Hi I have avery old motorcycle and found it is not getting a spark at the plugs.?

Question

I have replaced the points /plugs and made sure they are to the right gap Im suspect about the condenser (capacitor) or maybe the magneto,is at fault could some tell me how to do a test to se if either or both are working, the magneto is expensive, so I hope its only the condenser.

Answer 1

Well,,seems pointless to tell you how to "check for spark",,You already Know that.

And pointless to tell you to check for power @ the points,,,
since You said it's a Magneto.
Mags aren't battery powered,,there is no power at the points to check unless the mag is spinning

I cannot discern what type of Magneto assy you have---

If being in UK + Very Old Bike + Mag is Expensive are all "clues,,,
I'd have a Hunch You are reffering to a Lucas or Bosch Unit.

If that's the case,,,Make certain points are installed correctly,,INCLUDING the Electrical Connection of the points,
make certain the contacts are Clean,,and actually CLOSING.Check with an Ohmmeter.

And replace the condensor in any case---especially if it's Lucas.
They often are "bad" when "brand new"---they're known leaky.

If it has a replaceable Cap for the plug wires,,,closely inspect that also

Beyond those things,,Points/Condensor/Cap---your best bet is to take Bike or Magneto to a shop which specializes in Mag Repair.
Yes,,it's expensive even to just repair them.
But they'll last 20~30~40 Years with just an occasionaly points replacement when properly done.

If Your bike has a Flywheel Magneto,,,,such as what's typical on smaller singles,2Cycle engines,,most Euro Dirt Bikes,etc,,,,,here's some general info that may be of some use.

Lots of tedious reading,,but it's all fairly simple.
Keep in mind that as powerful and reliable as magnetos are,,
One tiny fault can stop them dead.
So the procedure is to Verify each of the few parts is functioning ,,,and being methodical.
Ya can't skip over something that "Looks or Seems OK".

SOME of the following applies to Both Unitized Mags as well as integral /Flywheel Mags.
Points and Condensors for example.
And In Principle,,,"all mags are the same".

.Now here's some about Flywheel type
.................
Mags are simple on one hand,,,but the devil is in the details.
Each piece has certain specs and requirements which need to be in order for the whole unit to function.

You really need a multimeter to do a thorough check.
But there's some simple things that can be checked.

POINTS:----------------------------
New Points generally have a preservative coating on the contacts.
Quite often it's enough "insulation" to prevent firing,,or only produce Weak fire.

ANY/ALL new points need to be Cleaned at least as a matter of "Good Practices",,,
many actually Require it to function properly.

Easiest way is to use common,household rubbing alcohol.
*Put a drop on corner of a Business Card
*Open the Points and insert the soaked card
*Let the points Close so they "pinch" the card
*TWIST the card back & forth
*Open the Points again and remove the card
*Put the DRY end of the card into the points,&let them close
*Pull the card out a LITTLE,,sliding it thru the contacts
*Open the points again and remove the card
*You Dont want to pull the card all the way thru,,,because that usually tears off little paper fibers & leaves them between the contacts.
*If the card appears "dirty" where the contacts pinched it,,Repeat the procedure till Card comes out CLEAN.
*"Surgical Clean" is Ideal,,and easy to achieve--but not totally necessary,,,,just be certain it's Well Done and Clean

I prefer to do it before installing the points,,it's just easier.

MAKE CERTAIN the Points are actually CLOSING.
Use your meter connected to the Points wire from the mag and to Ground.
You should see Zero Ohms,,No resistance whatsoever when Closed.
You'll need to check that with Condensor disconnected.

Point's Connection:_________
This is a common error,,,and I've done it myself .

Most Bike Mags use a wire with a small eyelet or forked connector terminal which connects to the points.

On the Points there's a Screw/Nut Terminal arrangement.
And,,a series of Insulating washers.

"Instinctually",,or by error,,,,the Points Wire may get installed IN CONTACT with the Frame of the Points.
That's Incorrect,,,as that Directly GROUNDS the point's wire.
Has Same Electrical effect as points never opening,,or Kill Switch turned OFF.

The Frame of the points is insulated frome the wire by 2 insulating washers and a sleeve.

So electrical contact is limited to being only between
Screw,Points Wire,and Points Spring.

Here's a couple pictures which show the order of things.
In the Drawing,,,
Item#2 is represented by a narrow "band"--that's an Insulating washer.
There's actually 2 of them sandwiching the Points Frame.
You can see the 2 Brown-ish washers in the other Photograph.

What neither image shows is the Points Frame Hole which the screw goes thru has a small cylindrical Insulating Bushing in it,,,to isolate the screw's shank from the frame.

