Problems with Motor at Full Throttle

[pcmb]

I have just discovered and joined this site – great place to share experiences and expertise.

I own a 2006 Macgregor 26M and am very happy with it. It has an Evinrude 50 hp 2 stroke motor.
I live in Melbourne Australia

I wanted to see if anyone has had the following experience with this motor or other motors.

When the motor is at full throttle I notice that periodically it seems to hesitate (even a slight difference in engine noise) for a second. It is as if it has experienced an increase in resistance. The revs also drop fractionally when this happens. Some times this hesitation seems to happen quite often. It does not seem to happen at lower RPMs.

It has been back to shop twice and they cannot find anything wrong with the motor. Maybe it could be a cavitation
problem. Has anyone experience this and found ways to solve it?

Look forward to hearing from you

[Catigale]

Cavitation would actually make the rpms shoot up for a second, until the engine's limiter would kick in and limit the rpms back to the WOT (wide open throttle) rating

My guess is

- Bad spark plug or spark plug wire
- Bad ignition coil

in that order.

[Craig LaForce]

Maybe some dirt flopping around in the carb bowls?

[James V]

What RPM's?

Conditions? Waves? Winds?

Fuel older than 3 months?

The engins computer may be cutting you back in these conditions. To help this you can use a midgrade fuel or carb cleaner/dryer additive.

[Sleepy]

A out of the blue problem could be the prop's hub insert is slipping on you.
You can mark or spray paint on all of the parts,sleeve,rubber insert and the prop and run until it happens again. If that's it, take it to a prop shop and have a new insert pressed in.

[Frank C]

That momentary "increase in resistance" could be simply a lack of fuel. Our small engine fuel pumps are capable of sucking air right through the hose-clamped connections, resulting in fuel starvation. This is fairly common as the fuel delivery system, O-rings, fittings, hoses, primer bulbs, etc. begin to leak air. If this is truly the source of your problem, the engine hesitation will gradually worsen. Early discussions by searching on [starvation].

[pcmb]

Thanks for your help.

The problem occurs at 5500 rpm. Seems ok at 4000 rpm.

Another interesting problem is the last time I took the boat out I was able to get 5500 rpm but after a while was only able to get about 5100 rpm - don't know if this is related.
Sea conditions had not changed.

[Hamin' X]

Check your fuel supply. Could be an improper, or obstructed vent. Check fuel line for kinks. Run with temporary tank & line.

[argonaut]

If it's an Evinrude E-Tec he doesn't have a carb.
That's a 2 stroke EFI motor.
If it's an E-tec it has a lovely computer "brain" that should have motor "events" stored in it's little brain, that a qualified mechanic can plug his PC into and read. The motor has sensors all over the place... It'll tell ya all kinds of details about what the motor has experienced.

[James V]

Cooler Temps can affect RPM's

If it is not underwarenty I suggest a good fuel injector cleaner and fresh gas in both tanks.

Any nicks in prop?

[Boblee]

Ours has had little "misses" like starving for fuel but all attempts to tune these out have failed, we are now at the stage of replacing the injectors which the dealer says has been the only solution for a few others.
Ours doesn't see much WOT but the problems seem to be around 2000-3000 under sustained revs.
We did find the thermostat was locked open and that then allowed the motor to run at a warmer temp but really you are in the hands of the experts with the laptop program.
Except for the cost of getting our boat to the dealer there has been no cost but quite a few freebies such as spark plugs and oil changes provided under warranty, definitely can't complain yet.
Even the "misses" are not a problem but tend to be a worry in case there is something there that is not right.
James V Notice we have a nick in our prop from the last outing, is this a problem?

[26S Captain]

Go to marineengine com. They do not require registration to post questions and have many people who specialize in different brands.