Gas Tank Question

[bostonmike]

I'm a new boat owner with probably a really dumb question, but this forum has been great help so far, so here goes.

I have a 1988 Johnson 90hp VRO outboard. When I looked at this motor to buy, it started right up and ran perfectly. I have started the motor on earmuffs with no problem and again it ran great. After I trailered the boat to the ramp it would not start. This happened on two separate occassions. After trailering the boat home I again tried it on the ear muffs, this time it did not start. The second time at the ramp, I let the boat sit for about an hour and a half, backed it in again and it started right up. We took it out for about a half hour and it died and I could not restart it.

Now here comes the dumb part. I am using a 6 gallon gas tank. Each time that I have run into this problem it has been after trailering or running the boat on the lake for a while. The vent on the gas tank has always been shut. Is this the reason it will not start after bouncing around for a while? I'm assuming the pressure will build up in the tank while it is moving and the vent is supposed to be open. (Dumb newbie mistake??)

I know that I am getting a spark (did the spark test as I saw people recommend) and from what I have read, if something electrical was heating up and cutting out it would happen more quickly than 30 minutes into a trip.

Any help is greatly appreciated, this forum has been an awesome source of information. Thanks for your help.

 

[tashasdaddy]

Re: Gas Tank Question

1st you have to open the vent for the fuel pump to be able to suck gas. 2nd the idle needs to be set and about 850rpms, on muffs. the reason is that there is no backpressure on the exhaust of muffs. when in the water there is backpressure, as the exhaust exits thru the prop hub. once running in the water you want to adjust the idle to between 650-700 idling in gear. i have the same engine without VRO.

also a item to note is: when shifting the shift should be quick and deliberate, don't try to just slip it into gear. the gears have very square edges, and slow shifting wear these edges, causing problems later.

 

[bostonmike]

Re: Gas Tank Question

Thanks so much for the information. Do you think the gas tank vent was definitely causing my problem?

Another newbie question, how can I adjust the idle for the earmuffs? I'm assuming I have the correct idle rpm for the boat being on the water, I will have to check next time out.

The motor ran great when it was running, it was good fun until we got stuck in the middle of the lake. If nothing else, it made for a good story and a laugh after we got the boat back out of the water safely.

 

[ezeke]

Re: Gas Tank Question

Just for the sake of the poor gearcases of others, "when shifting the shift should be quick and deliberate" means in and out of neutral, not foward to reverse or reverse to forward.​

 

[iwombat]

Re: Gas Tank Question

Thanks so much for the information. Do you think the gas tank vent was definitely causing my problem?

Yes. What ever you pull out by volume in gas must be replaced by volume in air, or you create a vacuum. The fuel pump then plays a nasty little tug-of-war for fuel with the vacuum in the tank. The only way to get air in is through the vent.

 

[Windykid]

Re: Gas Tank Question

When I trailer my boat, the engine is tilted up and the carbs leak a little. So I have to reprime my system in order to start.