Trojan Boat Forum

Coming in yesterday I noticed my port engine was slightly surging.....up and down about 100-150 RPM while crusing at about 1500 RPM.....didn't have time to check it at other RPM....Motors are throttlebody injected merc 350;s, 330HP each. Thought I'd start by changing fuel filters, water separator and maybe spraying some carb cleaner in carb while running.......has anybode experienced anything like this????? Any suggesins?.....Thanks.............John

Lots of possibilities but fuel filters are the cheapest easiest and most likely cause. Put some startron fuel additive in your tanks and change the filters. If that isn't it, then check all the plugs and wires, then check the distributor and spray with a moisture dispersant. At that low a speed I wouldn't suspect a fuel pump yet. Might be sucking air so tighten all your fuel fittings.

Aren't boats fun.

Once you've done all that, if you're still surging, check your points, dwell, then timing. If they're all OK & the problem persists, then compression check each cylinder.

Thanks TAD and David.....i currently have Stabil in the fuel tanks and have electronic ignition so no points etc....can i add the startron with the stabil? The weird thing with this is it's not a miss but just a smooth up and down with the RPM's. I've built hot rod motors in the past and have never experienced anything like this............I'll follow your advice and let you know what i find........thanks again.......John

Thanks TAD and David.....i currently have Stabil in the fuel tanks and have electronic ignition so no points etc....can i add the startron with the stabil? The weird thing with this is it's not a miss but just a smooth up and down with the RPM's. I've built hot rod motors in the past and have never experienced anything like this............I'll follow your advice and let you know what i find........thanks again.......John

Yea you can add as much startron as you want. It is basically naptha and some enzymes so it won't hurt. Sure sounds like water in fuel, spark intermittently, or sucking air in fuel line. Have you checked all vacuum lines to carb and such. cheap to replace if they are old and gooey or split and cracked. Sometimes that messes with the idle and/or advance of throttle. Did you say you were fuel injected or carbed?

TAD... ..motors are throttlebody FI....................

surging is usually a result of a lean to rich , rich to lean etc,
I would check for a vac leak