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Old 05-12-2011, 09:06 AM   #1
atomicrider OP
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TY 250 Timing dohickey

Finally got my '77 TY 250 up and running and have been having a blast! It has taken a couple of rides to sort out the jetting (plug shows a nice golden brown color), but I think that it is getting pretty close. What I am having issues with is that it sounds like its back firing/missing during half to full throttle, and today it was doing it even more frequently. So I'm thinking that it might be a timing issue, but looking in the service manual, there is a specific dohickey that is plugged in to set the timing as well as a dial indicator. I have the dial indicator, but my local repair shop dosn't have anything like the yamaha dohickey. Is there an alternative? I have done a continuity check on the wiring and it checks out, it has new points and condenser. I just don't know what else to check or what to adjust.
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Old 05-12-2011, 09:28 AM   #2
lamotovita
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You just need to know when the points open. An ohm meter or continuity tester is all you need. in a pinch you can use cellophane or rolling paper with a light pull to tell you when the points open.
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Old 05-12-2011, 09:40 AM   #3
atomicrider OP
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Thanks! I'll see if I can work it over tonight.
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Old 05-12-2011, 10:14 AM   #4
Sting32
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Quote:
Originally Posted by atomicrider View Post
Finally got my '77 TY 250 up and running and have been having a blast! It has taken a couple of rides to sort out the jetting (plug shows a nice golden brown color), but I think that it is getting pretty close. What I am having issues with is that it sounds like its back firing/missing during half to full throttle, and today it was doing it even more frequently. So I'm thinking that it might be a timing issue, but looking in the service manual, there is a specific dohickey that is plugged in to set the timing as well as a dial indicator. I have the dial indicator, but my local repair shop dosn't have anything like the yamaha dohickey. Is there an alternative? I have done a continuity check on the wiring and it checks out, it has new points and condenser. I just don't know what else to check or what to adjust.
Timing ISSUES (in my humble experience) wont be fine at idle, then bad at some determined throttle or RPM. that backfiring or sputtering, makes me think you are having a carb plugged or air leak issue! the carbs run off combinations of air/fuel screw adjustmenst on the side of carb, the Slide's needle position, PLUS main and pilot jets are less the issue, at idle. WHen you open the throttle, then the air screws lose function and as rpms and carb opens it runs off the pilot and main, with some slight adjustablity via the slide needle. to me though, I think pops happen most of the time when engine is starving for fuel, in the air fuel mix.

Other more seasoned experts probably help out with this sooner or later in this thread, I could be all wrong.

ANYWAY< Check for carb problems first, then air leaks, then maybe you have a wire or something that is bare or cracked but is "not touching" anything, but as the voltages increase with RPM, maybe close enough it is jumping or arcing to short? Electrical, to me, that is a stretch though... Just from experience, IMHO. But it can be diagnosed in the dark easier.
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Old 05-12-2011, 07:56 PM   #5
atomicrider OP
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Thanks for the advice about the carb. I have ruled out the timing, because it idles just fine. The poping happens from 1/4 to 3/4 throttle, but will stablize at full throttle (at least it did 10 min ago). I took the whole carb apart, cleaned and blew out and put back together. adjusted the air and idle screws. It starts easy enough (1-3 kicks) and idles wonderfully, but the second I get on the throttle, it starts poping. I have changed out the main several times (130, 140, 150, 160, 210) and adjusted the needle up/down, but I just don't seem to get anywhere. Its currently set with a 150 main and the needle on step 3, the pilot jet is a 35. I live at an elevation of 5400' and go up from there, if that helps.
I had a friend suggest that the coil might be the culpret, had a spare, changed it, no change.
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Old 05-12-2011, 08:25 PM   #6
Sting32
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Originally Posted by atomicrider View Post
Thanks for the advice about the carb. I have ruled out the timing, because it idles just fine. The poping happens from 1/4 to 3/4 throttle, but will stablize at full throttle (at least it did 10 min ago). I took the whole carb apart, cleaned and blew out and put back together. adjusted the air and idle screws. It starts easy enough (1-3 kicks) and idles wonderfully, but the second I get on the throttle, it starts poping. I have changed out the main several times (130, 140, 150, 160, 210) and adjusted the needle up/down, but I just don't seem to get anywhere. Its currently set with a 150 main and the needle on step 3, the pilot jet is a 35. I live at an elevation of 5400' and go up from there, if that helps.
I had a friend suggest that the coil might be the culpret, had a spare, changed it, no change.
I still feel it is air leak or fuel starved... spray carb cleaner around carb & inlet to check for leaks, it should change how it is running if it gets a whiff of it...
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Old 05-13-2011, 03:19 AM   #7
gybeman
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Worn slide ?? Check the body of the carb and the slide for wear marks.
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Old 05-13-2011, 06:04 AM   #8
brewtus
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Worn slide ?? Check the body of the carb and the slide for wear marks.

