1994 135 Mariner surging

[gbapgar]

I have changed all fuel filters, rebuilt the fuel pump, done the Seafoam decarb procedure from the FAQ and changed spark plugs. At any given RPM, 3000 for example, RPM will surge up and down by 2-400 every few seconds. When I pull the plugs, they all look the same, coated with blackened oil, and black around the electrodes. This is a 2L V6 135HP 1994 carburated Mariner. What should I try next? TIA<br /><br />George

 

[AndyL]

Re: 1994 135 Mariner surging

May be an airleak on the carb side causing mixture changes inadvertently. Check all hoses and connections for any slackness. Does the fuel bulb stay firm throughout. Did this problem occur after you pulled the fuel pump or has it existed for some time and you are attempting to fix it?<br />Andy

 

[gbapgar]

Re: 1994 135 Mariner surging

I will check all of the hoses, although I have tried to make sure everything is tight as I go along. The problem predates the fuel pump job, that was an attempt to fix it. The bulb and fuel lines are new, also attempts to fix. We will watch the bulb to make sure it isn't deflating.

 

[LubeDude]

Re: 1994 135 Mariner surging

Can you ease into the throtle, or do you have to slam it to get on plane? Is it caughing and sneezing at an Idle??? How far apart are the fluctuations accuring?

 

[gbapgar]

Re: 1994 135 Mariner surging

Yes, I can ease into the throttle, but I'm never sure how much of a response I will get with a small increase in throttle. The boat is a heavy, round chine, semi-displacement lobster style, so it doesn't plane well even with motor in top shape (there is enough power, but hull is unstable at 21+ Kts). I normally run between 3000 and 4000, 14 to 17 Kts. Motor runs most smoothly at idle, although you can still hear the changes if you listen. Fluctuations are 1 second to maybe 30 seconds apart randomly.

 

[LubeDude]

Re: 1994 135 Mariner surging

Reason I ask is because my 150 is somewhat erratic like yours, I have no Idea why though, I have done everything short of a new engine trying to solve it. Im going to change the whole intake system as I bought one resonable off ebay, Im thinking it may be weak reeds.

 

[gbapgar]

Re: 1994 135 Mariner surging

I think that I have found, but not fixed, the problem. Yesterday, we pulled the plug wires, one by one. The top two cylinders in the V6, which share the top carburator, don't change the RPM. So I think its a carb problem. The boat still runs pretty well, so I will wait till I pull it in a month to do anything more.