How did I lose 10 MPH?

E

ebsworj

Petty Officer 2nd Class
Joined
Mar 7, 2005
Messages
173
How did I lose 10 MPH?

I took the boat out yesterday and I noticed she would only do 32-35 mph. Usually I can get here to 44mph w/ trim adjustments. Its a 120 HP OB on a 18' bowrider. 2 weeks ago i ran into a little submerged sandbar in the sound at slow speeds. The prop tips got polished but I don't see any visible bending or warping. It almost seems like the throttle cable slipped or somthing since it dosen't seem to rev up like it used to. Any ideas how to check if the throttle cable came out of adjustment? What to do?
 
roscoe

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,667
Re: How did I lose 10 MPH?

Speed trap got you and took your 10 mph. :) <br /><br />Don't be embarrassed to tell us you have a Force motor. :) <br />Be proud of it, it still runs don't it? :) <br /><br />I would say you are running weak on one cylinder.<br />So check the compression ( gauges are $29 at Sears or NAPA) , and the spark, and for gas to each cylinder. I bet you will find either no spark or low compression on one cylinder. <br /><br />What do the sparkplugs look like? Do they all look the same?<br />What year is this motor?<br />How high are the rpm going?<br />How is the holeshot?<br /><br />Could be just a head gasket or a bad coil, or it could be a lot worse.<br /><br />Let us know what the compression readings are.
 
E

ebsworj

Petty Officer 2nd Class
Joined
Mar 7, 2005
Messages
173
Re: How did I lose 10 MPH?

Ok I'll check the compression... I'm somewhat scared to do that since I don't have the funds to fix a major outboard issue.<br /><br />The motor seems strong though. Holeshot is good. It has been idling a bit high lately also. <br /><br />Wouldn't i notice a lot of vibration if it was running on 3 cylinders?
 
LubeDude

LubeDude

Admiral
Joined
Oct 8, 2003
Messages
6,945
Re: How did I lose 10 MPH?

Maybe the prop lost some of its pitch in the sand.
 
TOHATSU GURU

TOHATSU GURU

Admiral
Joined
Jul 22, 2004
Messages
6,164
Re: How did I lose 10 MPH?

Check the double bottom of your boat for water if the engine turns out ok.
 
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umblecumbuz

Lieutenant Junior Grade
Joined
Sep 25, 2004
Messages
1,062
Re: How did I lose 10 MPH?

Might sound kinda basic - but you haven't told us what revs you got before and after the bump.<br /><br />If they've dropped, that's the reason for your loss of speed.<br /><br />Have you got a rev counter? What does it tell you?
 
jtexas

jtexas

Fleet Admiral
Joined
Oct 13, 2003
Messages
8,646
Re: How did I lose 10 MPH?

Yeah, what about RPM's? Maybe the trim unit took some damage & won't trim out when you apply power?
 
E

ebsworj

Petty Officer 2nd Class
Joined
Mar 7, 2005
Messages
173
Re: How did I lose 10 MPH?

I wish i could tell you my RPM's! I bought a new gauge set when i got the boat (it didn't have a tach) but I haven't wired in the sender wire for the tach. I know for certain that the engine is not reving up as much as it used to. Its strange this happend in the span of a week. But it sounds likly that I may have a ******* cylinder... I have my fingers crossed for when I check my plugs this evening. What will the plug look like if its cylinder is low on compression?<br /><br />The trim works, i don't know if its damaged or not. <br /><br />No F-150... unless its invisible
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: How did I lose 10 MPH?

ebsworj.<br /><br />If you will just identify your engine I can move this thread to the proper forum
 
E

ebsworj

Petty Officer 2nd Class
Joined
Mar 7, 2005
Messages
173
Re: How did I lose 10 MPH?

Sorry... It started off so inocently <br /><br />1994 Force 120
 
JB

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: How did I lose 10 MPH?

To Force Troubles.
 
roscoe

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,667
Re: How did I lose 10 MPH?

If one or more sparkplugs look like it was steam cleaned, and has low compression, probably a head gasket, $25 for the gasket. No spark, hopefully a coil, $30. Broken rings, scored cylinder, damaged head, $$$$$$$$.
 
B

bnk999

Petty Officer 2nd Class
Joined
Mar 20, 2005
Messages
137
Re: How did I lose 10 MPH?

did it get hot at all after the sandbar incident? Sand in cooling system is what caused my overheat/ruined piston
 
E

ebsworj

Petty Officer 2nd Class
Joined
Mar 7, 2005
Messages
173
Re: How did I lose 10 MPH?

I looked at the sparkplugs yesterday, 2 were toast colored 2 were oilier but nothing excessive. I just had a theory that about why it started idling high (running lean right?) right about the time i wasn't getting top speed. I think its leaking somewhere letting air into the crankcase and making it run lean on idle. I've run in 3 times with a high idle so I hope i didn't do any damage!<br /><br />What should i do now? My plan was to pull the head and look at the pistons... can i crank the motor w/ the starter with the head off? I wanna check out the cylinders. So if my head gasket looks good what should i look for?<br /><br />I don't think it got sand in the cooling system, it still circulates good and no sign of getting hot.
 
roscoe

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,667
Re: How did I lose 10 MPH?

Check for air leak between the carb and the intake. If it is sucking air in there, it will cause a lean condition.
 
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