Dt1 spark quit while running

Dt1 spark quit while running

Hi,

This is a great board and I have lurked here for a long time learning stuff.
Well, finally I need to ask a question I couldnt find an answer for in the
search function.

Last week I bought a real nice 1974 dt 250. It had been garage stored 1999
and is in great condition. So I did the usual with a bike that hasnt run for
a while; cleaned out the carb,checked spark, etc. Lo and behold it started on
the third kick! I tuned the idle and set things so it ran and idled good. Oil
injection worked fine.

I hade a blast driving it around the neighborhood for about 15 minutes and
then it just quit. No spark!

So I dont know anything about 2 stroke magneto ignitions. How do I go about
diagnosing 'no spark' situation on this neat little bike? ISomeone told me
that if you ran a magneto ignition with a bad battery that could damage the
magneto. Any truth to that? Sho ' nuff the battery was toast but the as I
said, the bike ran fine.

Thanks for any tips and advice!

Thanks,
Dave R

Re: Dt1 spark quit while running

"graybeard" <u42342@uwe> wrote:

> Thanks for any tips and advice!

I'd start with the spark plug.

Then the coil/HT lead.

Then the wiring connections.

--
BMW K1100LT Ducati 750SS Honda CB400F, SL125 & SH50
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
chateau dot murray at idnet dot com

Re: Dt1 spark quit while running

"graybeard" <u42342@uwe> wrote in message news:81989869af134@uwe...
> Hi,
>
> This is a great board and I have lurked here for a long time learning
stuff.
> Well, finally I need to ask a question I couldnt find an answer for in the
> search function.
>
> Last week I bought a real nice 1974 dt 250. It had been garage stored 1999
> and is in great condition. So I did the usual with a bike that hasnt run
for
> a while; cleaned out the carb,checked spark, etc. Lo and behold it started
on
> the third kick! I tuned the idle and set things so it ran and idled good.
Oil
> injection worked fine.
>
> I hade a blast driving it around the neighborhood for about 15 minutes and
> then it just quit. No spark!
>
> So I dont know anything about 2 stroke magneto ignitions. How do I go
about
> diagnosing 'no spark' situation on this neat little bike? ISomeone told
me
> that if you ran a magneto ignition with a bad battery that could damage
the
> magneto. Any truth to that? Sho ' nuff the battery was toast but the as I
> said, the bike ran fine.
>
> Thanks for any tips and advice!
>
> Thanks,
> Dave R
>

Had a 72 RT-2(360) that quit running after a ride down a railroad track bed.
Ran fine without the old battery connected. Only battery I've ever owned
that actually shorted out. Bike also ran fine with a new battery. IIRC
manual said to remove the battery for off road use, so it didn't need a
battery.

Don't get ahead of yourself. Don't recall any fuses but has to be a
rectifier between mag and battery. Check that all connections are clean and
tight. Check the points. Bad condenser(capacitor) could cause them to arc
and burn. Condensers age even when not in use. Cam lobe not being lubed in
decades might cause accelerated point block wear. Looking back you don't
mention having checked the points at all.

Re: Dt1 spark quit while running

Thanks guys...
I 'm a pretty fair mechanic and have checked the basics. All connections are
clean, I checked for spark with a new plug and the points check out O.K. .

When I crank over the engine my voltmeter shows a minimal amount of voltage
at the hot input to the coil. It's hard to read it when I'm kicking the
starter and lookling through the damn bifocals at the tester but it looks
like maybe 1 or 1 1/2 volts going into the coil. What is the 'normal' amount
of voltage from the magneto when kick starting?

Dave




T Shadow wrote:
>> Hi,
>>
>[quoted text clipped - 21 lines]
>> Thanks,
>> Dave R
>
>Had a 72 RT-2(360) that quit running after a ride down a railroad track bed.
>Ran fine without the old battery connected. Only battery I've ever owned
>that actually shorted out. Bike also ran fine with a new battery. IIRC
>manual said to remove the battery for off road use, so it didn't need a
>battery.
>
>Don't get ahead of yourself. Don't recall any fuses but has to be a
>rectifier between mag and battery. Check that all connections are clean and
>tight. Check the points. Bad condenser(capacitor) could cause them to arc
>and burn. Condensers age even when not in use. Cam lobe not being lubed in
>decades might cause accelerated point block wear. Looking back you don't
>mention having checked the points at all.

