Commando Suddenly Won't Start (2014)

judah · Nov 8, 2014

Im a new commando owner. Its a 1972 750 with a single mikuni carb. boyer ignition.

Since i got it several months ago its always kick started pretty easy. Usually on 1 or 2. Once in a while it would take several kicks but that was rare. Rode it just yesterday and it started up twice, no issues. I will say i noticed a couple of stutters or misfires on my ride home. Its happened off and on occasionally. Not sure it its related to the current issue.

Today I went out and turned the key (all the appropriate lights came on) kicked it and kicked it again (about 50x) and nothing. I mean NOTHING happened. Not even a sputter. Thought maybe it got flooded (i usually leave the petcocks open because i ride most every day and have never had any issue) so i went thru the usual routine to dry it out, closed the petcocks, turned off the choke, cranked it several times and let it sit for an hour, then came back and went thru the whole routine again and… nothing.

Clearly there could be a lot of explanations but i was wondering what a decent course of action would be to diagnose the problem. Where would you start and what tests would you do?

Any help would sure be appreciated. Thanks in advance.

comnoz · Nov 8, 2014

judah said:
Im a new commando owner. Its a 1972 750 with a single mikuni carb. boyer ignition.

Since i got it several months ago its always kick started pretty easy. Usually on 1 or 2. Once in a while it would take several kicks but that was rare. Rode it just yesterday and it started up twice, no issues. I will say i noticed a couple of stutters or misfires on my ride home. Its happened off and on occasionally. Not sure it its related to the current issue.

Today I went out and turned the key (all the appropriate lights came on) kicked it and kicked it again (about 50x) and nothing. I mean NOTHING happened. Not even a sputter. Thought maybe it got flooded (i usually leave the petcocks open because i ride most every day and have never had any issue) so i went thru the usual routine to dry it out, closed the petcocks, turned off the choke, cranked it several times and let it sit for an hour, then came back and went thru the whole routine again and… nothing.

Clearly there could be a lot of explanations but i was wondering what a decent course of action would be to diagnose the problem. Where would you start and what tests would you do?

Any help would sure be appreciated. Thanks in advance.

#1 kill switch, flip it off and on several times and see if it startes
#2 ignition switch, check for 12 volts at the coil terminals when the ignition switch is on, the kill switch also has to make contact to give you voltage there.
#3 boyer wiring in the points cavity. Broken or dirty connections there cause a lot of problems.

kernel65 · Nov 8, 2014

comnoz said:
#3 boyer wiring in the points cavity. Broken or dirty connections there cause a lot of problems.

+1

How good is the battery/charging?

concours · Nov 8, 2014

OK, troubleshoot step ONE.. pull the plugs. Wet with gas? = getting too much. Dry and clean? = not getting any gas. black and fluffy fouled? = fouling from rich mixture, or burning oil. Also with the plugs out, check for spark. TEST, don't guess.
Do the homework, report back.

judah · Nov 8, 2014

the battery and charging seem to be fine. i tried pushing the kill button several times to see if it was stuck or there was an issue there. no dice.

ok now i have to reveal my profound ignorance. i don't know what "boyer wiring in the points cavity" means. i checked all the wires to and from the coils and boyer box. looks fine.

i tested the voltage at the coils. and maybe i did this wrong so please point me in the right direction if so. the coils have 3 electrical terminals - one to the spark plug and two on top. one going to ground on the engine and the other presumably coming from the battery via the ignition and boyer box. anyway, the voltage between the terminals, when i turned the key on, was 6 volts for about 1 second and then dropped to zero. it was the same for each coil.

you said something about there should be 12 volts at the coil terminals. which is what i expected. its a 12 volt battery. but right on each coil it says "6 volt coil". and obviously theres 2 of the so guess that makes 12. but does that sound right? 6 volts for 1 second then zero?

judah · Nov 8, 2014

and yes i pulled the plugs with my first attempts. not wet with gas. not black and fluffy. looked very clean. haven't directly tested for spark yet but kinda need another person to do that and would like to hear any input about the voltage i found at the coils.

anyway, thanks for the help all.

auldblue · Nov 8, 2014

If you pull both plugs with ign on and push the kill switch several times you should see a weak spark at the plugs that means you have spark. Have you fuel in the tank?

