nzpeterb Posted April 4, 2014 Report Share Posted April 4, 2014 Hi all, I have just purchased a TY250. When it arrived the numbers indicate its actually a 1986 TY350 frame and engine bottom end with a 250 barrel and head. What are the differences in the bottom end of the 250 and 350 engines? Do they use the same flywheel weight and gear ratios? For example I thought the 350 had a heavier flywheel? Regards, Peter. Quote Link to comment Share on other sites More sharing options...
utahpete Posted April 5, 2014 Report Share Posted April 5, 2014 Hi Peter, I've read that the top ends can be interchanged. After looking at brochures for the two bikes, it looks to me that there is some difference that can be seen on the right side of the crankcase (http://www.yamahaty.com/english/brochuresen/1985en.html). As far as the flywheel goes, many of us who have the 350 have taken some weight off anyway. If your bike seems a bit slow to respond, take a look at the flywheel. If it still has the whole weight band (almost 7mm thick), then you may wan't to have some taken off. I ended up shaving 60% of the band thickness (25% of the weight of the whole flywheel). The original TY350 flywheel weighs 2.97kg and its part # is 46Y85550-20-00. You might be able to find OEM part # for the 250 in NZ. I can't seem to find it here ... we only had the 350 offered in the states. I bet the gearing is the same. Pete Quote Link to comment Share on other sites More sharing options...
nzpeterb Posted April 5, 2014 Author Report Share Posted April 5, 2014 Hi Pete, Thanks for the reply. Have established I have the 250 flywheel and the sluggish performance which I thought might be the heavier 350 flywheel was due to the carburettor. I found a blocked pilot, partly blocked needle jet and wrong needle jet and needle. Cleaned out the carb, dropped the needle one clip at a time till it was 2 clips lower and all of a sudden the bike is peppy and responsive. Will have to order the correct jets and should be all good. By the way the 250 flywheel fitted does not have the metal outer ring that is fitted to the 350 flywheel so I can now tell the difference. Regards, Peter. Quote Link to comment Share on other sites More sharing options...
utahpete Posted April 6, 2014 Report Share Posted April 6, 2014 Peter, Glad to hear that you have figured it all out. If the bike still has the original set of reeds, you may want to consider replacing them with Boyesen Power Reeds and doing the recommended mods to the cage as well. It will require some more tweeking of the jetting, but I think that you will find it well worth the effort. I'm sure you can get plenty of help here on the forum to speed up getting the jetting tweeked. I went leaner on the main, richer on the pilot, and richer on the needle position. Pete Quote Link to comment Share on other sites More sharing options...
nzpeterb Posted April 6, 2014 Author Report Share Posted April 6, 2014 Pete, Thanks for the reply. The bike had Boyesen reeds fitted by the previous owner. Took it on a trial today and bike actually went pretty well. (In New Zealand there is an air cooled mono class). Still a few things to sort out including the carb, and rear shock linkages, and try and find a better seat or replacement seat pad. Regards, Peter. Quote Link to comment Share on other sites More sharing options...
tony27 Posted April 7, 2014 Report Share Posted April 7, 2014 Hi Peter, if you want a manual for the 350 send me a PM of your postal address & I'll send down the photocopied 1 I used when I owned a 350 in the early nineties Quote Link to comment Share on other sites More sharing options...
bruced_500 Posted April 9, 2014 Report Share Posted April 9, 2014 Hope you don't mind me jumping on this thread. I've got a few TY250-350 cross over questions also. I just purchased my first trials bike ( TY350) . Question #1 Do the forks off the newer TY Monos like the pinky etc. bolt directly onto the older 1985 so I could have a disc brake ? Question #2 would the kick start lever from the 85 and newer 250's bolt onto my TY350 ? Mine is missing and finding parts for the TY350 seems very difficult here in Canada. Thanks Quote Link to comment Share on other sites More sharing options...
nzpeterb Posted April 9, 2014 Author Report Share Posted April 9, 2014 Hi Bruce, I assume you are suggesting swapping fork legs in the existing triple clamps. From what I can see the fork legs on 250 and 350 are both 36 mm so you should be able to swap them out. Kick start levers also look to be the same. Note there are two versions. Steel for most, but aluminium for bikes originally sold in Japan. Looking at the codes in a 350 parts book suggests the following differences between 250 and 350: - Cylinder, cylinder head, piston and gaskets. - Reed valve. It looks like only the stops are different. - Carburettor jets and float? Same carb body though. - Stator and flywheel. - The lower fork triple clamp. Unsure of the difference here but the part number is 350 specific. Gearbox gears are the same for both models. Regards, Peter. 1 Quote Link to comment Share on other sites More sharing options...
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