Tohatsu 2.5hp 4 stroke starts hard then stalls - not the carburetor! -Solved

JustDoinMyPart

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Joined
Jul 17, 2020
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2
Mercury 1F02201HK (2006)
=Tohatsu MFS2.5

Intermittent Symptoms: difficult start most times, okay start sometimes, no start sometimes. If started, would mostly idle then stall. If it didn`t stall right away (3-5 seconds) it would be hard to increase throttle without stall. Sometimes I could increase throttle and it would run well for a short period (3 minutes, 5 minutes, 30 seconds) then stall.

Short story: if you have reason to not think it`s the carb, check the spark plug 90° connector where it connects to the high tension wire.

After searching far and wide for guidance on my issue, I wanted to make a post on this forum to potentially help anyone else that might be encountering a similar issue. I have found a fair number of posts with a description similar to this one but none of them helped. The typical advice was a carburetor problem/fuel problem and I would have to agree that this is the most likely culprit however after using fresh fuel and ripping the carb out and cleaning to spotless twice, playing with fuel filters, fuel lines, vent lines, and alot of pulling on the starter, I was ready to use this engine as a deep line weight.

Out of desperation, I ventured away from the advice of the forum posts and started going through the electrical checks in the service manual. In the course of checking the resistance of the spark plug connector and the coil, I had to remove the connector from the high tension wire/ This connector unscrews from the wire by turning it counter clockwise. I noted that the connector did not seem to really go back on properly. I put my wife's glasses on (cause I don't need them:)) and saw several strands of wire in the connector where they should not be. After cleaning this up by poking at it and bending them out of the way with a fine screwdriver, I reinstalled the connector and all my problems vanished.

This was found by accident in the course of doing the electrical checks. It did not show up as a failed check. Hope this helps someone else.

JustDoinMyPart up here in Canada
 

JustDoinMyPart

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Joined
Jul 17, 2020
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"Edit"
If I had had a basic spark tester, this would have given me a clue as to where the root problem lay but not specifically what the cause was. I would have seen the absence of spark as the engine conked out.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Or the spark tester would have shown not that bright spark or poor spark jumping from one tip to the other depending which spark tester model was used for troubleshooting.

In such case as yours, it's much better to cut with a wire cutter say 5 mm off the cable portion that screws to the plug cap and work with a new shinny cable portion. Sometimes will find corrotion, blackened wire portion that will reduce the electrical efficiency output to the plug cap and consequently to the spark plug...

Happy Boating
 
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