1972 LT2 Yamaha project.

11/4/2018 10:32am
Got a old bike my dad bought new and since I don't really wanna just sell it, I figured I'd make it a good town bike. Seems to be loosing rpms when you throttle up in neutral and will die if you don't throttle down. Needless to say this makes shifting and accelerating and adventure also. Was just wondering if anyone knows if it possible to put an Enduro 250 motor or something else a bit bigger than the 100 that's currently on it?
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teggers
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3689
Joined
8/15/2006
Location
Winter Park, FL US
11/4/2018 11:10am
What were the Yamaha models of that year? DT2, was a 250?
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11/4/2018 12:04pm
Not sure, I've only just started looking at restoration options. Pretty sure this is a LT2 100.
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11/4/2018 12:15pm
I know the 125/175 top ends will fit one another from that era. Not many options for the 100, displacement wise. A DT 250 is a physically much bigger engine than the 100. May ruin the bike by trying to graft one in there. If it is timed, good compression, clean fuel system, it should run fair.

It is an old bike, though, and just may be tired.
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11/4/2018 12:28pm
Sounds good, was just looking into options for replacement if possible. Carb was just serviced about 2 months ago. don't know if the compression was checked. it does run, just starts loosing power once it's warmed up. Was told it could be flooding, but after a week of playing with the setting screws I've not been able to improve it any.
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The Shop

teggers
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3689
Joined
8/15/2006
Location
Winter Park, FL US
11/4/2018 12:36pm
RT2 - 360?
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Whymee
Posts
563
Joined
12/17/2009
Location
WV US
11/4/2018 12:50pm
JT-60
GT-80
HT-90
LT-100
AT-125
CT-175
DT-250
RT-360
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clem
Posts
276
Joined
6/12/2009
Location
Thibodaux, LA US
11/4/2018 5:36pm
If it's losing power when it gets warm it is either jetted to rich or you have an electrical problem that is showing up. Remember that stock jetting for a vintage motorcycle needs to be adjusted to run the crap fuel that we have at the pumps now. Test your coil.
Bennett
Posts
75
Joined
1/13/2013
Location
Papillion, NE US
11/4/2018 7:07pm
Here is what my dad bought for me around 1984. Had 2 of them, one for parts, one to ride. Rode it all over, school, work, mx track. Heavy pig, but it was all I had, So, fond memories, I guess? Notice the dual spark plugs. Mine had the compression release welded shut, and oil injection removed. Painful to start it. This one recently popped up on Craiglist:

https://omaha.craigslist.org/mcy/d/1972-yamaha-360-rt2-enduro/673597989…
Bennett
Posts
75
Joined
1/13/2013
Location
Papillion, NE US
11/4/2018 8:14pm
You say the carb was serviced 2 months ago. By who? I would be a little suspect. Looks like parts are still available to rebuild the top end. Rebuild the top end, go through the carb, check everything.
Whymee
Posts
563
Joined
12/17/2009
Location
WV US
11/5/2018 12:53am
There is an o-ring around the main jet that if damaged, describes what you are experiencing. They get hard over time and deteriorate. Easy peasy fix if that is the issue.
11/5/2018 6:08am
Whymee wrote:
There is an o-ring around the main jet that if damaged, describes what you are experiencing. They get hard over time and deteriorate. Easy peasy fix...
There is an o-ring around the main jet that if damaged, describes what you are experiencing. They get hard over time and deteriorate. Easy peasy fix if that is the issue.
Had one of those O-rings go bad on a 76 YZ80. It always ran rich, as unmetered fuel was leaking past the o-ring.

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