alan_nc Posted May 29, 2009 Report Share Posted May 29, 2009 Didn't want to twist the other flywheel topic. Does anyone know where I can get the weight (ring) for a 74/76 TY250 flywheel? I'm looking for the full width one with as much weight as I can get. I have a 1/2 width ring and it just doesn't let the engine lug down the way I would like. I have emailed Trails and Trials, UK and Speed and Sport, Inc., U.S. neither have responded to my email. Alan Quote Link to comment Share on other sites More sharing options...
jon v8 Posted May 29, 2009 Report Share Posted May 29, 2009 I took the ring off the 250 that I use probably a year ago,cant remember how wide it was,but i'm prepping the bike for a trial in the morning so I'll measure the width of the ring - you are welcome to it if its what you are after.I've got used to it without the ring,its easier to stop it with less flywheel effort - and I have yet to stall it. Quote Link to comment Share on other sites More sharing options...
woody Posted May 29, 2009 Report Share Posted May 29, 2009 I don't think the full width weight was a Yamaha option. There were full width weights available for the Majesty but these were made by John Shirt. They were generally for the 320 not the 250. They are pretty heavy. One of those on a 250 will kill the motor and the throttle response will be really slow, the motor just won't pick up. It's interesting what you say as generally, we find that the 250 doesn't have a problem lugging at low speed but needs the standard weight skimmed or removed altogether to get any sort of urgent response from the throttle as they lack decent power and struggle to pull with the standard weight in anything other than bottom gear. I was riding a 250 Majesty at the weekend which we were setting up. The flywheel weight is skimmed to about half its normal size and the bike is fitted with electronic ignition. We started with the ignition reasonably retarded and it was flat with no pull. Moved it onto full advance and the motor was pretty lively for a 250 and would lift the front wheel in second gear off tickover speed with a twist of throttle. It lugged right down low and showed no tendency to stall. Although it is a Majesty it is a standard TY motor, they weren't tuned on normal customer bikes, only suppoted riders. As I'm pretty sure the big weight isn't a Yamaha part I think you may have trouble sourcing one. You could try Ellastone Offroad in the UK as he has TY parts and has broken Majesties in the past, so it's possible (remote though) that he may have a big weight. Or he may know of another source. I think he is on a trip to the USA at the moment though so may be away for a week or so. Craig Mawlam who bought up the remaining Majesty stuff from Shirt doesn't have any. I asked as I wanted one for a 320. Other than those two, I'm not sure there are any other options other than getting one made. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted May 29, 2009 Report Share Posted May 29, 2009 I think Alan's bike is a TY250A and I know from back to back testing of my bikes, that standard TY250A motor performance is very different to the B and later models. The weight band on the A model is a bit narrower than the band on the TY250B and later models, but if you put a B or later weight band on the A model, it actually makes riding the bike harder, not easier. I know because I tried it. The problem with the A model comes from the internal differences between the A model and later models. I suspect it is the port timing but my early TY250A motor has never had the barrell off so I haven't been able to compare it with a later model barrell. The effect I'm talking about is that at extreme low RPM, the A model motor responds to throttle input quite weakly, but at a bit higher RPM the throttle response is fine. This makes the A model a bit exciting in tight riding (when the RPM moves through the transition in either direction). Alan the guys at B&J Racing in Tennessee have a handle on this and have some sort of fix available. Another alternative is to find a B or later barrell for your bike. Quote Link to comment Share on other sites More sharing options...
alan_nc Posted May 30, 2009 Author Report Share Posted May 30, 2009 Group, Well I actually have 2 ,TY250A's. They run/ride quite different. I have not taken the time to pull the carbs apart and check jetting to see if they are the same. The one bike has a full width weight ring. It will run down to almost no RPM, I have actually never stalled it. I have a fairly fast-pull throttle on it and I think it responds fine. The other bike gets jerky when it gets that slow. It has a 1/2 width weight ring. Maybe my problem is jetting or timing rather than flywheel weight. Other than changing the point setting - is there a way to adjust the timing on a TY250A. My backing plate is a direct bolt on with no slots in the screw holes for adjustments. Any other suggestions would be appreciated. Alan Quote Link to comment Share on other sites More sharing options...