Washr} frame[=bushing=]frame {Washer

You can see how the WIRE connects,,,contacting the Screw or Spring ,,,,but NOT the Frame of the points..

So,,
Clean the Points,,
and make sure the Wire is installed correctly.
And You already know to gap them correctly.

http://www.kithalsted.com/images/NewPoints.jpg

http://www.dansmc.com/points1.jpg

Ya hafta look Close,,,but can see what-contacts-what,,,and not.

......................................................................
CONDENSOR:
There's actual Condensor Testers---they're scarce & expensive.

Frankly,,,on anything more than 2~3 years old,,,it's wise to arbitrarily replace the condensor.

You can use a Multimeter to perform 2 simple tests.
They wont "prove" it's GOOD,,,or CORRECT.

But they will prove it's BAD.
Which is a useful indication,,
and PROBABLY means it's OK if not proven Bad..

#1----
Remove Condensor.
DRAIN it by connecting a wire from Terminal to Case for a few seconds.
Use Ohmeter to check for any continuity between Case and Terminal.
There should be ZERO.
It may show a TINY amount....it's not unusual to see even NEW condensor leak a small amount.
They work,,somehow,,,but I won't use them.

If it's got much connection/continuity to ground at all,,,,it's internally Shorted to Ground>>>BAD

#2----
Get a flashlight battery,,,a 9v transistor batt is best,,,but any will do.
Connect Batt's (+) to Condensor Terminal
And Batt's (-) to Cap's Case
Hold it for a few seconds.
This is CHARGING the Condensor.

Then,,,using a Low Voltage DC Scale on your meter---
Touch Black Lead to Case,,and
Red Lead to Terminal.

Same procedure as if testing "battery voltage".
The Condensor Should have Stored the Charging Battery's same Voltage.

Your Meter should display a Voltage very similar to whatever the Battery's is,,,,and should continue for a Moment.

Testing the Capacitor will eventually Drain it.

Also ,,You can Re-Charge the Cap,,,let it sit for several minutes,,,and Test it again.
It should store the charge for Hours actually.

If you get NO Voltage ,,,the Cap is Bad internally "open" or the electrolyte is spent.
It's simply NOT storing voltage as it should.

If it Holds a charge for a couple minutes,,,
you can be certain it's at least FUNCTIONAL.
It's actual SPECS may be Off,,,but at least it
a)WORKS
b)Is Not shorted to Ground

General Rule-of-Thumb for ALL Electrolytic Capacitors,,
is a 7 Year Life Span.
.......................................................
Primary Coil/aka Source Coil

This is the lil' Coil Inside the mag.

It's a Laminated Frame ,,each layer is varnished for insulation.
It's then wrapped with a thin layer of insulating paper,,,
Then the Wire Coil is wound upon that.

IF the Frame is severely rusted,or physically damaged,,,it will conduct between the laminates and reduce efficiency dramatically..

The Coil Winding Wire itself is varnish insulated(or modern synthetics)....that can fail with Age,Heat,physical damage and short out to either itself ,or to ground.
No Spark is the result.

To test the Coil,,,Remove it from the backing plate.
Use Ohmmeter to check continuity between the 2 ends of the wire.
ONE end goes to Points,
Other end usually has an eyelet that is Grounded to the Coil Frame /Stator by the mounting screw.
Lift the Ground end away from all else.....so that Your checking JUST the Coil Winding end-to-end.

Each Coil has it's own Specific Resistance.
It's POSSIBLE to be able read simple Continuity thru the Coil,,,but all while it is shorted internally to itself.
That's Rare.

It's like a sorta Coil Tap,,,You're only reading continuity thru a Portion of the windings.
You'll KNOW,,if you happen to know the Coil's actual resistance specs.

But Primary Coils resistance is so low ya just about need a accurate Digital meter to make a proper assesment.

Fortunately ,,,it's Rare as i said.

They are usually either Good,,or BAD>open winding or shorted to ground.
There are other ways they CAN fail,,,such as going Open only when Hot,,or shorting only when wet or in hi-humidity.
REPAIR-BY-TRIAL is then in order----Coil Fault Gremlins are "fair assumption" when all else is proven good.

You can also test AC Voltage Output of the coil.....but again,,without Specs it's almost a moot point.
Except if it puts out NOTHING.
Coil needs to be isolated from points/condensor(disconnected) so you can check raw output.

...............................................
MAGNET:

Odds are almost ZERO Magnet Probs are your culprit,,,but it DOES happen.
Usually,,even a Very Weak magnet will produce some spark.

I never seen a published Gauss figure for any Motorcycle Magneto Magnet.
"Nobody" has a meter to check it anyway,,,'cept a Mag Repair Shop.

