Racing of a Honda 160 CC lawn mower engine

When a small engine "surges" in all speed ranges the possible causes are:

*Dirty air filter

*Water or contamination in the fuel system.

*Breaks in the spark plug wire (leaking), loose or corroded terminal connections causing an intermittent failure.

*Misadjusted or malfunctioning governor.

Problems with surging only when under load or at idle are likely caused by carb blockage or misadjustment.

Hope this helped and good luck to ya!