No, I doubt that you would ever notice any difference at all. Mounting it upright would be great for getting the glow plug on it but I guess it just depends on where it's going to be situated on the firewall and how it will look sticking out of the cowl. I would try to mount it sideways and see what that's going to look like and if you can postion it at a place where the carb isn't too much lower than the tank.