Should I run engine dry after use?

[frankc]

It is a petroleum issue which can form gum in the jets when not operated for a length of time. The four cycle should be much better at not plugging jets as there is no oil added to the fuel.

The 2 cycle depends on oil mixed with the gas for lubrication whereas the 4 cycle has its own lubrication system. Running lean is not good for either design, but should affect the 4 cycle less. You only run lean for a very short time when running the carbs dry.

It is a catch 22 situation though. With the large 2 cycle engines, I stripped down the carbs and cleaned the jets before each season after experiencing gum in the jets.

My practice has always been to run until the engine stumbles from leaning out and then pulling the choke to draw as much fuel as possible through the engine.

There are additives available which are supposed to prevent the formation of gum, but I am not familiar with their results. Running fuel injector cleaner through a 4 cycle injected engine should probably prevent the problem.

My experience with jets clogging has all been with 2 cycle engines.
The 150 HP was a six cylinder with three carbs. One high speed jet plugged which allowed the engine to run but with less than normal speed. It scuffed a piston and damaged bearings after warming the engine and accelerating immediately after attaining planeing speed. Lack of lubrication caused extreme damage.

We have recently purchased our first 4 cycle fuel injected engine, so it is a learning experience at this time for me. I lean towards fresh gasoline and fuel injector cleaner at this time, but am no expert regarding the engines.

Many years ago, we found it necessary to manually clean carbs in automobile engines from time to time. They developed carb cleaner which allowed us to basically forget manual carb cleaning.

[thomas]

Originally Posted by ShinyShoe

But how often do you run your car on two stroke and how often do you park your car up for weeks on end letting the petrol evapourate out and leaving the gunk behind...

Never, it's diesel.

But my mower, strimmer and chainsaw are all two stroke and get left for months without being run dry and all start first time.

I once have a 3.3 Mercury s stroke, left it in my shed for 3 years, dug it out to sell and it ran third pull perfectly.

[frankc]

If you leave 2 stroke engines for months of inactivity with fuel in them and have had no problems, you are a lucky person.

[uncle al]

The reason why petrol should be drained is 2/STR or4/ STR,
1/ it goes very stale and could/would cause engine problems
2/when it dries out it leaves a varnish type crust behind
That is why I always drained any petrol wether its 2/STR or 4/STR from any obm that I worked on. I also used a fuel additive that kept any fuel in the system a bit fresher for a bit longer

[frankc]

In the bad old days, the reason we cleaned carbs in automobile engines was the varnish you speak of. I have seen the inside of carbs which had quite a coating before the proper chemicals to dissolve it became popular.

They leave more light ends in gasoline today than they did in the past. That evaporates and leaves the heavy ends in the tank. I have tested old gasoline by soaking paper towel and lighting it with a match. Fresh gas will burn so rapidly that you can burn your fingers before dropping the paper while old gas will burn slower when stale.

Thanks for the reminder. I think I will treat our 4 stroke more like the 2 stroke engines after all

[jyasaki]

Originally Posted by Davie

Why would it stop?

See the last line in the part you quoted.

The dry break connector acts the same as a closed-vent fuel tank; as fuel is burned it forms a vacuum that overcomes the fuel pump, causing fuel starvation despite the presence of fuel.


jky

[shaun2020]

Hi,

I have purchased a new 20hp Mariner and the manual advises to let the petrol run dry,

I have forgot to do this the last two times the outboard has been used,

well only once by me and once after the supplier carried out the a PDI,

I can smell a few fumes but other than that no problems and I have travelled 300 miles plus recently with my outboard in the back of the car with no issues,

If anything it will make it easier to start the engine if there is a little petrol in the carb & fuel lines, or save a little time on priming

[Locozodiac]

On 2 strokes pre mix engines left with fuel on carb for extended time period besides varnishing jets could also stick float and engine will have hard times when restarted time after. Alwayas run my carb dry after each outting, as never know when will be my next one...

Usually while flushing engine, disconnect engine hose, when engine is about to die, push connector pin in for some seconds, engine will revive again, then will drop fully dead. This gives a nice 5 minutes minimum good engine flush at idle.

One issue most boaters don't take into account is that gasolines which have ethanol added are not much fuel pump friendly, that is ruins thin diaphragms & rubber parts much early than on larger engines. Fuel is no good after some time. Usually burn most of the fuel bought for that outing, and always re fuel tank with fresh fuel. Engine runs much better.

Happy Boating

[Slaphead]

I understand the logic of doing all of this with a premix engine but is there a risk of flooding the carbs with oil on a two stroke with separate oil tank, ie the oil pump continues to inject oil as the engine begins the stalling process?

[jezza2011]

I have never ran mine dry in 22 years.
In fact I flood the engine if its going to stand for a while.
my loging being.....
ITS A 2 STROKE.... FULE LUBRICATES THE WHOLE ENGINE. ;-)

so no fuel = no lube in engine = metal to metal wear = ££££££

and never had any issues with stale fuel, Dirty Carbs ( I check the blows and they are spotless and fuel is clean)
I even had to leave it for 1.5 years and it still started 2nd click that time instead of the first spin.

my compression is spot on so I will never run it dry( dry- its description says it all DRY = NO LUBE).

and we did a 40 mile run yesterday and she never missed a beat.

I also always double oil it for the first tank of the season.

[9D280]

Ignoring all the stale fuel etc issues, skyemutt is putting it ion the back of his car.

Bottom line is carb floats are designed to work by floating, so as soon as you turn the thing on it's side / back / front / any angle other than the right way up, the bowl seal is broken & the fuel will dribble out into the carb then onto the air intake & the car will honk of petrol for days after.

So, theories of deposits aside, I'd be empting the carb(s) regardless......

[sergeant]

I run mine dry by simply disconnecting the fuel line - its incredible on idle just how long the engine runs for, mine went for at least 2 minutes before it finally cut out!

[tehguy]

Originally Posted by sergeant

I run mine dry by simply disconnecting the fuel line - its incredible on idle just how long the engine runs for, mine went for at least 2 minutes before it finally cut out!

I agree - I pull the fuel line off just before I jump out, by the time I've walked up to get the car and put the trailer in the water it is just about to run dry and conk out

[chris.moody]

Originally Posted by Slaphead

I understand the logic of doing all of this with a premix engine but is there a risk of flooding the carbs with oil on a two stroke with separate oil tank, ie the oil pump continues to inject oil as the engine begins the stalling process?

That's interesting as I have an autolube 2 stroke. Now should I disconnect the fuel or not if it's going to be left for at least a week unused?

[frankc]

That autolube could give problems when run dry.

[xs 400]

Originally Posted by frankc

That autolube could give problems when run dry.

why's that? ( I have an autolube )

[frankc]

Depending on how the autolube is set up, it furnishes oil depending on pressure or engine speed. As the fuel mixture leans out, you may find excess oil injected.

[9D280]

As it was probably run in on essentially a 25:1 mix for 10 hrs I doubt that will cause any long term damage.

[frankc]

Probably the best way to find out would be to run all the fuel out and pull a spark plug to examine. If the plug were fouled badly, then the pump put too much oil in, but as long as the oil did not go through the carburator it would not hurt anything.

Our old Evinrude only put a small ratio of oil to gasoline at idle speed, so it may be no problem at all to run it dry.