The reason I suggested a compression test is that a sticking jet valve will cause the same issue.

The basics are to pull the plugs and inspect them. Is one fouled? Or do they all look the same?


You need spark and compression. If one plug is fouled that cylinder is lacking one of those two.

Two ways to go , try some new parts to see if it fixes the problem or do some testing.

A compression test takes less than a minute and will tell you a lot. If you have good compression than the culprit is probably ignition.

Another test is to pull one plug wire at a time with it idling and see if you have one dead cylinder.

Kevin