Re: Dt1 spark quit while running

"graybeard" <u42342@uwe> wrote in message news:8199ac9bd926a@uwe...
> Thanks guys...
> I 'm a pretty fair mechanic and have checked the basics. All connections
are
> clean, I checked for spark with a new plug and the points check out O.K. .
>
> When I crank over the engine my voltmeter shows a minimal amount of
voltage
> at the hot input to the coil. It's hard to read it when I'm kicking the
> starter and lookling through the damn bifocals at the tester but it looks
> like maybe 1 or 1 1/2 volts going into the coil. What is the 'normal'
amount
> of voltage from the magneto when kick starting?
>
> Dave
>
>

Haven't had anything with points for 30 years. Never needed to work on a
mag. I think I'd try checking coil resistance instead of voltage though.

Re: Dt1 spark quit while running

On Mar 23, 10:30 pm, "T Shadow" <blackh...@nowhere.void,com > wrote:

> Haven't had anything with points for 30 years. Never needed to work on a
> mag. I think I'd try checking coil resistance instead of voltage though.

Coil windings can short when they get warm. I still own a coil tester
that heats up the coil by running DC through the primary before
doing the test itself. Actually I turn the knob to 'heat',
wait for a while and then turn the knob to 'test'.

Usually the coil does not show a total short. I suppose the
resistance lowers somewhat. Anyway, we never measured
the resistance. The test was a simple IS OK/IS JUNK test.
A junk one usually worked ok again when it was cooled
down. Only to give up again later.
But I wrote usually(!) Some would not work when cooled
down.

I own the cheapo tester. The pro version also had a tiny
chamber for a spark plug test and a small hand pump
to pressurize the chamber.
Bad plugs would stop sparking when the chamber was
pressurized.
Thus holding a plug against mass to see if it sparks
tells nothing about the plug. I've seen too many fail
under pressure.

Rob.

Re: Dt1 spark quit while running

Thanks for your advice. It's helpful to have more than one mind thinking
through stuff like this! So, when I was removing the coil I noticed that the
high tension lead had a hidden crack under the factory insulation sleeve....
the Yamaha coil has the HT tension lead encapsulated into the housing so you
cant just change out the lead. A little shadetree engineering fixed that and
with a new HT lead she started right up. Cool.

Now that's taken care of so I'm going to start a new thread about how to tune
the Mikuni carburetor.

Cheers,

Dave

--
Message posted via MotorcycleKB,com
http :// www .motorcyclekb,com /Uwe/Forums.aspx/tech/200803/1

Re: Dt1 spark quit while running

"graybeard via MotorcycleKB,com " <u42342@uwe> wrote:

> Thanks for your advice. It's helpful to have more than one mind thinking
> through stuff like this! So, when I was removing the coil I noticed that the
> high tension lead had a hidden crack under the factory insulation sleeve....


Told you!

<snip>
>
> Now that's taken care of so I'm going to start a new thread about how to tune
> the Mikuni carburetor.

Oh God.

--
BMW K1100LT Ducati 750SS Honda CB400F, SL125 & SH50
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
chateau dot murray at idnet dot com

Re: Dt1 spark quit while running

On Sun, 23 Mar 2008 17:57:07 GMT, "graybeard" <u42342@uwe> wrote:

>So I dont know anything about 2 stroke magneto ignitions. How do I go about
>diagnosing 'no spark' situation on this neat little bike? ISomeone told me
>that if you ran a magneto ignition with a bad battery that could damage the
>magneto. Any truth to that? Sho ' nuff the battery was toast but the as I
>said, the bike ran fine.

Dunno about the 250, so treat the following with caution, but the
smaller 175 used an energy transfer ignition system: there were two
coils in the alternator. You can see these through the slots in the
flywheel. One (with fewer, thicker windings) powered the lights etc
and the other exclusively powered the ignition: effectively two
completely different circuits. If this is your set-up then the battery
condition won't affect the ignition at all: my 125 (a re-barrelled
175) was used for a couple of years without a battery fitted before I
put it back on the road.

The energy-transfer system spends much of its time 'shorted out' by
the points; it's only when the points open that the energy stored in
the magneto core transfers to the ignition coil.

ISTR that the voltage with the points open is quite high and you get
spikes of much higher voltage the very instant the point contacts part
(as I found out when my kill-switch had a faulty earth connection
once!) but because these are very short a meter won't necessarily show
the full peak voltage.

So what I'm saying is, it's difficult to measure just by kicking it
over.

--
-Pip