ancient IT250: beat off moths, now coughs

El Seed

Jan 10, 2000
After a year and a half of sitting (becoming eco-system :'|), my old beloved beater '78 Yamaha IT250 ('Leon') was re-invigorated with a carb cleaning, fresh plug, and fresh tankful.  Fired right up, but high-end he seems to sputter.  Believe it is starving, but intermittent firing and blue smoke makes me wonder.. rich?  Tried fooling with misc. jets and needle positions.

Background: Owned the bike for 10 years and always a 'do no wrong' 2-kick screamin' demon.  Never had to do anything like this before to revive him.    Any thoughts on effect of sitting?

Carb. is clean, running a 360 main
Low-range decent, mid-range good, high-range sputters
Smaller jet worse (problem occurs earlier -- like lean)
Bigger jet (quite a bit bigger) wouldn't start
Reeds rotten?
Intake is old and petrified - sucking air?
Oxygenated pump gas giving me fits?

Theories welcomed


Nov 7, 1999
El hombre, que tal, no tan bueno con su Yamaha es verdad?

well I have a go!

Could be the crank seals have hardened and you are sucking tranny oil into the engine and burning it so you get the blue smoke, but if you are only burning half the inlet charge I think you may get a similar haze.

If your inlet boot is a little poorly try some 'EasiStart' the sort of alchocol in a spray can that makes diesels start a little better when its cold...spray all around the inlet tract, if the engine speeds up you need a new inlet boot.
Are you really sure you have all the jets clear...these new clean gasoline fuels don't seem to last as long...the lighter hydrocarbons leave the fuel so much quicker and leave some right nasty gummy liquid behind...just try throwing some fuel on the floor, it don't evaporate so much like the old days...another thought try running with the fuel cap loose..any blockage will create a vaccum if it's marginal you may see the same symtoms....oh and does is this worse when the engine is warm..could be the coil or lead breaking there a fuel filter in the petrol fuel tap..could be gummed up....

good luck!


Richard, rode today but still have the flu'...wish I hadn't!

El Seed

Jan 10, 2000
Thanks for the reply, Comben.  Though my situation was vaguely stated, wise advice from such as yourself seems to inevitably point back to the tranny seals.  Tried every jetting combination, bracketing rich and lean -- behavior the same in all cases at high revs.  Have personally licked the carb. clean, and everywhere else fuel travels.

EasiStart is a good procedure for testing inlet boot -- indeed old and hardened.  Could be a leaker.

Tested ignition circuit to best of my ability -- do magneto pickups malfunction at higher revs?  Don't have a timing light or such for adequately testing the spark.

Anyways, 'Survey Says?!' -- Ding!: Seals deteriorate in an engine at rest.  Will pursue this angle.

Thanks again.
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