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Desperate...Won't go past 3000rpm (2000 sometimes)

L

Lior Samfiru

New member
I am sorry if I am posting in the wrong forum.

Hi. I am a first time boat owner. I have a 1994 Silverton 310 with Twin Mercruisers 5.7. When the season began, the starboard engine would not go beyond 2000 RPM, no matter what. It would idle fine and run fine at 2000 RPMs. My mechanic initially said one of the cylinders was not getting pressure. That was fixed. The boat ran great for 10 minutes and then the starboard engine slowed down to 2000 RPM again and won't go beyond. The mechanic just rebuilt the carbeurator. Also changed plugs, fuel filters and checked the fuel pump. Yesterday, boat ran great for 20 minutes, then went down to 3000 rpm and won't go beyond. It runs fine at 3000 and idles great. It starts great too.

Mechanic thinks it is bad gas. The problem is that both engines get gas from both fuel tanks at the same time. So if I had bad gas, I would have a problem with both engines and not just the one.

I know nothing about boat mechanics. I have already spent a ton of money and still have a boat that is not running. Any ideas?
Lior
 
Look at the dacal on the top of the flame arrestors ( "air cleaners") on your engines. It stipulates an RPM range. This is the RPM range that your engine should rev to at wide open throttle with a normal load if it has the correct size prop. This in NOT the RPMs for continuous operation. Engine life @ this max RPM range is measured in tens of hours. You said.. "ran great for 20 mins and then went down to 3000 RPMs" What RPMS were you runng @ for 20 mins? FWIW, for reasonable engine life you should not be running above 80% of the actual maximum RPMS you can geet. For most 5.7s this puts your maximum continuous RPMs ( and I would consider anything over a minute or two occasionally, as continuous) in the low to mid 3000 range.
 
sandkicker said:
Look at the dacal on the top of the flame arrestors ( "air cleaners") on your engines. It stipulates an RPM range. This is the RPM range that your engine should rev to at wide open throttle with a normal load if it has the correct size prop. This in NOT the RPMs for continuous operation. Engine life @ this max RPM range is measured in tens of hours. You said.. "ran great for 20 mins and then went down to 3000 RPMs" What RPMS were you runng @ for 20 mins? FWIW, for reasonable engine life you should not be running above 80% of the actual maximum RPMS you can geet. For most 5.7s this puts your maximum continuous RPMs ( and I would consider anything over a minute or two occasionally, as continuous) in the low to mid 3000 range.
Click to expand...

Thanks for the answer. We were running at around 3300 RPM. Then the Starboard engine went down to 3000 rpm and would not move, no matter how much throttle was given. The port side engine was great. Earlier in the day, it did the same thing, except it stopped at around 2500 RPM.
 
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