dazid1 Posted November 24, 2007 Report Share Posted November 24, 2007 I have a 1978/9 320 Majesty, its been hanging araund for years with hardly any use. It was started up every two or three years and always started second kick or so and ticked over superbly. The problem was it would not rev and was very hard to ride as it 4 stroked when you tried to ride it, so it just sat there. I have recenty tried to sort it, I was reluctant to try and remove the flywheel as I had no puller and had been told that even with one its sometimes a pain. But get this, it started to come off while I was messing with it I heard a slight scraping and it was the flywheel touching the inside of the cover. I removed it and changed the points, I fitted the new points on the back plate in the same position, and as the old ones were ok really I thought it was about right.The comming loose of the flywheel had turned the key to dust so I made another one. The keyway was a little damaged so the key was loose, so loose that the magnet pulled it off each time I tried to fit it, so I stuck it in with locktite. Before I did this I put it back without a key and alough it was a pig to start it ran much th same as before. (Back to square one) Its now stuck in with the flywheel on and it will not run (timing)??? I have got a good spark and fuel to it but it will not run. I don't know the correct points gap but have a feeling it is big (something about the timing as its now a 320) and the back plate is all the way forward in the slots as it was before, the only other point worthy of note is that I had to tweak the coils as the flywheel was catching them when i put the flywheel back. the only comclusion to this is that they must have been knocked by the flywheel when it came loose, I undid the four cross points and adjusted them so the flywheel did not catch If they have to have a specific clearence I am not aware of this. Sorry about the long thread but it may save a lot of questions. Thanks in advance Daz Quote Link to comment Share on other sites More sharing options...
feetupfun Posted November 24, 2007 Report Share Posted November 24, 2007 The things that sounded a bit dodgy to me in your story are that: TY backing plates don't normally have slotted holes (maybe yours has been modded or is from a different bike). There is an ideal range for points gap that has nothing to do with the capacity of the motor. It is chosen to give the best spark. For Yamaha motors/ignitions like yours the ideal gap range is 0.3mm to 0.4mm, and you should be able to get the timing right without going outside that range. If the backing plate is moved too far away from the ideal position in either direction, the flywheel magnets won't be in the right spot relative to the ignition coil when the points open (causing weak spark). I suggest you set the timing from first principles ie using piston position and measuring the advance when the points open and also make sure the backing plate is in the right spot. If you have a picture showing the position of the backing plate on a standard TY250 you could probably get yours close enough to the right spot to eliminate that as a possible issue. To start with I would try somewhere between 2 mm and 1 mm BTDC with that motor. The ideal clearance for the coil laminations is as close as you can get without anything touching. If your bike has been sitting around for a while it is possible that there is now a bit of movement in the crankshaft bearings which could have caused the magnets to hit the laminations and maybe even loosen them and the flywheel. It would be pretty unusual for the not-revving issue to be caused by the timing being set a bit too far either way. Much more likely to be: Blockage somewhere (air inlet/filter, exhaust pipe/muffler, carbon buildup in exhaust port/ inside head) Worn rings Broken or bent reed/s Something wrong in the carby (some OEM TY carbys have an o-ring that seals the main jet into the needle jet and when this o-ring leaks, the bike will run very rich above low throttle openings) Quote Link to comment Share on other sites More sharing options...
micky Posted December 18, 2007 Report Share Posted December 18, 2007 Gents, Sorry to go back to this old item, I have just seen Mr Feet ups reply which is all good info but I seem to remember Mr samb saying the factory Majesty 320's that were over bored had slotted back plates? Quote Link to comment Share on other sites More sharing options...
woody Posted December 18, 2007 Report Share Posted December 18, 2007 My 320 has a slotted backplate and welded up crank pin - Shirty mods ?? A mate who looked at the barrell said that it had been ported but I wouldn't know/can't tell. Maybe an ex-team bike Quote Link to comment Share on other sites More sharing options...
tony283 Posted December 19, 2007 Report Share Posted December 19, 2007 Does sound as though this motor is in a bit of a mess! The 320 motor that I have does not have a slotted back plate as the "donor" engine was a 74 TY250A. My advice would be to obtain a standard unslotted back plate and fit that or compare where the standard holes are relative to your slotted version. Mark it as a reference. If this bike is only started once every 2 years go back to all the basics. Clean fresh fuel at around 40:1 clean all jets in the carb and note what sizes the main and pilot jet are. I'm using a new Mikuni with a 290 main, 35 pilot and mid setting on the needle. Remember the point gap should not exceed 15 thou. Set a long reach plug at 22 thou and it should run. Good luck! Tony Quote Link to comment Share on other sites More sharing options...
samb Posted December 19, 2007 Report Share Posted December 19, 2007 the back plates were slotted on all the later majesty,s 320,s , to stop the engine from running in reverse . when pulling 3rd or 4th at low revs . this could be very frightening whilst riding a section .the critical bit is setting the ignition timing using a dial gauge in the spark plug hole and a meter from the wire that comes out of the engine ( black one ) with the positive from the meter and the earth clipped to the enging casing . the magneto wants turning in reverse there is a directional arrow on the face of it . until the dial gauge reads top dead center . then push the dail gauge down until 4 full revolutions have shown on the face , the screw on the addaptor needs nipping up . Turn the magnetot 2.3mm b.t.d.c the points should now be closed , if not using a flat screwdriver about 10mm wide adjust the points . by inserting the screwdriver through the hole at the top of the magneto there is a slot wher the points are attached to back plate . it only requires a small adjustment , then go through the same process until you get the timing set at 2.3 mm b.t.d.c . i have never set the points gap on any majesty i have built or worked on .did u clean the points faces before fitting them as they come with a hard plastic coating on them it may be worth while getting a genuine yamaha woodruff key , before fitting it if the matching tapers on the crank stub and inside the mag can be cleaned up using , grinding paste . you said that the magnets were catching when you rotated the flywheel . is there any up and down play in the main bearings . the 4stroking could be caused by the condensor breaking down . the float height valve sometimes sticks when a machine has not been ridden for a period of time , so strip the carb down and remove his and check it,s action . whilst the float bowl is removed check the pilot jet is clean by removing it and blowing through it either way , the hole is smaller than a pin . never wipe the carb out with rags as the fluff only blocks the jets and holes . good luck sam b Quote Link to comment Share on other sites More sharing options...
tony283 Posted December 19, 2007 Report Share Posted December 19, 2007 Have to agree with Sam b. The new OEM points come with what looks like a teflon coating on the faces and no spark will jump through that so emery or lightly file the faces until bright metal comes through. While you are in there, yes change the condenser..... leave nothing to chance and clean up the inside of the flywheel as little bits of metal can stick to the magnets between the gaps (bits of your old key). A clean carb is essential so do as sam says... Stick to the simple things.. Wont start..... usually blocked choke Won't run without choke......normally plugged pilot jet poor response off idle...... airscrew or incorrect pilot jet fuel everywhere......... inlet valve may have a calcium like deposit..... light emery it off Other simple things to inspect are the plug wire.... has it touched the exhaust and melted a bit? Condition of plug cap both inside and out ? Carry on taking the tablets! Tony Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.