4 Stroke draining carburetor
- Thread starter davidpbo
- Start date
RichardS
N/A
+1
My old 2T was always running out of fuel on the main tank. It won't do any harm at all.
Richard
macd
Well-Known Member
Particularly as with an outboard you're unlikely to get a lorry up the chuff as you fiddle for the reserve tap with frozen fingers
Seajet
...
Well it won't, will it ?
But if you disconnect the fuel supply and run it dry, the air / fuel mixture will lean right off and the engine will briefly speed up, so with a modern 100:1 engine that's not much lubrication during the last gasps is it ?
And yes I have stripped plenty of 2 and 4 strokes; I used to run my outboard engines dry, as mentioned so as not to risk carb's spilling into the locker, but now think twice about that, especially as the engine doesn't seem to leak anyway.
When you hear of a ' Kaboom ! ' please add that last sentence on my gravestones scattered around Chichester Harbour.
Pete54
Well-Known Member
You'll find quite a number of outboards which have drains on the float chambers specifically to allow them to be drained. My old 10 hp Honda had some specific advice about doing that before taking it out of use. Thankfully the guys that sold it to me had not followed that advice and so I got it for a song. But it took a lot of carb cleaner and compressed air to clean out the idle jets and make it run reliably.
Seajet is absolutely correct in that running a two out off fuel is not a good idea. With a Seagull it would make no difference, to a small air cooled engine it will start to melt the piston top and leave it prone to corrosion. To a modern two stroke, cylinder corrosion is a possibility as the short period of high temperature burns 'that lovely oil film' off and leaves the cylinder bare.
Seajet is absolutely correct in that running a two out off fuel is not a good idea. With a Seagull it would make no difference, to a small air cooled engine it will start to melt the piston top and leave it prone to corrosion. To a modern two stroke, cylinder corrosion is a possibility as the short period of high temperature burns 'that lovely oil film' off and leaves the cylinder bare.
macd
Well-Known Member
Evidence for those assertions? In my view, poppycock - unless, perhaps, you're daft enough to run the carb dry at full load and throttle.
Happy Dayz
Well-Known Member
Surely the answer is, pull off the fule line while funning at tick over, engine starts to race kill engine?
To start i prime heavily, to fully fill fuel bowl.
Store engines upright in a corner, secure with chain for anti-theft and safety concerns, protction gainst of nosey grandkits.
To start i prime heavily, to fully fill fuel bowl.
Store engines upright in a corner, secure with chain for anti-theft and safety concerns, protction gainst of nosey grandkits.
AngusMcDoon
Well-Known Member
When I used to have 2T outboards I used to run the carb dry. Never seemed to do any harm. Small engines die from corrosion, not wear.
VicS
Well-Known Member
The only 2T outboards that are likely to suffer any damage from running the cabbs dry are large multiple carb engines. The layout of the fuel system tends to mean that the upper carbs may run dry before the lower carbs. This means that the engine can continue to run, firing only on the lower cylinders, for a period after the upper cylinders have run out of fuel and lubrication.
steve66
Well-Known Member
Another piece of great knowledge from Vic. Btw I mean that and am not being sarcastic
Seajet
...
I have explained the process whereby I now think running 2-stroke engines dry is a poor idea; very experienced mechanic chums who have the same engines on their boats and also have worked on and owned racing motorbikes & cars for long careers agree with me.
Instead of silly names, people could always just say they disagree and why, but I haven't seen anything like that yet; Vic is laking about totally different engines and reasons / processes.
NormanS
Well-Known Member
I have always shut off the fuel to drain the carb, before stopping my 2 stroke outboards. I can't see how that can cause any harm at non-driving idle revs. The original question was about draining the carb on a 4 stroke, - well I don't do it with my car, so why would I do it with an outboard?
macd
Well-Known Member
Well, this particular former mechanic and racer of two strokes disagrees with you, and has already said why.
