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Author Topic:   Run motor out of gas?
jaydelmonte posted 09-15-2002 04:40 PM ET (US)   Profile for jaydelmonte   Send Email to jaydelmonte  
I have a 1978 Johnson 2 stroke on my 13'. Guy at the ramp today told me I should disconnect the fuel line and run the motor out of gas at the end of a ride. He says it will keep the carb from gumming up. I have never heard of this tip before. Is he right?
North Beach posted 09-15-2002 04:50 PM ET (US)     Profile for North Beach    
Here is PAscoe's 2 cents

Peter posted 09-15-2002 05:34 PM ET (US)     Profile for Peter  Send Email to Peter     
I used to do that after every trip with a 1977 Evinrude 35 on my 13 Whaler. I never had a problem with the carb gumming up so I say it can't hurt.
jimh posted 09-15-2002 06:01 PM ET (US)     Profile for jimh  Send Email to jimh     
David Pascoe's article has quite a bit of advice for owners of large inboard vessels on winterization, but it does not seem to be much of an oracle for outboards. It does not address the questions being asked here at all.

Disconnecting the fuel line and letting the engine run out of fuel was a popular technique when all outboards were fitted with carburetors. The idea is that you will drain the caburetor bowl of fuel. The notion is that if you left the fuel in there, the gasoline would evaporate over time and leave behind a residue of oil.

I don't think it is necessary to run the engine out of fuel after every use if there is any anticipation of using the engine again in a reasonable time. If I think it might be 3-months before I run the engine again, I run the fuel out of it.

On newer engines there seems to be some reservation about running the engine out of fuel. Some larger horsepower engines now have the fuel hose running into the cowling without a disconnect--to discourage people from disconnecting the fuel and running the engine dry I assume.

In my case, with carburetor engines, about the only time I disconnect the fuel line and let the engines run out of fuel is during winterization procedures.

tocobill posted 09-15-2002 11:50 PM ET (US)     Profile for tocobill  Send Email to tocobill     
On that small Evinrude motor without oil injection, running the motor out of fuel isn't a problem. If you don't use the motor often, it would be a good idea to run fuel stabilizer or OMC's 2+4 fuel conditioner all the time even if you do run the fuel out. Old time school of thought was to leave the fuel so that gaskets (cork & paper)wouldn't dry out, new motors use rubber based gaskets, however the fuel would evaporate after any extended period of time anyway. The new larger motors eliminated the fuel connection at the motor to eliminate the possibilty of an air leak at the fitting and to rule out using a portable tank on the larger motors. Also disconnecting the fuel supply on a VRO oil injected motor would load the carb bowls with oil.
whalerron posted 09-16-2002 09:10 AM ET (US)     Profile for whalerron  Send Email to whalerron     

I had a 1975 70hp Johnson that I "ran the gas out of" after every outing. I did that for 25 years with the motor and it apparently never did the motor any harm. But, I don't know that it did much good either. That motor was a 3 cylinder and once 2 cylinders run out of gas, it stops running. That means that one carb still has gas in it which can gum up. On 2 occasions, the motor sat for about 2 months in warm weather and on both occasions, I had problems with gumming in at least one carb. Also, "running the motor out of gas" does not guarantee that all gas is removed from every carb, every orifice and every inch of fuel line.

My new tactic is to mix Sta-Bil with every tank of gas. Now, gumming and old gas issues are a thing of the past.

BQUICK posted 09-16-2002 09:50 AM ET (US)     Profile for BQUICK  Send Email to BQUICK     
I would think running it out of gas would run it out of oil, too.....which could cause piston scuffing.
lhg posted 09-16-2002 03:57 PM ET (US)     Profile for lhg    
The instruction manual for my 1985 Merc 115's (3 1-barrel carbs), using pre-mix, is to IDLE the carbs dry, to prevent gum & varnish build-up from evaporation. For 17 years now, I have done this every time when the boat won't be used for a week or so. No problems ever experienced, because the lubricating oil runs out when the fuel does.

With an EFI engine, you can't do this with a direct plumbed fuel line, nor would it be necessary. Evaporation of fuel from carburators are the only issue here.

Monnas Rock posted 09-20-2002 02:12 PM ET (US)     Profile for Monnas Rock  Send Email to Monnas Rock     
I have faithfully, run my 70hp Evenrude out of gas after each use, for the past 5 years and not had a carb. problem. It seems to work.
Jay A posted 09-22-2002 12:36 PM ET (US)     Profile for Jay A    
Since 1975 I've dis-connected the fuel line at the tank and run the engine(1975 40HP Merc) in a tank of fresh water. The only thing I've replaced are the spark plugs!
where2 posted 09-26-2002 01:22 PM ET (US)     Profile for where2  Send Email to where2     
Up until the introduction of VRO or similar oil mixing (not oil injection) systems, running the carbs dry would help keep the volume of fuel left in the bowls to a minimum, thus reducing the amount of gum which could be made. (You've only got so many atoms to work with. If your puddle of fuel is smaller, you have less gum at the end of the chemical process which creates gum).

