valve timing

[alehman]

Hi all,

I've been trying to get my CB750 to start for a few months now, working on the weekends when I can. I had some backfiring out of the carbs, so I wanted to check my valve and spark timing. Spark timing is okay, but when I pulled the valve cover off, the timing marks on the cam sprocket were a few millimeters off (relative to the valve cover surface) on the intake side (with the engine at 1.4T). I measured it by laying a straight edge on the valve cover surface and extending it to the timing mark. How exact should it be (do I even need to change it), and if I need to move the cam a tooth or so, can I do it without removing the brackets that hold the cam down?

[seestheday]

Backfiring out of the carbs?  Is it not firing at all - or just running very rough?  Not sure how you would get ignition happening in the carbs, but I'm kind of new here.

Have you checked all of the basic stuff?  Spark (pull the plugs - make sure they spark), compression (do a compression test), gas (are the plugs wet when you pull them after trying to start it)?

[TOOLS1]

The timing should be dead on! Has someone had the engine apart? Has the chain slipped? Backfiring through the carbs is a sign of early ignition timing, or cam timing.
TOOLS