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sirjn
06-20-2008, 06:35 PM
hello all
i have a 2005 maristar with 5.7l mcx FI inmar motors and the boat is new with less than 40hrs. this is my second summer with it and it is acting up. it feels slower and less potent this summer. last summer i would be able to hit 50mph routinely and if i recall correctly, 5100+rpms.
this summer i am wheezing at 40+mph on smooth water no wind and can not get over 5k in the rpms. what are some speeds and rpm details out there on this model.
many thanks

dsoby
06-20-2008, 06:48 PM
If you are turning the same RPMs and have not changed props, you should be going the same speed. 50 is unusually fast for an inboard. You may have been getting bad speed info last year. Check your speedos with a GPS.

bigmac
06-20-2008, 06:52 PM
The fact that RPMs are down too suggests a problem. I'd start with the running gear (prop integrity, shaft alignment). If that's not it, it could be the engine - something keeping it from spooling up - fuel related would be my first guess, but check your oil level - make sure it's not overfull. Check fuel pressure, maybe. Throttle position. If I couldn't find it easily, I'd take it to the dealer - that engine can get complicated to diagnose.

Assuming ballast is empty, no water in bilge, trailer's not still attached...etc

trickskier
06-20-2008, 06:54 PM
When's the last time you changed your fuel filter?
Assuming ballast is empty, no water in bilge, trailer's not still attached...etc
:uglyhamme:uglyhamme:uglyhamme

sirjn
06-20-2008, 10:32 PM
thanks for the follow up
what sort of speed and rpm numbers are out there..
i am pretty sure that we have likely a fuel problem as the engine has not thrown codes ..has fresh oil..etc
i just remember seeing 5500rpms on the tach and speed in the low 50s and with gps confirming and now i am getting the word from the dealer that redline is at 5000. so basically i am 10miles off on speed and yet to bounce off the rev limiter.
just currious as to what sort of stats are out there
thanks

JimN
06-20-2008, 11:18 PM
Have you cleaned the flame arrestor?

bigmac
06-20-2008, 11:53 PM
thanks for the follow up
what sort of speed and rpm numbers are out there..
i am pretty sure that we have likely a fuel problem as the engine has not thrown codes ..has fresh oil..etc
i just remember seeing 5500rpms on the tach and speed in the low 50s and with gps confirming and now i am getting the word from the dealer that redline is at 5000. so basically i am 10miles off on speed and yet to bounce off the rev limiter.
just currious as to what sort of stats are out there
thanks

"Redline" or Max allowable RPT at WOT on the MCX is 5200. If you were turning 5500, you are underpropped. Don't do that anymore. There is a rev limiter, but I don't think it has anything specifically to do with redline. Look into getting a little more pitch or a little more cup. Get in touch with Eric Johnson at OJ about that one once you get the boat up and running right.

JimNn makes a good point. An engine starved for air and going way rich could do what you have described. Your manual has instructions on how to clean it, or you can find that info at the K&N web site http://www.knfilters.com/clningacc.htm .

edit: I note that my boat this year is down about 3 mph and about 175 RPM compared to last year. It just occurred to me that I've never cleaned the flame arrestor...http://mccollister.info/gifs/Doh.gif