GO BOTH!!!
I got a dual gasser for my Z cause I couldn't make up my mind as to thumb or twist.
It's bloody great. You can lock the twist off if you want ( with a little silver pin underneath ) or ride with both live.
Depending where I'm riding or what type of riding I'm doing I can choose either.
It's a great piece of kit and probably the best mod I've done to my trike.
I guess you can tell I love it.
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My Rides-
1985 Yamaha YTZ 250 Tri Z
another 1985 Yamaha YTZ 250 Tri Z
1985 Honda ATC 200 ES Super Red
1975 Bultaco Pursang 250 ( Hey I know it's only got two wheels)
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It's not an optical illusion, it just looks like it.