Hi All,
New member here, this is my first post.
I have recently been given a 1986 XT600, that came off a farm. Previous owner has stripped headlight, taillight, indicators, battery etc off the bike, and has cut up the wiring harness so that it is now just at the minimum. Has a kill button on LHS handlebar but switch block on RH bar has had all of its internals removed.
I have cleaned the carby and refitted it, fresh fuel in the tank, and when I ground the spark plug against the frame and kick it over, there is spark but it looks weak and yellowish. Have ordered a manual and while I wait for it to arrive, thought I would ask some questions. Am ok with mechanical stuff but am a bit dumb with electrical stuff. Might seem like a dumb question to most of you, but does this bike need a battery to start, or was the battery a power supply for the headlight and indicators etc ?
Also, as there is no keyed ignition switch, can anyone tell me what wiring I should be checking for or how to test if ignition is in fact on when I kick the bike.
Thank you in advance for any advice you can give me.
Oldlonely

The fact that you are getting a spark with no battery fitted means you have a CDI ignition. No battery required.

The presence of spark also indicates that whatever the state of the rest of the wiring, the ignition is on.

Keep kicking and using a puff of ether starting spray every now and then.
You should get some sign of life.

Let us know how it goes.

I struggle with the concept of no battery with a CDI ignition purely on the ability for the magnetic flux via the generating coils to generate a decent enough current in order for the coil to deliver the spark. I know a lot of people fit capacitors in lieu of battery to give it a boost. I am know expert but without seeing a pic of the installation it is a job to see how much is lost in the circuit hence poor pulse compared, or ineffective generator etc. But as said I am know expert!

Hi, thanks you for your reply and advice.
I will keep persisting, as I want to hear the bike run before I pull the engine apart to fix a oil leak from the cases.
Think the next thing to try after the new spark plug is a compression test, which should eliminate low compression.
I also thought that the decompressor may be the problem, but when I kick thru slowly, I can hear it click so think it must be doing its job.

If the spark is weak many things could have gone wrong. Most expensive being a weak coil in the generator, which generates the ignition energy.
Cheapest fix would be if one of the connections has corrosion build-up. Would suggest you clean all the connectors between generator, CDI, kill switch, ignition coil. Then give the high voltage stuff a good shower of WD-40 or any other repair spray. This would temporarily seal up bad insulation there. Finally try a new spark plug.

With a helper you could check what gap the spark can jump to a cooling fin, with spark plug cap removed. This should be in the 6mm ore more range for a healthy system, else one of the coils (generator or ignition) may be starting to fail. If the spark without the plug is good enough, changing the plug may be worth a try.

Also any kill/ignition switch could draw some of the ignition current if not in good working order (dirty/moist), and therefore weaken it.
On a fully equipped bike that would mean ignition switch, kill switch, side stand switch (if on that model).

That kill button you mentioned, is that a proper one, like for motorcycles? If it is just a multi purpose switch the internal contact gap may be too narrow, as on CDI ignitions this will see 80-100 Volt peak there, which may well jump the gap.

For the decompressor, this is done via cable, right hand side of the cylinder head. There should be a bit of play (say 1 mm) on the end of that lever when not actuated. You can pretty much see that when kicking over by hand. If you just remove the counter bracket of that cable (1 bolt) there is no decompressor active and you can feel the real compression with your foot. If you are not able to kick the engine over sitting, that should be OK.

Andy

charliext1vj wrote: Wed Oct 23, 2019 8:14 pm 1986 CDI ....I don't believe it...

Why?

Hi.

If you have gasoline, ( and proper ) spark and air. Then the only thing stopping the engine to fire, is the timing ( compression ). Since the timing on these bikes is not adjustable, you most likely only has to adjust your valve Gap to the proper settings.
0,002-0,004 inch on the inlet, and 0,004-0,006 inch on the exhausts valves on TDC. Top Dead Center compression stroke.

If this clearances is not set properly, the engine will be difficult to start.
It is an very easy task, to adjust the valve clearance on this engine/bike .

Try

Best regards Brage

There are CDI engines after 1986, up to 1995 at least.

A spark outside the engine in uncompressed air is will NOT be the same spark in compressed air, as air insulates quite a bit. And more of it (as in compressed) insulates more. So if you do not see a hell of a spark, making actually a sound when gapping, it may be too weak to combust inside the cylinder. This is what brage refers to as "proper".

A yellowish spark is NOT a proper spark, which will be blueish-white.

Andy

Hi, Thank you all so much for your replies and great advice.
I will work through all of the things you have suggested and hopefully eliminate them off the list as reasons not to start.
I bought a new spark plug today but will do a compression test first, before I fit it.
Will have to do the test with the engine cold as bike wont start.
Can someone please advise what range the max and min should be for compression with a cold engine.
Bike is a 1986 XT600.
Thank you again for your help.

Compression range should be between 120-150 psi.

A good way that I’ve discovered to do a compression test is to truck your bike to the top of a hill and ride it down in third gear with the gauge attached, throttle wide open. Gravity turns the engine over so much better than the kicker and gives you a very strong reading, or as good of a reading as you can get if your top end is leaking