no balance Posted July 10, 2021 Report Share Posted July 10, 2021 Hi, last time out on the Ossa Mar it decided to pack up, after stopping, I tried to restart it but it would only kind of four stroke with the throttle wide open. Back home and the bike cooled down, it would start and run ok for a few seconds and then start four stroking and cut out. I changed the coil with a good spare one I had but still the same, when checking the spark it was very weak. So I ordered a new electronic ignition to replace the notoriously troublesome Motaplat electronic system, with the new ignition fitted the bike started first kick, the problem I have now is the bike lacks throttle responce to the point that it would be useless, on the old system it was quite lively for a Mar and equally as good as my Bultaco M91, any suggestion as to why it's not what it was would be most welcome. Cheers. Quote Link to comment Share on other sites More sharing options...
teamferret Posted July 10, 2021 Report Share Posted July 10, 2021 Have you checked that the timing marks are in the right place and that it srobes up correctly? Quote Link to comment Share on other sites More sharing options...
no balance Posted July 10, 2021 Author Report Share Posted July 10, 2021 Thanks for your reply, but his ignition comes pre-set and the fitting instructions say not to move it from that setting!! it can be advanced and retarded and doing this has made no difference. As for timing marks for strob use, I will have to check that out. Cheers. Quote Link to comment Share on other sites More sharing options...
no balance Posted July 12, 2021 Author Report Share Posted July 12, 2021 Been looking at the ignition again tonight and I think I've sorted it, after returning the stator plate back to the position it was supplied in, I noticed it had another set of threaded holes next to the one's being used, so I moved the fixing bolts into the other holes and moved the stator plate as far to the left as it would go, refitted the flywheel and cover and started it, the differance was huge and it was back to how it was before the old one packed up. I'm hoping all I need to do now is strobe time it to get it spot on. I'm only used to timing bikes with points and can't find any marks on the flywheel or case to use for strobing it and the flywheel doesn't have a hole for a timimg pin/tool. So if I use my DTI gauge and set the piston at 2.5mm btdc and put my own marks on and strobe it with the engine reving fast to get full advance, would I be doing it by the correct method? Quote Link to comment Share on other sites More sharing options...
TL350 Posted September 13, 2022 Report Share Posted September 13, 2022 That describes my bikes symptoms perfectly and it still has original Motaplat ignition. Could you please supply details of replacement ignition system you have used so I can replicate you success! Quote Link to comment Share on other sites More sharing options...
feetupfun Posted September 13, 2022 Report Share Posted September 13, 2022 On 7/13/2021 at 6:56 AM, no balance said: Been looking at the ignition again tonight and I think I've sorted it, after returning the stator plate back to the position it was supplied in, I noticed it had another set of threaded holes next to the one's being used, so I moved the fixing bolts into the other holes and moved the stator plate as far to the left as it would go, refitted the flywheel and cover and started it, the differance was huge and it was back to how it was before the old one packed up. I'm hoping all I need to do now is strobe time it to get it spot on. I'm only used to timing bikes with points and can't find any marks on the flywheel or case to use for strobing it and the flywheel doesn't have a hole for a timimg pin/tool. So if I use my DTI gauge and set the piston at 2.5mm btdc and put my own marks on and strobe it with the engine reving fast to get full advance, would I be doing it by the correct method? Be aware that some 2 stroke ignitions have a curve that advances the timing as the RPM rises and at some point then start retarding it as the RPM rises further. You will be able to see what your ignition does when you put a strobe on it. Yes make your marks somewhere near where you think you want the spark. If it's got a flywheel similar OD as an MAR I would think that 22-24 mm measured around the rim of the flywheel BTDC would be in the ballpark. With a trials engine, the spark timing at low RPM is probably the most important thing and trying out different timing settings for low RPM will yield the best result. 1 Quote Link to comment Share on other sites More sharing options...
no balance Posted October 4, 2022 Author Report Share Posted October 4, 2022 Hi, sorry for the slow responce guys, haven't looked on TC for a long time. Truth is I never did get the electronic ignition to work, I sent it back to be checked for a fault but was told it was fine and the most likley cause was the crank case oil seals or a carb issue. I did get it to run again using the old Motaplat electronic ignition by fitting another HT coil. I also replaced the new Mikuni carb because of over fuelling issues, no amount of jet changing etc made any difference, so I fitted a old 70's Mikuni (the bolt on flange type) that I removed from a 250 Bultaco Sherpa years ago and it's run spot on ever since, and it's now my bike of choice. Plug colour is good and it starts cold or hot really well, it pulls from nothing so well, cutting down the use of the clutch in sections. I still don't know if the new electronic ignition will now work on the bike because I haven't tried it, I did try to fit it to my other Mar but when I pulled the fly wheel it was the wrong type, sods law!! Quote Link to comment Share on other sites More sharing options...
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