Is this a simple fuel problem for a 2 stroke 75 merc?

[scorpionNQ]

Hi Guys,

Just bought a near new custom plate side console Barra punt with 2005 low hour 3 cyl merc on the back. I have used it a few times now and notice that it is starting to surge a bit when cruising at about 4000 rpm and at idle it sometimes cuts out. The priming fuel bulb is under the coaming where I sit so I have found that when it starts to drop revs I pump it a few times and the revs go back up.

1/ Do you think that I may have an air leak?

2/ Is the fuel primer ok to be 3m away from the engine or should I move it to in front of the motor?

PS...fyi.....the fuel tank is kept full and I purchased this off a good mate you had it serviced with a clean bill of health a few moths ago.

Any help will be appreciated.

Cheers Leeroy:(

[gtonks77]

Start by changing your fuel filters. Its logical from what you say that it's starving for fuel when it needs it so start by eliminating the easy things you are capable of yourself. Check fuel lines for cracks where it may be sucking air or any new kinks and next change the filters. If it's still doing then next step is the carbies

[scottar]

First thing to do any time you have suspicions about fuel is try to get your hands on a separate tote tank and fuel line and try it. That should isolate whether the issue is the boat or the motor. Just be cautious about keeping a motor running by pumping the fuel bulb too. Not sure how the Merc system works but with an OMC if the fuel pump is misbehaving doing this can effectively run the engine without oil and cause bigger problems.

[Moonlighter]

If pumping the primer bulb overcomes the issue, there are a few possibilities that spring to mind, these are the simplest and quickest things to check first before going deeper.

1. The primer bulb may be badly positioned. It should ideally be upright so the end closest to the motor is highest. That way the internal valve works best and stops fuel flowing backwards to the tank. If it is a genuine Merc primer bulb they are usually very good quality, but if the installer used a cheapo one, it could have failed and a new, good quality OEM manufacturer one would be the best replacement. Merc, Yamaha both are good.

2. The fuel filter could be partially blocked. You DO have a decent inline fuel filer (Racor style water separating filter) between the tank and the engine, dont you? (If not, that is your next job, to fit one ASAP). If so, suggest a new element be fitted and chek the old one for water and other contaminants.

3. There may be a restriction in the fuel tank breather line. So find the breather outlet and see if it is clear. Mud wasps seem to like making nests in there! A tank that doesnt breathe wont let fuel flow to the engine. If it looks clear see if you can blow air thru it (open fuel cap first) and that air flows freely.

4. a fuel line could be lettig air in, pinched or breaking down internally. Check the lines between the tank and the motor, make sure they are tightly fastened, no signs of damage or kinks, and flex/bend the pipes around a bit to test if internally they feel OK - should not be hard to bend or "crunchy" inside, if so, replace all lines if any of them are suspect.

Hope that helps.

[scorpionNQ]

Thanks Lads.....all good answers. I was going to replace the fuel line/primer but thought I might ask first.

Moonlighter.....
1/ Primer is upright but not sure if OEM. Will check and replace.
2/ I do have a racor filter ......It looks a little rusty so am wondering if it was actually replaced when serviced last? Will replace now.
3/ I have recently played around with the breather hose....and after what you said I will go and re check it.
4/ I will inspect the whole fuel line now and if it even looks slightly damaged I will replace it

Thanks for the tips mate.
Cheers Leeroy

[No Excuses]

Once you've done all of the above and it's still happening you might find its the low volume fuel pump. The diaphragm could be perished inside.

[terryc]

I had the same problem on a early 90's 60Hp 3 cyl mariner, ended up being junk in the fuel line & carbies, just disconnected the fuel line at carbies, pumped fuel through with bulb to ensure free flowing, then just removed carbies, dropped the fuel bowls & emptied out junk, after that running great.

[ericcs]

i had this exact problem last month on my 90 merc. ran fine while someone constantly squeezed the primer bulb. go buy a a fuel pump kit($26) genuine. common problem, mine was a busted gasket

[Spaniard_King]

I frequently find the inside of the merc fuel lines to delaminate and clog the fuel system, by the book they are to be changed every 2 years!!!

if this has happened you will need to strip and clean the fuel system as well as putting a diaphragm kit through the low pressure pump

[Dignity]

As Spaniard King mentions, I recently had my 30 hp merc serviced and my mechanic replaced the hoses as it had been 3 years, we cut it open and the lining was starting to show signs of delaminating, probably wasn't long before it gave me trouble. There are many back yard motor mechanics and it is small things like this that often get missed. Hopefully you get a quick and relatively low cost solution to your issue.

PS. Is the fuel bulb hard or soft when you have to,prime it.