Vapor Lock???

[LI Grady]

Yesteday with the boat running great we set up on a drift for stripped bass.

Both motors were idling and drawing off the main tank. I switched both motors to the aux tank while still idiling and with in 4-5 minutes both motors stalled and would not start.

Switching back to the main tank did not help.

The motors would crank over on the first turn of the key, run for a few moments and then stall. We tried advancing the throttle, removed cowlings, etc. This went on for about 45mins before we called SeaTow. We had called the local Yamaha guru as well to trouble shoot.

It appeared to be a fuel issue. The tanks/fuel was polished this year (Sept. 08) and the gas in that tank was treated with Startron and is a little more then 30 days old. Both tanks were filled at the same time and the same location.

While being towed back and at the dock we tried again to start the motors and the results were the same.

I pulled one of the Racor filters off and dumed out the contents....nothing...pure clean gas.

Hit the key again....started and ran longer. I keep playing around and low and behold got the motor to run. Let it run at a fast idle for a bit and then perfect! Same for the other motor only I didn't bother pulling the filter.

I'm thinking vapor lock or something similar with the vent. We did get fuel out the over flow when we filled that tank.

Thoughts?

 

[Grog]

Was the bulb hard? When you switched tanks, you probably got an air pocket in the fuel line.

 

[LI Grady]

Grog

No bulbs on the Marlin. It has electric pumps. I did try and hold the pump switch on while starting them but it didn't help.

I'm with you that I got an air pocket in there which I termed vapor lock for lack of a better term.

Is there a trick to switching tanks that I'm missing?

 

[megabytes]

What year boat?

There was a recall one year due to a batch of faulty fuel hose. The supplier ponied up to have fuel lines on a bunch of boats of many brands replaced. We where in the ditch one day when I hit the throttles and one engine stalled. After a few times, I limped back a mile or so on the other engine. The next day I found out about the recall and had my lines replaced.

This was a 97 272. Your issue may not be related but I thought I would mentioned the this.

 

[LI Grady]

Thanks. You never know, right?

It's a 1990 Marlin

 

[Grog]

Those pumps are junk, I used to have them and went to bulbs. When I redid the fuel lines, they couldn't prime the motors. With a bulb you have an added tool to solve problems. When you switch tanks, the air has to work its way through the carbs but the line is full past the switch. It can take a while to get the air pocket out.

 

[LI Grady]

Grog

Thats very interesting. So if I understand it this can happen any time I switch tanks.

Someone had suggested to me (after the fact) that I could/should open the deck fill if it happens again.

Your thoughts?

 

[jehines3]

I'm not buying the air in the line. The filters hold pelnty of fuel to keep the system well primed. I switch tanks with the motors running all the time. It sounds more like something blocked your tank pick-up. I've seen this happen with a small foil seal from a bottle of Star-tron.....Don't ask how I know, and don't let your friends add the Star-tron either (at least unitl you personally remove and discard the foil seal first)...My money is on a piece of crap floating around the fuel pick-ups in the one tank.

Opening the deck fill would have stopped the vapor lock if that was in fact the probelm.
jh

 

[LI Grady]

jehines

That's exactely what a mechanic told me....open up a fuel fill....unfortunately that advice and the diagnosis came back at the dock.

It does sound like this problem is, if not common, at least not uncommon. Live and learn I guess.

 

[jehines3]

Trust me inspect the inside of the tank through the fuel sender. If there is a little gremlin inside he will always resurface when the other tank is empty. Just what I found on mine and it drove me nuts-o. As a test, refill the last known working tank but keep running off the suspect tank... jh

 

[Grog]

Once the air is purged from the lines you can switch back and forth. If it sat for a long time the gas could have drained back into the tank.

But with the electric primers you never know.

 

[LI Grady]

Trust me I'm taking nothing for granted and will be checking out the tanks. Not sure how much I'll be able to see once I pull the sending unit but I'll give it a shot.

I do plan on filling up the main tank and will (if possible) run each motor on its own tank for now on so with luck I'll have side stepped this problem

Its bad enough to have to be towed in but it outright sucks to leave the fish biting....and SeaTow tows to fast to troll a bunker spoon :lol:

 

[BobP]

Add a signature to your posts with the boat model and year, and model and year of motors, so we know what you have.

Vapor lock, no way.

Another place to check out -

The tank pickups may have anti-siphon valves - I had a problem with one of my NEW (!) motors where the squeeze bulb was collapsing, not just from one tank but from the from both tanks, didn't make any sense. Sometimes it was ok other times not.

I changed the squeeze bulb and racor - didn't find anything plugging it, same for gas selector valve.
I traced back and pulled out all the lines to the one motor from both tanks. There was nothing wrong with the lines or valve, no blockage, no debris in there.

Then I unscrewed the hose nipples on the pickups.

What I found was the two pickups had anti-siphon valves, the two pickups for the other good motor didn't have them (why ?).

I unscrewed all four hose nipples on the tank pickups, the anti-siphon valve is a spring loaded ball bearing in a seat at the threaded end of the nipple. Someone knocked out the ball from the two fittings of the good motor, so I did the same with the remaining two nipples.

It never happened again. The E10 and whatever mixed with it may have been making the anti-siphon valves sticky.

Good idea to retire the electric primers and add squeeze bulbs, you can then see if the bulb is collapsing as the problem happens. That is very important - the bulb should always stay fully shaped, you can't tell now if there is too much vacuum on the fuel supplies.

Make sure you look at the bulb as soon as a problem happens if it does again, get back there to inspect it immediately. Leaning out fuel to the motor this way can destroy the powerhead.

Periodically, and when you first go out with the new bulbs, and have a mate on the boat, crank up the boat to high speed, in a minute go back there while the mate mans the wheel, and inspect the bulbs, if they are fully shaped, you are getting proper fuel supply to the motors.

I'd use OEM Yamaha bulbs.

 

[Grog]

When the motors finally fired up, what tank was it on?

Doesn't the Marlin have dual feeds from each tank? Something clogging both feeds at the same time is pretty slim unless there is a lot of junk on the bottom.

 

[LI Grady]

Grog

Both motors fired up on the Aux tank. I didn't get to take the boat this weekend but did run the motors at the dock. Both started right up.

I'll check the fuel line distribution when I'm down there next time.