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Old 04-16-2013, 06:15 PM   #1
fishheadstew OP
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1974 TY250 Trials bogs down upon acceleration

I have a TY250 (Yamaha Trials) -1974 that is in great shape. It starts up fine, revs, as well as idles just fine. When I place in gear and accelerate it bogs down. It's like it's choking for fuel. I can hold the choke down and this helps a bit, but eventually dies. Does anyone have any idea what might be causing this. I've been through the fuel system about three times already. Taking all advice as would like to get this thing up into the hills and start riding the ridges... thanks for any help you can provide..
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Old 04-16-2013, 06:23 PM   #2
nwcycle
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Maybe..........

It would most likely be in the carb, first make sure it is not restricted, and check installed jets as to what was stock,
With todays oxygenated fuel , you need to make the pilot system a bit richer, When it sits and idles and rev it, does it come down to a clean and steady idle?
Or if it revs and stays on a high idle its possible way to lean..
If there is a lot of blue smoke out, then its possible you might have a right hand crank seal leak.
Try a few of these things and re post, I know the old bike very very well,, will do my best to help.......
One other thing you can check... pull carb and make sure the float is working correct, is it a aluminum needle or one with the rubber tip.
If it has a rubber tip, take a Q-tip, put in a cordless drill and stickk it in the needle seat and go to town, go in and out and push the tip into the seat.
If its a aluminum you need a bit of valve grinding compound. do same,
clean out with carb cleaner and give this a shot...

nwcycle screwed with this post 04-16-2013 at 06:29 PM
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Old 04-16-2013, 06:33 PM   #3
lineaway
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Wait a minute! Something is ringing a bell here. Does the bike ever move!!!!!!!!!!!
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Old 04-16-2013, 08:09 PM   #4
fishheadstew OP
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Thanks guys.. Yes.. acceleration does get me down the road for a bit, but eventually bogging down. Will check the float, and follow through on the other advice.. Appreciate the help.. thanks
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Old 04-16-2013, 08:31 PM   #5
lineaway
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How about more info. Is this bike new to you. Is the tank clean. Does fuel flow. The carb cleaned completely.
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Old 04-17-2013, 11:26 AM   #6
fishheadstew OP
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yes, the tank is cleaned and the carb was boiled. It takes a couple kicks but starts right up. It idles great, and also revs, and derevs just fine when in neutral. When I put in gear and accelate it seems like it just isn't getting any fuel. It bogs down, barely idling with eventual shut off. Put it in neutral and it starts right up again. When in gear, if I hold the choke down a bit it seems to help a bit, but minor. Hope someone can help define a solution. I plan on pullling the carb, as well as evaluate the needle seat as previously recommended.. Thoughts
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Old 04-19-2013, 07:53 AM   #7
oldyams
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Quote:
Originally Posted by fishheadstew View Post
I have a TY250 (Yamaha Trials) -1974 that is in great shape. It starts up fine, revs, as well as idles just fine. When I place in gear and accelerate it bogs down. It's like it's choking for fuel. I can hold the choke down and this helps a bit, but eventually dies. Does anyone have any idea what might be causing this. I've been through the fuel system about three times already. Taking all advice as would like to get this thing up into the hills and start riding the ridges... thanks for any help you can provide..
I had about the same symptoms with my Ty250a a couple of years back. It was a barn find that had not been run for a long time. I had put a new mikuni vm26 carb on it and it started dying on heavy accelleration only to start right back up again. It would run fine in neutral but in gear under a load it would start sputtering and die. I posted the trouble on TC and someone said to change the points and condensor as it was probably the condensor. I had thought it was fuel related all along also but thought it was worth a try as I had no idea what shape the points were in. Thats what it was! Ran perfect ever since. If you do, put a new crank seal in it while you have it open.
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Old 04-20-2013, 09:03 AM   #8
fishheadstew OP
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appreciate everyones help.. going to replace the condensor and see if that helps.. just need to locate a puller.. thanks again
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Old 04-20-2013, 02:04 PM   #9
wb22rules
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Good call, I forgot about condensers, I had a bad condenser in a 70s honda as a kid, as soon as it warmed up it would fail and the bike would die, as soon as it cooled it would work again. Took a little while to figure it out. Hope that gets you straight
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Old 05-11-2013, 06:57 PM   #10
fishheadstew OP
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After Market Carb

Would anyone know an aftermarket carb available for the 74" TY250? Unfortunately I found out that the carb on mine isn't the original, and i've been trying to source parts without luck. Hopefully someone can let me know what I might be able to put on this to make 'er go. Everything else works great... thanks
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Old 05-11-2013, 07:08 PM   #11
lineaway
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A mikuni would be the vintage mod, but these have been around lately.
http://www.mid-atlantictrials.com/OKOGallery.html
http://www.mid-atlantictrials.com/OKO.html
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Old 05-11-2013, 08:32 PM   #12
fishheadstew OP
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would this be the best one

Thanks for forwarding this information. Would the following be the best one for my bike? Sweet deal..and I certainly appreciate your help with this. Been struggling with this bike for a month now and looking to get it on the trail... thanks



OKO K-101 Carburetor for Yamaha TY 175 & 250
Item # K-101YamTY
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Old 05-11-2013, 08:33 PM   #13
Old Geezer
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B&J can fix you up with a new carb. www.bjracing.com
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Old 05-11-2013, 08:44 PM   #14
fishheadstew OP
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Best One??

so is the mikuni of OKO the best one to go with. Not looking so much to restore the bike but to get me up and down the hills.. thanks
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Old 05-13-2013, 08:54 AM   #15
gloud
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Honestly it is up to you. I would lean toward the Mikuni VM but I know them very well.
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