engine acting strange - help im all thumbs -could it be a simple gas vent cap

I just got in from my 3rd use of my 1974 starcraft with a 1977 70 hp evinrude and there seemed to be a problem with power.<br />I started up the engine (let it warm) after useing it all day and hit the throttle .The engine took off well then started lossing power .Everytime Id give it some throttle it just slowed down .<br />(It idled ok)<br />I stopped and fished while I tried to figure the problem out . I noticed the plastic fuel tank sucked in some so I played with the vent and boy did it have a vacumm behind it.The boat ran fine after that.<br />My question is could it be a simple vent cap doing this? <br />Thanks for your replies , as you can tell im all thumbs with motors and am still learning.

Re: engine acting strange - help im all thumbs -could it be a simple gas vent ca

Re: engine acting strange - help im all thumbs -could it be a simple gas vent ca

Sure could be that. In fact, it's almost a certainty. Since the motor ran fine once you had vented the tank, you've solved your problem.<br /><br />Plastic tanks are cheap as dirt. If you can't straighten out the vent on this one, toss it and get a new one.<br /><br />Just one guy's opinion.

Re: engine acting strange - help im all thumbs -could it be a simple gas vent ca

Re: engine acting strange - help im all thumbs -could it be a simple gas vent ca

Sounds like you solved your problem reddog.<br />If the vent on your tank does not let air in to replace the fuel that has been sucked out by the motor you will get a vacumm in the tank, the fuel pump can't pull against the vacumm and the motor is starved of fuel.<br />A major problem when this happens is that the motor will run lean which can do a lot of damage.