Same RPMs. A lot less speed

[Robodoc]

There we were, perfect day, beer, women,glassy seas, heading out the jetty at 1000 RPMs when suddenly the engine (Mercruiser 5.7 outdrive) died. Restarted easily, but a lot less speed at same RPM. Lifted outdrive, no line around props and props (counter rotating) turned easily in neutural. Vented gas tank to be sure it wasn't fuel starved. Couldn't plane even at 3400 RPM's even though the engine sounded OK. I usually plane at 3,000 RPM's. Couldn't return at idle speed because the engine would die, and had to come in a little hot in the fairway (no accidents fortunately). Any ideas shipmates?

Robodoc

 

[Dakota47]

Re: Same RPMs. A lot less speed

Wow thats one high reving motor,

 

[Bondo]

Re: Same RPMs. A lot less speed

There we were, perfect day, beer, women,glassy seas, heading out the jetty at 10,000 RPMs when suddenly the engine (Mercruiser 5.7 outdrive) died. Restarted easily, but a lot less speed at same RPM. Lifted outdrive, no line around props and props (counter rotating) turned easily in neutural. Vented gas tank to be sure it wasn't fuel starved. Couldn't plane even at 34000 RPM's even though the engine sounded OK. I usually plane at 30,000 RPM's. Couldn't return at idle speed because the engine would die, and had to come in a little hot in the fairway (no accidents fortunately). Any ideas shipmates?

Robodoc

Ayuh,... Let's try again,... The operating speed range of your motors is 600 rpms to 4800 rpms....

What's your's Really turnin',..??

 

[insanity]

Re: Same RPMs. A lot less speed

A bike like a FZ1 turns max rpm around 10,000 prm, when you ge into the 30000+ range we ar looking at nitro RC car motors LOL.

Im gonna say we could safely drop a 0 off each rpm range given and that is what he ment to post.

 

[Robodoc]

Re: Same RPMs. A lot less speed

Yeah, drop a zero off the RPM's. I forgot it is x 10 not x 100 on the gauge. Any ideas?

Robodoc

 

[Don S]

Re: Same RPMs. A lot less speed

Does your Mercruiser have a year or serial number? Have you checked the water separating fuel filter to see if there is water in it, if there is, how much and I sure hope you put a new element on it.

 

[Robodoc]

Re: Same RPMs. A lot less speed

I think it's a 2005. I just replaced the fuel/water separator at the end of a trip a month ago and checked it again couple of weeks ago.....no water in the filter. Fuel pump replaced this year. I can get the engine to rev to max, 4000 RPM's and get about 20 mph, way under what it is capable of. I think the fuel delivery is OK. If the transmission is connected to the prop OK, than the prop should give a certain push at certain RPM's, so regardless of the engine, if I could get the RPM's up to 3000 I should still get the speed I normally get at 3,000, which I'm not. To have it happen so quickly makes me think some link up in the prop/transmission axis is whacked. Am I wrong in this thinking?

Robodoc

 

[Robodoc]

Re: Same RPMs. A lot less speed

Maybe the grey whale with the bloody back that surfaced under us was related? Naw, just kidding. I'm thinking along those lines, too. There was a lot of debri in the water since it was after a storm but we were just putzing at 1,000 RPM;s and no bang or bump. I think I'm just going to have to scratch a line from the prop hub to the lower end cowling and see if it moves. Any other suggestions?

Robodoc

 

[Robodoc]

Re: Same RPMs. A lot less speed

Bilge is bone dry. I'm gonna pull the boat, but before I do I'm gonna mark the prob hub. On the way to the ramp I'll goose it a few times and check for slippage. I'll post the post mortem. Thanx.

Robodoc