Hi. I’ve completed a full rebuild of a 01 250 sherco. Bike was a not running when brought. Tried starting it yesterday and found that it would start but only tick over at idle rpm. Throttle position and mixture screw adjustments made no difference. Spark plug very black. 
Timing light shows around 5 degrees advanced and the stator plate is in the fully retarded position and firing also seems intermittent. I’m guessing that stator trigger circuit or CDI is the issue - anyone seen this before and can suggest anything to try before sending the stator out for repair? Many thanks. 

Have you connected the carb breather pipes wrong if you connect the breather outlets on both sides it will not run right,take all breather pipes off apart front the overflow. Check your petrol cap breather isn't blocked. take the float bowl off there is a tiny choke inlet that runs in the cast section of some of the sherco carb float bowls it's tiny it runs to the brass looking thin pipe jet that stands up in the float bowl can't think of what it actually called make sure it hasent become filld with like a varnish sludge. You may also have put the stator back on slightly out of position but it's not that likely as thay usually only go in its original position. Blow compressed air up the fuel over flow pipe not much just a tiny quick blast. 

2 hours ago, fat kiwi said:

Hi. I’ve completed a full rebuild of a 01 250 sherco. Bike was a not running when brought. Tried starting it yesterday and found that it would start but only tick over at idle rpm. Throttle position and mixture screw adjustments made no difference. Spark plug very black. 
Timing light shows around 5 degrees advanced and the stator plate is in the fully retarded position and firing also seems intermittent. I’m guessing that stator trigger circuit or CDI is the issue - anyone seen this before and can suggest anything to try before sending the stator out for repair? Many thanks. 

I found over the years of owning old knackered bikes its never intermitant cdi, regulator or coil thay usually either work or thay don't. Bad on off switches are the usual culprit or corroded earths. If it sparks well enough to see and hear your stators fine, its pretty hard to get old sherco stator timeing wrong on all the shercos iv had the stator will only fit in its original position with one timeing mark unless you bend and pull all the wires about and ovalise the bolt holes. Unless you have an aftermarket stator. 

Thank you for your insights and suggestions. Stripped carb again. Ultrasonic clean - all appears as it should. Float hight ok etc. All electrics in good condition with low impedance earth connections. Timing is correct when strobed when kicking over but as soon as it starts running the timing is all over the place, maybe firing every 3 - 4 revolutions and no response to throttle. Upon closer inspection it looks like someone has had a crack at replacing the Hall effect sensors for the stator trigger. I’m convinced that the problem lies with the ignition. Hoping that someone can say they had the same symptoms and that it was the stator. 

Last option a broken or poorly fitting wood ruff key on the crank the fly wheel may still seem tight but once it starts the fly wheel shifts on the crank and creates bad timeing, some times clicks back in place to seem OK. I had this happen on a 1991 yz125 it took ages to work out the problem went down the it must be cdi stator rewind route, it would run one minute and the next become erratic. 

Is that still Ducati Electronica ignition of Leonelli?

Have a look through the manuals pinned at the top, I'd set the stator back to standard position to start with & see if that helps. Splatshop has the readings for Leonelli stators on their site

Check the condition of the o-rings in the carb, if damaged they'll throw the jetting out

Thank you for your insights and suggestions. Stripped carb again. Ultrasonic clean - all appears as it should. Float hight ok etc. All electrics in good condition with low impedance earth connections. Timing is correct when strobed when kicking over but as soon as it starts running the timing is all over the place, maybe firing every 3 - 4 revolutions and no response to throttle. Upon closer inspection it looks like someone has had a crack at replacing the Hall effect sensors for the stator trigger. I’m convinced that the problem lies with the ignition. Hoping that someone can say they had the same symptoms and that it was the stator. 
 

Thanks Tony - Its for he twin map Leonelli system. Checked readings of pulse triggers as you suggested - one reading dodgy. Would make sense that it would be causing the problem of inability to Rev beyond start up rpm as it needs both triggers to operate the CDI system. I’ll try changing the Hall effect chips and there associated pull up resistors next week once I receive them (ebay). Hopefully a cheap fix. If it solves the issue I’ll put the trigger circuit diagram and parts required on the post.

 

Thanks Tony - Its for he twin map Leonelli system. Checked readings of pulse triggers as you suggested - one reading dodgy. Would make sense that it would be causing the problem of inability to Rev beyond start up rpm as it needs both triggers to operate the CDI system. I’ll try changing the Hall effect chips and there associated pull up resistors next week once I receive them (ebay). Hopefully a cheap fix. If it solves the issue I’ll put the trigger circuit diagram and parts required on the post.

Spoiler

Just a quick update on the Leonelli stator repair. The twin trigger circuit is really basic. To completely rebuild it like new you need 2 SS543AT Hall effect sensors (eBay/Amazon), two 22uF capacitors, some epoxy glue and a small soldering iron. Dig out the old epoxy with a knife, replace faulty item(s), test using Splatshop’sohm/diode values guide on their website. If ok - reseal with epoxy and enjoy. Took me about an hour to do- cost a tenner.  Bike started first kick and learnt a fair bit about ignition timing in the process. Hope this helps if it happens again.