4 Stroke draining carburetor

[davidpbo]

We had a 8HP 2 stroke engine which at the end of each period on the boat (assuming no return for a fortnight or so) I used to disconnect the fuel feed and allow it to run out of fuel.

We have now gone to a 4 Stroke, should I do the same?
I think probably not although I would at end of season.

Engine stays in position on the boat.

 

[Arcady]

Why not? That's exactly what I do at the end of each trip with our 6 hp Tohatsu.

 

[steve66]

Why not? That's exactly what I do at the end of each trip with our 6 hp Tohatsu.

You absolutely must drain the carb if your leaving the engine for a while. Jets are much smaller in 4 stroke engines than 2 stroked

 

[davidpbo]

Why not? That's exactly what I do at the end of each trip with our 6 hp Tohatsu.

You drain it?

You absolutely must drain the carb if your leaving the engine for a while. Jets are much smaller in 4 stroke engines than 2 stroked

But are they smaller than say a lawnmower's jets or that on a (Older) car carburetor?

How long do others class as "A While" I am thinking maybe a month or six weeks.

 

[Arcady]

You drain it?

I disconnect the fuel feed and run the motor until it stops. I suspect that leaves some fuel in the carburettor bowl, but running the carb dry worked fine for 15 years on our smaller Honda BF 2. We never had any carb problems.

 

[pessimist]

We have a small Honda generator. If we leave it for a month or two without draining the carb. it tends to have a fir of the sulks. We also have a three cylinder 4 stroke Yamaha. Draining the carbs. is not an option but we do find it necessary to have them cleaned each year.

I'd drain the carb.

 

[Seajet]

I used to run my 2 stroke engine with the fuel disconnected until it stopped, so I could stow it in the locker ( and put the well fairing plug in for sailing ) to avoid the possibility of petrol spilling in the locker, but it never seemed to spill anyway and I'm reluctant to do this now as the last gasping revs of the engine will be without any lubrication - this is mainly a 2 stroke issue though unless one tilts a 4 stroke when running.

Whether 2 or 4 stroke I'd definitely run it in fresh water then drain the float chamber - of course -at the end of season; with my Mariner 2 & 5hp 2-strokes they're excellent engines but I do find it a good idea to remove the heads and get the salt buildup out of the waterways every other year.

New gaskets are still easily available from Ron Holland Marine, Portsmouth.

 

[spannerman]

It doesn't make any difference whether its 2 or 4 stroke, water in the float chamber will do damage if its not drained out before laying up for several months.

 

[Seajet]

Why should there be water - apart from maybe condensation - in the float chamber ?

 

[fisherman]

Our local engineer says he is repairing lots of outboards that have suffered from
fuel left in the carb. The hygroscopic bio additives are, he says, causing the problem. Local diesel engineer, when I asked about the injectors in my Ford dover and new fuels, held up a pencil. "If your nozzles are this size, that car out there has nozzles the size of a needle. That's why it's in here, the injector nozzles get eroded by the high pressures needed"

 

[davidpbo]

Outboard is used predominantly in fresh water. No question about draining carb at end of season or for prolonged periods of no use, I am not sure i regard 2 weeks or so as a prolonged period of lack of use and an interested as to what others regard as a long enough interval to warrant running out of fuel.

Imho when running a 2 stroke out of fuel it is not being run without lubrication. Surely the lubrication doesn't stop until the engine does I suppose the reverse is true on start up though.

 

[Fantasie 19]

Why not? That's exactly what I do at the end of each trip with our 6 hp Tohatsu.

Me too (4HP Tohatsu) - run it dry that is... not drain it...

 

[Seajet]

Outboard is used predominantly in fresh water. No question about draining carb at end of season or for prolonged periods of no use, I am not sure i regard 2 weeks or so as a prolonged period of lack of use and an interested as to what others regard as a long enough interval to warrant running out of fuel.

Imho when running a 2 stroke out of fuel it is not being run without lubrication. Surely the lubrication doesn't stop until the engine does I suppose the reverse is true on start up though.

If you run a 2 -stroke until it runs out of fuel - so the air / fuel mixture leans right off and it speeds up then stops - the last revs are without fuel, so without the oil in it either.

 

[Len Ingalls]

If there is ethanol in the petrol,it will make water, & a white slurry. Drain it or clean the carb after a month of non-use with ethanol gas.

 

[thinwater]

Vital? Hmmm.

Haven't drained a carb in 20 years, and some of them are that old. I think good fuel filters, regular use, and an additive that can stop corrosion are more important. The trick is identifying an additive that isn't snake oil.... A good starting point would be OEM (Merc has good ones) or the airport guys (Biobor EB).

And close your vent every time, if that is applicable. Full tanks and silica gel filters also help, though not the carb.

We've been living with e10 in the US for decades and at least some of us have learned the tricks.

 

[Seajet]

I have had to leave my Mariner 5hp 2-stroke for probably 6 weeks, put it in the well and it started at second pull - no problem.

Of course something to be very wary of is the lay down stowage position of 4 strokes or the lubrication oil may flow into the head and cause an inconvenient, potentially expensive hydraulic lock.

This can happen to 2-strokes too with the cooling water, I always transport, carry and stow my engines with the head uppermost.

Possibly a tip; for stowing engines in lockers, rubber car mats are ideal to prevent the pointy engine skeg damaging the inner hull; in my case I lay the engine head on a redundant fender to keep it higher than the leg - but of course when stowing the engine I always give it a good chance to drain first, this is surprisingly easy up to Force 6, maybe as I'm half Scottish and the £ signs are flashing before my eyes if I mistreat the engine !

 

[davidpbo]

If you run a 2 -stroke until it runs out of fuel - so the air / fuel mixture leans right off and it speeds up then stops - the last revs are without fuel, so without the oil in it either.

How can it fire without fuel?

 

[aquaplane]

It's not firing, it's momentum spinning it until the friction wins and stops it.

 

[Momac]

Turning off the fuel tap to stop the engine prior to lifting the outboard off the dinghy is a sound plan.
I have a 2 stroke and have been advised to do this by a very knowledgeable friend who has overhauled my outboard.

 

[macd]

It's not firing, it's momentum spinning it until the friction wins and stops it.

Compression is by far the bigger factor.
I'm suprised at Seajet's remarks, as I imagined that he might have stripped plenty of two-strokes. The internals of a healthy one are coated in a beautiful film of clean oil, well able to supply lubrication for a handful of revs. If it were otherwise, imagine what would happen every time a premix two-stroke motorcycle went onto reserve...