charliechitlins Posted September 20, 2011 Report Share Posted September 20, 2011 Tidying up the wiring is good, but it probably wouldn't help a problem that doesn't occur right from start-up. I know this is a long shot but...do you have an in-line fuel filter? Is there any metal on it? Is that metal resting on the head, cylinder or exhaust? Also...check your fuel delivery. A float bowl that isn't staying full enough could cause a problem that wouldn't manifest for a couple minutes...or when the engine is under more load and requiring more fuel. Quote Link to comment Share on other sites More sharing options...
black111r Posted September 20, 2011 Author Report Share Posted September 20, 2011 I have been test running it with clear hose as a fuel line. Petrol flow is constant, though the misfire, when warm, feels and sounds like it is running out of fuel. I do not think this is the case though as I have tested it with two carbs, one of them being brand new. I am thinking that the issue lies with the LT/HT wiring. ie something is getting warm/hot then expanding and contact being lost. Will revert later Chris Quote Link to comment Share on other sites More sharing options...
charliechitlins Posted September 21, 2011 Report Share Posted September 21, 2011 Not being a wiseguy here, but... Did you check the fuel tank vent? Quote Link to comment Share on other sites More sharing options...
keychange Posted September 21, 2011 Report Share Posted September 21, 2011 The LT problem can occur as the engine warms up and things expand - actually I think David also suggested that you check the mounts etc - I think he is looking at earth problems. I had similar issues with my TLR which was simply a loose earth connection on the frame - although for me it only caused an issue under higher revs. Also ensure that your earth connections are on bare metal not painted if so scratch the paint off. Charliechitlins is of course correct - check your tank breather as you may have an air lock Quote Link to comment Share on other sites More sharing options...
black111r Posted September 21, 2011 Author Report Share Posted September 21, 2011 Got the bike back together again today. I had glued the HT lead back into the HT coil (as it was v. loose - most likely due to hundreds of plug changes that I had made over the last couple of months). All the earth contacts points were cleaned and the HT lead cut back, recapped and the cap cable tied tight to the HT lead. I also encased the HT lead , to sheath the flatten (burnt) areas, then cable tied all to the under tank frame. Air box cleaned and a good seal to the carb flange. I did not undertake David rewiring trick but took a heavy hammer to the aluminum bash plate and made a bit of space for the LT wires where they exit from under the stator. The wires looked OK but one had some slight damage.(red). Put it all back together, filled it with 25-1.................and the bloody thing started first time and proceeded to run flawlessly, with a beautiful idle for half and hour or so. The bike now has a good clean idle with a good plug colour. (this must be the new Mikuni - Speed and Sport in the US, jet sizes as mentioned before - $US120) So to summarise I think that it was the HT lead and previous to that it was the combination of a worn Amal carb that had me changing plugs that caused the damage to the HT cable. Or it might have been loose, who knows ? Anyway thanks for all for the advice and encouragement to keep going. I am new to trials and haven't touched a motorcycle since I was 15 (some 37 years ago) Its a big learning curve, but great fun (somethimes!). See you at the next trial................have to learn to ride it now! Chris Quote Link to comment Share on other sites More sharing options...
brian h Posted September 24, 2011 Report Share Posted September 24, 2011 The Ossa MAR uses the dreaded Motoplat ignition,I am not familiar with the points type ignition as my Ossas have always been pointless. If you have this system, the stator coils are very finely wound with very fine gauge wire, these break down when hot and everything else stops. First you need to remove the flywheel, mark and remove the stator and examine the wiring that you can see as most of the stator is encapsulated in resin. The ignition wires from the Primary windings to the HT coil are Blue and Black, these ideally need to be repositioned to exit the flywheel case at the 1 oclock position by drilling a hole for the wires to pass out alongside the front engine log then silicon seal and take the two wires up the front RH frame tube to the HT coil under the tank. The original design with wires coming out at 6 oclock position is fine until a rock hits the bash plate and they get crushed or waterlogged! Miller Products sell the PVL Motoplat HT coil replacement for the pointless ignition - these are good, however, the next step I would suggest is to swap your ignition stator with one known to be good if you can find a friend with one that works. I rewind the trigger coil and the primary stator coil with more turns and thicker wire for each, this produces an excellant spark, there can only be three defects - ignition, carburation or mechanical!!. Hope this helps Quote Link to comment Share on other sites More sharing options...
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