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DT3 - No Spark

  • Slymeister
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DT3 - No Spark was created by Slymeister

A few weeks ago, I had picked up a 1973 DT3 that was being sold for parts for cheap. Minus the seat, it was a complete bike that just wasnt running.
Ive since replaced the points and condenser, as they had corroded. Got my timing set properly, and finally got spark.
Finished going thru the rest of the bike to confirm everything was working as it should. Autolube, brakes, and clutch.
Was finally able to take it for a quick test run up and down the street, and it ran great until it stalled out. It wouldnt restart, so pushed it back to the garage. Pulled the plug and checked for spark, bike wasnt getting spark no more.
Ive gone thru and tested the ignition circuit, and everything appears to be operating properly. Triple checked my timing, and it appears to be correct as well. I also used a 9v battery to induce a current into the circuit, and i would get spark at the spark plug.
Im currently stumped on what could be causing my no spark issue now.

Thanks in advanced,
Sly
15 May 2021 19:15 #1

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Replied by RT325 on topic DT3 - No Spark

I'll guess it's sheared off the flywheel Key, "gotta be super tight on the nut'. But that guess doesn't work as it should still spark, just not in the right place. Unless the nut fell right off & flywheel is sitting there looking pretty & not turning. Not that then. I'd get back into the points area. Damned annoying eh!!. I'm annoyed at the mo & having a cuppa. Just put 'one' float in upsidedown & one right way up "black separate floats" in my 36mm Mikuni on my 360, & wondered why no fuel getting in the bowl haha. Come in ta get me glasses. good luck.
15 May 2021 19:46 #2

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Replied by Slymeister on topic DT3 - No Spark

The flywheel key is still in one piece, and shows no signs of wear to it. Same with they keyway slots in both the crank and the flywheel.
Its definitely an annoying issue! Kinda wish it stalled and went to no spark due to something coming loose and falling off, would be alot simpler to figure out.
15 May 2021 20:01 #3

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Replied by MarkT on topic DT3 - No Spark

I'm really not sure how you managed to get spark on a magneto using a 9 volt battery.  Doesn't seem possible unless maybe you lost the stator coil connection.  I really don't know.  Never heard of that being tried before.

Do you have an ohmmeter with a Rx1 scale?  Reading on black wire that goes to ignition coil with points open and closed?
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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15 May 2021 22:57 #4

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Replied by RT325 on topic DT3 - No Spark

With the 9 volter were you just testing the plug coil by scratching the wire 'at the coil' with the battery to earth. As Mark says, check the points are registering contacting & breaking via the black wire--i disconnected from the loom "but not certain that's necessary" so long as ignition key is 'on' but is easy to disconnect. Very very small needle movement on ohms x 1 but is visible & only a small movement of the flywheel over 'that' point of breaking & closing back & forth.
16 May 2021 01:21 #5

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Replied by Slymeister on topic DT3 - No Spark

Thanks for the assistance!
And your correct in how I was using the 9 volt to test for spark. Was using it in place of the magneto and points to send a momentary voltage thru the circuit by scratching/tapping power to my coil.
What I ended up finding, as you suggested, was that my points werent making proper contact. Wether they were open or closed, I couldnt get a reading from it on the multimeter. I cleaned up my contacts with a terminal file, and was getting a reading when the circuit was closed, and it would read open when the points were open.
With that all sorted and with the bike running again, took it for a longer road test. It started to lack power then quit and wouldnt restart. Got it back to the garage, rechecked my timing and found that my points had backed off just a bit. The mounting screw for the points is in pretty rough condition, and the sides are mostly rounded from the previous owner. As well as the lock washer is flat at this point, and not really holding. So im suspecting that they are ratting loose while the engine is running and throwing off my spark. Gonna pick up a replacement screw and lock washer tomorrow, and that should hopefully resolve my issue!
16 May 2021 20:59 #6

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Replied by RT325 on topic DT3 - No Spark

Ok, sounds like you're solving problems as they arise so that's good. Loosing power doesn't sound like points as such but then again if they've gone from about 15 thou to almost closed then yes it'll retard off a lot but still shouldn't have to push it home unless not opening at all. So hope you find the source of the problem Exhaust can get quite blocked up too which kills any top end performance but wouldn't be bad enough to stop the motor.
17 May 2021 01:41 #7

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