Mariner 150, fouled plugs, missing

[BScherling]

I've got a 1991 150 hp Mariner Magnum II. I bought it used last summer. The original owner was a DNR official so it probably has many hours. Earlier this year, when I pulled the boat out of storage, the engine started and ran/idled great (out of the water with muffs).<br />Since then it has been difficult to start. Once it does start the engine idles a little rough. It also runs a little rough under low throttle. At full throttle it seams to run smoothly. When the engine is warm it restarts easily but still idles like it's "missing". All six spark plugs are wet/damp with oil. I replaced the plugs and nothing seemed to change. <br />I have a few gallons of "old" fuel (with Sta-bil) left in the tank. Is there a way to drain the tank, or does it need to be siphoned?<br />I plan to replace the fuel filter and plug wires. Any other suggestions?

 

[WillyBWright]

Re: Mariner 150, fouled plugs, missing

Welcome to iboats.<br /><br />There are tiny hoses routed all over your motor. There are tiny fittings on the intake side where those attach. Those tiny fittings are check valves and I think a few are probably clogged. They can be removed and cleaned with carb cleaner and compressed air most of the time.<br /><br />When a 2-stroke is running slow, raw gas/oil builds-up in certain places and those hoses allow the raw fuel to be sucked out and burned. If something keeps them from working, that raw fuel just puddles and makes the motor run pure awful at idle and low RPMs and foul plugs. Motors with a lot of hours are pretty much guaranteed to have things clogged-up here and there.<br /><br />The check valves are challenging to get to, but you don't usually have to take too much apart to get to them. About all you should need for tools are a 5/16 wrench and a needlenose pliers.<br /><br />As far as the gas, stick your nose in the filler neck and if it smells like gas, use it. If it stinks, get rid of it.

 

[rodbolt]

Re: Mariner 150, fouled plugs, missing

hello<br /> a lot of mercs used press in check valves. after you test the recirc system test the low speed charge coil input voltage. I had one doing just as you describe and found a low voltage condition on the coil primaries that lead to plug fouling and rough running. all the subsystems must work as designed. you need to systematicly test and eliminate each one as a source of problems.<br /> good luck and keep posting

 

[KCLOST]

Re: Mariner 150, fouled plugs, missing

I'm kind of on the same page as rodbolt....<br /><br />I'd check the spark on each cylinder.... Use a spark gap tester, and make sure each lead has a good strong spark... Up to 7/16"....

 

[achris]

Re: Mariner 150, fouled plugs, missing

As well as what's been mentioned before, it would be worth trying some Seaform or Power Tune. You may have some carbon build-up on the piston crowns or in the ring grooves. Also (LD's favorite subject) what brand of oil are you using?<br /><br />$0.02<br /><br />Chris............

 

[BScherling]

Re: Mariner 150, fouled plugs, missing

Thank you for all the information. I see I have a little work to do.<br />Willy, where in Wisconsin are located?<br />achris, I use Quicksilver.

 

[achris]

Re: Mariner 150, fouled plugs, missing

achris, I use Quicksilver.

Good choice.