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TOPIC: Running superbly after refresh ready to shut down in the garage then died!

Running superbly after refresh ready to shut down in the garage then died! 11 Jul 2019 11:11 #1

  • PigDoc
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How's that for a subject! My DT3 was just magnificent. I refreshed it just cleaning and touch up. Everything was working. It would start first or second kick. The seals were replaced although I am getting slight drip on left side from the back case/shifter,suspect oil seal.

But my immediate issue is lost spark. At first I thought it simply died because of low idle but when it didn't pop after kicking it, I pulled the plug and no spark by grounding and kicking it over. Tank is off and all connections are perfect that I can tell. I don't have a puller yet but removed the cover. I will comment that the rotor/flywheel seemed pretty hot even after the cylinder is cool? The oil injector checks out and I'm also using 32:1 in the tank. Plug looks gray. Tried different plug and different positions on the switch. Nothing. When it died the switch was on the light side/position. Tried position I. No go. Battery is fully charged. Before this happened, light would brighten from idle to normal op rpm. Makes me believe charging system working.

I was hoping there was no spark check list from start to finish in the how too or search but didn't see it. First thing (obvious) to the least likely. Spark questions for sure but seem all over the place? Any help would be appreciated. Flywheel tool looks like the first think I need to get. I have a AC/DC volt meter but no amp meter. Thanks for this terrific group and site. My ride before this happened was worth the 45 years since the last one! I bought a DT1 new and sold it in 1974.

Thanks

Charlie
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Running superbly after refresh ready to shut down in the garage then died! 11 Jul 2019 12:31 #2

  • HouseofEnduro
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My first suspicion would be a sheared Woodruff key at the crank/flywheel connection. Often following an overhaul this key shears shortly after initial startup, generally because the nut wasn't quite tight enough and it loosened as it ran. I always recheck that nut after the first startup. I believe that is the simplest cause, and likely. If the key is intact, begin diagnosing the points and wiring behind the flywheel.

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Running superbly after refresh ready to shut down in the garage then died! 11 Jul 2019 13:45 #3

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Great answer. I definitely know what a sheered Woodruff key will do. When I was 12, 52 years ago, I took small engine mechanics for 4H. I overhauled a 1.5 hp Briggs with a rope, manual start. It was complete rebuild since the motor blew a rod so new everything except valves but did grind them. Got it all back together 3 days before the 4H show. Pulled the rope and it fired once. I worked all day trying to figure out what happened. Finally my Mom rescued me and called a local mechanic. We brought it to him and in about an hour he called to come up to the garage. He wrapped it, pulled out the choke pulled the starter and away it went. Sheered key. He said i likely didn't place it firmly in the slot or damaged it when I was driving the flywheel back on! Incidentally, I got a blue ribbon with the help of my brother. He was emphatic that I have a muffler on the engine so he and I built a stainless "stack" from a drain pipe and a Harley Davidson M50 baffle that we had. I wish I still owned the M50! Anyway, the judge was blown away over the stack. I sounded like a mini-thumper! But there's more...

So now my bike! Always check the obvious. Which I thought I did. The spark plug. Note in my narrative that I am adding 32:1 plus the oil injector. At low rpm I think that's a bad recipe for plug fouling? It was my first thought and the previous owner had removed the cylinder plug (which I replaced) and had an accessory spark plug in the head. It was new but I never cleaned it when I used it to test for fire. I went out a few minutes ago and repeated this process. Still no fire. Next I took some 600 grit sand paper and cleaned up the plug. I tested for spark and voila!

I did check the coil and it was registering on the OHM gauge using my voltmeter. Also tested the plug wire. I was about to test a direct wire from the battery to the coil but no switch handy. In retrospect that might not be a good idea. I suppose there could still be a problem and all this plug stuff is coincidental. But I just took it for another spin, same amount of distance as before and no issue. Again, I love this group and so happy have one of these back. Next project is my 1969 T120.

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Running superbly after refresh ready to shut down in the garage then died! 11 Jul 2019 15:10 #4

  • MarkT
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glad you found the problem! It's usually the simple stuff.

You don't need a battery for spark on your model... It's a magneto similar to what you had on your Briggs except the Yamaha ignition has a primary stator coil feeding a secondary primary in the ignition coil (AKA "Energy transfer" magneto) which will give a better spark than the Briggs type that only has the one ignition coil primary winding running directly off the flywheel magnets

You do need a good battery to keep from blowing bulbs.

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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

Running superbly after refresh ready to shut down in the garage then died! 11 Jul 2019 17:25 #5

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Yep on the battery. In fact when I bought it was non functional. I thought battery was really only needed for signal lights, horn and maybe horn?

I ordered a puller today anyway and a pair of clutch vise grips. When I peered into the open slots it looks spotless except there are some rusty spots on the inside surface of the rotor where it contacts the coils? Likely from long term setting?

Thanks for your reply.

Charlie

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