has compression, spark, and fuel but won't fire / start - cam chain issue?

[JOHNDADDY]

Have you had the spark advance weights apart? have you had the points apart? Could the advance rod been spun 180° while doing other things?
It's been a long time but I have done this and had your results. Pull the spark weights off spin the shaft they are on 180° reassemble and try that. You may be fixed. She'll pop backfire and kick at you making you think timing and you're almost there but it's just 180 out. Thumper. Best of luck.

 

[toglhot]

It's firing after TDC, so if your points are set correctly the cam chain is stretched. You can get aroumd that by increasingn the points gap, but realistically, you need a new cam chain. How many miles on the bike, cam chains normally have a fairly good life span.
Things to check:
Valve lash
Cam chain tension
Points gap
Timing
Carbs,
valve seats
Leaks in the induction system
Cam timing
Auto advance unit
+++
Can of worms!
Nice looking bike BTW.

 

[Westfalia]

I am reading this with much attention, as we are struggling with a 78 or 79 SE with almost the exact issue, with the exception that the left cylinder has strong spark, but the right cylinder is very weak. We got the bike running for about five or 10 minutes and then it just quit and will not come back to life this bike to have been sitting for over 30 years before we started working on it.

Best of luck and I’ll be reading and let you know what we find out if we fix ours.

 

[Jan_P]

Thinking out loud
No rotor Woodruff key so the rotor has turned on the Axle and ignition marks are at the Wrong Position ??

 

[Wingedwheel]

However it is reported there are a solid blue spark which I have never seen in 40 years

I was thinking the exact thing?

How do you know if it’s 180 degrees out ?

If it kicks back hard flip the plug or point to coil wires. It’s a very easy rookie mistake to put the rod in 180* out. So I’ve heard……….

 

[Raymond]

This one really is clutching at straws, so to speak, but perhaps that's where we've reached now. In your first post you wrote about kicking the bike 'Multiple occasions each time 20 kicks without pulling throttle, with choke, no sign of life at all!' Both plugs wet but not starting.

Maybe too much petrol, not enough air? Try kicking without choke and throttle a little bit open? Many bikes seem to require a knack to start?

FWIW.

Good luck, and I know you will get there.

 

[Bruno_c]

I suggest you check the position of the ignition marks. As Jan_p said, the rotor may have slipped.

 

[Jan_P]

Yes that is the way to do it
Half an hour I would make it cough backfire kickback or do something
Its physics
If there is spark
And there is fuel
Anything looking like kompression

Moving the Ignition position stepwise small steps Disregarding the marks on the rotor it will fire up or do something Machine start talk back to us

 

[Jan_P]

One way forward is to line up the TDC mark top dead center on the rotor .
With one spark plug out ( or two )
Insert a wooden stick in the plug hole feeling ..check if the Piston actually is at the TDC turning the motor on the nut holding the rotor
check if it is correct

 

[Westfalia]

Agree with Jan. Double check that you are on the compression stroke with a wire down the hole.

 

[homebrew]

Aeehh The Plugs have spark when You are grounding them against the Cylinder head out of the engine
Strong fine spark Both sides ?
And the plugs are wet ?

Is that right so far Please report.

If wet and spark -- I would shift the ignition timing in small steps gradually .se if anything changes

Yup as far as I can tell by eye and by using the spark gap tool I'd say both coils have really good spark now.

Still always wet after attempts to start.

 

[homebrew]

One way forward is to line up the TDC mark top dead center on the rotor .
With one spark plug out ( or two )
Insert a wooden stick in the plug hole feeling ..check if the Piston actually is at the TDC turning the motor on the nut holding the rotor
check if it is correct

I will take a closer look at that once again.
Even though it all seems to be assembled correctly, maybe she's firing on the wrong cylinder.
I'm totally with you, the way she is reacting when trying to start her up definitely leaves the impression that this is the case.

TDC mark on rotor is fine, lines up with actual TDC.

 

[Jan_P]

Ok Thank you Sir lets try it methodically

Is the Spark we are talking about here with the spark plug out and held against the cylinder so it is actually sparking at the spark plug gap

And is it also sparking between the points contacts surfaces on the left side of the engine cover off

And as i Mentioned before from the points is leaving 2 x 2 wires 2 from each point
If those are switched so the 2 that is supposed to go to A Instead is going to B the ignition timing will be off
It wont start.
Why not switch those as a test it is simple to do
i dont remember the coloring if there is a Upside and a Downside please check

 

[Bruno_c]

If, as I understood, the bike ran fine for a while and then died, IMHO, it is not possible that It started to fire the wrong cylinder. Anyway, if you want to check, the easy way is to Switch the HT leads.

 

[Jan_P]

If, as I understood, the bike ran fine for a while and then died, IMHO, it is not possible that It started to fire the wrong cylinder. Anyway, if you want to check, the easy way is to Switch the HT leads.

Yes Sir Mr Bruno you are right .. lets se what facts we get ..
TDC and rotor checked if ignition is set it should fire at the right time
Making something to happen
I would like to ensure the spark at the spark plug .Plug grounded against motor / Cylinder head
Both sides .

If so the small step wise moving of ignition timing would make a difference after a while
Shooting in the exhaust or kickback.

With fuel and spark something should happen a little service here can change things

Pictures and info there

https://www.xs650.com/threads/wiring-for-2-coils-76-xs650-points-ignition.39895/

Should spark there on both points

 

[Wingedwheel]

If it was firing with the points reversed it would kick like a mule, you say you have spark but the plugs are wet. Are you checking the spark across the plug electrode or a in-line tester? By chance did you change the plugs and if not, what are they?

 

[Jan_P]

I don't think it will kick back -- It only does that when it is closely wrong -- It did not do so when I hade mixed them up on a Boyer Bransden setup after a Rebuild It just refused to start or make any sounds.
It is a quick flip to test .
But yes to the electrode spark check.

Perhaps getting ahead of it here .But it wont start either if massively over fueled

But the ignition timing I would check first Cant see any reason why both carburetors should be massively over fueled all of a sudden
Once the ignition is correct we can reevaluate

 

[homebrew]

Hey y'all, sorry for the silence.
Sometime stuff gets so frustrating that you just throw the bike in the darkest corner of your shop for a while.

I got my hands on another spare parts bike and simply swapped the engine block with top end.
Kept the old exhaust, carbs and ignition system and even advance unit.
Bike runs fine! A bit more tweaking on the idle system but seems to be all good now.
Interestingly, the engine sounds different. It jused to be kinda raspy/tinny but now it is more deep.

I am assuming there is something off timing-wise on the old engine.Even though it did not look like the chain jumped when looking at the pin on the cam, that's kind of how the engine seemed to behave. Maybe I'll take it apart during Christmas. Or put it onto a stand in my living room and never touching it again, as that engine that consumed more of my time and mental health than any other engine in my wrenching career, ha.

Thanks to all of you for the support, I learned a lot.
Especially
@Jan_P @Wingedwheel @Bruno_c

Cheers and never lose the fun of it