No sparks.

[dawes3524]

Hi to everyone. I'm a newish member having purchased a 79 350 Sport back in July.[realising a teenage dream.....some time ago!!!] All has gone well until I put it away for the winter. When I tried to start it recently it would not respond. I checked for a spark, but had nothing on either cylinder. Could someone give me an idea where to start & the most likely cause. It has NLM ignition. Many thanks. Baz.

[Al B]

Whereabouts are you?

The "no spark back cylinder" thread has information about what you can do to check the ignition out

Alan

[dawes3524]

Hi, Thanks for the reply, I'm in Tunbridge Wells

[julianharty]

Here's a link to that discussion on the forum viewtopic.php?f=4&t=5448

If you have a working electrical multimeter, a spare new spark plug, plug cap, and HT cable then you can
1. measure the resistance of the ignition coil (and make sure it's actually connected to the wiring loom just in case the fault is in the wiring between alternator and the patch-panel/junction-box under the right-hand side panel).
2. have a go at reading whether it generates any AC voltage when the engine's turned over (by electric-start or kickstart), might be good if you have someone else to help you read the meter while you start the bike if you're using the kickstart...
3. do some fault-finding by substituting your current spark plug, cap and HT lead.

Good luck, do please keep us informed on what you try out and the results you get.

[norbert]

If you have no spark at all as Julianharty says first thing should be to measure the resistance of teh ignicion cpol of the generator.

Have a look at your engine-off-button (if you have one). I onces needed some time to find out that it was off Take the green cable off from the ignicion switch and the engine-stop-button to make sure that the fault is not there.

norbert

[dawes3524]

Apologies for the lack of communication, i've been laid up with a back problem. Finally, have been able to test ignition coil resistance......290 ohms. I assume thats pretty good? When cranking the engine with e/start the a/c volt reading was 47 ish. What next??? Thanks!!

[julianharty]

47 volts AC sounds low, are you able to kickstart the bike to compare the voltage when using the kickstart to spin the bike over? Also, is anything on the bike's wiring connected to the leads when you do the test?

Oh, and are you testing with the spark plugs fitted or removed?

Good luck.

[scbond2@yahoo.co.uk]

hi i live in tunbridge wells too we could meet up at the local bike club huntsman mcc tues
steve

[dawes3524]

Ok, I have now tested the a/c voltage using the kickstart. The best reading I got was approx 30. the spark plugs are fitted in the heads.

[mbmm350s]

Hi,

I hope that you are not having problems with your back still.

Finally, have been able to test ignition coil resistance......290 ohms.

This indicates that the winding is either new or recently rewound,IF it is wound using the correct gauge of wire and is not a higher resistance vespa coil.


Since you are measuring an A.C. voltage with spark plugs and leads connected I think we can eliminate Norbert's sensible suggestion:

Have a look at your engine-off-button (if you have one).

Your notes suggest A.c voltage increases with engine speed, as expected.
Although the reading may be low its difficult to judge with an a.c meter designed to measure sinusoidal (i.e mains) type waveforms.

Please remove spark plugs and leads, bare the end of the lead and see if there is a spark by holding the lead near to the head and cranking the engine.

The spark should jump a minimum distance of 5mm in air, any less than this and it will not jump 0.7mm inside the engine under compression.
CDI sparks are often difficult to see in bright light and your comments so far seem to have eliminated the common components
with the exception of the generator rotor magnetism, which would be indicated by a spark but not strong enough to jump 5mm

If there are still no sparks
Please check engine earths, NLM ignition unit earths and coil connections are sound.
Check that the NLM pickup clearance to rotor is "rizla or equivalent fag paper" , I am assuming you have the NLM pickup and not the original pickup.

I would be surprised if there is no spark whatsover.

Mark

[Ming]

A not very accurate test for the rotor magnets is to take a fairly large spanner (eg 20mm) and hold it lightly near the rotor, if there is enough magnetism to pull it onto the rotor you should be OK.

[dawes3524]

I have now removed the plug caps from the HT leads & checked for spark against the heads, absolutely nothing no matter how close the lead is to the head. The clearance between pick up rotor & magnet is 0.05 mm on both. Incidentally, the pick up base plate is not red or black,but metalic. As suggested, I have done the spanner check on the generator rotor. Absolutely no attraction to the rotor itself, but a slight pull to the starter cone. Could this be my problem????????

[julianharty]

Are you testing with the rotor removed and with the spanner on the inside of the rotor? I don't believe the 'spanner test' works from the outside of the rotor... I can't find a rotor to test with though...

[Ming]

Are you testing with the rotor removed and with the spanner on the inside of the rotor? I don't believe the 'spanner test' works from the outside of the rotor... I can't find a rotor to test with though...

I think you're right there, Julian. I can't remember trying it from the outside, as it were. The inside is where it counts, as that is where the induction between the magnetic poles and the soft iron cores takes place. (I'll try teaching people to suck eggs next )

[mbmm350s]

Hi Baz

Incidentally, the pick up base plate is not red or black,but metalic

It think you already said it is an NLM pickup, which has a metal base.

I have now removed the plug caps from the HT leads & checked for spark against the heads, absolutely nothing no matter how close the lead is to the head.

First is to check (and perhaps check again) the common components.

Common components to be checked:

Engine and headstock frame earths to ignition coil and NLM/transducer unit for continuity.
Connections of green wires to the NLM unit/tranducers
Ignition switch and kill/engine stop switch

Rotor magnetism (needs rotor to be removed as Ming says)
generator winding. This we would need to see if it is the bastard Vespa coil.

It has NLM ignition

From this i take it to mean you have the NLM dual CDI unit + two external CDI coils - is that correct

Fault in one half of the NLM transducer unit (or similarly in an original transducer), this I have seen, here the thyristor has failed in one side and is shorting out the green wire
(For the cognoscenti this is over simplification - but i don't want to get bogged down in the electronics)
Please disconnect both the green lead and pick up trigger to each of the transducers inputs in turn, effectively isolate each half of the NLM unit.
If there is spark on one cylinder then the unit has a fault.

Do you have any spare ignition components?

Mark