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Boat turning 400 rpmbs less at WOT

F

floorplay

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I have a 1998 5.0L Mercruiser

I have a 1998 5.0L Mercruiser 2 barrel. The boat started by running a little surge at 2000 - 3200 rpm. I've cleaned gas screen at carb. Sprayed carb cleaner while boat was running. I noticed there may be a bit to much oil but not crazy high. The boat was running 4750 rpm wot and now it is running 4400 rpm. I boat idle and putts around the lake great. I'm certain this is a carb issue. The engine is also got a slight bog. Like the carb is loading up.
 
Get some actual carb cleaner l

Get some actual carb cleaner liquid and pour in gas and run for a while. If that doesn't help rebuild the carb. seems like the carb might have a little gunk in it.
 
I'd change the fuel filter

I'd change the fuel filter and make sure the flame arrester screen on the carb is super clean
 
stp doesn't change the fil

stp doesn't change the filter..you have to physically change the fuel filter every season. google image search flame arrester. I recommend a Seloc or Mercruiser manual.
 
I put the STP carb cleaner in

I put the STP carb cleaner in based on a earlier post. There are to filters the screen that goes into the carb looked clean. So I should change the inline fuel water seperator filter. I'll grab one today and try it.
 
I had 2 hours running on the b

I had 2 hours running on the boat today and it didn't clear up. I installed a new fuel water separator and that wasn't the problem. The boat had its first signs of a problem at wot today. Two very quick SNAP sounding noises from the engine. I'm thinking a backfire. Still starts and idles like a dream !

Thanks
Tony
 
"Tony,I have a 86 305,it idled

"Tony,I have a 86 305,it idled great but after a half hour or more would backfire when more fuel was given.I changed wires,cap,plugs,coil,still backfiring after a half hour.Then I changed the ignition module,so far so good.I'm not sure if your year has this,but just another idea"
 
"My problem happens after 2 mi

"My problem happens after 2 mins or 2 hours of running. I'm thinking timing ? carb rebuilt? fuel pump? Also, The boat had plugs, wires and rotor cap done end of last season."
 
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