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Collection, Preservation and Display of Old Lawn Mowers

controlling speed of Qualcast16 2 stroke

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I have been having difficulty in controlling the speed of my mower recently. It was completely stripped down and restored about 2 years ago and I have been using it to mow the lawn successfully ever since. Then for no apparent reason recently it started to accelerate at the end of each strip of grass as I turned the mower around. I started by adjusting the taper needle in the carburetor in and out several times by increments of about .25 of a mm to see if the air/fuel mixture was incorrect but this did not get the mower working correctly.  Each time I made an adjustment I stopped the engine and there was no problem in restarting it hot.  Sinc e then, to cut a long story short, I checked the fuel tank and pipe stripped and cleaned the carb. twice fitted a different carb.,changed the condenser,checked the coil with a multi-meter, cleaned the points and reset the timing, checked for crankcase leaks by spraying WD40 around and put a new spark plug in.  In between doing all these things I kept testing the mower and altering the taper needle in and out ad nauseam but it still does not run properly, ie. accelerating issues.  There is no problem in starting the engine hot. I am thinking that air could be drawn into a leaking crankcase or worn bearings but I can't see how and I don't think the bearings are that worn. I am using Millers classic sae 40 oil in the original proportions of 16:1  Could forum members please comment and suggest/say what the problem is please and whether or not I have missed or overlooked anything.  Thanks very much.

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