Mercury 4 Stroke 6HP Running Badly

Y

yachtorion

Well-Known Member
Joined
4 Oct 2009
Messages
1,025
Visit site
Hello,

My 2008 Mercury 6HP 4 Stroke outboard engine is running unevenly - intermittently slowing down - when at full throttle... Unless a little bit of choke is left on.

Any suggestions please?

Thanks,

James
 
I had a similar problem with my Tohatsu 5HP (same motor).

I nailed it down to water in the fuel tank. As the pick-up is above the bottom of the tank quite a bit of water can get in there without causing problems, but then when it reaches a certain level it will get sucked into the pick-up. It can be in the fuel already or be condensation. Every time you fill up it adds to the water, but it stays at the bottom of the tank.
I tried all sorts like a new fuel filter etc. Another problem could be air getting sucked into the fuel pipe at one of the connections. There are about 6 push fit connections between the tank connector and the carb. New fuel pipe clips will probably solve that.
 
The need for choke suggests the engine is running weak. The fact that the problem is intermittent suggests it's not something like an air leak at the manifold, more likely a partly-starved or contaminated fuel supply. A little water sloshing around in the tank could fit this bill, as Lakesailor suggests. Because the engine continues to run it's unlikely to be huge gobs of water, just partial and intermittent clogging of the main jet.

I'd drain the whole fuel system and fill with fresh, then take off the float bowl and ensure it's clean. While you're at it unscrew the main jet (the biggest one, at the bottom, with slot for screwdriver) and blow it clean on an air-line. Don't poke anything hard into it.
 
Thanks for the replies all. I'm not the original owner of the engine so I don't think the 5 year warranty applies?

It did feel a bit like fuel starvation. Recently I've started disconnecting the fuel line and letting the engine run until the fuel is gone when I'm not going to be using it for a while. This is because if left with fuel in the carb it was very reluctant to run well until that fuel was gone.

I wonder if this change of practice has drawn some dirt in? But that said...

The fuel tank, line, primer bulb and all the fuel currently in the system is pretty new... only a month or two... so hopefully not wet... but I certainly couldn't rule it out.

Would it be worth trying spraying some carb cleaner into the intake before disassembling and cleaning the carb?
 
Pointless spraying carb cleaner around. If it needs cleaning, it needs stripping.
When the motor falters have you tried pumping the bulb in the fuel line?
Is the fuel connector on the fuel line a manufacturer's item or a pattern part? Try holding the connector tight up to the motor when you get the problem. The "O" rings can be rubbish on some cheap connectors.
Is the vent opening properly on the tank? It will usually breathe a sigh of relief when you unscrew it.
 
Lakesailor said:
Pointless spraying carb cleaner around. If it needs cleaning, it needs stripping.
When the motor falters have you tried pumping the bulb in the fuel line?
Is the fuel connector on the fuel line a manufacturer's item or a pattern part? Try holding the connector tight up to the motor when you get the problem. The "O" rings can be rubbish on some cheap connectors.
Is the vent opening properly on the tank? It will usually breathe a sigh of relief when you unscrew it.
Click to expand...

Vent works well... tank sighing no problem. Now that you mention it, the engine fuel connector is a pattern part and though I wouldn't call it cheap it has felt a lot less tight the last couple of times I've attached it.... I wonder if that could be it.

Oddly the engine seems to run perfectly if you back off the throttle a little.

I've ordered a genuine connector. When I get up to the boat at the weekend I'll try that if it's arrived, or if not just hold it on tight. If that doesn't do it try pumping the primer just to see.... then check the fuel filter and if necessary see what I can do with the carb, though I really hope I won't need to!

I managed to get a copy of the maintenance manual off ebay so at least I've got some instructions to follow!

Thanks.
 
Solved!

changed the engine connector for a genuine part, tightened up all the hose connections. now it's working normally again!

Thanks all.
 
Great. It's not always blocked jets.
I had that problem with a Honda outboard. £20 for the genuine connector, but the peace of mind is worth it.
 
Just back from spending a few days on the boat and I too had the same problems as the op described in the opening post with the same outboard a Tohatsu 6hp 4stroke.
It has happened a few times when first running the engine after non use of a week or 10 days but I have always managed to get it running sweet again in a short amount of time just by running it. However this last time it ran rough and continued to do so. I purchased a bottle of this:
Alt_Fuel%20System%20Treatment%20&%20Stabilizer.jpg


from the chandlery and after a few minutes it was running sweet, it's a little expensive £8.86 but it did the job and I have plenty left should I need to use it again. It seems to me that petrol is not what it used to be and if you fail to run of all the fuel before storing it away you are asking for trouble.

Read about the product here:http://www.seabreeze.com.au/News/Sailing/Protect-your-engine-against-modern-fuel_1916178.aspx
 
You must log in or register to reply here.

Share this page

Top