Need Toro 2 cycle help!!

I have a Toro 2 cycle with the Suzuke engine. Great engine. BUT!! When it is gear with the blade engaged and going forward, the engine goes up and down, up and down, up and down. VARoooom. VARoooom. VARoooom. If the blade isn't engaged it will self propel fine. Idle fine. Run at high speed fine. But engage the blade, up and down, up and down, up and down. Any small engine repair readers that might have a fix??
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