outboard motor newbie question

[calamitas]

Just got a 1976 O'Day 25 with a nice Yamaha 9.9 hp outboard. Question: is one supposed to crack (slightly open) the fuel tank cap when operating the motor? Or should one keep it tightly closed? I have heard both. Thanks!

[pmoyer]

I have a Johnson 8 on my boat, and I keep the vent plug opened. Physics kinda tells ya you want to avoid creating a vacuum in the tank, or it'll be hard to pull fuel out.....

Cheers!

[astraeus]

I agree with pmoyer, open the vent. I have made this mistake, it took about an hour and a half of motoring, but the motor stopped running as I approched the slip. Fortunately I had the momentum to get in.

After securing the boat, I checked the whole outboard before reaching over and opening the vent to hear a telltale wooshing sound. The outboard could no longer pull fuel from the tank.

Fair winds

Jason
S/V Astraeus

[Hawkwind]

You shouldn't have to "crack the fuel tank cap".

As previously pointed out, you will need some form of air leak to prevent a vacuum. Every cap I've used had a thumb screw in the center of the cap that when loosened, allows air in the tank. Cracking the fuel cap would work, but it could get messy if the tank is near full.

[sailingdog]

Some have a dedicated thumb-screw air vent in the cap, others have a separate vent cap. I have yet to see one that doesn't have a vent. You need to open the vent when motoring. Don't forget to shut it afterwards. It will help reduce condensation and water-in-the-gasoline problems.

[rperret]

every person I have talked to or read states you need to open the vent valve when you start and run the motor, then close it for storage. opening the valve allows air to enter the tank and thus fuel to flow smoothly.

Originally Posted by calamitas

Just got a 1976 O'Day 25 with a nice Yamaha 9.9 hp outboard. Question: is one supposed to crack (slightly open) the fuel tank cap when operating the motor? Or should one keep it tightly closed? I have heard both. Thanks!