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Author Topic:   Gas Filters and gas procedures
jimh posted 06-07-2000 08:24 AM ET (US)   Profile for jimh   Send Email to jimh  
I often see larger boats (that have built-in gas tanks) are equipped with a gas filter. These are often substantial affairs,
mounted on a bulkhead, and they look like they might contain a quart of fuel or more.

A couple of questions:
1. For smaller boats with portable tanks, say 6-12 gallons, is it adviseable to insert a gas filter in the line? If yes, what type? The big, spin type, or the small in-line type?

2. Where is the primer bulb, between tank and filter or between filter and engine?

Also, because there might be several weeks between use of my boat, it is my normal procedure that, when hauling it out at the end of each use, I disconnect the gas line from the engine and let the engine run all the fuel out of the carburetors. I do this on the assumption that it is bad for the engine to have a couple of carburetor bowls full of fuel, which would likely evaporate and leave behind a residue of sticky varnish.

My guess is that people with large engine(s) probably don't do this every time they shut down. It is not too handy to crawl out there on the transom or bracket and disconnect the fuel lines.

Now, if the boat's in the water and we're using it everyday, I don't follow this fuel burn-off procedure; I just do it when I am using the boat occasionally.

Question: Does anyone else do this (fuel burn-off) procedure? Is it worth the effort?


goldstem posted 06-07-2000 10:03 AM ET (US)     Profile for goldstem  Send Email to goldstem     
A filter is definately recommended. I used to
have a 13 whaler with a 40 johnson, and the
filter (screen) on the motor was a joke. Had a few carb problems before I put an in-line
(tempo?) filter on it. no problems since.
As for running the motor empty, you'll get a lot of opinions on that one. I didn't. I would disconnect the line at the tank - usually as I got near the dock, and that was it - just to take some pressure out of the line. If you don't run it out, make sure the fuel has stabilizer. I almost always put stabilizer in the tank when I gas up, unless
I know I'll be back tomarrow.
bigz posted 06-07-2000 11:10 AM ET (US)     Profile for bigz    

1. yes even if it is just a simple $4 inline one, though a large permanent mount is much better West has a relatively compact one made by Fram also the Racor 110A is relatively small and a plus for Racor most marine stores sell their replacement filters.

2. Primer bulb goes between the filter and engine.

For your small boat and particularly if you won't use it for a few days then I can't see why not drain the engine of fuel, can't hurt and only takes a few minutes .

We don't bother to do this with our 27's twin 200 Yamaha's (we did do it with our 20 Outrage 175 Johnson each day though)--- however if the boat were to be laid up for an extended time we would burn off the fuel --- the best way to keep water out of the equation is keep the fuel tank full --- in essence after your through for the day refuel so the tank or tanks are toped off.

I think Clark Roberts if I remembered correctly when I was down at his home, used the permanent mount filters even on his 13!

Just some thoughts --- hope they are of some help --- Thomas

Walt Steffens posted 06-07-2000 12:51 PM ET (US)     Profile for Walt Steffens  Send Email to Walt Steffens     
Jim: Most larger engines are hard plumbed. Meaning that the quick disconnect would starve them for fuel. However most engines I have owned since the late 70's have had internal filters of some sort, although not water separators. I would think that if you were going to use an external (add on) you would definately want the water separator ability that a standard automotive would not give you.

As for running the carbs dry at the end of the weekend, again most large engines (150 hp & up) are 3/8" hard plumbed. Also in the case of the OMC VRO system if you would run the carb bowls dry you would fill them with lube oil, making restarting impossible.

reeltime2 posted 06-07-2000 02:23 PM ET (US)     Profile for reeltime2  Send Email to reeltime2     
I use a large spin on type filter/water seperator Kind of looks like an automotive oil filter. It is manufactured by seiera they sell the kit at all the supply stores (i.e. west marine, boat u.s., B.O.W., ect.) I have it mounted to the side board, its between the tank and the primer ball. I completly drained the fuel tank when I got the boat and replaced the filter about 2 months later I checked the filter and it had about 2 oz of water inside. I was very suprised after only 2 months I had that much water in there.
Needless to say I replace the filter about every 4 months. There is always water in there, at about 4.99 a filter its no big deal. I suggest everyone ues one of these types of filters. If anyone needs the part # let me know and ill check tonight and post it for you.
bigz posted 06-07-2000 03:02 PM ET (US)     Profile for bigz    

Maybe the VRO system OMC's are hard plumbed or the shop rigged them that way --- however our '87 oil injected 200 hp Yamaha's aren't for fuel, just oil, and neither was our '82 -- 175hp Johnson (wasn't VRO) --- I also almost bought a 1997 150hp Ocean Runner to replace the 175 and it didn't need to be hard plumbed and you could either use the VRO system or just add oil to the gas your option --- in fact Yamaha recommends removal of the fuel line after shut down --- on our 175 with out oil injection it just seemed the prudent thing to remove the fuel line and burn off the gas/oil mix in the bowel before shut down -- on the Yamaha's this can't be done due to the oil injection hook up ---

