Tillerman6

I have a 74 model 250A serial number 434-011251 and I need the shop manual for it. That's the downside. Now the good side is that I also have a 1975 B model shop manual if anybody needs one.? Maybe we can trade? I have been using the info from the B model shop manual to do all a the tune up and work on the ignition (Magneto and Points/condenser) up to a point. I checked out the schematic for the B model and it seems to have a couple of things different about it that I can't find or explain on my A model. #1 There is NO DIODE in my wiring harness now. ( at least I can't find one) I don't know if it has been removed, or it never had one? Normal for a 74?. THe B model shop manual says the diode is to prevent the engine from running backwards. Now I'm not sure if they really mean running backwards or just back firing, which my bike does A LOT! (TOO MUCH). Now on a 250 that is not a leg breaker, but I would be more than happy to make that problem go away. If the diode was a modification or addition to the 75 model that fixed the back firing problem, then by all means where do I get one? #2 the left side coils on my A model (there are two of these on this bike) do not resemble the photograph of the left side coil in the 1975 B shop manual. There is only one coil on the left side of the 1975 B model) Is that right? The TY 250B 1975 book shows only a single coil on the left side and I am wondering if: #1 Does it have a stronger spark? #2 if there is any reason to swap out my dual coils for that single coil on the 75 model? Has anybody done this? So I'm wondering if the dual coils are the stock ones for this 74 model A? Ignition timing- This bike is a points and condenser bike. The magneto system seems to be very difficult to set up properly. This is mostly due to the fact that the magnet rotor wheel (flywheel has only 3 small holes in it for access to adjusting the points. All the adjustments are done thru these holes since the flywheel must be in place to time the engine. And the Yamaha parts are extremely expensive for me! They want 50 bucks for the points and 30 bucks for a condenser or there abouts. (any alternatives anyone?) The Yamaha part numbers (if they have not been superseeded) are Points 434-81321-10-00 and condenser is 207-81326-90-00. I am running OK right now, but I would like to have the next set in the box waiting for the next time I need them. Since you are supposed to remove the head and set up a dial indicator on the piston, you have to remove the gas tank, seat, exhaust pipe and the magneto rotor too if you are going to inspect and or replace the points or condenser. There has to be an easier way! So what I did was I put marks on the flywheel and a mark on the side of the crank case to line up when the crank was at TDC with the factory spec of .122" BTDC. I set this up perfectly and set the points gap for .016" while at TDC, but the engine would never start. Kick back a lot, but never start! My feeling is that this is too much advance, so I ended up fudging a bit and just eyeballed the setting when the timing was more like .080" BTDC with the .016" of gap. The locals at the Yamaha shop say that this timing is not critical, so I am going with their advice for now. The bike does start a lot better now, and even though it back fires aganst the kick starter, at least it does start and run pretty well. Don't know if I need that diode? Is there anyone on here that has a TY250A model with some experience with these problems or solutions? I am all ears! Thanks! - Tillerman6