Hi steve Well first off if you use an Marvel carb from a 85 Hp engine and put it on your 0200 the main jet will have to be replaced as it will run lean at full power and high cruise If you used a stromberg carb you will have to change the venturi and the main jet to the 90Hp model as stromberg dose not have a model for the 0200 movement in the throttle shaft side to side in line with the shaft is normal movement front to rear or up or down requires replacement movement in the mixture lever up and down is normal as it is spring loaded to seal against this spring pressure side ways movenent then it i worn (don't see this too much as the mixture has such a small movement and a short arm seldom wears out) air coming in through the throttle shaft will usually effect the idle will make it rough you will seldon notice in cruise or high power unless it is to the point of loosenes that it will rattle in the bearing pivots the accelerator pump has to have a good plunger and the check valve on the exterior of the carb should be cleaned and checked this will only effect rapid acceleration and lever should be in the center hole this pump will expel more fuel with a rapid throttle opening and not quite as much with a slow throttle opening when the carb is at rest,,,, with the engine running the ammount of fuel from the pump will change due to the pressure drop in the air chamber of the carb also make sure the economiser jet in the top half of the marvel carb is installed as this causes a suction on the fuel head in the carb bowl and if it is missing it will cause the carb to run lean also check that the primer is not leaking air and make sure the hoses on the intake tubes do not leak and check that the plug in the upper part of the throttle body (facing forward) is in place and tight (a carb ice dectector prob can be installed here) just check carefully as other small prblems can make the carb seem at fault when it is ok Here is some old engine widsom A CARBERATOR CAN ONLY BE ADJUSTED AND WILL ONLY WORK PROPERLY WHEN ALL ELSE WITH THE ENGINE IS CORRECT THE CARB IS DEPENDANT ON THE CONDITION OF THE REST OF THE ENGINE TO OPERATE PROPERLY such as mag timming, valve lash, plug gap, Out side of dirt in the carb most of the time I find that after I adjust the mag points and retime the mags and clean and gap the plugs the engine is fine and the customers carberator problem has gone away (a very big price difference between the two) as a new or overhauled carb will not mask the other problems joey