Engine locks when starting

Hi, so, when I hit the starter it turns over fast, but then hits a point and stays there - pressing the button again just makes a brief straining sound.

If I put the bike in first then rock it back once or twice, it starts just fine - if I rock it back before I try starting at all, works fine too. My first thought was gas in the cylinders, but my oil level is stable and it happens if I turn off the petcock, and it happened whej the carbs were totally drained. 

Confession: I'm talking about my recently acquired ZX-6R. I hope you'll have some ideas despite that. Coolant level seems the same, but maaaybe it's leaking into the cylinder? Can't see down the spark plug holes without a probe camera. I'm also wondering if it's a weak starter or battery - new good quality battery but you never know. It starts fine once I get it going, whether it's warmed up or still cold. 

Thanks for reading. 

 

How is your battery?

Battery and connections first.
If motor was hydrolocked  you would have found it by now by checking crankcase level and by pulling plugs,
Possible bad spot on starter , but doubt it.
Nice bike
Dave

As streetfitgher indicated check the battery and connections as they are pretty easy to check.  Second it could be the starter clutch, which makes a rather distractive sound.  I am sure that I am not telling you anything you do not know, but the starter system is by far the largest draw on the electrical system.  At this point I would put up a link to a page on the motorcycleproject.com about making and using a high current shunt.  But that page is no longer active on the site.  I pulled down this pdf from there in the past and converted it jpg files it makes sense to me and appears to be easy to make and use.  Using it will tell you if it is a battery or starter issue. To use it does require a VOM.  Anyway here is what was there in the past. 

The info from gd4now is very useful.  I like the idea of making a shunt to measure the battery current.

It seems like the key point would be to figure out if the current is very high or fairly low during that time when you say it "just makes a brief straining sound."  

If the current is very high, the starter and starter clutch are likely working correctly, but the crankshaft is mechanically stuck or blocked by something.  This would be bad, I'm pretty sure...  

If the current is low, then you could have an issue with a number of components, such as the battery, starter (brushes, commutator, etc.), starter solenoid, some other electrical bit. 
The starter clutch was mentioned, but I think that would sound different than what you describe.

Does it stick with the bike in neutral?  Are you rocking it back and forth with the bike in neutral?

 

Thanks for the shunt info gd4now, I'll have fun using that to test. 

I haven't checked my resting/cranking voltage at the battery, so I'll start there. I took the bike out to a friend's house and was there for almost 4 hours - long enough to need choke again to hold idle - and it started immediately.

DOHC, I put it into first and rock backwards a couple times, spinning the engine backwards.

If this is an electrical problem, I'm curious as to why it's solved by the reverse action...I suppose we'll find out soon. 

I'd also eliminate the fluid locking (be it fuel, oil or coolant). If that was the case, then the engine wouldn't make a single full revolution. You say it spins over first and then "locks".

I'd also be looking at battery, wiring, starter motor.

How often does this happen? Every time you start the bike without rolling it?
Has the bike done this ever since you acquired it?
How long will it crank normally before it hits the spot? 1 second? 2 seconds?...
Does it consistently hit the spot each time you hit the starter button?

Do a voltmeter test
DC V
key on-ignition on-engine not running
black probe on negative battery post
red probe on positive battery post
note voltage

press the starter button
note voltage

turn off bike
 

It´s not an electric problem!!!  Had the same problem like you on my Hayabusa, new battery, jump starting, no way.
Three of four glued magnets broke loose from e-starter housing and block the starter rotor from turning over!!!

kzrider.com/forum/4-electrical/610443-ho...arter-housing#802131

 

Thank you to all who chimed in with ideas; I plan to check them all out, but honestly...it's been under 20 degrees since posting this and I'm not as resilient to it as I was last year (oh, to be 24 again...!)

Anyway, the situation has - for now - resolved itself. 
I noticed that the rubber cover for the positive terminal was off, so I put it back on and it starts no problem now. It feels too good to be true, hence my decision to check everything you've mentioned once it warms up a bit, but here we are. 

Thanks again everyone. I'll update if anything changes or I find any other culprits.