feetupfun Posted May 30, 2009 Report Share Posted May 30, 2009 Yes change the timing by changing the points gap. It doesn't take much difference in gap to move the timing a lot. Are you sure that both your TY250As have TY250A barrels? http://www.trials.com.au/phpBB3/viewtopic....f=16&t=3938 Quote Link to comment Share on other sites More sharing options...
alan_nc Posted May 30, 2009 Author Report Share Posted May 30, 2009 Well you gave me hope for a minute or two. Went to the garage and checked - both are standard "A" barrels. The one that is jerky at low speeds I know to be stock bore, the other I haven't had the head off. Both have the stock "T" (whatever) carb. My assumption would be that you advance the timing by a smaller points gap and vice versa. Thanks for the information. Alan Quote Link to comment Share on other sites More sharing options...
feetupfun Posted May 30, 2009 Report Share Posted May 30, 2009 Oh well it was worth checking the barrells. Yes except it is the other way around. Opening the points gap makes the spark happen earlier. Quote Link to comment Share on other sites More sharing options...
jon v8 Posted May 30, 2009 Report Share Posted May 30, 2009 Looked at the flywheel ring I took off this morning,its 27mm wide and the engine is the later type with parallel fins and no oil feed boss at the base of the barrel.All 4 of the engines I have are 493 prefix - is there a way to date them more accurately ? Is it me or are Venhill clutch cables not very good ? I wonder if the genuine Yam ones are still available..... Quote Link to comment Share on other sites More sharing options...
alan_nc Posted May 30, 2009 Author Report Share Posted May 30, 2009 Jon, Let me measure my ring and see if it is any different. Can't help on the cable - I have a local fellow who makes up cables, which seem to work fine. OK, question for everybody: If I'm jerky at slow (I'm talking very slow) speeds which way should the timing go to possible correct the problem? Thanks Alan Quote Link to comment Share on other sites More sharing options...
jon v8 Posted May 30, 2009 Report Share Posted May 30, 2009 Retarding the ignition will calm it down,but if its jerky I'd be looking at the carb too - a lean mixture will make the motor play around,esp on a hot day.Any air leaks,perished inlet rubbers or failing main bearing seals will make the carb untuneable.(As will a worn carb.) Quote Link to comment Share on other sites More sharing options...
feetupfun Posted May 31, 2009 Report Share Posted May 31, 2009 Looked at the flywheel ring I took off this morning,its 27mm wide and the engine is the later type with parallel fins and no oil feed boss at the base of the barrel.All 4 of the engines I have are 493 prefix - is there a way to date them more accurately ?Is it me or are Venhill clutch cables not very good ? I wonder if the genuine Yam ones are still available..... Unless you know the engine number that the barrel came off originally, no you can't date them any better. What does it matter what year it was made if they didn't change the design between C, D and E models? From memory here is a guide to the 493 models numbers: The unique engine number starts after the 493- . If the number starts with 1 that means C (1976) model. 2 is D (1977) and 3 is E (19??). Check out John Cane's guide here and see if I remembered it right! http://www.tytrials.co.uk/technicalarticles_302159.html I had problems fitting a Venhill KT250 clutch cable to my KT250. It was the first Venhill cable I tried and I haven't bought any more since and so haven't tried the Venhill clutch cable made for the TY250. Apart from the KT, my bikes have clutch cables made by myself with inner and outer bought from the local bike shop and from some imported universal clutch cable kits and they work great. While Yamaha front brake cables are available (in black) and are very good, Yamaha TY250 twinshock clutch cables are not available any more/yet. Quote Link to comment Share on other sites More sharing options...
jon v8 Posted May 31, 2009 Report Share Posted May 31, 2009 Ta for that,it doesnt really matter what year they are,but people come into my workshop and see all the bikes and ask how old they are - seems a bit odd that I dont know.Mr Canes site has sorted that out.Think I'll get going making my own cables too,as I'll need some for the TY/XT225 project that I really need to get on with. Quote Link to comment Share on other sites More sharing options...
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