I have a 1973 Evinrude 70hp that has started acting up. When I first put it in the water it runs fine. When I put it at full throttle it runs great for about 1/4 of a mile and then starts missing really bad. When it does this it makes a rattling noise and loses power. If I try to give it throttle is just bogs down. After it does this it goes slow (just popped into gear) just fine, with a miss about every 15 seconds. By the way, it runs great without a load on it. I have taken it to a mechanic and he has done the following:Checked compression...goodChanged fuel pumpCleaned out fuel filterRebuilt the carbsTried different gasAfter he did this stuff, I took it to the lake and it was exactly the same. Any help would be appreciated.Thanks
It almost sounds like you have a float stuck. By this I mean, as the motor sits it has time to fill the bowl. When you run the motor the bowl becomes empty, and it causes the miss. To verify start and run motor until it starts to miss. Spray a little carb cleaner in each of the carb intake barrels, one at a time. If the motor picks up on one of teh barrels check float.
my 74 was breaking down and loosing power after a short run . let it sit for a while maby 5 minutes it would go full throddle and break down after a short full throddle . replaced a coil and rectofier it ran great . papasage