115 mariner surging at high rpm

[captbjack]

hey guys my 97 115 mariner is still surging at high rpm. i have cleaned all carbs, new plugs,changed fuel filter, and all new gas. anyone have any other sugestions? thanks in advance.

 

[roger3645]

Re: 115 mariner surging at high rpm

Have some one squeez the primer bulb when it is acting up if this helps then tends to point to fuel restriction or starvation. Could be fuel pump, if this is a carb model try turning idle screws 1/8 turn out.

 

[captbjack]

Re: 115 mariner surging at high rpm

it is carburated but only top 2 carbs have whats looks like idle mixture screws is this normal if so is this what you say to turn?

 

[captbjack]

Re: 115 mariner surging at high rpm

anyone know anything about these carbs?

 

[big_b16]

Re: 115 mariner surging at high rpm

That is correct, this engine is a 2+2 setup where the top 2 carbs are only used at idle, thus they are the only ones with idle screws on the port side at the top of the carb, there is a hole in the throttle cam to access #2. If carbs are good, look into the stuff mentioned before. Good luck. BTW, I've got a 96 mariner 115.

 

[Lone Duck]

Re: 115 mariner surging at high rpm

Check fuel pump and tank vent. Also anti siphon valve .

 

[captbjack]

Re: 115 mariner surging at high rpm

where would i find the anti siphon valve

 

[hkeiner]

Re: 115 mariner surging at high rpm

Mercury issued a Service Advisory that provides some troubleshooting guidance on fuel starvation (see link below). In short, it describes how to determine if you have (or don't have) a fuel starvation situation caused by a restriction in the fuel line, an air leak in the fuel line, or a failing fuel pump. All you need is a vacuum gauge, some clear hose, and a T connector. Monitoring for any change in vacuum level in the fuel line during an engine surge would probably be the most telling test.

I suggest that it is usually better to do the presribed tests (to definitively confirm or eliminate these possible fuel starvation causes) before spending the time and money to randomly replace/fix parts on a hunch or educated guess, only to find that it did not help any. This has been by my experience anyways, others may have additional and better advice.

Good luck

http://www.marinepartsman.com/Mercury-Marine-service-bulletins/Mercury-Mariner/2001/EN_17.PDF

 

[captbjack]

Re: 115 mariner surging at high rpm

alriht guys just got my vacuum gauge and tested fuel pump as the last post suggested and everything is up to spec. i know its easter but if anyone has any more suggestions i am all ears because i'm at my wits end.thanks

 

[Faztbullet]

Re: 115 mariner surging at high rpm

Is it a slow or rapid surge?? Slow is as loses couple hundred rpm then eases right back or rapid as ok then 3 or 4 hundred drop then right back.

 

[captbjack]

Re: 115 mariner surging at high rpm

it loses about 3-400 rpms then comes back very consistant rythum.

 

[Faztbullet]

Re: 115 mariner surging at high rpm

Look where your fuel line attaches to your fuel tank. If the hose barb is aluminum it is a anti siphon barb , either gut it or replace it. Here's is a fuel flow on that engine. Check the accelerater pump as it may be bad and weeping fuel. ( usually low end problem) I would tend to lean toward it being a carb problem. Either a bad gasket seal ( fuel bowl,mounting) or float levels being off ..

 

[1crazyfordguy]

Re: 115 mariner surging at high rpm

When it's surging, are the carb linkages moving up and down (are the carb butterflies opening and closing)? I don't know much about your motor or if it's governed, but I have known a few cases like this where the governor, if in need of adjustment, will oscillate the throttle up and down.

 

[Faztbullet]

Re: 115 mariner surging at high rpm

Fuel flow diagram............

 

[captbjack]

Re: 115 mariner surging at high rpm

not sure about it but i think it does not have governer. could be wrong.

 

[Faztbullet]

Re: 115 mariner surging at high rpm

no governer!!