Low RPM's 1989 85hp Force

J

Jeffreyi

Petty Officer 2nd Class
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Jan 9, 2007
Messages
107
1989 85hp Force

Recently I had a mechanic check out my motor, on the water, because I was only getting it to 3000rpm. He checked out the linkage, fuel lines, etc...and could find nothing obviously wrong. He suggested that we eliminate the easy things first. We adjusted the tilt and he suggested that I replace the plugs. I replaced the plugs that day and took the boat out and it went to about 4000rpm, which is fine for me. That was about a week and a half ago.

It sat idle until today. I took it out and it only reached 3000rpm. Any ideas?

Thanks.
 
roscoe

roscoe

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Oct 30, 2002
Messages
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Re: Low RPM's 1989 85hp Force

Your mechanic need a lesson or two in troubleshooting.

Check throttle plate for full movement to open position at full throttle.

Check for spark on all cylinders.

Check for fuel delivery to each cylinder.

Check compression on all cylinders.

Decarb the motor, then recheck the compression.



You need to get the wide open throttle (WOT) rpm's up around 5000, or you are doing long term and short term damage to the engine.

My guess is that you are dropping a cylinder, which could be from :
fuel starvation
ignition failure
or low compression.
 
Frank Acampora

Frank Acampora

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Re: Low RPM's 1989 85hp Force

Yep! Roscoe said it all. There is no quick, easy diagnosis.
First check compression since it is the easiest and will tell you a lot about the condition of the engine.
Second check the ignition since this system usually causes the most problems on outboards.
Third check linkage and synchronizing. While you are at it, clean the carbssince floating crap in the bowls may cause intermittant power loss.
Fourth, check the complete fuel system from tank to carbs.

Once you get it running correctly, if it doesn't come up to 4500-5500 range, then re-prop to get it there. If I remember correctly, that engine is supposed to produce 85 horsepower at 5000 with operating range of 4500-5500 at full throttle.
 
J

Jeffreyi

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Messages
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Re: Low RPM's 1989 85hp Force

Thanks to Frank and Roscoe.

I intend to continue my diagnostics as you both suggest. I did, however, perform a decarb as suggested and explained in the FAQ section. Briefly, here's what happened. I decarbed the engine as per the instructions in FAQ. After doing that I barely got back to the dock. The RPM'S topped off at about 1000-1500 with surges. In short, things didn't sound or run well.

What do you think?

Thanks.
 
gregmsr

gregmsr

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Re: Low RPM's 1989 85hp Force

Did you change the plugs after decarb? Same thing happened to me after decarb, changed plugs and was ok.
 
J

Jeffreyi

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Re: Low RPM's 1989 85hp Force

Thanks.

I just changed the plugs about a month ago. Does the decarb "damage" the plugs? I guess I'll get new one's anyway.

I forgot to mention in last post that the engine seemed to run poorly only AFTER I re attached my gas tank (no Seafoam). The change was almost instantaneous!

Any ideas
 
B

bowhuntrrl

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Re: Low RPM's 1989 85hp Force

Jeffreyi said:
Thanks.

I just changed the plugs about a month ago. Does the decarb "damage" the plugs? I guess I'll get new one's anyway.

I forgot to mention in last post that the engine seemed to run poorly only AFTER I re attached my gas tank (no Seafoam). The change was almost instantaneous!

Any ideas
Click to expand...

The decarb knocks all kinds of crap and carbon loose in the cylinder and generally fouls the plugs. That's probably all that is wrong. Replace them and you should be good to go. At less than $3 each, it's also the cheapest fix.
 
J

jnk111

Seaman Apprentice
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Aug 4, 2007
Messages
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Re: Low RPM's 1989 85hp Force

Jeffreyi said:
Thanks.

I forgot to mention in last post that the engine seemed to run poorly only AFTER I re attached my gas tank (no Seafoam). The change was almost instantaneous!

Any ideas
Click to expand...


You may want to try an external/different tank with just a gas/oil mix. That would rule out a blockage in the tank.
 
J

Jeffreyi

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Re: Low RPM's 1989 85hp Force

When I pulled off the plugs after the decarb two of them were pretty black and oily, on however, was fairly clean. What would that tell us?
 
B

bowhuntrrl

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Messages
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Re: Low RPM's 1989 85hp Force

Jeffreyi said:
When I pulled off the plugs after the decarb two of them were pretty black and oily, on however, was fairly clean. What would that tell us?
Click to expand...


To replace the plugs !!! Like I said above, this happens nearly every time a decarb is done.
 
J

Jeffreyi

Petty Officer 2nd Class
Joined
Jan 9, 2007
Messages
107
Re: Low RPM's 1989 85hp Force

Thanks.

There was a typo in my last post. It should read:

When I pulled off the plugs after the decarb two of them were pretty black and oily, one however, was fairly clean. What would that tell us?


I fully intend to change the plugs but about my question (What would that tell us?).
 
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