Post by R. Pierce Butler Post by The Older Gentleman Post by JerryG
Hello, all. Any history on this bike of throttles sticking open or
You've crashed it, and you're looking for someon to blame, right?
And AFAIK *no* motorcycle throttle can open spontaneously.
I have not heard of any motorcycle make or model having a tendency to do
FWIW: Long story, you may not want to read it. I bought another Honda
MT250 this spring with the intent of getting it on the street. After a
quick and dirty rebuild I was having trouble getting it to idle.
MTs have a funny idle circuit. They use a huge jet and have a mixture
screw with a hole in the middle of it. It is kind of like a banjo
fitting in that even with the screw all the way in, the hole makes it so
it is still open.
The mixture screw on the MT was completely corroded in. I ended up
having to drill it out. I didn't have an exact replacement, so I just
scavaged one w/o the hole in it off another carb.
So with the wrong screw the new MT didn't idle worth beans, not a lot of
throttle response down low, that kind of stuff. Thinking maybe I was
loving the pooch with my rebuild I switched the carb over to my 'good'
MT to see if it displayed the same symptoms.
Sure enough, same symptons on the same model but a different bike. I
ended up screwing the idle screw all the way in/max opening. It would
still die after 5-10 secs with the throttle off.
So I decides to maybe it just needs to be wrung out a bit to clear any
gunk left in it. As I am starting it I notice the over flow is over
flowing, the rebuild kit hadn't got here yet, so I shut off the petcock
while I am kicking it over. The puppy starts, I shut off the
choke/enrichment lever, and take off down the road for a couple of WOT
roll off throttle cycles.
Notice I didn't say I turned the petcock back on. That is because I
didn't turn the petcock back on. Turned out at idle it was running so
rich it was killing the engine. Soon as the float bowl emptied a bit and
leaned out the carburation it was suddenly trying to idle at ~6,000
RPMs. I crashed so hard my dead relatives felt it.
Punch line is There is at least one other senario where you can get an
engine that to the casual observer would seem like a spontaneous
Anyway, I agree I haven't seen a throttle spontaneously open. I think
there was one time where I had a throttle cable got hooked on something
and everytime I made a left hand turn it pulled the throttle open, but I
wouldn't call that spontaneous.