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Kohler M-18 Surging

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Trying to get an M-18 up and running over the weekend. It had previously been hard to start and surged badly. Took the carb off and cleaned everything (has both idle and high speed needles) and got the engine to idle great.

However advancing the throttle would result in (after running from 10 - 30 seconds) surging and the engine stopping unless the choke was applied.

Here's what we tried:

Removed carb and cleaned it again - Had an extra carb took it apart and cleaned it too.

Installed orignal carb - no change in results

Swapped carbs - got the same result

Checked spark - Good spark - when the engine dies there is spark until the rpms stop

Checked fuel pump - pumps plenty of volume

Removed fuel line at fuel pump inlet and blew back into fuel tank - reconnected and got the same results as before

Removed fuel tank cap and started engine - No change - same results

I didn't remove the high speek jet nor did I do a leak test around the carb / manifolds connections points.

Does anyone have advice on removing the high speed jet or other items to be looked at?

Thanks in advance.


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