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SummerSunsetter

Only 3000 RPM at WOT..??

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SummerSunsetter

Last year at WOT I could only achieve 3000 RPM's. Carb was old, so I put a new one on this year thinking it would fix the low RPM problem. It didn't. Engine runs good, sounds good. I'm using Premium fuel. I should be getting to around 4500 RPM.   Where do I start?

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Michigan boarder

Start with the basics:

  • When was the last ignition parts tune up? (cap, rotor, plugs, wires)
  • Check the timing

If you are starving for fuel, typically it will want to shut off or sputter really badly at WOT.  If you are starving for air, engine RPM's will be restricted but it will still run smoothly.

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Eagle River Mike

Did you put a bigger pitch prop on it?

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JeffK

I would absolutely start with a tune up and the above suggestions.  They can sound fine without being under a load.  As soon as you tax the motor, your lack of power will show.  I'd do a general tune-up before I start looking at timing.  You may solve it without having to mess with the distributor and a timing light.

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tvano

the temperature sending unit can cause the ecm to limit rpms until the engine is warmed up on a fuel injected engine.

a bad sending unit can do the same.

i have no idea if the same applies to the older (carburated) rigs but thought i'd throw it out there hoping to get feedback from others who own a better memory.

i know a lot; just can't remember it.

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Woodski

@SummerSunsetter:  Was your issue a step change or a gradual issue?  If a step change, what was done just prior to that, good chance that is the culprit.  I would do more root cause analysis rather than simply start throwing parts at it hoping you hit the target.  Some troubleshooting tools -  1.  check ignition timing which will include idle (make sure it is in spec, should be around 8 deg BTC but find your specific specs), higher RPM (make sure advance curve is correct, total advance should be 32-34 deg BTDC) and check for ignition scatter and intensity at the timing light.  2. check fuel pressure at idle and watch the pressure as you ramp up to the problem speed.  Low fuel pressure can be caused by plugged filters, anti siphon valve, weak fuel pump or debris in carb / bad calibration (you noted a change) / incorrect install (do you get WOT).  Those two tests should point you in the correct direction and if those are fine, check plug wires for installation accuracy, followed by a compression and leak down test if all has checked out at that point.  None of that will require a credit card, just your time and if you don't have those tools, many local auto parts stores will loan them to you.  I am making the assumption that your '89 vintage boat is carbureted and has early electronic ignition, if points need to verify dwell setting.

Edited by Woodski

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SummerSunsetter

Plugs, Wires, Cap, Rotors, Carb adjustment got me to 4700 RPM. Thanks

 

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