Merc 90 fourstroke stutter and stall

Hightower · 30 July 2005, 18:26

Yesterday when having just started my voyage, the outboard was stuttering almost like it was missing when I throttled up (only when accelarating), at low revs. Seemed to clear at 2000 rpm and lasted for about 20 mins. When doing some low speed (tickover) manuvering in the harbour every so often the outboard would stall. And finally everytime I tried to plant the trottle from tickover to full throttle the engine coughed and splutterd and died.

What's up Doc?

bogib · 30 July 2005, 18:36

Sad to hear this Andy, I do not have solution to the problem but if I can help get in touch

Bogi

Hightower · 30 July 2005, 18:43

Thanks Bogi! Engines always started fine and performs very well. Had a frozen throttle linkage a month ago and copias amounts of maintenance spray with PFTE on the carb butterfly linkage points and turning the flats off the cam roller have sorted that. I have noticed the stuttering on the last couple of trips, but the stalling.....I've never had that one before. Just trying to understand the problem.

Biggles · 30 July 2005, 19:01

Andy,

Had a similar problem with my newish engine last week. It was dirty carbs. So they said. It was under warranty so I didn't play with it.

Best of luck.

Mark Halliday · 30 July 2005, 19:09

Andy

I have had this on cars before and it ususally turns out to be lack of fuel or air.
Duff electrics tend to either go or no-go.

Hightower · 30 July 2005, 19:16

Lack of fuel....Goes like the clappers still

Lack of air....Checked that

On the fuel side of things, I was thinking in the way of an accelerator pump or something. Or perhaps a mixture problem, but none of that has changed.

Turbodiesel · 30 July 2005, 20:40

Is it an EFI model or a Carb?

Mark Halliday · 30 July 2005, 20:44

I still go for fuel starvation.

Something loose in the tank, collapsing fuel line, dodgey fuel filter or manifold air leak. Summut like that.

Should have stuck to a 2 stroke.

Mark Halliday · 30 July 2005, 20:46

Turbo

I think it is a carb one. He has told me, but ............

Nick Hearne · 30 July 2005, 20:59

HT, my new tow goes like stink, then it starts to splutter, give the fuel bulb a pump & all sorted! guess air is getting in, have not had a look to sort it out yet! Dose it sound similar?
Nick

Hightower · 30 July 2005, 21:52

Quote:

Originally Posted by Turbodiesel

Is it an EFI model or a Carb?

Carb one.

Fuel starvation...Wouldn't that get worse the wider the throttle and bigger the demand for the fuel?

The only other things I can think of that hasn't been mentioned is a vacum device on the throttle linkage and a timing problem Adance/retard

Biggles · 31 July 2005, 18:26

Andy,

If its a carb engine. Then shouldn't the carbs have two sets of jets. Idle and fast run. Maybe the idle side is playing up. That might explain why you can rev it hard and its okay but on tickover it plays up.

Best of luck.

Turbodiesel · 01 August 2005, 07:39

If the problem goes away when you squeeze the primer bulb its almost definatly going to be the fuel pump diaphragms. When you squeeze the primer all your doing is doing the job the fuel pump is doing. Usually you can hear the pump is noisy, it make a ticking noise if it has no fuel in it. If you think you have air in the system try putting a piece of clear hose in the fuel line so you can see what is going through your fuel hose. You should have no air in the fuel line.

Nick Hearne · 01 August 2005, 07:47

Turbo D
So you are saying I have a problem with my fuel pump as well?

Nick

Turbodiesel · 01 August 2005, 07:52

Possibly, really you need to have the fuel pressure checked. But as i was saying usually if the problem goes away when you squeeze the primer its probably going to be a fuel pump problem. Have a listen to the pump though, the usually noisy if there is not alot of fuel in it.

wavelength · 01 August 2005, 09:32

very occasionally we have a similar problem on our merc 4 stroke carb 90. engine will lose some power at full throttle but pick up as soon as the bulb is pumped. Fuel pump diaphragms are ok and quiet. Might be an idea to check that your tank is venting ok? Ours is so very infrequent as to not be a problem to us, it has been going on for a couple of years but by the time it goes for a service I have forgotten to mention it to our mechanic.

Nick Hearne · 01 August 2005, 09:39

Quote:

Originally Posted by wavelength

very occasionally we have a similar problem on our merc 4 stroke carb 90. engine will lose some power at full throttle but pick up as soon as the bulb is pumped. Fuel pump diaphragms are ok and quiet. Might be an idea to check that your tank is venting ok? Ours is so very infrequent as to not be a problem to us, it has been going on for a couple of years but by the time it goes for a service I have forgotten to mention it to our mechanic.

The tank vents no problem, too well, so that when filling if you are not careful it will pour out of the vent B4 it clicks off the pump

wavelength · 01 August 2005, 11:50

See if this forum can help (always assuming I can post the link OK)
http://www.iboats.com/cgi-bin/ubb/ul...ubb=forum;f=29

Hightower · 01 August 2005, 12:27

Am I right in saying there is only one accelerator pump/damper on the Merc 90 and that it seems to work on the throttle linkage and not direct to the carbs?

How much would one of these cost?

PS: I can't see that it'll be a fuel starvation/air inline prob, surely this would make the problem worse the faster the revs!

tue · 01 August 2005, 12:38

Have you checked the engine fuel filter for water? Had a Mariner 75hp fourstroke with the same symptoms. The idle jet had become blocked so would run rough below 2000rpm, then the main jet kicked in and the engine would run fine above 2000rpm.