How fast can I run the motors on the hose? I was hoping to check a few things at about 3000rpm without having to go to the local river ramp.
It would only be for a 10-20 sec or so, not sure if the hose would have enough flow??

Merc had a service bulliten out several years ago recommending about 1,200 RPM and not too much water pressure when running on a set of muffs. This was to prevent reversion. The problem I see with a lot of RPM in neutral is if there is enough lubrication in the upper part of the drive. Remember, the input shaft of the drive is always spinning with the motor running. With the drive out of gear, is there enough oil splash to lubricate the top end of the drive? I've always wondered this when I hear guiys revving their motors in neutral on the lake.

I don't like going above 1500.

If you remove the seapump intake hose from the transom and shove the garden hose down it, you have rev as high as you like. That's how I set all in timing on my engines which is to about 3500rpm.

I've rapped mine several times no problems. Hose pressure on full. Hose isn't a cheapy that will suck flat if pulling too much. Not sure I buy the too much city watar pressure. Your seawater pump won't let any more past it than it can pull and any access will just blow past the muffs. Your drive is always getting oil regardless if in water or out, in gear or out. It just won't have a load on it in N.

I wanted to see if the rpm gauge was off, went up to 1500rpm and yes its about 300 off. So my motors are in sync. the gauge is off

Hey Dan, the tachs will have a selector on the back of them. It should be labeled 4-6-8. Obviously they need to be on 8 for a 8 cylinder. Be sure it is, and move it back and forth between all positions several times, before replacing the tach. It could just be a dirty connection inside the tach.

I do the same thing. Although I've broke in several cams with the muffs and full advance timing and never had a problem either. I just like the garden hose shoved in the intake hose so I have no worries about muffs falling off or anything especially when alone and having a lot going on at one time.