And you seem to misunderstand Vic's post: he wrote that the 'totally different' engines are the only ones on which it would not be wise to run dry. On our little put-puts, it's fine.
chewi
Well-Known Member
"I have always shut off the fuel to drain the carb, before stopping my 2 stroke outboards. I can't see how that can cause any harm at non-driving idle revs. The original question was about draining the carb on a 4 stroke, - well I don't do it with my car, so why would I do it with an outboard?"
1. The fuel mixtures have changed in recent years, and fuel goes off more quickly than it used to.
2. you use your car more frequently, so its less likely to have stale fuel.
My new Honda warranty says so much about using old fuel (> 30 days?) that I doubt the warranty is worth a candle.
I haven't worked out how to supply my 2.3 with fresh fuel. I can't use a gallon in a month,( my car is diesel).
Last edited:
Happy Dayz
Well-Known Member
Guys, can we remmember this is a forum? idea being to discuss our sum knowledge or the lack of it so others can learn or form their own democratic opinions, not have brexits type farcial 'debates'.
As a kid i was mad keen on anything that had gears belts or wheels. First job from school i started in a m/c and car garage called Rivetts of Leytonstone as a trainee mechanic.
I if likely being laid up for a while as boat engines often are, i run my engines 'dry' at tick over, especially during winter. Back in the day i did it for security ti make the bike or scooter harder to start.
Ti stop oil that had separated in the tank from filling the fuel pipe, i'd giving the bike a vigourous shake side ti side before turning on the fuel tape ti remix the fuel.
my opinion is with older two strokes, oil is directly mixed with the fuel in the tank, then both travel together eventually reaching the combustion chamber, the oil performs all its tasks before being burnt off, which is at the same time as the fuel.
no fuel = no spark = engine stops = so engine don't need any lubrication.
When restarting you prime the fuel, filling the float bowl. Depending on the condition if the engine it will fire up very quickly, and until that happens their is no fuel so no oil. no harm in turning over the engine with the safety switch off to avoid this possible damage, but din't flood it.
The above is fine for single carbs and i'd think fuel injected engines, multiple carbs where one carb is last to dry out so still feeding 1 or two cylinders, all carbs (having being properly balanced) would not run for more than a few seconds in this way.
i acknowledge the thinking that will damage 'dry' bores, but what about when your at full bore and the fuel runs out of fuel on a racing bike? engine can't be stopped dead due to the bike pushing the engine, so could it be damaged to some degree?
I consider the engine designer might be just be aware of this issue, so would (i hope) allow for that situation and calculate to be within the margines for tolerances, even on a screeming pop! pop! or grass bashing motor.
Why would we not do this with cars? Today most are 4 stroke oil is recycled ifrom the sump and not burned off.
if carbureted and layed up for a while, even if possible draining the fuel will be very inconvenient - and likely why we don't do it! ?
If you do this above tick over then fuel less, so oil less 'run on' will occur, as the fuel is first thinned then completely exhausted, but thats why you act ti turn off when the engine revs ?
The engine won't just stop 'dead' in either scenareo unless you bust a con rod ?.
Alan
As a kid i was mad keen on anything that had gears belts or wheels. First job from school i started in a m/c and car garage called Rivetts of Leytonstone as a trainee mechanic.
I if likely being laid up for a while as boat engines often are, i run my engines 'dry' at tick over, especially during winter. Back in the day i did it for security ti make the bike or scooter harder to start.
Ti stop oil that had separated in the tank from filling the fuel pipe, i'd giving the bike a vigourous shake side ti side before turning on the fuel tape ti remix the fuel.
my opinion is with older two strokes, oil is directly mixed with the fuel in the tank, then both travel together eventually reaching the combustion chamber, the oil performs all its tasks before being burnt off, which is at the same time as the fuel.
no fuel = no spark = engine stops = so engine don't need any lubrication.
When restarting you prime the fuel, filling the float bowl. Depending on the condition if the engine it will fire up very quickly, and until that happens their is no fuel so no oil. no harm in turning over the engine with the safety switch off to avoid this possible damage, but din't flood it.