Best of luck J

L.A.B. · Nov 8, 2014

judah said:
but does that sound right? 6 volts for 1 second then zero?

Boyer boxes switch off when there's no pulse from the pickup.

http://www.boyerbransden.com/faultfinding.html

The Micro-MKIII, Micro-Digital and Micro-Power units all turn off when not being triggered,.........you may not always have a spark on turning on and off.

6v coils (connected in series with a Boyer) is normal.
http://www.boyerbransden.com/pdf/KIT00053.pdf

Do you have 12v at the Boyer box white wire connection?

judah said:
ok now i have to reveal my profound ignorance. i don't know what "boyer wiring in the points cavity"

There are two wires (black/white and black/yellow on the Boyer diagram) which connect the Boyer box to the Boyer 'stator' or 'pick up' inside the original points housing.
These wires can eventually fracture from vibration either at the soldered joints on the stator plate, or between the stator and where the wires enter the crankcase. A visual inspection isn't always sufficient as the wire strands can be broken inside the insulation.

judah · Nov 8, 2014

so as i mentioned, when i turn the key on i get six volts at the coil for 1-2 seconds. i tried kicking the crank with the voltmeter hooked up to see if that was somehow tied to things getting voltage. no dice. stayed at zero volts at the coil.

then i tried this… with the voltmeter hooked to a coil, switched the key on, saw i got voltage, and immediately kicked… for the FIRST TIME in about 100 kicks i got a sputter like things had ignited. the voltage again dropped to zero like before and obviously it didn't start. but seems to explain something. question is why am i not getting consistent voltage to the coil? bad boyer???

judah · Nov 8, 2014

soooo… i checked the wires going from boyer box to stator. looked fine. wiggled them a bit down where they enter the crank case… gave a kick and boom… fired up first kick. and seems to run fine.

so now. what does it all mean? leads me to believe theres a bad wire or connection somewhere there. what to do next???

also, if I'm riding and this mysterious disconnect disconnects, do you think the bike will just die?

comnoz · Nov 8, 2014

judah said:
so as i mentioned, when i turn the key on i get six volts at the coil for 1-2 seconds. i tried kicking the crank with the voltmeter hooked up to see if that was somehow tied to things getting voltage. no dice. stayed at zero volts at the coil.

then i tried this… with the voltmeter hooked to a coil, switched the key on, saw i got voltage, and immediately kicked… for the FIRST TIME in about 100 kicks i got a sputter like things had ignited. the voltage again dropped to zero like before and obviously it didn't start. but seems to explain something. question is why am i not getting consistent voltage to the coil? bad boyer???

The reading you are getting on your coil means it is working correctly and the ignition and kill switch are OK.

Are the plugs fouled?

The wiring to the pickup plate in the points cavity could be causing you problem also. The points cavity is at the from of the RH engine cover. Two screws hold the cover in place. There are two wires in there that commonly break if they are not prevented from shaking when the engine runs; Jim

Jagbruno · Nov 8, 2014

judah said:
and yes i pulled the plugs with my first attempts. not wet with gas. not black and fluffy. looked very clean. haven't directly tested for spark yet but kinda need another person to do that and would like to hear any input about the voltage i found at the coils.

anyway, thanks for the help all.

As with most electrical problems, this one is most likely carb or fuel related (the opposite being true, of course).

If your plugs are not wet with gas after 50 kick attempts, then look no further.

