motor surge

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jddens
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Joined: Tue Jul 24, 2007 5:02 pm
Location: Northern CA

motor surge

Post by jddens »

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
1972 Trojan Sea Raider F30 - FI 350's "Time Warp"
1998 Kawasaki ZXi 1100
1972 Chevy Fleetside Shortbed hotrod.......450hp
10.5 Newport Inflatable w/15hp Rude
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TADTOOMUCH
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Joined: Thu Jul 12, 2007 9:58 am
Location: S.W. Michigan

lots of possibilities

Post by TADTOOMUCH »

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.
Boat Name: A TAD TOO MUCH
Model: 1978 F-32 Sedan Cruiser
Engines: Twin Chry 360's 666 hrs original engines

2013 Mercury 300 Ocean Runner 9.9hp Merc 4 stroke
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David Kane
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Post by David Kane »

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.
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jddens
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Joined: Tue Jul 24, 2007 5:02 pm
Location: Northern CA

Post by jddens »

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
1972 Trojan Sea Raider F30 - FI 350's "Time Warp"
1998 Kawasaki ZXi 1100
1972 Chevy Fleetside Shortbed hotrod.......450hp
10.5 Newport Inflatable w/15hp Rude
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jddens
Moderate User
Posts: 676
Joined: Tue Jul 24, 2007 5:02 pm
Location: Northern CA

Post by jddens »

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
1972 Trojan Sea Raider F30 - FI 350's "Time Warp"
1998 Kawasaki ZXi 1100
1972 Chevy Fleetside Shortbed hotrod.......450hp
10.5 Newport Inflatable w/15hp Rude
Top
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TADTOOMUCH
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Posts: 526
Joined: Thu Jul 12, 2007 9:58 am
Location: S.W. Michigan

startron

Post by TADTOOMUCH »

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?
Boat Name: A TAD TOO MUCH
Model: 1978 F-32 Sedan Cruiser
Engines: Twin Chry 360's 666 hrs original engines

2013 Mercury 300 Ocean Runner 9.9hp Merc 4 stroke
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jddens
Moderate User
Posts: 676
Joined: Tue Jul 24, 2007 5:02 pm
Location: Northern CA

Post by jddens »

TAD... ..motors are throttlebody FI....................
1972 Trojan Sea Raider F30 - FI 350's "Time Warp"
1998 Kawasaki ZXi 1100
1972 Chevy Fleetside Shortbed hotrod.......450hp
10.5 Newport Inflatable w/15hp Rude
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guglielmo6160
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Joined: Mon Nov 10, 2008 10:07 pm
Location: cape coral florida

Post by guglielmo6160 »

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