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A mysterious ignition problem Yamaha XT 600

21 Jan 2020 12:36
norway1
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A mysterious ignition problem Yamaha XT 600 #1
Hello !

A few years since i have been active here :)

For the time i am fiddeling with a xt 600e 3TB.

This week something occurred with the bike, and i wonder if any of you have experienced something like my problem.

1. The bike got a sudden engine stop on the highway, a little bit shaking, and then the engine died (not mechanical).

Following status:
- Good spark on plug (Have also replaced plug just in case).
-Plug is wet
-When pressing starter engine turns, but no signs of life
-Compression is very good, almost as new(over 150 psi)
-Valves checked, within manufacturers limit (Camchain ok)
-Carburetor opened and checked, all ok i accordance with manual(float settings, jets, etc..)
-Battery as good as new
-Coil primary and secondary + plug cap measured iaw manufactures documentation = 100 %
-Pick-up coil measured = ok

But: when connecting spark plug and turning starter, the plug ignites good, but after 4-5 seconds after starter has stopped,
there is suddenly coming one single spark ! this occurs every time i try.
I have ordered a new coil for troubleshooting, and i hope i do not have to order a cdi.(Expensive case).

Anyone seen this ?






-

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22 Jan 2020 02:57 22 Jan 2020 03:02 by RT325.
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A mysterious ignition problem Yamaha XT 600 #2
Can't think where to start but--has it damaged the crank key for the flywheel & flywheel has slipped taking timing miles away from a running position. It would be more likely if the flywheel has been off recently for some reason. Also with electric start there's a lot of force on the flywheel to turn against compression. That doesn't explain sparking after start button released though.
Not broken exhaust rocker arms [not likely]
Exhaust cam lobe worn round [had that on a chinese suzuki copy motor nut did 'just' still run. Run out of ideas but flywheel key is first thought. Line up the tdc mark on the flywheel through the inspection place & check it against true tdc with something down the plug hole.
Ok, one more. Something left under the seat or around the air box inlet & its blocking the inlet.
Another one--muffler fell apart internally & plugged it from the inside after going over a large bump.
Ok, no more silly ideas.
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22 Jan 2020 08:37
norway1
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A mysterious ignition problem Yamaha XT 600 #3
Thanks, actually i had of the L/H cover today to check the flywheel key, and it was where it should be (as far as i could see without taking of the flywheel, because it sits like a beast). I will check the true timing against piston as next troubleshooting.
Air filter box is complete cleaned 3 weeks ago, with a new filter. checked the filter and carburetor again yesterday.
Waiting for new coil . . ..
And i tried one more time today. Same as last time. A single spark after 4-5 seconds, while engine is not moving.

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22 Jan 2020 09:01
MarkT
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A mysterious ignition problem Yamaha XT 600 #4
Here's the troubleshooting list from the 1990 service manual...



Here's the end that says if it passes the above checks, ignitor is faulty.



If you need any other sections, let me know.

A battery-cdi will often spark when turned on or off... I'm not exactly sure how that system works but since it's sparking I'd be looking at the pulsar coil and wiring connections... the rogue spark might be happening because the capacitor is charged up waiting for a trigger signal... then when turned off the trigger circuit bleeds off slowly and eventually triggers the transistor which discharges the capacitor? Just a wild guess.

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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22 Jan 2020 09:21
norway1
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A mysterious ignition problem Yamaha XT 600 #5
Thanks,
All that bedring done... twice:D

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22 Jan 2020 09:43 22 Jan 2020 09:57 by norway1.
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A mysterious ignition problem Yamaha XT 600 #6
I think this link should work. Wait after starter stopps, then you can see a ' self systemer spark
www.dropbox.com/s/wy9t25syzypeyng/receiv...4%20%281%29.mp4?dl=0

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22 Jan 2020 15:17
RT325
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A mysterious ignition problem Yamaha XT 600 #7
Re the flywheel key, by looking i the end even if its broken it'll still look ok because all you see is whats above the shaft. So only true test without removal is to check tdc mark against piston position. But--it's probably ok, so forget that idea for now because i was thinking it was source coil driven but ok its battery cdi/tci so new can of worms although if key was gone that'd still muck up the timing/firing point of the trigger. So is it a tci box problem. Does it have a ballasted coil that the starting gives 12 volts then cuts it back. I'm outa my zone but my old honda car had issues similar that i never solved where it wouldn't fire randomly on starting unless i flicked the key. Eyeballing the spark at the coil lead so got 5 times as many sparks [5 cylinder] it'd spark as i let the starter off, so flicking the key would catch it & start. Changed everything except the trigger [hall effect trigger on that] so might've been that. Since wrecking it i found under the major fuse box by the battery under the car bonnet all the large multi plugs were chokka block full of corrosion So i'll be forever wondering if that was my main problem now. So was just a thought--check connections to everything remotely ignition related.
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22 Jan 2020 23:44 22 Jan 2020 23:58 by norway1.
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A mysterious ignition problem Yamaha XT 600 #8
Thanks. The igintion-mark on the flywheel is just some millimeter beside the valve check- mark, and when adjusting valves, i put a screwdriver in the spark plug hole to check piston postition, and it looked very well (on top).

I think also the valve clearance should be out of range if the flywheel had come off position. By the way, looking into the flywheel key hole, i can (barely)see that the key is lying in its "groove" on the shaft, and also in the groove in the flywheel.

The new coil will arrive in next week i think, will try that first. Found another example on internet of a guy that had a almost similar problem. Good spark, all ok, but no start. He replaced coil= up and running.

If that will not work, i probably have to pay for a new cdi :/

Here is a guy with common problem (exept that i dont consider my spark as intermittent/weak):
yamahaclub.com/forums/topic/9379-1991-xt...-start-noweak-spark/

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23 Jan 2020 00:38
RT325
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A mysterious ignition problem Yamaha XT 600 #9
Ok, so we will all hope for a good outcome. Nice to know the end result for sure when she's up & running. One might think [me lol] we've seen all the problems but there's always another new one waiting in the wings [so to speak],

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23 Jan 2020 01:12
norway1
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A mysterious ignition problem Yamaha XT 600 #10
I will give an update. Maybe we should make an troubleshooting/experience chart on this forum :likey Thanks for all replies.
The electrons have done much good for the world, but also much pain in the a## :)

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