My outboard motor, evinrude 40mph, is only running at half speed. The problem just arised out of nowhere.?

Question

Also it has trouble idling unless I am choking it often. Any help?

Answer 1

Sounds like a small piece of c**p made it past your filter and has restricted the jets. One "hail Mary" attempt at cleaning this out is to remove the front cover from the carbs and run the motor up to 2000rpm (in the water right?) and slap your hand over the intake one at a time and see If the high vacuum won't suck the piece thru.  Start it up again (no choke some throttle) If the problem is gone-good other wise you will need insulated pleyers to pull the spark plug leads off and find out which carb is junked up.-Hearing the spark as the leads come off will tell you if the problem might not be electrical. Some of evinrudes had a drain plug on the float bowls. Some times you could remove the drains and pump fuel thru the carbs and out the drain removing the offending  piece. Other wise it is carb over haul time.

Should you think the spark didn't sound exactly the same you may have an ignition problem. Start with a tune up and get some more info on your model. and re post.

Answer 2

If choking makes it run, then you need a carb rebuild.

Do a spark test before you take it back out, though.