150 Merc won't go over 4500 RPM?

C

Conn

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Apr 29, 2006
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i think i've finally got my idle/midrange problems figured out with uneven float levels in the carbs, but ever since I've had the boat, it won't go over 43-4500 RPMS trimmed out at about 52 MPH. <br /><br />17.5" fish and ski with XR2 Merc 150. <br /><br />it gets up on plane fine. RPM in the manual is saying around 5800? what should i look for? my uncle (previous operator) said the boat would run about 62-63 MPH at WOT. <br /><br />#s on the prop are QUICKSILVER 48 11074 A40 23P, which all i can understand is 23 pitch? <br /><br />any suggestions? <br /><br />Thanks. <br /><br />Conn
 
LubeDude

LubeDude

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6,945
Re: 150 Merc won't go over 4500 RPM?

Have someone pump the bulb while under way and see if the RPMs improve. Fuel pump time if it does. Whats your elevation compared to where your Uncle lives?
 
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dajohnson53

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Re: 150 Merc won't go over 4500 RPM?

First thing I'd check because it's easy and I don't know much else to do - check all of the plugs and/or change them. Could be mis-firing a cylinder due to fouled plug, lack of spark, etc. A friend had a similar problem (low WOT RPM, otherwise ran pretty good). One plug was completely fouled. when he changed it, he got his normal WOT.
 
C

Conn

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Apr 29, 2006
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27
Re: 150 Merc won't go over 4500 RPM?

yeah, same prop as my uncle and elevation is the same. <br /><br />it's got a new fuel pump and new plugs. (haven't tried WOT since the new fuel pump though). <br /><br />I'll know more tomorrow afternoon.
 
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dajohnson53

Lieutenant Commander
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Apr 28, 2004
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Re: 150 Merc won't go over 4500 RPM?

Even with the new plugs - you might still see if you think it's firing all cylinders. The plugs should show you and you can also disconnect one at a time and see if it affects the idle at all. Good luck.
 
P

phatmanmike

Captain
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Oct 24, 2003
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3,869
Re: 150 Merc won't go over 4500 RPM?

23 pitch is an awfull lot for a 150. i hav a 200 and i only swing a 19.
 
R

ronnieboy

Petty Officer 2nd Class
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Feb 5, 2006
Messages
149
Re: 150 Merc won't go over 4500 RPM?

i run a 150 xr4, i use a 4 blade turbo 2+2 21, my ranger runs bout 63 loaded or not. turns 5800+ rpm, i'd check the prop. good luck ron
 
C

Conn

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Apr 29, 2006
Messages
27
Re: 150 Merc won't go over 4500 RPM?

whatever it was, i must have fixed when i took the carbs apart for the 2nd time. trimmed out to about 5500 this past weekend. it's still not idling right and the throttle cable needs some adjustment, but 1700-WOT it runs great.
 
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