belldane Posted February 19, 2009 Report Share Posted February 19, 2009 Hi all I recently posted a message about the old TY I am restoring. As some of you may know I managed to find an original carb for it on ebay (TK) I cleaned it it all up and came up superb. Installed it and to my dissapointment the bike still has no whoomph. The number of the motor is 434-008250 so I am pretty certain it is an A model (You experts out there correct me if I am wrong) The bike starts first kick every time, seems to have some power down low, but when you hit the throttle, just wont rev right up. I suspect that I may need new rings ( they have not been changed in about 25 years and I also thought the timing could be out. What should the timing be set BTD on an old A please. This bike is driving me to drink!!!! I have restored 4 Montesas which are now in the shed but this Yamaha is driving me nuts. Any help you can give me much appreciated. Thanks Quote Link to comment Share on other sites More sharing options...
dave dix Posted February 19, 2009 Report Share Posted February 19, 2009 Could be a crank seal and have you checked that the crank drain screw is still present Dave Quote Link to comment Share on other sites More sharing options...
tony283 Posted February 19, 2009 Report Share Posted February 19, 2009 The TY250A, which from those numbers is what you have, is a very simple machine to get running VERY smoothly. First thing are you running on posilube or on pre mix? Second despite having acquired a used carb, what were the jettings? If you are running on premix, was there, or is there any of the old fuel in the tank? What spark plug are you using? Should be B7ES. Points and condenser? Points should be cleaned and set to 15 thou, plug to 22 thou. You can get to the points through the flywheel holes. The timing is a Fixed stator, no adjustment. If you are on premix is the oil hole into the cyclinder sealed off? Finally the wiring from the coil to the top coil .... is it hard and brittle, very common problem? Having checked all that lot, it might be the ignition side oilseal or poor inlet air from the filter. If it starts well I would suggest it is unlikely to be the oil seal as you need crankcase compression, usually 3 kicks. Most TY250A engines run forever but being old the rings could be stuck in their grooves. You might also check the reed petals and see if they open and close. Good luck! Tony Quote Link to comment Share on other sites More sharing options...
stork955 Posted February 19, 2009 Report Share Posted February 19, 2009 After you have have checked all above - Clean exhaust system? Cheers, Stork Quote Link to comment Share on other sites More sharing options...
feetupfun Posted February 20, 2009 Report Share Posted February 20, 2009 If you want to check if your timing is right with a timing strobe, it should be about 22mm BTDC as measured on the OD of the flywheel. You will probably have to make your own marks on the flywheel because Yamaha did not mark them. You will know when you have everything right because with the TK carby, and everything set to normal, that motor is one of the smoothest and most even running two strokes you will find, and has plenty of stick to boot. Quote Link to comment Share on other sites More sharing options...
woody Posted February 20, 2009 Report Share Posted February 20, 2009 If you want to check if your timing is right with a timing strobe, it should be about 22mm BTDC as measured on the OD of the flywheel. Typo - 2.2mm Quote Link to comment Share on other sites More sharing options...
feetupfun Posted February 20, 2009 Report Share Posted February 20, 2009 (edited) Typo - 2.2mm Not typo. I'm giving a measurement for the outer surface of the flywheel, not the distance the piston moves. Standard TY250A spark timing measured using piston movement is 3.1mm BTDC. Edited February 20, 2009 by feetupfun Quote Link to comment Share on other sites More sharing options...
woody Posted February 20, 2009 Report Share Posted February 20, 2009 Not typo. I'm giving a measurement for the outer surface of the flywheel, not the distance the piston moves.Standard TY250A spark timing measured using piston movement is 3.1mm BTDC. Yes, sorry, I forgot the question mark at the end as wasn't 100% sure which measurement you meant - I strobed mine with a timing gun the other day so am going to check out of interest to see how the distance between my timing marks compare with yours. Coincidently I run at 2.2 BTDC on the timing guage as I run mine retarded from standard (320 Majesty) hence my confusion Quote Link to comment Share on other sites More sharing options...
belldane Posted February 21, 2009 Author Report Share Posted February 21, 2009 Dave dix - crank case screw still there. I plugged it up when I started using premix. Will have to change crank case seals as the crankshaft bearings are a bit dodgy. Tony 283 - See above about the premix. New fuel was put in tank, spark plug replaced. Will check points and condenser tomorrow. I have to replace the crank bearings so will replace rings while I am at it. On the reed petals, they appear to open and close Ok. Just one thing, or two actually, the bent pieces of metal next to the reeds (the bent ones appear to be a bit rusty. Does this matter. The straight ones on the inside are fine. The other thing, when I took the reeds out I didn't notice which were on top. They appear to be the same either way they go in. Is that right? Stork 955 - exhaust was cleaned out a few months ago so I don't suspect that may be the problem. Feetup fun and Woody - Have got a dial gauge so will set timing at 3.1mm. Just another question please. I don't know if the TK carb has been fiddled with. The main jet which I assume is the one piece job with the nut at the bottom of the bowl does not a number for the size. If there is one there where is it? The pilot is 50. Does it sound right? Give me a Monty any day!!! Thank all for your help. I will get this b-----d sorted out. Ps Up until now I have been getting some parts from bultacouk.com. Do any of you know where I can get parts in Australia? Thanks again. See ya all Quote Link to comment Share on other sites More sharing options...
belldane Posted February 23, 2009 Author Report Share Posted February 23, 2009 Hi all Just tolet you know that I have sorted the old TY out. I readjusted the points and timing, cleaned the jets out again and I noticed when I screwd the main jet back into the fuel bowl that the holes in the whatever which deliver the fuel to the jet could not be seen through the small hole at the bottom of the bowl. I just unscrewed it a bit and lined up the hole in the whatever with the hole in bowl, put it all back together and it is a different bike. I really don't know whether it was one thing or the other or both combined. Thanks for the help Quote Link to comment Share on other sites More sharing options...
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