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post #11 of 16 Old 08-09-2010
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I have the same motor. The raw water goes through the transmission before it goes through the engine on mine. It''s not uncommon for the water passage around the transmission to clog up and restrict coolant, which would can cause over heating. I wouldn't expect overheating to lead to lower rpm unless it's overheating so bad that the pistons are starting to seize. If the motor has low rpm when the engine is still cool, that would rule that out.

BTW, we've had other folks who have experienced low rpms because of fouling either on the bottom or the prop.

Is your bottom clean?
Is this a new development?

Ray
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1983 Fraser 41
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post #12 of 16 Old 08-09-2010
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I dove on the prop to check it out and rotated it from forward to reverse and the pitch seemed correct.today the boat went about 4.5 knot5s at 1600 rpm. The motor has also been overheating. I have checked the pump, removed the thermostat, pulled out the exhaust hose and checked it for restrictions, checked the raw water inlet and strainer. Replaced fuel and filters, had the injector pump rebuilt, replaced an injector. Thanks to all for your replies. jeff
4.5 knots at 1600 rpm isn't too bad. A bit overpitched, but you should be able to make 6-7 knots at full RPM (if you could get there). Looks like you are down on power. The overheating may be part of it.
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post #13 of 16 Old 08-09-2010 Thread Starter
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engine problem

There is a mechanical fuel pump that supplies fuel to the injector pump. I replace3d that with a used one and am beginning to suspect that one is bad too.
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post #14 of 16 Old 08-09-2010
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have you changed the fuel filters? if not , restrictions in the fuel line can cause low power. also check to see that your throttle linkage opens the fuel injection pump lever all the way.

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post #15 of 16 Old 08-10-2010
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why not just replace the mechanical pump with a electric one,very cheap at any auto parts,[low pressure 7-15 psi]
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post #16 of 16 Old 08-10-2010
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Quote:
Originally Posted by ampro View Post
There is a mechanical fuel pump that supplies fuel to the injector pump. I replace3d that with a used one and am beginning to suspect that one is bad too.
My guess would be that the lift pump is okay. I think that's a diaphragm pump. One of the common failures of those types of pumps is that the diaphragm gets a hole in it. If that were the case, it probably wouldn't pull fuel out of the fuel tanks if they are located below the level of the pump.

There is a bleeder valve on top of the injector pump. You could crack that valve and use the little finger lever on the mechanical pump and pump it manually to see if it will bleed the injector pump. If it does, I would move on to something else in the troubleshooting chain. But that's just me.

Ray
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1983 Fraser 41
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