Like I mentioned the water separator fuel filter large type like a Racor is the ideal --- yet you can also purchase inline fuel filter/water separator filters which are pretty reasonable and for what Jim needs would probably fill the bill ---

The key is to keep water out of the tank in the first place --- chuckle which is almost impossible to do, so a filter is necessary --- might note the Racor with the see-through bottom bowel let's you drain off the water that accumulates so a complete filter change is only necessary at the prescribed intervals --- for most folks once a year ---


Walt Steffens posted 06-07-2000 04:58 PM ET (US)     Profile for Walt Steffens  Send Email to Walt Steffens     
Thomas: I can't speak for all engine manufactures, however the V6 150's I have w/VRO (91's) came out of the box without the tradidional OMC quick fuel disconnect. When I questioned the dealer/rigger about this he explained that the quick dissconects wouldn't flow sufficient fuel at WOT and that the higher HP engines also required 3/8" vs the 5/16" lines used on the smaller engines. That is why I refered to them as hard plumbed. As for the VRO, I know several of the forum users don't care for the system as they may have had a bad experience with it. The VRO system can't be disconnected as it takes a careful priming of the system at installation to eliminate air in the lines leading to the pump and carbs. I would guess very similar to your Yamaha injection system. As for stablizer I agree with you, I use a fuel treatment/stablizer from OMC that not only stabilizes the fuel but collects condensation ammounts of water as well as cleans carbon. Seems to be cheep insurance as my boat may not get used for several weeks at a time over the summer. Sorry for the confusion, my experience is primarily with OMC products with some Merc. I know very little about Yamaha.


jimh posted 06-18-2000 12:20 PM ET (US)     Profile for jimh  Send Email to jimh     
Following up on the topic of fuel and filters:

I just got the boat back from K & M Marine, the MERC shop where they kindly rebuilt the carb needle/float valves again, this time "polishing" the valves and seats, to reduce the tendency for them to stick.

You may have read about their untimely sticking while we were miles offshore in Lake Michigan in my "Sail-Logs" article at

Fortunately, this was a "warranty" repair, so it did not cost me anything, except the boat out of service for 4 days while it rained here in Michigan. They had previously rebuilt the carburetors last fall.

But I did ask the long-time outboard mechanic what he thought of installing a large fuel filter: he recommended against it because the fuel pump in this older engine (1976) might have difficulty drawing the fuel through it.

He also pointed out to me that the plastic fuel connector fitting on the line from my aftermarket (TEMPO) tank was warped and did not fit well. I replaced that with a MERCURY branded metal fitting.

The fitting engages the mating connector on the engine much more easily.

In the process of replacing the fitting, I found I had the wrong size barb on the new MERCURY fitting, so I headed off to West Marine--it's closer than the MERC shop--to get another barb. There are three common sizes of barbs and two common sizes of threaded connectors. Of course, they were out of the combination I needed.

On the way back, I stopped in a hardware store and got the precise adaptor I needed for only 89-cents. At West Marine they were priced at $2.89!

So now the fuel system is back together and flowing better than ever. Total out of pocket was $0.89 (barb) and $10 (fitting). As for the lack of a filter, I am putting some stock in what the mechanic said, and also thinking that most of my gas comes on the highway, not from marina pumps. With the small topsides tanks I don't think I have the water ingress problems that many others have with internal tanks deep in the bilge.


dougs posted 06-18-2000 11:07 PM ET (US)     Profile for dougs  Send Email to dougs     
The thing I've always wondered about...With a 2-cycle engine the lubricant is carried with the fuel. When you run it dry are you accelerating engine wear by running it out of lubricant as you dry it out? Any informed insight would be welcome.

Thanks in advance,
Doug Sowles
Portland, Oregon

reeltime2 posted 06-19-2000 08:46 AM ET (US)     Profile for reeltime2  Send Email to reeltime2     

How much did it cost to rebuild your carbs?
I am thinking about having it done. does your eng. have three carbs or two?
Eric posted 06-22-2000 02:44 PM ET (US)     Profile for Eric  Send Email to Eric     
I see a question that I had as well: running out the fuel does eliminate the lubrication for the engine as well. Something to ponder.
jimh posted 06-23-2000 12:14 AM ET (US)     Profile for jimh  Send Email to jimh     
Cost to rebuild carbs (2) at MERCURY shop:

(2) Gasket Kits @ $17.26
(2) Diaphram Kits @ $12.54
(2) Inlet seats @ $10.34
(2) Floats @ $23.70

Total Parts: $ 127.68
Labor: $ 120.00
TOTAL $ 247.68 + tax

The engine was 24 years old.


