PULSATING MOTOR IDLING CAUSE?

[greyhawk]

Had the opportunity to troll L.O. this week and noticed my idling revs on a Mercury Optimax 150 would surge then slow only to re-surge again. There was no noticeable anomaly while running at 10-15 mph. Any suggestions as to a cause would be appreciated.

Considering a spark plug and/or poor quality gas (boat has been sitting for awhile leading to water infusion) situation.

Thanks in advance.

[SpoonPullers.com]

[Tom McCutcheon]

Your fuel quality and water separator/fuel filter would be the first places I would look.
Hope it's not the same problem as our 135 Optimax...Port Fuel Rail was Kaput. Not repairable with parts anymore, so needed to replace the whole rail at $2500.00 plus tax and labour. Just under $3900.00 all in.

Good luck

[FishFarmer]

How about running some Sea Foam in you gas, could maybe help.

[greyhawk]

Thanks for the suggestions. With nicer weather coming this week want to change the fuel filter add sea foam and injector cleaner then check out results out of Fifty Point. Still think I may need to change the plugs. Have done it before but that dam port side lower plug is a bitch.

[Tom McCutcheon]

   YEP. Articulating knuckle on the ratchet helps, but it's still a bitch. I have been told it's easier when the lower cowling is split, but that's not easy either.

If the Sea Foam and fuel filter doesn't fix it, another item you might check would be the alternator/compressor belt under the fly wheel. If it's worn with teeth missing, it can cause depleted PSI from the compressor for the fuel injectors. 

[drjoe]

Check and clean up all electrical contacts , make sure you have a good ground to start ! Probably not spark plugs but may be a good place to start .

[greyhawk]

Thanks again guys. Really appreciate the input.

[greyhawk]

Changing the fuel filter, adding sea foam and mercury fuel injector cleaner did the job. Motor ran without pulsation/misses and quieter than an optimax usually does.

[Tom McCutcheon]

Glad it worked out for you at a reasonable price point. These items are considered normal fall/winterizing maintenance items on my list and very easy to do it yourself. Similar to draining the lower end gear oil and checking for water prior to refilling and storing for the winter.

Not done yet though.