she's in, she's slow

put the boat in the drink for the first time ever (since she's been mine) friday and ran fine until it started cutting off at planing speed against the chop. would start right back up, and i couldn't figure out what was causing it. after looking up the problem on the net, i determined it was either old gas (at least a year and a half) or the ignition coil. then i remembered how sensitive (not to mention beat up) the key cylinder was, and how it would shut off with the slightest provocation. spent a few bucks and a few minutes and she hasn't cut out since, and that's been about 5 times out. she runs smooth and quiet (esp. for a 25 year old motor), but lacks power. i'm running at about 22 mph at "cruising rpm", 4200 from what i understand. this seems slow to me, but is it just normal for this old an i/o? should i prop up, or not risk stressing an old engine? currently running a 14 1/2" 15 pitch. any suggestions? anybody else have a merc 470 on theirs to compare?

oh yeah, got the garmin 178c gps/df, sweet little unit, easy to learn.

[chumbucket]

You probably should push the top end at least once to see if you're in the right range at least. Not much pitch to that prop, so you're not going to get a lot of speed from it anyways. Make sure your motor will reach the top speed per mfg recommendations and see if it needs to be re-prop'd.
Nice to finally have it in the water though.

[macojoe]

My I/O was proped the same way!! It had a top speed of about 30 and went about 22 to 25 cruz speed. Was a dog!!
Sounds like it is rightn to me.

Glad to see you in the water!!
Good Luck!!

I'm running a remanu'd 350 (Marine Power brand) and can push about 38-45mph (dependant upon load and conditions) top end and hit in the 4k-4200 rpm. I usually cruise at 3200rpm in the 25mph range.

[Brian_M]

My mercruiser 165 (250 ci GM straight six) cruises at 24 kts at 2500 erpm, prop is 15x17, I belive the engine is over propped 'cuz top end WOT is about 3800erpm