Either you are out of gas or your petcock is clogged. If it is not the case, something prevents the gas to go through the jet into the venturi of the carb. In any case, it is a simple situation to fix.

comnoz · Nov 8, 2014

judah said:
soooo… i checked the wires going from boyer box to stator. looked fine. wiggled them a bit down where they enter the crank case… gave a kick and boom… fired up first kick. and seems to run fine.

so now. what does it all mean? leads me to believe theres a bad wire or connection somewhere there. what to do next???

also, if I'm riding and this mysterious disconnect disconnects, do you think the bike will just die?

You found the problem. The wire is likely broken somewhere or the connector under the cover is loose.
Find it and fix it or you will be walking again soon.
After you fix it then fold a paper towel up under the cover to hold the wires snug and keep them from shaking. Jim

judah · Nov 8, 2014

Thank you all very much for your invaluable advice. Im new to norton and this forum, but absolutely love the bike and this forum has been a wealth of knowledge. ill look for the bad connection and fix it as advised. its too dark now so will go after it tomorrow. will let you know what i find. and thanks again.

i just signed up for vip so i could load pics easier and will get some of my bike on here. and hopefully with some time i can actually contribute to the knowledge here and help some others out.

concours · Nov 8, 2014

judah said:
and yes i pulled the plugs with my first attempts. not wet with gas. not black and fluffy. looked very clean. haven't directly tested for spark yet but kinda need another person to do that and would like to hear any input about the voltage i found at the coils.

anyway, thanks for the help all.

Easy enough for one person, pull both plugs, snap them into the wire lead, lay them on the cylinder head. Rotate them so the ground electrode is on the down side, allowing you to view the gap. Key on, kick the engine over, (it's laughably EASY now) look for spark. Roll it inside a garage if possible, makes the spark easier to see than in direct sunlight. Next time you're bike is DOA, remember the drill.

Onder · Nov 8, 2014

Be sure the plugs are grounded reliably as if you kick and they roll off the head or lose their
ground you can make you electronic ignition unhappy...

concours · Nov 8, 2014

Onder said:
Be sure the plugs are grounded reliably as if you kick and they roll off the head or lose their
ground you can make you electronic ignition unhappy...

While cautioned against on modern high energy systems, it's not applicable to this machinery.

L.A.B. · Nov 8, 2014

concours said:
Onder said:

Be sure the plugs are grounded reliably as if you kick and they roll off the head or lose their
ground you can make you electronic ignition unhappy...

Click to expand...

While cautioned against on modern high energy systems, it's not applicable to this machinery.

It isn't good for any EI ignition system, or the coils, as far as I know.

concours · Nov 8, 2014

L.A.B. said:
concours said:

Onder said:

Be sure the plugs are grounded reliably as if you kick and they roll off the head or lose their
ground you can make you electronic ignition unhappy...

Click to expand...

While cautioned against on modern high energy systems, it's not applicable to this machinery.

Click to expand...

It isn't good for any EI ignition system, or the coils, as far as I know.

I'd love to learn why :?: :idea:

Nater_Potater · Nov 8, 2014

concours said:
L.A.B. said:

concours said:

It isn't good for any EI ignition system, or the coils, as far as I know.

Click to expand...

I'd love to learn why :?: :idea:

Click to expand...

A points-type ignition builds voltage "slowly" enough that it's voltage won't get high enough on a disconnected plug wire to cause serious damage to the coil, whereas a typical electronic ignition either:
1) causes a rapid-enough voltage spike that it can get a spark to jump through the insulation inside the coil. Once that happens, you have a carbon trail that is a short to ground, or
2) Creates enough EMF in the brain box that the somewhat fragile electronic devices get fried.

Nathan

Commando Suddenly Won't Start (2014)

judah

comnoz

kernel65

concours

judah

judah

auldblue

L.A.B.

Moderator

judah

judah

comnoz

Jagbruno

comnoz

judah

concours

Onder

concours

L.A.B.

Moderator

concours

Nater_Potater

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