Hello guys,

I have a question for you, tell me what do you think or if it has happened to you :

I have two 525sc clones on my boat, and when I am running wot, i have 1 at 5280 rpm, and the other one at 5080...
I have sent the prop to be labbed, and the same thing happens..
I have changed all the spark plugs, and nothing new....
I have checked the carburator/accelerator cable, and it is ok...

What can it be...? compressor....? timing...?

I want to know if someone had the same problem before?

Thank you.

Try a different tach

Swap props and run the boat in reverse (which will be forward)....or swap sender wires on the tachs to see if the problem is the tach.

x2 check the tachs first. Does it pull to one side?

Did you look down the carb bores and see if they were actually WIDE OPEN ? Throttles plates vertical ? One may be not fully opened.

Hello, the tach are digital floscan, I haven't swap them, I will do it, to see.
And yes the carbs look exactly the same when wide open....

In fact the problem is begining after 2000rpm : the port engine begins to loose power and throttles must be seperated to keep engine rpm's equal to the starboard engine, and, when wot there is still these 200 rpm........

Is the boost equal? My first thought was a slipping belt. If you have an IR gun see if the upper pulley is getting hot on the one dowm on rpm.

could be a stretched throttle cable.

A friend of mine had a similar problem with a pair of 1997 carbed HP500 Mercs. Turned out to be fuel water separator filters one clogged before the other, changed filters problem went away.

Do NOT do this if you have TRS or speedmaster drives, or you will burn up the transmissions.

Just swap the wires at the back of the tachs and verify the tachs are correct.

Also, when you are out there running the boat, synch the engines "by ear" at say 3500-3800rpm. You will be able to hear them in synch. They kinda "hum". Take note of the tach readings. Also, take note of the boost gauges when they sound in synch.

Checking the timing would be a good idea too. Not necessarily for only this problem, but timing is crucial on blower motors.