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Joe, Marine Mechanic
Category: Boat
Satisfied Customers: 7251
Experience:  ASE, electronics, Marine mechanical and electronics, pwc, wiring, all around repair tech,
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I have an Indmar 5.7 V8 engine with a carbourator. The

Customer Question

I have an Indmar 5.7 V8 engine with a carbourator.
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: The engine is brand new from 2015. The engine revs full when in neutral, but under load it stops at around 3.000 rev/min. We have changed fueld filter twice and empptied the tank. The fuel hose is brand new. The carb is a Holley with vacuum secondaries. My mechanic has spend several hours adjusting the carb (after removing the pomps from factory to get to the adjustment screws) and troubleshotting. His next advice is to buy a new carbourator, Edelbrock instead of Holley. It seems wrong as the engine is brand new in 2015.
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: the engine was running at 34 kn for about 1.5 hour in the beginning of the season. After that it suddenly stop at 3.000 rev and only does 14 kn. When we manually manipulate the secondaries (vacum) during load, we get a few more knots in speed. Take the power to full throttle, the spped is lower. Taking it back a little bit, it goes faster again. Perhaps the fuel/air mix is to rick.
Submitted: 1 year ago.
Category: Boat
Customer: replied 1 year ago.
I have had several problems with engine since new which the supplier never fixed. My new mechanic removed the top block and noticed that some valves had rust (i.e. water in the engine), a pressure test revealed the engine was ok, so it was put back together with a new head gasket. Compression tests shows all fine. Last year the boatd did about 45 knots on full speed, now it is only doing 14 knot.
Expert:  Joe replied 1 year ago.


Thank you for allowing me to assist you, my name is Joe and I will be happy to assist you with your concern today.

Water does not just get into the heads, this would mean that the engine either sat long term stored and condensation got in the heads (can be normal) or you're getting water ingestion which needs to be diagnosed. On top of this the carb should have the bowls removed to check for debris and clean and rebuild as needed, it's very likely it could have got dirt in it. Timing should be checked, fuel under load, check for misfires, going through standard diagnosis such as ignition and fuel related considering the problem only being under load.

Thank you!
- Joe

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