ES 250 Trophy starting problem

[stogadog]

Hello everyone! This is my first post as I came across this site today whilst looking for some tips about my ill ES250.
I got the bike last month and have been well chuffed with it until last Friday when it stopped working.
Here's a piccy of it -

Here's what happened. I was riding along when it started to miss , almost like it was running out of fuel - then pick up again. It just about got me where I was going but then wouldn't start afterwards.
When I got back home (recovery truck ride!) I cleaned out the choke mechanism and it started up but wouldn't rev properly then died and would not start again.
I have cleaned out the carb, reset the flost height etc and it made no difference - the only thing I can get out of it is a backfire and the occasional brief burst of life.
Right then - time to look at the ignition system. It has a twin plug head fitted and also has Boyer Brandsen points assist ignition. The points were sticking slightly so Ive cleaned them up and regapped and the timing hasn't moved. I checeked the voltage on the battery and that was 6.2 V. I've heard that Boyers are quite sensitive to voltage so I charged it up for a couple of hours to 6.6V (static) and after a couple of kicks it fired and ran for a while but would not start again after that.
I'm thinking that ignition problems seem the most likely now - has anyone else had problems with these Boyer units? Or any other ideas of stupid things I may have missed. Oh I also put new plugs and that made no difference either.
Phew - well that was a long winded first post - I don't usually witter on!

[djsbriscoe]

Hi,
Have you tried running the engine without the petrol filler cap on as an experiment? It could be a vapour lock. There should be a small air bleed hole in the filler cap. This could be blocked. Just something to try.
Are you a member of the MZ owners club yet? Just thought you could attend the section meeting at the Eagle and Child in Leyland (near Preston). The club can be very useful for advice. I've been once or twice when I was living in Manchester.

David.

[GDMZ59]

You have to check first if it is fuel related or electrical. Check if the plug is wet or dry after several attempts to start. If its wet it means you are getting fuel. Try removing the plug and earthing it on the engine head and with a small screw driver open and close the points and see if you are getting a decent spark.
If its fuel related check the fuel from the tank to the carb. Turn off the tap and remove the tubing and turn on the tap, you should have a good flow. As per the previous post did you try the bike with the filler cap off?
Try removing the plug and put a thimble full of fuel in the plug hole. Replace the plug and kick and see if the bike runs.
Did the bike get wet?
Have you sprayed WD40 or the equivalent onto the coil and plug leads?
GDMZ59

[stogadog]

hi . Thanks for quick replies! I do have a decent fuel supply to the carb and are getting a spark - this is what's confusing the hell out of me. It's not the best spark in the world but I'm not sure with having the twin plug head whether this would kind of "dilute" the spark as there is two at the same time. I haven't tried putting any fuel into the barrel itself although I did try some easy start yesterday into the air filter and that made no difference. I've also cleaned out the vent hole and even tried it without the fuel cap to no avail.
A few people have mentioned the club meet up at Leyland. I think I shall go over there and join up next month.

[Eric Frith]

A freind of mine used a Boyer system on his race bike.............the thing broke down at nearly every meeting.

The system was removed, sent back, tested, refitted three times and then went in the bin.

Eric

[djsbriscoe]

Hi,
I've re-read your post and to me it points to a defective condensor across the points. A faulty condensor would also upset the transistorised ignition.
Best to put a new set of points and a new condenor in first of all. If it still doesn't work go back to a standard ignition setup and try it without the boyer setup.

David.

[stogadog]

Well been playing around today and removed the Boyer from the ignition system and replaced it with a normal 6V coil.
To no avail... Nothing changed at all.
I hadn't thought about the condensor - I don't know what they actually do! The only thing I do know is that only once have I replaced one when I've had problems with other bikes and it's made any difference so didn't consider it as there was a spark.
I guess a new one and points will rule those out as well.
This frustrating the hell out of me now!!!!

[GDMZ59]

If you have a multimeter, measure the voltage across the + and - terminals of the battery. Turn it to DC volts and it should measure 6.2 to 6.4 Volts. If the voltage is well down it wont start. You could then try charging the battery overnight and see what you have in the morning.
GDMZ59

[djsbriscoe]

Hi,
The condensor/capacitor stores the back EMF from the primary of the ignition coil when the magnetic field collapses as the points open. It prevents burning of the point contact surfaces. However they can fail and end up shorting the points. If they do short out the engine will not run. The short can be intermitent and may only happen when the component is stressed. If you could remove the condensor and test it with a portable appliance tester (set to test insulation resistance) it should fail the test (not an option unless you're an electrician). An ordinary multimeter set to a high ohms range may not detect the failure however.
Having said all that I could be wrong, but you said you had to clean the points.
Just try it and see.

David.

[stogadog]

Ordered a new condensor and points from Burwins today so in a few days I'll see if that makes any difference. The battery is fine by the way - reading between 6.2 and 6.3 last couple of times I checked it.

[stogadog]

Well - had another go at it tonight and still no life. Ive replaced the condensor and points this evening and it's still exactly the same. I guess the next thing to check is the compression. I think I can borrow a compression tester off a mate but does anyone know what sort of compression it should have when it's right??

[djsbriscoe]

Hi,
Have you tried it with a another coil, any coil would do just as a test? You could try testing the primary and secondary resistance of the coil with your multimeter set to Ohms. The coil internal insulation could be breaking down, so do a test with the meter probes between the HT lead and the primary.
Have you tried putting the electronic ignition back?
Best to exhaust all the electrical checks first then you can definately rule them out if everythings OK.
I'm just suggesting the approach I would take.
I'm not sure how you test the compression on a two stroke, do you feel any resistance when you use the kick starter?

David.

[stogadog]

I'm goint to try putting the electronic stuff back on over the weekend now that the new points etc are on it - as said the coil I swapped over to may be knacked as well. Also someone suggested at work to day that the crankcase couldve flooded with fuel as a result of the float being damaged. This is something Ive heard of happening with Bantams quite a lot so has anyone heard of it happening on mZ's as they are a similar design. If so how do I check and drain it etc??

[GDMZ59]

Hi Stogadog, Have you measured the voltage at the ignition coil is the same as what it is at the battery prior to starting. Check that that you dont have any bad connections at the ignition switch etc or damaged wires under the tank or coming up from the points etc.
Just want to say to try all the simple things first as 99% of the time it is something small. You can look at compression testing and adjusting the squish etc. Crankseals may be knackered but these all involve a bit of work. I would eliminate all the easy things first.
GDMZ59

[stogadog]

Certainly trying to eliminate all the easy things first! The voltage across the coil compared to the battery? Would that mean testing across the coil terminals or testing across one terminal and earth? Forgive my lack of knowledge - I hate electrics! I have also tried putting the electronic ignition back on today and it still doesn't work.