses its conductivity at a dodgy joint then all the starter current will attempt to use the jumper wire, excessive smoke will be the result.

kommando said:

Not recommended with a Starter fitted, if the thick red starter earth cable loses its conductivity at a dodgy joint then all the starter current will attempt to use the jumper wire, excessive smoke will be the result.

Click to expand...

The cNw starter ground is a 6 ga wire from the battery to the primary chaincase. If that goes dodgy smoke will escape. Adding a jumper from the TriSpark's ground wire to the battery wouldn't provide a path to the starter. This is just for testing anyway.

maylar said:

The cNw starter ground is a 6 ga wire from the battery to the primary chaincase. If that goes dodgy smoke will escape. Adding a jumper from the TriSpark's ground wire to the battery wouldn't provide a path to the starter. This is just for testing anyway.

Click to expand...

A jumper from the Trispark to the primary case ground would be much safer.

I’m with Schwany , made a simple wire harness years ago , only what was needed , simple to trouble shoot for most part .... I hope you have the patience to trace , find and correct your problem quickly ! .... even the simple stuff can catch a person from time to time ....good luck !

Try Jumper wires direct from the battery to the tri-spark so it isolates your wiring loom and switch gear at the handle bars. Since you installed a e-start system you are jabbing at a button that was never used before. If the bike then runs fine I would turn my attention to the switch gear if its still original.
T

With the battery freshly charged you should see something like 13.2 (+-), more than 12.7, less than 13.5. If you hit the horn a few times and turn on the headlight, using both beams for about 15 seconds each, the battery should settle down to about 12.7 --->12.9. disconnect the battery from the motorcycle; pulling the fuse will work unless you have additional circuits wired directly to the battery, point is to give the battery no reason to discharge through the harness.

Measure the voltage in the morning you should see something between 12.7 and, possibly, 13. If significantly less, say below 12.5 the battery may need to be retired.

If the battery checks out, start the motorcycle; when warm at idle the battery voltage may well be near 12.0, bring the RPM up to about 2800, you should be measuring between 13.9 and 14.3, if so turn on high beam, add the brake light, should be no change. When you add the left or right directionals you will see a significant dip, not a problem given the limited use of same. If the measured voltage at 2800-3000 won't get to the 13.8/13.9 and 14.2/14.4 time to give the charging system a good look.

If the battery and charging system checks out the issue could be that the system may not be keeping up with the drain imposed by the starter.

Do you have a single or 3 phase charging system? Watts? Do you (have you) taken a lot of short rides lately? The cNw starter is a real 4 brush, 4 field power house.

Best.

There I was thinking this was going to be a funny thread but no, just another technical fault finding thread

Did you wire the starter relay switch polarity correctly? I'm not sure if it was wired backwards it would be making a "good enough ground" through it's handlebar attachment to the frame to act like a kill switch, but it could work that way under load causing an intermittent short effect.

Maybe take the battery terminal connections off the battery and connect up a continuity meter to the terminal wires. I like the beeping kind of tester myself. You'll know pretty quickly how well your switches are working by using each component switch and getting a strong "BEEP" out of your tester. A worn key switch can cause intermittent voltage too, which can cause backfiring and then the engine dies.. If you have nothing switched on and you are getting a beep then you need to trace each circuit for a short. The continuity test is one I do to see if I can narrow down the search for electrical issues. It works well for that.

If there's no "BeeP" with everything turned off, then wiggle the harness here and there to see if there's a skinned wired somewhere. Also, the inside of my headlight is a real rat's nest. If I get an electrical issue, I always end up looking in there to see if something is rubbing or came loose...

I think that the gauges going funky is a clue. If the ignition gets power from the same point it could be being starved for power. I had the battery become disconnected on my bike and even at idle with 7.5 volts from the alternator the TriSpark kept running and got me home.

I would put in a new battery and see if that solves the problem

The fact that you say it is charged up does not verify that it can
no longer take a load, I learned this twice on fully charged batteries