RPM decrease

[aquarama]

Good afternoon everybody
I'm Florian from caribbean, i have a boston whaler montauk with a DF115 Suzuki 2006 with 400 hours.
The motor run good, i just bought the outboard and i a mechanic did the service, sparkplug, oil, oil filter, fuel filter, pre filter.
i use the boat, everything is good. But at 4000 RPM after few minutes like 10 or 15 minutes, the RPM go down by itself, no alarm on the gauge, and i need to stay neutral few secondes to go again normally and after that the problem come more rapidly, like 1 or 2 minutes.
Second information, if i go at 5000 rpm or 6000, the problem come faster.
Does somebody know what s happen ?

[Moonlighter]

This is sounding like a fuel restriction.

And as it happened immediately after the service, I would suspect an air leak in the fuel system, so check that all the connections to those filters that were changed are airtight and that all fuel hoses were reconnected and are tight and are not kinked anywhere.

Also check the fuel tank breather hose in case some mud wasp has made a nest in the end and blocked it up!

- A fuel restriction that is happening BEFORE the primer bulb will see the bulb sucked flat when the engine stalls....

- when there is an air leak or restriction after the bulb, the bulb will probably be soft but not suck flat. Pumping the bulb hard may even force fuel out of a loose fuel line hose on the engine eg where it connects to a filter so might help figure out where the air leak is. But sometimes air can get in thru places where fuel doesnt come out.

Anyway thats where I would start looking.

[aquarama]

Hello Moonlighter,
thank yiou for your reply.
I check all the tank, vent, clamp, and change with new until the Low pressure pump. but still have the problem. I think it can come from the Vapor separator tank. Check the strainer i guess, what do you think ? How to remove it ? i hear that it s possible to remove it without removing the manifold ? Do you have the service manual or where i can get it ?

[Moonlighter]

Have a read of this thread and see what they found

https://www.suzukioutboardforum.com/...er-and-surging

[aquarama]

Hello
it s what i am planning but normally i should remove the manifold to have an accès to vst but i read somebody did it without removing the manifold..

[Solarman]

Hey Grant, is this motor old enough for the exhaust plug problem?
just a thought.

[Moonlighter]

Hey Grant, is this motor old enough for the exhaust plug problem?
just a thought.

It is possible, that issue was fixed 2009. Although the symptoms dont sound like it.

Aquarama - what Solarman is referring to is a corrosion issue in the engine holder which allows exhaust gases to escape and accumulate under the engine cowl, which chokes the engine due to lack of oxygen. Easy to check - but you do need to take the cowl off as well as the plastic lower engine covers, then look just above the fresh water flushing attachment on the port side of the engine. You will see what looks like a welsh plug (casting plug) about 20mm round there. Check thatbthere are so signs of corrosion having eaten thru that plug or around the edges of it.

[AndrewF]

It is possible, that issue was fixed 2009. Although the symptoms dont sound like it.

Aquarama - what Solarman is referring to is a corrosion issue in the engine holder which allows exhaust gases to escape and accumulate under the engine cowl, which chokes the engine due to lack of oxygen. Easy to check - but you do need to take the cowl off as well as the plastic lower engine covers, then look just above the fresh water flushing attachment on the port side of the engine. You will see what looks like a welsh plug (casting plug) about 20mm round there. Check thatbthere are so signs of corrosion having eaten thru that plug or around the edges of it.

Does the engine holder problem exist in all Suzuki four strokes prior to 2008? I'm looking at a boat powered by a 2007 Suzuki 70 4 stroke. Is there a replacement part or other fix which prevents this problem?

[Moonlighter]

Does the engine holder problem exist in all Suzuki four strokes prior to 2008? I'm looking at a boat powered by a 2007 Suzuki 70 4 stroke. Is there a replacement part or other fix which prevents this problem?

No, it was mainly the DF90-140 series that all shared the same basic specifications and engine components, same cc displacement.

Havent heard of such issues on a 70. They were a completely different engine.p to the 90-140.