2 questions: '72 65 hp Merc

[myelo]

First, I want you guys to know that this board has been a lifesaver for me!! <br /><br />Now, for more questions. <br /><br />1. What compression numbers should I be seeing on this motor?<br />2. The last owner put a new gas tank in the boat that does not have a vent. This boat goes and then dies all the time, until i manage to prime the bulb again, which sometimes it does, sometimes is doesn't. When I loosen the gas cap, the classic "hiss" is heard. Do I need a vent in the tank? If so, why would they even sell a marine tank (the kind that has the fuel gage built in on tank) without one?<br /><br />Once again, thanks so much for your help!!

 

[graddy]

Re: 2 questions: '72 65 hp Merc

compresion reading should be with-in 15 psi of eack cylinder. <br />The gas tank needs to be vented or it will cause fuel restriction.<br />Not sure why somebody make a marine gas tank with no vent.

 

[tmcalavy]

Re: 2 questions: '72 65 hp Merc

No question about it, you need a vented tank. Compression should be 90-105 on a dry test, and higher by 10-25 with a wet test. It's tough to get the compression gauge fitting in to the bottom plug hole, unless you remove the bottom cowl...but it can be done if you are patient enough. Get the Seloc manual for your motor...a very good investment.