Anyone got any ideas why our MT500 won't start?

[Cliff]

Hi, We have an MT500 we bought last year, couldn't get it started, checked spark, plug gap, etc., tried bump starting as well but would not fire at all, not even a quick misfire. Took the Amal carb off and dismantled it to clean, found a few things wrong with it so we have bought a new Mikuni VM-32 carb to replace it.
I have fitted it, and checked we are getting petrol to the engine, but it still won't fire at all. Rechecked for a spark, checked the plug gap, checked that fuel is getting to the engine (plug was wet and smell of petrol from the exhaust), tried starting with the choke on, off, throttle closed, open, feathered, not getting any sign of ignition at all. I know there is a 'knack' to starting them, but the law of averages would say that we should have at least one bit of ignition, even if it doesn't run.
We're running out of ideas, we must have tried starting it about 2-300 times so far, if we can't get it running soon it's going in the bin.

[deadgrass.]

is the cam timing set corectly ?

dave.

[12royal]

hi Cliff, ive posted an image on the Facebook mt page showing the correct timing set up on my 500.
im unsure how to post images on this forum so until then have a look on Facebook mt forum
hope this helps, Alan

[Cliff]

is the cam timing set corectly ?

dave.

Hi Dave, yes, checked it twice, also measured the low and high coil impedences, all OK, and checked the generator windings for the ignition bits, also OK.

Cliff

[Cliff]

hi Cliff, ive posted an image on the Facebook mt page showing the correct timing set up on my 500.
im unsure how to post images on this forum so until then have a look on Facebook mt forum
hope this helps, Alan

Hi Alan, thanks for this, I'm going by the workshop manual, which hopefully is the same as your photo!

Cliff

[Chris001]

I had a problem that sounds exactly the same. Good spark, timing ok, fuel ok. In fact I hand riden to work on my MT that morning. Had to get AA home. After going through everything again for the third time with the AA man. It took about 30 minutes to fix once I'd got home.
What I did was went throught every connection in the ignition circuit. There aren't that many. Make sure they are alll clean with no tarnishing/ corrosion, it doesn't take much. Use white vinegar and a teaspoon of salt in a small dish. Enough to submerge the connectors once they are apart. It will take about 15 min. Of soaking a quick rub with wire wool and then a generous rinse of with water to stop any further reaction. Once all of the connections between the cdi, coil and stater are clean she should start and run if all is well also try disconnecting the black and white ground wire from the cdi. This wire is used to kill the spark.
The up short is, even though you have a spark in air outside the cylinder you may not have a spark under compression within the cylinder. This is usually a sign that tge coil is breaking down under load. This can only be diagnosed by swoping it for a good one. Other causes see the connections around the ignition circuit "See above". Other causes could be the slow running ignition winding on the stator. I've had that fail on mine twice. The first time it was the wire from the coil to the cdi that had broken. They get damaged overtime by the heat from the exhaust. The insulation can brake down and stiffen, leading to it cracking and allowing a short. These wires can be replaced with high temperature wire down to about a cm away from the coil itself and then sealed with heatshrink tubing.
All of the ignition components, the cdi, coil and ignition windings can be replace with aftermarket parts from rex's speed shop if required.
I hope this helps.