Modern Ignition issues

I have been having issues with my new Power Arc system. Before I get into it though I want to make it clear I have been in contact with Fred and Power Arc, both have been extremely helpful and accommodating but we have run out of different things to try. So here I am.

Anyways the story is I had a Power Arc system before and never had an issue until my voltage regulator failed and proceeded to fry the ignition, battery and half the bulbs on the bike. Very sad. So I sorted out the voltage issue replaced the battery, bulbs, and bought an updated Power Arc from Fred and did nothing else. I got everything installed and this thing would misfire at a specific RPM (guessing 4500ish) any gear, any load, any throttle position. The only thing that would make it better or worse was playing with the ignition curves.

Fred sent me a whole new setup again and I changed the ignition module itself, the coil and extensively checked the plug wires. None of this made a difference so I did not get a defective module from Power Arc. Eventually Power Arc concluded it has to be with my carburetors being too lean. They ran fine with the older system but to try something new I raised the needles and enriched up the pilot circuits to the point it was almost smoking black. None of this seemed to make a difference.

I have tried running the ignition purely off the battery as a total loss system with no difference. I have played with the encoder disk spacing, no difference. I have played with plug gap with no difference (wider and smaller than originally set). I have also played with ignition timing (by adjusting the encoder disk advanced or retarded from TDC) just a little bit and it changed the miss a little but did not fix it.

So I am looking for more ideas so if anyone else has something to try I would love to hear it. Thanks for taking the time to read my essay.

One logically possible explanation is that you rec’d 2 funky Power Arc units, both with the same fault.
This hypothesis cd be tested by installing a different EI (from another maker).

Were there any other indications that it might be lean?

Plugs? (very hard to read today) exhaust tail colour? Excessive heat.

If I read you correctly, you have changed the ignition box but not the pick up? (or was this only the second time).

Did Power Arc change the advance curve between the older system and the newer one?

If it occurred at 4500 and above due to being lean that suggests main jet not pilot, needle position would affect it though.

Might be a vibration effect. Have you checked all connections and had the coil(s) tested and replaced the spark plugs and their HT leads ? If the miss is due to being too lean the needles, lifting them should correct it - obviously it did not remove the miss. I don't believe the advance curve would cause this type of problem - it would have to be a pretty radical error in the curve.

As said by Rick , if you could try a cheap Pazon (or buy it!), that will give you more way of thinking ........I had the same trouble with a Pazon Altair, at 4000 (ish revs), no enough time to try what I said!!!!! but that will be done soon.........!

acotrel said:

Might be a vibration effect

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If it happens at the same revs in all gears then I would suspect electrical

acotrel said:

Might be a vibration effect. Have you checked all connections and had the coil(s) tested and replaced the spark plugs and their HT leads ? If the miss is due to being too lean the needles, lifting them should correct it - obviously it did not remove the miss. I don't believe the advance curve would cause this type of problem - it would have to be a pretty radical error in the curve.

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I have had exactly that on a triumph t140 it would missfire at 4500 rpm it turned out to be a corroded bullet connection

Same symptoms as my 71 Commando with the points so I changed to a Power Arc. Same thing again so further checking showed up a bad ground connection under the tank due to a split female bullet connector.

Vibration induced wiring issue is a decent hypothesis, use temporary wiring to test.... "test, don't guess"

acotrel said:

Might be a vibration effect. Have you checked all connections and had the coil(s) tested and replaced the spark plugs and their HT leads ? If the miss is due to being too lean the needles, lifting them should correct it - obviously it did not remove the miss. I don't believe the advance curve would cause this type of problem - it would have to be a pretty radical error in the curve.

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Agree. Check also the pick up sensor(s) and the mounting plate for a vibration effect.

Slick

Wow thank you all for the replies. I like the vibration idea so I will make a new harness with new connections everywhere just to eliminate that. As for fuel mixture I normaly run it a little on the lean side as it pops on decel. Plugs were brown before I adjusted to make richer now they are black and decel backfires are gone. I've got 260 mains and 105 (I think) needle jet with center notch on the needle itself. Its a 74 850.

I am not sure if power arc changed the advance curves between models I know they added two extra for different fuel. I changed the module twice now with a different updated module that goes in the points cover and the coil twice which is everything other than connections with the power arc system.

I will make a new harness and get back to you all.

Rather than a new harness, try jumpering the ignition live and return and whatever trigger wires are there.

You know- the wires that might be causing an ignition power fault??

Triton Thrasher said:

Rather than a new harness, try jumpering the ignition live and return and whatever trigger wires are there.

You know- the wires that might be causing an ignition power fault??

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Yep a dedicated power source and earth would eliminate any other possibilities

Cam end float is critical with the power arc. If a little too much end float, there may be a harmonic issue at 4500 where the cam moves about causing all sorts of mis communications with the pick up. This would make sense with multiple units and no change in issue.
Ping Comnoz on this.

I am not just a pretty face. I have sometimes torn my hair out over problems such as this. These days I get to the answer much quicker - not something of which to be proud ? It is evidence of a mis-spent childhood. If I had not played with motorcycles when I should have been studying, I would have become a doctor.

No disrespect intended, but Doctor of what?

pete.v said:

Cam end float is critical with the power arc. If a little too much end float, there may be a harmonic issue at 4500 where the cam moves about causing all sorts of mis communications with the pick up. This would make sense with multiple units and no change in issue.
Ping Comnoz on this.

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yes that makes very good sense

Dirtrider said:

I have been having issues with my new Power Arc system. SNIP, never had an issue until my voltage regulator failed and proceeded to fry the ignition, battery and half the bulbs on the bike.

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Perhaps your regulator fried because your rotor/stator gap is misaligned. Perhaps, At 4500 rpms the rotor could be grounding out against the stator causing that misfire. You can't ignore your rotor/stator condition by assuming it's good, then go on to rebuild your electrical system. You may end up with the same result again...

My commando was sold (to me) precisely because the previous owner couldn't figure out the electrical problem. It was a misaligned rotor/stator that rubbed each other, which would rub a while, then heat up and short circuit the bike. The previous owner would go for a short ride then eventually have to be trucked back home. He'd charge the battery thinking it was a crappy battery, The bike would start when it cooled off and had a fresh battery charge, then he'd go out again the next weekend and get trucked home again... He finally gave up and sold it to me for $500. (40 years ago)

Well I tried a few more things and have a bit more information. The new Power Arc has a dedicated unswitched pos and neg that goes straight to the coil (from battery) and then all it needs from the bike is a switched positive (I am negative ground) to the ignition module itself. Just to be sure I ran a whole new line pos and neg from the battery to the coil and to the unit. I ran the trigger wires direct to the coil bypassing all the connections, so I was using all different wires. I had the same result. So bad wiring is probably not it.

I was going to look further into cam end float but I am actually thinking its not an electrical issue after all. I took it on a long ride and it still did the same thing the whole time, being that it misses at around 4500 rpm but is fine both before and after it struggles through the misses. The new power arc has 4 ignition curves on it. It misses the worst on the tamest curve at the same rpm, but as you run through the more aggressive curves it gets better and better until you are on the most aggressive curve and it almost disappears. I think this means the unit is functioning correctly, it is not missing its trigger if the advance curves changes the dynamic of the miss. Correct me if I am not thinking this through right. Then on my way home after the long ride, the bike sat for about 3 hours and it was much cooler out it ran even better yet indicating that the carbs are rich. It still missed at the specific rpm on the way home but it was not as bad and I was able to use the less aggressive curves.

So as of now I am thinking it may be carburetors all along. I am going to play with the mixture further and see if I can find something more useful and concrete.