Troubleshoot help. No Spark R90/6

[Kurt in S.A.]

An R90/6 won't have a beancan ignition system...that came later. That "box" that Charlie showed is the "brains" of the ignition system...technically not a booster. It is nothing more than an electronic switch, reading the signals from the Hall effect sensors that are on the points replacement plate. That round donut has a magnetic piece installed in it and each time it comes near the dual pickups, a signal is sent to the "brain" to change the voltage to the coils to cause them to spark.

On my /7, I've been able to install the box for the Dyna III on the front frame cross bar to ensure it gets adequate cooling. That cross bar is not there on the /6. Not sure how well the box works if it's installed somewhere aft of the engine. It might look ugly, but I'd be inclined to install it on the down tubes of the frame in front of the engine.

That donut can slip on the shaft of the advance unit. It shouldn't be tightened too tight...if so, it can change the shape of the advance unit cam and affect timing. The points replacement plate must have a good ground on the backside with the engine case...a poor ground there could also affect timing.

Kurt in S.A.

[jjwithers]

The beancan bike is a different bike that i was referring to.

That box is installed between the two horizontal tubes on the frame behind the steering neck. The bike has no fairings and an aftermarket headlight so that box should get enough air in that location... or perhaps the steering neck tube is blocking all the air and causing it to overheat?

[Airbear]

Thanks for the clarification, Josh. If the box is mounted 'outside' it should be getting enough cooling.

Looking at the current symptoms, you wrote:

"Humm... the bike owner contacted me and is having issues again. SO it seems that I found many small gremlins but there may be something larger still looming about. He is referring to a backfire/rough running issue. So, the backfire could mean timing, or rough running could mean carbs."

Given that there were difficulties with fuel getting through I would give some attention to the carbs just to remove them from the list of suspects. On my old girl I had the situation where the bike would not rev properly. It would start and idle but revs would not get over about 3k RPM. There was some odd backfiring too, when I tried to ride it. The problem turned out to be a blocked main jet. A tiny lump of black rubber from the fuel line lodged in the little chamber (atomiser?) under the main jet on the left carb and was sucked into the main jet as the needle lifted. Simple enough to check this without removing the carbs - just drop the bowls and you have access. If you find any junk in there then removing the carbs and giving them a thorough clean is advised.

Another possibility is a problem with the Dyna III box. I have no idea how one would check the box, apart from installing a known good one. Have you looked at things under the cover? Is everything mounted properly, nothing loose? Have you checked timing? Shining a strobe on the ATU and sender plate with the engine running can highlight problems there.

[jjwithers]

Thanks! Carbs are easy enough to take apart and put back together. That is next on the list.
Today he rode to the cafe, rode to work, then tried to go out for lunch and the bike would not fire up. Then at the end of his work day, it ran poorly, roughly, then OK for a few min, then poorly again...which I am translating as a carb/fuel issue. He supposedly limped home 5 miles like that.

[hudson]

Not saying this is your root cause, but just for assurance:
Coil & Spark Plug Wire Testing with Multimeter

Primary:

1. Select lowest Ohm setting.
2. Positive lead on positive of coil; Negative lead on negative of coil
3. Ohms reading usually between 3-5 ohms (check your manual specs)


Secondary:

1. Select Ohm setting around 20K
2. Positive lead on positive of coil
3. Negative lead inside coil (check manual for specs)
4. Also take negative lead and insert into spark plug boot


Spark Plug Wires:

*Cable lengths will vary results, average 5-8K per foot

1. Select Ohm Setting around 20K
2. Positive lead in one end, Negative lead in the other
3. As you check reading, bend wire some to make sure there is no shorting

[jjwithers]

OK... bike went to my Guru for his expertise. Turns out that the coils were wired in series (not my doing).
And the carbs needle was at the lowest setting (not my doing either).
It seems that both of those issues, along with a leaking head gasket that ended up in a top end rebuild... and now the bike is alive again.

[Rob]

I thought the 2 6-volt coils were supposed to be wired in series.
Does he have a different coil?

Was there a previous owner that might have changed the needle position? That is weird, unless they were trying to fix another issue.

And a fresh top end is never a bad thing.

[jjwithers]

I'm thinking that due to the original single dyna green coil set up, it may have been wired for that and not for the 2 6V coils? To be honest, I'm not totally sure I understand it all... which is why I stick to mostly a stock set up when it comes to running and tuning these machines.