74 xl350 sparking but wont fire.

[johnny]

I just picked up a 74 xl350 from a friend.  The timing chain had gone out on him, and he replaced that and thee bent valve that occurred.  He is a fairly mechanical guy, but could not get it to fire up.  There is decent spark.  The manual is missing the 2 pages on timing.  If anyone can give me help on how to check the timing id appreciate it.  I have tried changing the plug, priming with gas,checked point clearances,...no luck.  HELP PLEASE

[GB500nz]

Is there a punch mark on the cam sprocket that's supposed to line up with something or be at the top at piston TDC?

[peterj]

If it follows the same practice as the 125 from the same era, it will have a small "o" that should be at the "top" of the vertical centreline of crank and cam. Watch out though, if the the cam is 2 bolt like the 125, the cam sprocket fits fine upside down in which case it will fire (I think the points are on the end of the cam on the 350?) on the exhaust stroke.

[bikeseamus]

Also

    Keep in mind that a marginal or bad spark plug will "fire" in the open air, but may fail to fire under compression through an atmosphere of fuel molecules. They are two entirely different tests. When in doubt, substitute a known good correct plug and try again.    Good luck.

[Ken]

There is a 500 manual here  maybe it will help

Ken

http://blackbears.ru/index_en.php?get=manual

[johnny]

If it follows the same practice as the 125 from the same era, it will have a small "o" that should be at the "top" of the vertical centreline of crank and cam. Watch out though, if the the cam is 2 bolt like the 125, the cam sprocket fits fine upside down in which case it will fire (I think the points are on the end of the cam on the 350?) on the exhaust stroke.

I have retimed it accordingly, still no luck.  however it seems upon further investigation that my compression is too low.  I have spareparts from old engine.  I think I may try and swap out top end.  I hope a valve isnt cooked.

[peterj]

Just a thought before you start pulling it apart. In case it's actually fuel related, you could try starting it on some aerostart/ether/start ya bastard. Holts de-icer also works well. This brought a GT500 that had been sat for a year, and wouldn't even bump, back to life for me once. You need to squirt and kick at the same time.

That said, if you can kick it over easily without a decompressor (I'm assuming it's pre auto-decompressor technology) there probably is a problem.

Presume that you know the timing marks on the flywheel (again, only if it follows Honda practice from the era) are TDC = T mark, points should just be opening at the "H" mark (I think it's an H - long long time since I looked at a Honda single), and that both tappets should have clearance when the points are open.

Best of luck with the old beast, I'm sure you'll get her running with a bit of perseverance.