301 SAXON .

[IAN1157]

Hi all , Is there anyone who has experienced this before ?. Saxon 301 purchased, only running on choke, found main jet holder loose , fixed , started bike and the engine proceeded to run ok until revving flat out with no control from myself . Ignition switch would not turn it off, neither disconnecting the battery ( well ripping the leads off ! ) pulling the spark plug lead off , turning petrol off, running flat out at this stage until after about a minute it slowed to a stop. Does anyone have any ideas on this ? any help appreciated , thanks.

[vicar]

images explosion.jpg (8.6 KiB) Viewed 7678 times

Its called dieseling normally the spark plug provides the ignition source but all you need is a speck of carbon glowing red hot to provide the heat to ignite the fuel, if then you have a stuck throttle/air leak/jet/float ,problem you get the symptoms described,and as you have tested your engine at max + revs with no explosions you must have a good un .

Make sure your throttle cable is in good order, check for air leaks and sort the carb and it will never happen again. Dont let the experience put you off your MZ .I had a kawasaki do the same thing.......Victor

[IAN1157]

Thanks Victor , Yes the motor must be a good un ! i thought it would expire terminally ...

Going to follow your advice and run through all mentioned , will notify if successful , cheers , Ian .

[DAVID THOMPSON]

might take a look at the head and piston top for crud
being the head is easy to remove

and run the piston to bottom of stroke and check the cylinder walls
dave

[IAN1157]

Thanks for the reply Dave , Going to strip the barrel tomorrow to see what there is , I have had m z's for years including a T.S. 250 that I ran for 9 years winter and summer , never had this problem before , as Victor says it happened to a 4 stroke Kawasaki he had so probably a one off with any motor ? . Will keep you posted! , cheers , Ian.

[pmorris4562]

Also, If it happens again, I would put the bike in gear and deliberately stall it rather than let it thrash itself to death before the fuel in the float bowl runs out!

[vicar]

Please don't try to stall the bike if its a stratospheric revs it wont work, you will just burn the clutch out I have tried it will not stop the motor.
If its not reving too high you might stand a chance . And before anyone says oh yes you can stall a 10.000 rpm two stroke go and try it and post the results on you tube for us all to see.
Sorry to go on

[DAVID THOMPSON]

i had a MAC go kart motor go mad like this about 1969
it was in a test stand my dad shoved me out of the shop
just before it came apart it was like a bomb went off
dave

and stand clear of guys burning rubber with a bikes rear tire
saw one blow once it took the rim and swing arm with it..

[IAN1157]

Thanks for the debate fella's , I don't think I would have tried stalling it , even getting the bike into gear would not seem a good prospect .... off into the garage to strip the head off to see if any carbon build up e.t.c.. Point of interest , the throttle cable seems free enough but showing signs of rusting , this may have stuck when I revved it ? , new one on order , also does anyone think with keep starting the motor on choke only this may have filled the crankcase with petrol mix causing the problem?, it certainly ran for a lot longer than the fuel in the float bowl only ...cheers , Ian.

[IAN1157]

Heavy carbon deposits to piston crown / cylinder head found , also removing the engine mount bolts found 2 offside sheared , engine removed , swinging arm seized , copious heat and large hammer applied to no avail so far , May have to cut through the swinging arm spindle to liberate ... keep you informed !

[IAN1157]

Does anyone have any info on timing the electronic version on my Saxon ?, done this numerous times on points motors , where would the firing point T.D.C. reading be taken from , guessing the coil but any info appreciated , cheers.

[Cerberus73]

i have never timed a electronic ignition mz, but if its anything like other small capacity (500 under) bikes I've worked on with electronic ignition, then is it not just a case of lining marks up on the rotor? and the black box takes care of the rest? i could be wrong, as they may just have fitted a kit that still needs the timing set like the add on kit I've just bought for my mz. that gets set once just like the points version, but won't need resetting once its fitted unless disturbed by removing the rotor for example. so be 2.5mm before tdc or so (memory here not the manual)

[IAN1157]

Update on this , the bike is now up and running having had a new piston as the old one holed after the mentioned previous problem . The swinging arm / engine mounts have been replaced and fired first kick after all that ! .Running o k although I would still like to know if anyone knows how to set the timing ( using a dial gauge ) , any comments as to where to read the t.d.c. using a meter would be appreciated , thanks.

[davegsm82]

Hi Ian,

Which version of the Electronic ignition is it? If it's the VAPE version, with the magnetic rotor then you just bolt it up and that's it. I think the timing is set to a specific value, I don't believe it advances or retards at all.

If it's the original MZ alternator with the PVL igntition unit then you have to slide the PVL pickup back and forward to time it up. Values are in the haynes manual or i'm sure someone will come along with them.

There was another version with a flat magnetic ring on the end of the alternator and an 'Amplifier' box under the seat, never had experience of this one but timing is the same as for points/PVL units.

You were unlucky to hole your piston, quite surprising really. I've had my 301 'dieseling' before, got to the end of a slip road and it just went nuts. Tried everything and eventually I had to pop it into gear with the clutch pulled and the rear brake on lightly. It did lurch but not badly. My piston was ok, but it eventually melted a little due to other problems and had a slightly concave area in the top. Was never the same again.

Dave.

[IAN1157]

Thanks for that Dave , not sure what the ignition type is but it has the reg/rectifier underneath with the pick up ( I presume ) above , I have set the sliding plate mid-distance and all seems well !, point of interest is that I have changed the Bing carb for a BVF30-N2 from my etz 250 project and the running is now 100% better i.e. no over run lurching and better pick up thro the range.The choke needed the ETZ cable but otherwise was a straight swap . cheers , Ian.