Cylinder dropping in and out?

jdavis6855

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Sep 18, 2014
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I have a 1988 Force 125HP. I'm not sure what's going on but I think I have one cylinder droping in and out. At full throttle the power surges. Any one have any ideas what may be the cause? how do I figure out which cylinder it is?
 

roscoe

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Oct 30, 2002
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21,657
Welcome to iboats jd.

Is this surge continuous?

Or is it more intermittent? How long between surges? Any noticeable speed loss when surging?
 

jdavis6855

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Sep 18, 2014
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Its like a miss. When it first started it only accurred sometimes then it would level out and run fine. now its getting worse. I cleaned the carbs and that didnt help so i'm thinking it in the ignition system. there is a definite lose and increase in speed. Thats why I described it as one cylinder miss firing. there is a surge and loss and a surge and lose......... of power if that makes since.
 

Jiggz

Captain
Joined
Oct 23, 2009
Messages
3,817
Loss and surge could either be a misfire (ignition) or fuel starvation. The latter is easy to diagnose by installing a clear fuel filter between the fuel outlet and the carbs' inlet. If the clear fuel filter gets empty it means you have fuel delivery problem. If it stays full, it means it could be electrical or carburetion problem. Electrical can be diagnosed with an inline spark tester by noting if the sparks are constant in each cylinder.
 

roscoe

Supreme Mariner
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Oct 30, 2002
Messages
21,657
If each "loss" lasts for only a second, it may be something as simple as water in the fuel.

But it sounds more like electrical to me.

Search all wires on the motor for loose connections, corroded connections, breaks in the insulation.
Make sure you check that all sparkplug wires are completely seated on the plug.

Pick up a $9 inline spark tester, and check each plug wire for a strong spark.

Hopefully this will narrow it down a bit.

From there, follow the wires back to the coil, then the cd module.
It really helps to have a service manual in hand to diagnose ignition issues.
The Clymer Force repair manual is good for this, and cheaper than a factory manual.

There are instructions for testing, here, on this site, hopefully you can find them, or someone else will point them out to you, I can't seem to find them right now.
 

jdavis6855

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Sep 18, 2014
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Today i found a wire that connects to one of the coils that had broken insulation and was touching metal. I hope that is the problem. I may go out tonight fishing so we will see how she runs. Thanks for all the help!!!!!
 

roscoe

Supreme Mariner
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Oct 30, 2002
Messages
21,657
Today i found a wire that connects to one of the coils that had broken insulation and was touching metal. I hope that is the problem. I may go out tonight fishing so we will see how she runs. Thanks for all the help!!!!!


Sounds like a likely cause.
Please post back with results.
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
Replace ALL the connectors on the terminal bar.
I had the same problem and found under the shrink wrap on one of the trigger leads the wire connector was bad.
 
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