Motor Not Running Right...

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JGibson

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I finally got to take my boat out the other day and see how the motor runs. It started great, idled fine...when I started giving it throttle it wanted to start acting like it was missing, I had it at WOT and was barely moving. Every now and then it would try to stop "Missing" and take the gas I was giving it and run right, but it would always go back to "Missing". I pulled the plugs and checked for fire and believe me, they are firing, firing great, my hand will never forget it :shock: After a few minutes of running it out to the end of the small lake and back, it shut down and would not start back. Plugs were still firing, getting gas but no engine start, it would try to start but no go. The motor is a 1976 40hp Johnson. Any ideas of what could be causing this and what I can do to fix it? I hope this is enough info, I hate having you guys read my posts and there not be enough there to describe whats going on...
 
have you cleaned the carb? if yes, did you set the float and change the small washer in the carb?

how old are the points?

also could be a fuel issue, fuel pump and fuel lines.

2 strokes are simple, compression, spark, fuel. check compression, sounds like you have spark (i would still change the points) and fuel (carb, fuel pump, fuel lines, fuel connections)

dino
 
Noticed today that someone has replaced 2 bolts on the intake, the 2 on the bottom are 7/16 bolts while the others are flat head screws. The 2 that were replaced, one of them was loose, tried to tighten it but wasn't able to, I'm thinking it is either stripped or not long enough. Would this be part of the problem? I'm looking into getting a little longer bolt to go back in it. If it's stripped, I have another motor that I can just change everything over to and use it.
 
It's probably stripped, your gonna have to drill and tap new threads with a larger bolt or insert a heli-coil to keep the same size bolt. If the intake is not tight enough to seal it will draw in air causing it to run way lean which is not good.
And like what dino stated, wouldn't hurt to do a compression check.
 
Did the compression check, both cylinders were right at 90. I took the fuel pump off and there was something in it (looked like dead ants?). Fuel lines all blown out, I changed carbs with one from the parts motor I have after cleaning it (my father in law has the other one). Not sure how old the points are but they looked pretty new when we first started working on the motor. I have very good spark (checked with a spark tester at 7/16 gap). I didn't get to take it to the lake because of rain yesterday to see how it ran but I did run it in a barrel for a few minutes. Hopefully I will get to the lake today, if I do I will post my results, may try to get some video of it.
 

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