Help needed, zongshen wont fire, good spark&fuel

[b44]

Hi guys help needed; got a 250cc zongshen ohc aircooled 2valve dirt bike,
I have spark and definitely getting fuel and still won't fire up,?
Not sure where to start?
The engine looks pretty new, so maybe check valve clearances?
Pick up/ magneto?
Tried kick starting for ages -no go
Even tried pull starting with tow rope around the block and still no go
I can get complete electrics for $110 shall i just bite the bullet and get it done? Bearing in mind i only paid $300 aus for it so would like to keep solutions on the cheap side
Thanks in advance

[bogieboy]

sounds like you may have compression issues.... or you may have just flooded the engine... pull the sparkplug. is it wet?if so kick it over a few times to get the fuel out, then blow off the plug real good and try it again. when you kick it over, (with the spark plug reinserted) is there a good bit of resistance from compression or does it spin over somewhat loosely? also, try kicking it over, while checking to see how much crankcase pressure there is at the vent (top of the crankcase, usually towards the rear.) if theres a fair amount of pressure coming from there, you may have cooked/stuck rings.

[Mag00]

I would need more specifics as to your testing methods. Motors will start with minimal compression, but if the timing chain jumped it will not. Find your timing marks on the side case and make sure the valves are opening at the proper time. You can check clearances at that time as well. Pay attention to spark as well. I'm not familiar with the flywheel on the bike, but on a briggs engine the keyway could sheer. Don't see how that could happen on a bike though. But check all the alignments.

I had a KX 125 that had spark and fuel and compression and would not start. To test the spark, I removed the boot and plugged in a spark plug and grounded it, had great spark. The problem was when putting it back into running config, it quit working. Just a simple plug wire had me perplexed for weeks.

Anyway, compression test and timing chain check would be a good spot to start with. While I would not rule out the cdi, it doesn't sound like the problem at this time. Document the procedures with pictures and notes.

[Mudflap]

Check compression, spark timing, valve timing. I'll bet you find one of the 3 lacking.

[jct842]

X2 on compression, spark timing, valve timing.................has to be one missing

[humanbeing]

Originally Posted by b44

...Pick up/ magneto...

What's the readings (ohm/ volt) of CDI/ HT coil/ pickup/ AC source... ?
I had some m/c pdf somewhere in my computer that list data similar to http://chinariders.net/showthread.php?t=16179&page=2 #24 format

[b44]

Thanks guys got 3 days off so will be checking everything, the condition of the engine looks barely used,is it possible for engine relitvely new to have timing out?
The plug was wet everytime ive rechecked spark and she let's out a kind of backfire (but no ignition/detonation )on kick starting
Yup ive searched this forum for similar prob; 1 guy had same drama but no fix,
Appropriate the help

[Azhule]

If the plug is always wet, I would check the Gas Overfull Float in the carburetor, and make sure it's clean/easy moving and installed/seating properly

[humanbeing]

From my untrained eyes, i though it's a 65.5 http://www.zse.cc/Upload/motor/CB250DG-09475128876.jpg (ie. 165FMM) rather than 69mm http://www.zse.cc/Upload/motor/CB250-09474981799.jpg

[BlackBike]

You'll get it. If it sneezed out of the carburetor, (as you said backfire like) then you know that timeing cycle sequence is off. Looks new , parts are cheap. Seems like you could set it up on a bench and get it diagnosed easy enough. Like mudfflap said 3 things

[b44]

Thanks guys, ive put engine back into frame, is timing easy to do with engine still in frame?

[Mudflap]

Both valve timing and ignition timing should be easy to do in frame. First thing I would do based on what we know so far is check valve adjustment. A tight valve could well be the problem.

[humanbeing]

Originally Posted by Mudflap

A tight valve could well be the problem.

0.1mm in these engine http://sawmee.jugem.jp/?eid=187

[b44]

Ok so,done valve clearance, checked carb,tried starting fluid, still nothing, as far as i can see the timing is ok,there are 2 line marks on top cam sprocket does this look correct being at 9-3 o'clock at tdc?piston is at top aswell, ive taken pics just for you guys to check, its a zs169mm, also on kicking over the compression does feel weak (in comparison to xr600 )is there another method testing compression without $120 tool? getting good blue spark right through the kick cycle but still nothing, also electrics (led speedo & head light )light up with every kick,its doing my head in
Cheers

[humanbeing]

$120?
"Nameless" 9 pcs can bought <$30 http://www.ebay.com.au/itm/121548433819 (~$11 in motherland https://item.taobao.com/item.htm?id=521677500982 "Name brand" is at least 2x https://detail.tmall.com/item.htm?id=18999111369 of "nameless"...)