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Dec 30th, 2023
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 need help with merc. xr4 150
#680505
08/14/06 06:12 PM
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Joined: Jun 2006
Posts: 6
bgddyfrmcin
OP
Green Horn
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OP
Green Horn
Joined: Jun 2006
Posts: 6 |
when run wide open rpms max out at 39000, after run a while the rpms shoot up to 45000. just started doing this.....the rmps never have been above 39000...just curious what to look for
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 Re: need help with merc. xr4 150
#680506
08/14/06 07:21 PM
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Joined: Oct 2005
Posts: 20,755
kingdad101
TFF Guru
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TFF Guru
Joined: Oct 2005
Posts: 20,755 |
If it only turns 45000, I think you have a serious prop problem. I'm not a Merc guy, but I think that 150 should turn 55-58000.
maybe a Merc expert can lend a hand here..
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 Re: need help with merc. xr4 150
#680507
08/14/06 07:53 PM
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Joined: Aug 2004
Posts: 3,600
Boatman1
TFF Team Angler
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TFF Team Angler
Joined: Aug 2004
Posts: 3,600 |
Could be electrical or fuel, take it in and have the carbs rebuilt, and a tuneup. I would bet that it runs about 5300-5500 after that.
PS..........you do have fresh fuel?
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Re: need help with merc. xr4 150
#680508
08/14/06 08:20 PM
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Joined: Oct 2004
Posts: 1,258
Bullet Driver
Extreme Angler
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Extreme Angler
Joined: Oct 2004
Posts: 1,258 |
another thing that might have caused this is that your hub might have spun, does your speed increase or decrease or stay the same? but it should be running around 55 to 5800
  "When all else fails, use a Grenade!"
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Re: need help with merc. xr4 150
#680509
08/14/06 11:20 PM
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Joined: Dec 2005
Posts: 5,269
gander
TFF Celebrity
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TFF Celebrity
Joined: Dec 2005
Posts: 5,269 |
my 1983 merc 150 turns 5700....
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Re: need help with merc. xr4 150
#680510
08/15/06 01:25 PM
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Joined: Jun 2006
Posts: 6
bgddyfrmcin
OP
Green Horn
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OP
Green Horn
Joined: Jun 2006
Posts: 6 |
yeah I do have fresh fuel. after all it is a 150 kind of hard to keep fuel in it...........thanks for the info I look into all of these idea's
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Re: need help with merc. xr4 150
#680511
08/16/06 02:19 AM
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Joined: May 2003
Posts: 12,334
PGR Mike
TFF Guru
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TFF Guru
Joined: May 2003
Posts: 12,334 |
Bgddyfrmcin,
I would like to know what boat you have, what is the model number, and what prop you are running.
3,900 is a little low for most applications, but I need to know what you are running to know what direction you need to be pointing in.
So please feel free to email me.
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Re: need help with merc. xr4 150
#680512
08/20/06 02:40 AM
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Joined: Dec 2005
Posts: 71
scanos
Outdoorsman
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Outdoorsman
Joined: Dec 2005
Posts: 71 |
Just some thoughts:
If it ran at higher rpm before and this is a recent change...probably not your prop
If not your prop it is either fuel related or ignition:
On the fuel side could be:
Carbs, fuel pump diaphram or a major fuel restriction or leak
On the ignition side could be your stator, trigger, switchboxes or a coil.
If you can service yourself and have the manual this should point you in the right direction....if not get her into a good Merc mechanic.....OPTI is good and so is Tommy at Rockwall Marine.
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Re: need help with merc. xr4 150
#680513
08/20/06 03:32 AM
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Joined: Dec 2003
Posts: 3,180
2-stroke
TFF Team Angler
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TFF Team Angler
Joined: Dec 2003
Posts: 3,180 |
What year? Had it long? What recent maintenance was done to it?
If you want to work on it yourself, I strongly recommend a shop manual.
If your prop is spun, the engine will rev up while the boat speed stays constant or slows down, like a slipping clutch in a car.
Surging from 3900 to 4500 sounds like you've been running short at least one cylinder.
Could be a number of things but the way to find out is to start testing and eliminating things one by one.
Start with a compression test and a spark test. Spark should jump a 1/2" gap.
Note the appearance of the spark plugs.
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