When VRO came along, running the fuel out of the carb caused you to fill the carb with oil because VRO is a mixing system which mixes oil with the fuel in the VRO pump. (as opposed to Yamaha Oil Injection which inserted oil just after the carbs). Introducing air into the fuel side of the VRO pump was also a bad thing, so eventually they plumbed the system without a disconnection at the engine to keep air out, and to keep you from running the carbs dry. Introduction of air causes excessive oil input and foaming in the pump, leading to plug fouling.

My first-hand knowledge of a 1981 70Hp Johnson purchased new, run for 20 years pulling the fuel line after each trip and letting the engine idle until it died, resulted in the owner having to disassemble the carbs Zero times. Whalerron is right, running it dry doesn't get every molecule of fuel out of the engine. However, it does lower the total number of molecules available to decay into gum in the first place.

It's not perfect, but it's better than nothing as long as you don't use VRO. Perfect would be being able to use the boat every day! In that case, we'd be discussing how many hours you really can get out of a 1978 2-stroke engine...

Jiles posted 09-26-2002 06:21 PM ET (US)     Profile for Jiles    
I am a mechanic. I have worked on all types of engines for over 40 years. When I am through running ANY small engine, be it a chain saw, boat motor, lawn mower etc.,I drain or run dry. I do this if the engine will not be used for an extended period of time--like several weeks or months--. I also use STA-BIL fuel stabilizer. I have done this for many years and have not had a problem. It is true that the gaskets will dry out, but they are under mounting pressure and will not be harmed. I used my Craftsman chain saw last week that had been stored for TWO years with gas tank and carburetor dry. With fresh gas,it started on the third pull and ran beautifully.--- JUST MY OPINION ---
newt posted 09-27-2002 11:32 AM ET (US)     Profile for newt  Send Email to newt     
From the posts here, it seams clear that running a non-VRO carburated engine out of gas has it's merits.

What is recommended for an engine with VRO?

Salmon Tub posted 09-27-2002 02:17 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
I don't think that running dry would raise the issue of lack of lubrication in a VRO or similar set-up. As the fuel/oil enters the crankcase, it is basically a mist rather than a liquid. It settles on all the parts, moving and not, and then the mist gets sucked into the combustion chamber. So, even after the fuel has left the crankcase, gone through the piston, and out, there is still residual oil that is left coating all the parts. The only way to get rid of this oil is to burn it off if the block is hot enough, or to wash it off, by say pure gasoline that has no oil in it. Even Gasoline, to an extent will act as a lubricant. At idle, the engine does not create enough friction to do any damage in the short amount of time it takes for the cylinders to go from getting the normal amount of fuel, to where there is not enough fuel to keep the engine running.
lhg posted 09-27-2002 02:42 PM ET (US)     Profile for lhg    
With or without oil injection, with a carbureted engine, it makes sense to avoid the gum and varnish deposits from evaporated gasoline, or gas/oil mix.

Regarding the inferior OMC VRO (their specific trade name) systems, I remember reading that an OMC engineer indicated, after the bankruptcy, that the system design was faulty from "day one" and that OMC would never spend the money to design a correct, 100% reliable system.

Has Bombardier finally redone it, or just fixed it up a little more? With the end of carb two stroke production in three years, it may not have been worth the investment to them.

where2 posted 10-02-2002 01:16 PM ET (US)     Profile for where2  Send Email to where2     
My 1967 9.5hp Evinrude sat in my garage and my parents garage for 5 years ('97-'01)after having been run out of gas before storage. Started on the 3rd or 4th pull when removed from storage, mounted on a saw-horse, connected to a can of fresh gas, and started in a garbage can full of water. A week later, I took the engine on my honeymoon, and it ran like a champ. Ran it out of gas for the trip home, and stored it back in the garage... Maybe I won't wait 5 years before I use it again.
WSTEFFENS posted 10-02-2002 08:20 PM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     
For who it may concern:

You should never run a VRO engne out of gas as you will fill the bowls of the carbs with pure oil as the pump (VRO) works on crank case pressure pulses and pumps both oil and gasoline at the same time. When the carbs are full of oil, restart is next to impossible. Use fuel stabilizer and its no problem.

As for the VRO system and LHG's comments, I suspect a small part of his Mercury Marine bent is showing. I too read the line string about the OMC engineer and his comments. I took it as (natrually founded) sour grapes due to the way Mr Sorros tanked the company and the fact that he lost his job because of it.

I have owned several (more than 2) VRO engines and had no problems, other than the failure of early (mid 80's) pumps that had a very low tolerance for alchol laced fuels. The only things that make the system fail is cracked hoses, and poor calmps that cause vacuum leakes and make the engne run lean. I got this same information from two local very experienced OMC tech's.

As for other oil injection systems I haven't any relevent information.


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