spokerider Posted April 7, 2009 Report Share Posted April 7, 2009 I took the 1984 TY 250 mono [ new to me ] out for a ride after stripping and cleaning the carb. I seemed to run great [ with the TY carb ] and pulled strong on the run. I had ridden some fast logging roads in 4th and 5th gear, then went to a single-track trail up a mountain. An hour into the ride I turned around to come back, and began picking my way down the rough single track in 2nd and 3rd gear using engine compression to slow the decent. 10 minutes later, the engine quit and would not restart, so, out with the spark plug and it looked to be very black. A new plug and I was good to go.....engine started easily and away I went. The black fouling on the plug *felt* on the oily side, but was not shiny / wet looking, nor was it dry / fluffy looking. Now, I'm wondering, is this oil fouled or rich-gas fouled? I'm using Amsol synthetic oil at a 50:1 ratio. Plug is a NGK BP6ES. Exhaust system has been cleaned out by previous owner, and I have the air filter well oiled with air filter oil. Jetting in the TK carb is factory as far as I know....... Will a TY foul the plug [normally] when using engine compression and running slow down a steep hill for 10 minutes? How many spare plugs you guys taking on a ride? Hummm....I'm thinking I'll be needing three, lol. In fairness, this was my first ride with the bike. Next, a question about the mono shock. The 84 shock does not appear to have any adjustment for preload to the spring in which to set sag. There is an air valve on the top of the shock that slows rebound when I add air, but that's it. Mine has a blue colored shock spring. Can a heavier spring be obtained and put on? Perhaps from a different model Yamaha?? I need a stiffer spring as the stock one is too soft with too much sag. Other than that, the bike was a blast to ride! Quote Link to comment Share on other sites More sharing options...
dave dix Posted April 7, 2009 Report Share Posted April 7, 2009 I have often fouled the plug usually by too much oil in the mix so its quite possible to oil up by running on compression and with an oily air filter. Just take a spare along with you (as you did) and enjoy yourself. Later bikes had a better rear shock so you could get a newer one to replace it with Dave Quote Link to comment Share on other sites More sharing options...
spokerider Posted April 8, 2009 Author Report Share Posted April 8, 2009 I've been looking a little for a newer rear shock, one that has the remote resevoir, but have not seen any around on ebay, etc... Did Yamaha offer different spring options on the 84's to match different riders weights? The damping is great on the oem shock, I was just hoping for a stiffer spring. Even a spring from a different bike might work. Dunno what weight the bue spring that I have is rated for. Just wondering if anyone else has experimented with different shock spring weights. Quote Link to comment Share on other sites More sharing options...
spokerider Posted April 9, 2009 Author Report Share Posted April 9, 2009 I took the fouled plug to my local bike mechanic.........he said running very rich and it's not fouled from oil, but gas. Having done that, I raised the needle in the TK carb up one notch, so it'll be a tad leaner. Also tried leaning the slow air screw a little too. The needle was in the middle position, is now clipped in second notch from top. The mechanic says these carbs never were really good even when new....... What setting are you running your TK carbs? Can you even get different jets for these carbs? I'll fart around with this TK for a while longer.......... Quote Link to comment Share on other sites More sharing options...
kuelmuel Posted May 7, 2009 Report Share Posted May 7, 2009 I've had loads of trouble with my TK carbs, they always seem to run rich. On my current one it has a brand new 140 main jet, which is the smallest standard one and the needle is in the lowest position, and it still oils the plug up every so often. From what I hear they always did run a bit rich, so with 20 years of petrol and air running through it, they tend to run even richer. My next port of call will be the needle, it appears to me to run rich from having the throttle about half open to fully open, but as it has a brand new jet it should be sorted. You just have to keep testing and fettling, each one is different, the one in my 88 doesn't seem that bad, but the one in my 84 was fairly knackered. Quote Link to comment Share on other sites More sharing options...
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