More likely a worn jet needle and needle jet (the insert that the needle slides up and down in located in the carb body). Take a peek at the needle, if it's shiny around the middle, it's worn. Replace both if so (they wear together, just like chains and sprockets). Don't be fooled if you can't feel the worn spot, because you won't.
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Old 05-13-2011, 12:27 PM   #9
atomicrider OP
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Well, checked for air leaks with the carb cleaner and had no effects to the engine rpms. Had an extra slide, changed it out and still no difference. I'm going to try the needle jet and jet needle next.
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Old 05-13-2011, 05:16 PM   #10
KilgoreTrout
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Idaho TY 250

Was this the TY for sale in Bellevue ? Looked to be complete and very well priced!
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Old 05-13-2011, 05:37 PM   #11
PSchrauber
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If the engine is not running well between around 1/4 to 3/4 throttel, it's normally an indicator for a too big main jet.

You have aready tried out a lot of main jet as I understand, (sadly not familiar with your altitude.

As brewtus already stated abd you had already done a lot of research on other places there I also believe that there might be an issue with your needele and needlejet.

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Old 05-15-2011, 05:52 PM   #12
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Why do guys always want to change a main jet when it covers only the top1/8 of throttle op? Put the stock main back in! As brewtus says it is very likely a needle problem/worn slide or something you have not thought of at all... it needs crank seals first before you entirely screw up the carb. This is a likely problem on a 34 yr old 2 stroke. Crank seals need freshening about every 10 yrs at least. When they leak you will not get a carb set correctly.
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Old 05-15-2011, 09:24 PM   #13
atomicrider OP
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I went down to my local shop and they are going to look for a needle jet for me, then the carb will be back to stock components and will be essentially freshened up. Buls4evr, you got me thinking about the condition of the motor itself, I just took it for granted that the compression was good and that nothing else needed to happen with the motor. This is my first 2 stroke and just realized how important the case is in the operation of the motor. So that is where I will look next.
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Old 05-15-2011, 09:33 PM   #14
atomicrider OP
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Originally Posted by KilgoreTrout View Post
Was this the TY for sale in Bellevue ? Looked to be complete and very well priced!
Nope, I didn't know there was one for sale over there, its only an hour and a half away. I got this one from my dad, he bought it back in '81 for $300 and I was able to find a second in a guy's field about 1/2 mile away that he just gave to me for spare parts. Spent the last 8 months dabbling on it here and there with some help from the guys at bjracing and lurking around here. Luckily it runs great at the optimum speed for trials, slow, allowing me to climb over junk in the yard. Hopefully I can get the rest sorted out because there are alot of great trails a 1/4 mile from the house.
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Old 05-17-2011, 05:21 AM   #15
buls4evr
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Atomicrider...Also while you have that flywheel removed check for up-down play on the crankshaft itself. Also a good time to check that reed cage or replace reeds (they are likely ALL 34 years old). Are the piston rings w/in spec? This is all stuff you have to have correct BEFORE you start blaming your carb for incorrect running. Think of it this way....the bike probably ran fine with stock jets in it(and autolube too)in 1977. What has changed with the jetting? Go to stock and start there. These carbs need cleaning after sitting for just a short time and the slides do wear but not needles so much. I would not trust a 34 yr. old air-cleaner or old fuel lines. Uni-Filter probably makes a filter for it. And someone probably sold you on how simple, cheap and easy vintage bike ownership is right? These are very reliable bikes after you put some time into them. Learn to do this work yourself. Most shops other than vintage shops know less about this bike than you do. Their "shotgun approach" will cost you a fortune. You are actually going to get far more satisfaction from changing your crank seals and reeds than replacing that needle(very expensive BTW)then finding out it is still the same. Just think the stuff through in an orderly progression.
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