Ger posted 06-23-2000 09:46 AM ET (US)     Profile for Ger  Send Email to Ger     
Eric, regarding running the fuel out of the engine, my local merc dealer mechanic who is highly regarded, says never run the fuel out. The lean condition and lack of oil is a lot worse than the old gas in the line..some fuel treatment in the tank is the way to go.
wds posted 06-25-2000 09:17 AM ET (US)     Profile for wds  Send Email to wds     
I've used isopropyl alcohol with the fuel for years to absorb any water in the tanks. It mixes with the water and combines it with the fuel, so it gets burned.

It's available (at least in the North) as auto dry gas, but make sure to use the isopropyl type as it is harmless to o-rings and rubber hoses.

It costs about 0.60 a 12 oz container, which will treat 10-20 gallons.

lhg posted 06-26-2000 01:59 PM ET (US)     Profile for lhg    
There is another product out there for getting water out of boat built-in tanks, and
doesn't contain alcohol, which in the presence of water is what causes the tank corrosion in the first place. It's by MDR and is called "Water-Zorb". A 12 oz bottle costs about $9 and treats 300 gallons.
lhg posted 06-28-2000 04:35 PM ET (US)     Profile for lhg    
Regarding running a carbureted outboard out of fuel before periods of non-use, the information from "Ger's" mechanic, mentioned above, may not be correct. Here is a direct quote from the "Operation and Maintenance Manual" that came with my Mercury 115HP in-line six 2-stroke outboards, 1985: (Page 31)
(engine has 3 1-barrel carbs)


"If motor will not be operated for a period of time, if it is to be removed from boat, or if it is to be tilted up, prevent spillage
from the carburetor throat & bowl, and gum formations in the carburetor during storage as follows:

1. With motor running at idle, disconnect the fuel line from fuel tank, thus allowing carburetor to run dry (motor stops).

2. Turn electric start key to Off. Disconnect positive battery lead to prevent accidental starting or shorting." (I think this applies to storage conditions only - LHG note)

I have been doing this for years now, with no problems encountered. My Dealer told me they shold be allowed to IDLE out of fuel, not revved up. In 2 stroke engines, the lubrication comes from the fuel charge, so as the engine runs out of fuel, the lubrication is still being supplied as the last fuel charge is burned. Non of this would apply to EFI or DFI engines, as there are no float bowls to get gummed up! My Merc EFI engines do not even have a fuel disconnect at the engine.

Highwater posted 10-18-2001 12:39 PM ET (US)     Profile for Highwater    
I just installed a Tempo in-line fuel filter. I put it between the bulb and the engine. Then I read this thread which people seem to agree that the filter belongs between the tank and the bulb. Have I made a serious mistake? Should I replace the hose and put the filter ahead of the bulb?

On a somewhat-related subject, is there any problem (aside from the added cost) with running 93 octaine "super unleaded" gas in a 2-stroke engine?

TampaTom posted 10-18-2001 02:42 PM ET (US)     Profile for TampaTom  Send Email to TampaTom     
I asked the local "JohnRude" dealer where to locate the Tempo inline filter. He says between the engine and the bulb as squeezing the bulb will purge air from the filter. That's his opinion. I don't necessarly agree.

I do agree that running the fuel out of the carbs on "premix" engines to be laid up is a practice that works. I have a little kicker on a sailboat that gets used about every two months. Before I started running the carbs dry about 3 years ago, I would usually have to remove the carb and soak in cleaner. I havent' had to do that anymore.

Metal under deck tanks need water seperators. I don't think its necessary (but can't hurt) for portable above deck tanks. Next time before you refill, pump the last gallon out with your primer bulb. Better way to get rid of water in the tank than running it through the engine with alcohol.

where2 posted 10-18-2001 06:06 PM ET (US)     Profile for where2  Send Email to where2     
To be honest, the 70Hp Johnson on my 15' Sport has VRO and a quick disconnect. BUT: Trailer Boats Magazine's commentary in '99 about the widely disliked VRO system mentioned that the Main Problem with the system is "air being drawn into the incoming fuel before it reaches the VRO pump". This leads me to believe that running a VRO dry is not the same as running my '67 9.5Hp evinrude dry (sat for 5 years, and only took 5 pulls to get it started, but I ran its carb dry before I stored it!!).

If I ran my VRO, I would probably hard plumb it to avoid the possible entry of air at the quick disconnect (leakage is common with or without VRO on OMC engines at the QD). But since I don't use the VRO, I have no concern about running the carbs dry, and will continue to. I think my dad is still running the carbs dry on his '00 50Hp Yamaha 4-stroke. It does lessen gumming of the carbs, even on your lawn mower...

billh1963 posted 02-22-2004 10:44 AM ET (US)     Profile for billh1963  Send Email to billh1963     
I would like to install a fuel/water filter/separator on my Montauk. I've been searching the archives and decided to resurrect this thread. I would like to get a quality filter of small size with a clear bowl and think I want to go with something like this mounted on the transom in the splashwell...

Does anyone have a recommendation on one that fits good in that area of the boat? Also, is the final word to mount the bulb betweeen the filter and the engine? There seems to be some debate on this.


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