Small Engines (Lawn Mowers, etc.): 14hp briggs surging while driving, gas tank, crankcase

Question
We've just come into a 1998 canadiana (MTD) lawn tractor which has been well looked after and recently tuned up.  While running the machine, it 'surges'/looses power for no apparent reason.  When sitting running idle, there is none of this occuring, but while in gear, it stalls.  (It never shuts down, just drops power)  
Any ideas why?  What can we do?

Thank you
John

Answer
Hi John,

This phenomenon you described is called 'Hunting & Surging.'

1. Ensure the gas tank is at least 1/2 full of fresh gas.

2.  The ratio of gas to oil (if applicable is correct), and the line between the gas tank + carb is not plugged, or crimped.

3.  Check carburetor to see that it is set to specifications + adjusted correctly.  

4. Take out the spark plug and make sure it is gapped to spec's. Clean the electrode if fouled and you can square the end to give improved starting.

5.  Check if plug is firing.

6.  If there is ignition points, check them to see if they are dirty, burned or out of adjustment.

7.  Check the crankcase read valve mounted where the carb is attached to the crankcase, so you can see if it's stuck or plugged up.

8.  Check anything else that appears to be loose or damaged.

This series of checks should give an indication of what may be causing your problems.

Let me know,

Howard