Motor surged yesterday

  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's picture

Posts: 2358

Date Joined: 12/08/12

Can be an air leak

Sat, 2019-08-10 14:46

 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's picture

Posts: 15329

Date Joined: 11/03/08

 maybe check the fuel line is

Sat, 2019-08-10 16:26

 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

Posts: 251

Date Joined: 28/07/11

 Had a similar thing with my

Sat, 2019-08-10 19:20

 Had a similar thing with my yamaha, turned out to be a buggered diaphragm in one of the low pressure fuel pumps.

Rob H's picture

Posts: 5189

Date Joined: 18/01/12

Almost certainly a fuel

Sat, 2019-08-10 19:26

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's picture

Posts: 39

Date Joined: 24/11/18

No bulb

Sun, 2019-08-11 09:02

 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's picture

Posts: 5189

Date Joined: 18/01/12

I may be misunderstanding but

Sun, 2019-08-11 16:00

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's picture

Posts: 39

Date Joined: 24/11/18

fuel bulb

Mon, 2019-08-12 17:13

 I can't see one but the motor fires up first crank every time.

 

Scotte's picture

Posts: 994

Date Joined: 07/12/06

 The bulb is only really for

Mon, 2019-08-12 19:32

 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's picture

Posts: 720

Date Joined: 05/11/08

Six

Sun, 2019-08-11 12:56

weeks should be fine.

avatinni's picture

Posts: 154

Date Joined: 06/06/10

 Funny hearing that my 90

Sun, 2019-08-11 20:17

 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's picture

Posts: 5189

Date Joined: 18/01/12

its One of those things

Mon, 2019-08-12 04:44

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.

 

Posts: 332

Date Joined: 26/03/17

hmmm....good to know. i never

Thu, 2019-08-22 16:44

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's picture

Posts: 39

Date Joined: 24/11/18

No bulb

Sat, 2019-08-24 11:59

   Don't stress. If that bulb was so important it would be there.                       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Rob H's picture

Posts: 5189

Date Joined: 18/01/12

.

Sat, 2019-08-24 14:43

 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.