Service for rough running 4 stroke

[Fafnir]

It's a 40 hp Yamaha 4 stroke. Runs alright when I start it and at low speeds, but when I go to put the throttle down it coughs and splutters, starts to die and then surges again. Slow down slightly and it runs a little better but still rough, slow down a lot and it goes along fine.

I cleaned out the fuel tank a little while ago and found quite a bit of oil in it. Figure I will need to get it serviced again (started doing this a few months after a service). How much should I budget for a service? If it needs a carby kit how much will that set me back? Just looking for some advice from those more experienced than me.

[Noelm]

first off... found oil in the fuel tank??? is it a carby model (not EFI), have you done the very simple things, like check the plugs?

[Fafnir]

Yeah I know. I assume the oil came from the guy I brought it off. Maybe it had been used with a 2 stroke at some stage. It's a carby model. I have checked the plugs, they seemed fine. Mate checked them as well and we both thought they were ok. Might just need to bite the bullet and take it to someone else for another service.

[Fed]

Any oil in the fuel tank should have mixed with the fuel, are you sure it was oil?

[Fafnir]

No not 100% sure. Actually you make a good point. Didn't even think about that. It's not like you can see the oil in 2 stroke fuel when it's mixed. It was just a heap of dark fluid bubbles that at the time I assumed was oil. Any ideas on what else it could be?

[Gon Fishun]

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[Fafnir]

It looked like that except in bubbles floating around in the fuel.

So maybe it's just old/crap fuel that's the problem. Looks like a fuel/water separating filter might be the go.

[Noelm]

try running off another remote tank and hose, with FRESH fuel, and see how it goes.

[Dan5]

It looked like that except in bubbles floating around in the fuel.

So maybe it's just old/crap fuel that's the problem. Looks like a fuel/water separating filter might be the go.


Always run a filter of some sort mate.......even one of those little Ryco in line filters will help.........

Your engine should have a little fuel filter under the cowling on the right hand side at the back of the engine they are only about 35mmlong and 25mm diameter ......change that also they are a genuine part and only cost roughly $10-15 dollars.

Definatly invest in a water separating filter though.......One of the newer Nano Waterscreen filters are only around $50 and come with all the fittings and don't take up much room ......I recently fitted one to my new rig.

Dan

[Moonlighter]

It looked like that except in bubbles floating around in the fuel.

So maybe it's just old/crap fuel that's the problem. Looks like a fuel/water separating filter might be the go.

Bubbles floating around in fuel = water.

Yes, definitely clean out the filter unde pr the cowl, it will have water in it too.

Then, fit a good water separating filter in the fuel line, a RACOR style is good.

There is one of that style now made by Sam Allen Wholesale (will have SAW on it) that has a composite material head unit, so mounts on alloy boats without any corrosion issues like the ones with metal head units have. They have a clear bowl underneath so you can see any water that is caught. About $70 I think. Well worth it. Replacement filters are about $25, change every couple of years in a small motor like yours. I've seen these for sale on flea-bay.

p.s
link here to them:

http://www.ebay.com.au/itm/BRAND-NEW-MERCURY-WATER-SEPARATING-FUEL-FILTER-CLEAR-BOWL-DRAIN-FOR-MARINE-/331075537588?pt=AU_Boat_Parts_Accessories&hash=item4d15a3cab4

[Hole Shot]

blockage in the accelerator pump circuit,running lean on acceleration