Motor surged yesterday
Submitted by Manfish on Sat, 2019-08-10 13:56
Yesterday while returning from the D9 I noticed my 4 yr old Mercury 90 4stroke surge a bit (occationally missing a beat, about three or four times )The engine was sitting at around 4000 rpm so reduced throttle to about 3000/ 3500 and the engine settled down. I did add some Penrite fuel stabilizer to the tank last week and was wondering if this had anything to do with it?
ranmar850
Posts: 2702
Date Joined: 12/08/12
Can be an air leak
Could be any number of things, but a tiny air leak can cause air to be sucked into the sytem when running harder--you won't see a fuel leak.
Faulkner Family
Posts: 17861
Date Joined: 11/03/08
maybe check the fuel line is
maybe check the fuel line is connected to the motor properly, had similar issue and thats what it was
RUSS and SANDY. A family that fishes together stays together
Bluedog
Posts: 251
Date Joined: 28/07/11
Had a similar thing with my
Had a similar thing with my yamaha, turned out to be a buggered diaphragm in one of the low pressure fuel pumps.
Rob H
Posts: 5745
Date Joined: 18/01/12
Almost certainly a fuel
Almost certainly a fuel supply issue.
At the time you could have brought it back up to 4000+ til it played up and then feel the fuel bulb.
If sucked down there is a restriction tank to bulb.
if not, pump the bulb and if surging stops it’s after the bulb.
Look for blocked filters, kinked hose, air leaks as above.
Following all those the fuel low pressure pump
Give a man a mask, and he'll show you his true face...
The older you get the more you realize that no one has a f++king clue what they're doing.
Everyone's just winging it.
Manfish
Posts: 39
Date Joined: 24/11/18
No bulb
The boat has underfloor fuel tanks, so there is no bulb. I will check the above suggestions,the motor is due for a service anyway and will mention it to the mechanic.I was just wondering if it could have been stale fuel as it was about 6 weeks in the tank and maybe I added the stabilizer to late.
Rob H
Posts: 5745
Date Joined: 18/01/12
I may be misunderstanding but
I may be misunderstanding but if you do not have a priming bulb you should fit one immediately.
With underfloor tanks they are even more important.
Otherwise the only way to pull fuel up is to crank
and crank
and crank.
Not only to be able to start quickly after changing filters, but for diagnosing fuel problems
Give a man a mask, and he'll show you his true face...
The older you get the more you realize that no one has a f++king clue what they're doing.
Everyone's just winging it.
Manfish
Posts: 39
Date Joined: 24/11/18
fuel bulb
I can't see one but the motor fires up first crank every time.
Scotte
Posts: 1142
Date Joined: 07/12/06
The bulb is only really for
The bulb is only really for when you change filters or drain the vst.
Even if you change filters and don't prime it back up it will normally run on the fuel in the vst while the low pressure pump draws fuel thru but like others have said you need a bulb .
A mate of mine had his low pressure fuel pump shit itself 30mile of mandurah and had to squeeze the bulb often to get any sort of speed out of it for the trip home so it pays to have one.
piston broke
Posts: 776
Date Joined: 05/11/08
Six
weeks should be fine.
avatinni
Posts: 141
Date Joined: 06/06/10
Funny hearing that my 90
Funny hearing that my 90 2017 mercury 4 stroke never had a fuel bulb neither with a 90 ltr under floor tank & started first time every time.
Rob H
Posts: 5745
Date Joined: 18/01/12
its One of those things
that you only need when things are going wrong (or a filter change). In which case you need it NOW.
If you change a fuel filter and the lines are completely empty it is hard to see how it could start and keep running instantly, especially if the tank is not full?
When the outboard gets a few hours up and the lift pump isn’t as efficient as it once was, it may not be able to and Murphy says that moment will be as the Rotto ferry is bearing down on you, the southerly is kicking in and/or the missus is seasick
The tank is inevitably below both the power head and the filter housing meaning it is not possible to fill the filter prior to starting without a bulb.
As above, even if not needed to prime it serves a purpose to diagnose fuel problems at a time when you really need it (floating around at sea) and avoid a tow.
Its probably the cheapest tool/part in your arsenal...
Give a man a mask, and he'll show you his true face...
The older you get the more you realize that no one has a f++king clue what they're doing.
Everyone's just winging it.
Sea goat
Posts: 939
Date Joined: 26/03/17
hmmm....good to know. i never
hmmm....good to know. i never realised this. i have a 90hp 2017 mercury 4 storke and underfloor tanks. first boat, so just assumed it didnt need a bulb.... will certainbly be looking into it now.
Manfish
Posts: 39
Date Joined: 24/11/18
No bulb
Don't stress. If that bulb was so important it would be there.
Rob H
Posts: 5745
Date Joined: 18/01/12
.
Just like a seat belt or a fire extinguisher-its not important, til ya need it...
Give a man a mask, and he'll show you his true face...
The older you get the more you realize that no one has a f++king clue what they're doing.
Everyone's just winging it.