The above is fine for single carbs and i'd think fuel injected engines, multiple carbs where one carb is last to dry out so still feeding 1 or two cylinders, all carbs (having being properly balanced) would not run for more than a few seconds in this way.
i acknowledge the thinking that will damage 'dry' bores, but what about when your at full bore and the fuel runs out of fuel on a racing bike? engine can't be stopped dead due to the bike pushing the engine, so could it be damaged to some degree?
I consider the engine designer might be just be aware of this issue, so would (i hope) allow for that situation and calculate to be within the margines for tolerances, even on a screeming pop! pop! or grass bashing motor.
Why would we not do this with cars? Today most are 4 stroke oil is recycled ifrom the sump and not burned off.
if carbureted and layed up for a while, even if possible draining the fuel will be very inconvenient - and likely why we don't do it! ?
If you do this above tick over then fuel less, so oil less 'run on' will occur, as the fuel is first thinned then completely exhausted, but thats why you act ti turn off when the engine revs ?
The engine won't just stop 'dead' in either scenareo unless you bust a con rod ?.
Alan
davidpbo
Well-Known Member
As O.P.
I think I will run it (4 Stroke, main engine on boat, permanently in commission during season) out of fuel if I think I am not going to use it for more than 4 weeks but not if it is less.
My other 2 stroke on the tender I will continue to run out of fuel for transportation at the end of each session.
I think I will run it (4 Stroke, main engine on boat, permanently in commission during season) out of fuel if I think I am not going to use it for more than 4 weeks but not if it is less.
My other 2 stroke on the tender I will continue to run out of fuel for transportation at the end of each session.
RichardS
N/A
The reasons why running a single carb 2T at idle until it stops will not do it any harm have been well explained in previous posts.
If there is an easy to access carb drain like on my DF2.5 (where I don't even need to remove the cover and which I have extended with a fixed length of fuel hose) I always run off the fuel back into my fuel can when leaving the boat.
If there is no carb drain I run the engine at tickover until it stops. However, this often leaves a little fuel (2T or 4T) in the float chamber as the engine cuts out when the mixture gets too weak so using the carb drain is always the best solution if it's an option.
Richard
TSB240
Well-Known Member
I have had a huge amount of experience of single cylinder two stroke motor bike, outboards and high revving ultra lean burn kart engines.
I understand the theory in the posting of an assertion that running the carb dry causes damage on the run down of an engine as it runs lean for a short period.
I do not agree with this assertion because:-
I have stripped many an "air cooled" racing kart engine that has been run at 17,000 RPM on an extreme lean burn setting with timing highly advanced.
They will run for up to a minute at these revs and settings before failure (Usually Big end seizure).
On investigation the piston, bores, cylinder head, rings are still covered with a coating of oil.
The big end runs dry first and the heat build up is rapid.
Anyone in kart racing knows the trick is to keep dumping fuel in on deceleration into a corner by choking the air box with one hand. This has the added advantage of stuffing the engine and exhaust full of fuel to cool the big end and give you a kick up the ass when you put your foot back down.
2T Kart and Bike engines use and rely on exhaust scavenging(tuned exhausts) to boost the combustion process.
Outboards do not.
This both makes them very inefficient but also reduces the effect of fuel starvation at any revs on the top end of the engine.
All of the fuel for combustion is supplied from the crankcase through the piston port,transfer ports and boost port conveying the lubricating oil to all parts including rings and cylinder.
The stop cycle takes about the same amount of time as the start cycle and probably is less wear inducing due to the viscosity of warm oil deposits rather than cold.
So having debunked the theory you may still be concerned!
There are simple solutions to this
Either run at tick over and just as soon or if the engine starts to run lean apply full choke which will stop it dead.
If it is a direct drive motor it will most likely stop dead without any running lean period as it is under load and there is no need to choke.
If it has a clutch drive simply leave it in gear !
The assertion included a comment of using 100:1 ratio petrol oil on water cooled outboards.
