trike question

[Illiterite Wino]

I have never ridden a adult three wheeler before.. let alone work on one.

A friend of mine asked me to get his bike ridable.. picked it up, straightened one rear wheel (drive side), put a third mt. bike tire (so they all matched), and pumped up the tires.

Rides great... except I'll be riding down the street and all of a sudden it feels like the whole bike flops to the right.. starts almost steering itself to the right.. you have to turn to the left to get it to right itself. Yet when the bike sits still it has no flop at all.. i can sit on it and wiggle back and forth and nothing, I even try to make it do this mystery flop when it's going good.. wont do it..

am I just not used to riding one of these things or what? :roll:

here's some rear "suspension" pictures.. they all seem pretty even side to side

here's the whole thing

Arco Villager "3" (the three has to mean tires, cause this is a single speed lol)

thanks for any sugestions

 

[KJV]

if your riding on the road;
the roads taper on the right.
also, those brackets on those
trike seats seem to want to give.