Magnet strength & condition seems to never be a consideration in troubleshooting Bike Mags anyway
(except Lucas externals,,an H-D's FairbanksMorse units,etc)

Magnets DO fade in strength,,
and that DOES have a dramatic effect on Output.

Best suggestion I can offer is a rule of thumb,,
The Magnet should be strong enough to pick up and hold a 12" crescent wrench,,or a16oz claw-hammer.
AND take a bit of effort to pull it away from the magnet.

That FEEL is very subjective judgement,,,,but it should be Distinctly "SHARP" in it's magnetism.
Lotta good it does you,,but You'll Know a Mushy Magnet if you ever feel one.

They get demag'd from a variety of causes,,,beating on the flywheel,,and storing them with metal "stuck" to them are most common.
Which INCLUDES the habit of people storing Stator/MagWheel "assembled together" Off the bike.
Flywheels rubbing on Coils from coming Loose,,or bearing failure have killed a fews magnets also.

Almost not worth worrying about,,,
but worth 1/2azzed checking the pull with a wrench or screwdriver,etc.
............................................
Wiring:
Dont take wiring for granted.
There's obvious things like switches,,and broken wires,or pinched/cut insulation.

But also on Old Bikes,,,all the connectors are Crimped On(on Jap Bikes).
That can allow corrosion to build a formidable resistance in the Crimp.
Connector's Male-to-Female junctions can also build up a lot of resistance.

In itself,,,it's RARE to cause a No-Fire condition.
But when totalled with other marginal specs,,,it Can

.................................
Secondary Coil(Spark Plug Coil)
It's a coil,,subject too same types of probs as any wound coil.

You can check resistance from primary wire to spark plug wire,,,,How Much depends on the particular specs.
8,000 Ohms?? 5K to 10K range oughta FUNCTION on most coils.

You should see NO continuity from either end of the coil to Ground

Spark Plug Caps and cables can & DO go bad.
It's Common for the connection between the 2 to get corroded/eroded/"burned"

........................................
Other stuff:
You say " VERY OLD ",,,,I dunno if that's late '80's
or Twice that age,,,LOL

Even fairly NEW bikes ,,especially OffRoader's can suffer Corrosion in Mag's Stator Mount Plate.

As Aluminum Corrosion ages it get's VERY resistive.
Stator Plate to Engine-
Coils to Plate-
Points/Condensor to plate-
All of the various points-of-contact are Ground path.

A really nasty Stator and Engine case from years of mud>water>oil>air>heat can create small increases in resistances,,at various location.
They can total up to make for very weak ignition.

And it Really dont have to look all that nasty.
Aluminum Oxide is a poor conductor,,,heck,Good aluminum is not that great a conductor.
.............................................................................
Magnetos are unusual devices.

On one hand they are very simple devices,,,
while the science & physics principles are quite complicated.

They're Very Reliable,,and have the capability to function Far,Far outa specs in really bad condition.

Yet One tiny fault can kill them dead as far as making a spark,,
and some events can destroy them.

Recap:
--Check that Points are connected Right
and actually Opening & Closing (Electrically,,use Ohmeter)
--Condensor,,check from terminal to case for Short,,& check to see if it stores any voltage
--Primary Coil,,check continuity,check for short to ground,check for any output voltage
-Magnet,,,see if it's got ant decent strength
-Secondary Coil,,,check continuity & for any short to ground
-Plug Wire/Cap,,,Check cap's continuity,,check for clean connection PlugCap-to-wire
-Wiring & any Switches,,,check with Ohmeter & visual inspect for corrosion at any connections.
-StatorPlate,,,It and it's mounting needs to be clean,,,as do the areas on it where point/condensors/coils mount


Hope any of that helps,,Good Luck with it

Answer 2

Hi kradride check where h t lead comes out of magneto could be corrision if so clean it and wipe dry and try again good luck

Answer 3

Always give year, make, engine size and model # when asking questions. We need all of that info to give an informed answer.
--Engine kill switch
--Battery - if it's battery ignition (that's why we need to know what you have).
--Coil/coils (same thing, we need to know).
--Spark plug cap
--If you're uncertain about the condensor - remove it. It's not needed to produce spark.
--If you're getting power to the points while the engine is cranking, then I would focus on the coils.
--Purchase a shop manual.
http://www.motocom.com/motorcycles/

Answer 4

stick a steel nail in the sparkplug and put it on the exhaust turn the engine over if it arcs onto the exhaust you have a sparking point. do this with both cylinders. no spark from one means either bad high tension leads or bad sparkplugs.

Answer 5

Use a test light to see if you have power to the points.

Answer 6

I have an old whatever & im not getting any fraggelshit...

Ask a question....make it as general as possible...that way any answer is good....

cos if you ask the question properly...we can answer it easy & then have nothing else to do.....DUH!!!!