The majority of manufacturers recommend 50:1 minimum. I usually add an extra drop or two to err on the lubricated side!
I understand the theory in the posting of an assertion that running the carb dry causes damage on the run down of an engine as it runs lean for a short period.
I do not agree with this assertion because:-
I have stripped many an "air cooled" racing kart engine that has been run at 17,000 RPM on an extreme lean burn setting with timing highly advanced.
They will run for up to a minute at these revs and settings before failure (Usually Big end seizure).
On investigation the piston, bores, cylinder head, rings are still covered with a coating of oil.
The big end runs dry first and the heat build up is rapid.
Anyone in kart racing knows the trick is to keep dumping fuel in on deceleration into a corner by choking the air box with one hand. This has the added advantage of stuffing the engine and exhaust full of fuel to cool the big end and give you a kick up the ass when you put your foot back down.
2T Kart and Bike engines use and rely on exhaust scavenging(tuned exhausts) to boost the combustion process.
Outboards do not.
This both makes them very inefficient but also reduces the effect of fuel starvation at any revs on the top end of the engine.
All of the fuel for combustion is supplied from the crankcase through the piston port,transfer ports and boost port conveying the lubricating oil to all parts including rings and cylinder.
The stop cycle takes about the same amount of time as the start cycle and probably is less wear inducing due to the viscosity of warm oil deposits rather than cold.
So having debunked the theory you may still be concerned!
There are simple solutions to this
Either run at tick over and just as soon or if the engine starts to run lean apply full choke which will stop it dead.
If it is a direct drive motor it will most likely stop dead without any running lean period as it is under load and there is no need to choke.
If it has a clutch drive simply leave it in gear !
The assertion included a comment of using 100:1 ratio petrol oil on water cooled outboards.
The majority of manufacturers recommend 50:1 minimum. I usually add an extra drop or two to err on the lubricated side!
fisherman
Well-Known Member
Fascinating, thanks.
Happy Dayz
Well-Known Member
A very clear explanation, especially regarding 2T racing engines with my thanks as i've never been near one.
Being a biker i can't imagine how you'd stuff your hand over the air box while hanging on for dear life in a corner due to the extra acceleration gained - perhaps i'm just a coward ?.
Small outboards (returning to the o/p's subject) tend to be direct drive, mine is a 9.9 mariner twin, electric start, choke is electricially operated by depressing the ignition key while cranking - thus making using the choke to flood so stop the engine just a tad more of a challeng ?.
Joshing apart, it is a good 'bush fix' applied when cranking if you suspect a carburettor jet blockage, but i'd pull off the plug leads of and wear a protective glove if your not used to doing this, if only to prevent an unexpected ignition in the carb from removing your eyebrows ?.
I'd venture the difference in wear between starting up and 'starve' stopping might be more to do with the fuel/oil being better mixed before being starved, than starting from cold where prior separation may have occured.
Interesting views and discussion either way - so fancy us doing how rocket motors work next week - but don't think stuffing my hand over an air inlet would be such good advice ?
Alan
Being a biker i can't imagine how you'd stuff your hand over the air box while hanging on for dear life in a corner due to the extra acceleration gained - perhaps i'm just a coward ?.
Small outboards (returning to the o/p's subject) tend to be direct drive, mine is a 9.9 mariner twin, electric start, choke is electricially operated by depressing the ignition key while cranking - thus making using the choke to flood so stop the engine just a tad more of a challeng ?.
Joshing apart, it is a good 'bush fix' applied when cranking if you suspect a carburettor jet blockage, but i'd pull off the plug leads of and wear a protective glove if your not used to doing this, if only to prevent an unexpected ignition in the carb from removing your eyebrows ?.
I'd venture the difference in wear between starting up and 'starve' stopping might be more to do with the fuel/oil being better mixed before being starved, than starting from cold where prior separation may have occured.
Interesting views and discussion either way - so fancy us doing how rocket motors work next week - but don't think stuffing my hand over an air inlet would be such good advice ?
Alan