Would old petrol cause this?

S

steve yates

Well-Known Member
Joined
16 Oct 2014
Messages
4,106
Location
Benfleet, Essex/Keswick, Cumbria
Visit site
Outboard cuts out at low revs or idle, mariner 5 4stroke.
Had left it with a car mechanic who said it was fine, but still has tge same issue. It occured to he he would have fed it fresh petrol, whereas mine has been in it’s separate fuel tank for over 12 months.
I know petrol is supposed to go off after time, but would it specifically cause this issue?
Thx.
 
If the petrol tank has been properly sealed, with the vent closed, then I would expect year-old petrol to work fine.
I have had old petrol which won't start an engine, but only after several years or in vented tanks like mowers.
As johnalsion says, it's easy to try new fuel.

More likely, I would suspect a drop of water in the carb. A lot of small carbs have very small jets, a tiny amount of water will block them.
Very often, just draining the float bowl via the drain screw will help.
Removing the bowl and squirting with carb cleaner is the next step up.
stripping the carb, cleaning and re-assembling is a 'proper job'.
 
Used to have problems with my old Briggs & Stratton lawn mower till I used their “Fuel Fit” petrol stabiliser, especially over winter storage when carb would get gummed up, and starting was a pain all year. Plenty of other brands available.
Claimed to prevent build up of gums & varnishes in stored petrol for up to 3 years, keep carb clean & prevent corrosion.
Works well for me.
 
steve yates said:
Outboard cuts out at low revs or idle, mariner 5 4stroke.
Had left it with a car mechanic who said it was fine, but still has tge same issue. It occured to he he would have fed it fresh petrol, whereas mine has been in it’s separate fuel tank for over 12 months.
I know petrol is supposed to go off after time, but would it specifically cause this issue?
Thx.
Click to expand...

Not being clever but does the car mechanic know how an outboard is supposed to run. Maybe he doesn't realise its supposed to tickover and if he kept it revving it would probably sound ok to him.
I would check the pilot jet and make sure its not gummed up over the winter with fuel residue.
 
I had problems with rough running and cutting out - obvious symptoms of fuel starvation - that caused me to dismantle and clean the carb and filters several times to no avail. It turned out to be due to corrosion on the connection between the coil earth wire and the engine engine.
 
Some years ago I had a Mariner 4hp 4 stroke that was a pig to start if it had not been used for a while. It was an occasional use on a sailing boat.
An engineer advised me that the problem was most likely due to fuel evaporating in the float chamber leaving a small residue of water that the unleaded fuel had absorbed. When next trying to start the water droplets blocked the jet and made starting very difficult.
His advice back then was twofold.
1. Use leaded petrol (no longer available)
2. Always stop the engine by shutting off the fuel and letting it run dry.
Perhaps the second bit of advice is still relevant to the OP’s problem?
 
Leighb said:
2. Always stop the engine by shutting off the fuel and letting it run dry.
Perhaps the second bit of advice is still relevant to the OP’s problem?
Click to expand...

Relevant to most outboard users, even if not to this particular case. Even more so now with all the additives in modern petrol. The only reason I can see for not doing it is for 2 stroke multi-carburettor engines, as mentioned above.
 
Stemar said:
Relevant to most outboard users, even if not to this particular case. Even more so now with all the additives in modern petrol. The only reason I can see for not doing it is for 2 stroke multi-carburettor engines, as mentioned above.
Click to expand...

Maybe also 2 strokes with direct oil injection systems for almost the opposite reason ???
 
Older lawnmower carbs and modern outboard carbs are a totally different kettle of fish. Outboard carbs are built for American EPA pollution laws. They basically run much leaner. These carbs rely more on the "Lighter" gases in petrol. These are the gasses you see evaporating or hear when you open a fuel can. The less lighter gasses you have in your fuel the harder to start. It doesnt happen on modern fuel injected engines as the fuel is injected at high pressures. Older less eco friendly carbs have richer mixtures resulting in easier starting.
With an outboard stale fuel causes more serious issues. Some modern four strokes do not have steel valve seats and detonation causes by stale fuel ignition doesnt causes valve issues
 
My Honda 2.3 had been sitting in the garage for 18 months when my pal says "does that run?" I pulled the rope a few times then remembered to turn the fuel on. It started immediately and idled as well. Unfortunately, it was a bit close to one of my mooring buoys and sliced a hole with the prop.
 
Leighb said:
Some years ago I had a Mariner 4hp 4 stroke that was a pig to start if it had not been used for a while. It was an occasional use on a sailing boat.
An engineer advised me that the problem was most likely due to fuel evaporating in the float chamber leaving a small residue of water that the unleaded fuel had absorbed. When next trying to start the water droplets blocked the jet and made starting very difficult.
His advice back then was twofold.
1. Use leaded petrol (no longer available)
2. Always stop the engine by shutting off the fuel and letting it run dry.
Perhaps the second bit of advice is still relevant to the OP’s problem?
Click to expand...

Just to be clear guys, starting is NOT a problem, first pull and off it went merrily. The ONLY issue, is that if I throttle back from half power, the engine dies about halfway.
Obviously, it makes it a bit difficult to engage gears then, I have to hold the thing down to put it in reverse as it wants to jump up, and more to the pint, I will be manouvering at speed in the marina etc, which is really not ideal.


By the way, regarding shutting off the fuel and not stopping the engine, the ob is fed from a separate fuel tank with no on/off tap, so that's just not possible, unless I'm missing something?
 
I've always used the Honda fuel stabiliser on my Honda 2.3. Seems to work fine, no issues yet(4 yrs old). My ancient Honda lawnmower is no problem at all, but as said it's a much older engine but never had an issue with old fuel.
 
You must log in or register to reply here.

Share this page

Top