Fuel Vent Line Problems?

[bryanredfish]

I just drew a connection between some problems I've been having. It began to be VERY difficult to gas up the boat, and I almost have to put it in drop by drop -- takes forever! Around the time this started, the motor began to chug and miss when throttling up. It usually only does this a couple of times on the outing -- depending on how long I sit. The motor is a 2002 Merc 90 2 stroke. It's perfectly tuned, and runs great, aside from this issue. Is there a way that I can check to see if it's a fuel line venting problem? Thanks.

 

[DJ]

Re: Fuel Vent Line Problems?

bryan,<br /><br />You have a venting problem. I assume this is a permanent tank installation.<br /><br />1. Start looking for kinked hoses, under decks and gunwales.<br /><br />2. Blow through all vent lines. Check the overboard vent drain to make sure it's clear.<br /><br />3. Also, check the tank "anti siphon valve" that should be at the tank to engine outlet. It may be a part of the outlet. You can eliminate this valve for testing ONLY.

 

[bryanredfish]

Re: Fuel Vent Line Problems?

djohns19:<br /><br />Thanks for the response. Yes, it's a permanent tank, under the deck. Pardon my ignorance, but as far as I can tell, there's only one vent line, which runs parallel to the fill line (runs up through center console). Do I need to disconnect this line from the tank and blow through it? Thanks for your help. I'm tired of sitting at the gas pump for 1/2 hour to put 20 gallons in the tank.

 

[Luna Sea]

Re: Fuel Vent Line Problems?

Those lines do get clogged. Often, during winter layup/any extended period out of the water bugs and bees will nest in the vent itself. Not sure if I'd want to blow in, maybe a vet/dry vac could suck out? Just a thought, careful though, gas fumes...... Definately sounds like a clogged line though. Time to crawl down there and start pulling fittings/hose clamps. Good Luck!

 

[DJ]

Re: Fuel Vent Line Problems?

bryan,<br /><br />If your tank is in the floor, there should be a pry out or screw out type of deck plate(s) over the tank. You may have one over the feed line and another over the fill and vent lines.<br /><br />Remove those and determine which one is the vent (smaller of the two). Blow outwards through that one. You may also want to follow that line to see where it goes. If you have the type of deck fill that is a combination unit (vent and fill) you'll have to do your purging of the line with the cap off or open.<br /><br />I once took delivery of a new boat in which the vent line shipping cap was still on the tank vent fitting. Someone had knocked a hole in it so it would vent some, however filling it was painfully slow. It obviously was sabotage.

 

[bryanredfish]

Re: Fuel Vent Line Problems?

Just did a quick check on lunch break. I can easily access where the vent line runs into the tank via a deck plate. I'll give it a good look-over tonight. I'll tell you this -- I'll have a lot more fishing time now, since I won't have to put the gas in drop by drop. <br /><br />I'll let you know what I find out tonight.

 

[bryanredfish]

Re: Fuel Vent Line Problems?

OK. Found the line and disconnected, gave it a good blow, and about a cup of gas came flying out the fuel fill. Should the line remain clear at all times? The only thing I can figure is that there's a slight curve in the tube that might be holding gas. If I shorten the line to make it a straight shot, will this take care of the problem? Thanks.

 

[Reel Appeal]

Re: Fuel Vent Line Problems?

bryan,<br /> Touching on what djohns said,follow the smaller vent line from the tank to the vent fitting(should be on outer hull).From the outside of the boat,looking at the vent.Carefully look inside the vent fitting(with flashlight if necessary).There may(should)be a vent screen in there.Make sure the screen is not clogged from corrosion or plugged some other way.

 

[rickdb1boat]

Re: Fuel Vent Line Problems?

bryanredfish <br />The answers would be yes, it should be clear all the time and probably, if you can take the loop out of the line.

 

[DJ]

Re: Fuel Vent Line Problems?

bryan,<br /><br />I believe you've found it. The venting of vapors does not usually cause enough pressure to free the vent line of liquid fuel. Thus, slow fill.<br /><br />The vent line should not have any bows or dips in the line that would cause liquid fuel to puddle.<br /><br />Hopefully, you can re-route or shorten the vent line to make a downhill slope its entire length.<br /><br />Also, vent lines get clogged by "stuffing" too much fuel into the tank.

 

[bryanredfish]

Re: Fuel Vent Line Problems?

The vent line WAS the problem. After blowing the gas out or the too-long line, it ran like a dream. Not a hint of hesitation. Solution was as simple as cutting 3 inches of vent line to get rid of the bend, which was holding gas. Thanks guys for all the advice.

 

[DJ]

Re: Fuel Vent Line Problems?

Bryan,<br /><br />Glad you got it!!!