1989 yamaha 40elf squeak noise/ idle issue

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schmidty25

Cadet
Joined
Jun 2, 2014
Messages
11
First off Hi, I'm new to the forums here and just purchased my first boat. It's a 16' Carolina skiff with the above engine on it. I rebuilt the carbs, New thermostat, new diaphrams and gaskets on the side of the bottom carb and also the pump, changed waterpump, and lower unit oil.

The engine runs good when above half throttle but down low at idle it makes a chirp noise and will rapidly shut off. I've raised the idle and also adjusted the position of the black box on the side off the engine. This helped out but the engine still makes this noise and will shut off during idle. I've also checked all electrical wires found one that was badly frayed and repaired it. Also there was a inline fuse that was blown, fixed that. It seems when I take the plug off the bottom cylinder and let the top two run It wont squeak and idles fine but will occasionally run rough. I am wondering if it is the bottom piston making the noise, but why wouldn't it make it all the time like when given full throttle? anyway here are the videos if anyone has any input I would appreciate it before I start tearing this thing apart.
https://www.youtube.com/watch?v=Nj375Y7s5gc
https://www.youtube.com/watch?v=t6yrzT8H30o
 
9

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
9,099
lean sneeze
carbs need to be cleaned or there is a air/vacuum leak.
Jacking with stuff means you need to make sure to put everything back to factory specs once you clean and reinstall the carbs
 
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schmidty25

Cadet
Joined
Jun 2, 2014
Messages
11
Thanx for the input, yea I've re-checked all the lines and all of the fuel lines are new except that crazy junction area with all the t fittings but it looks fine. Now all the oil lines are the original. I put the idle screw positions on all threee carbs within spec which the manual calls for 1 1/8 +- 1/4 Turn. I just rebuilt all three of the carbs including the the diaphragm on the side of the bottom carb and the pump on the side of the engine. So I'm going to assume that there is a vaccum leak somewhere.. I also had someone else say the exact same thing.. vacuum leak.. I just don't understand the squeak noise.. I also checked compression and all three cylinders have exactly 110 psi... I'll have to look I didn't replace the gasket behind the main fuel pump... maybe it's got a leak or is damaged...
 
S

schmidty25

Cadet
Joined
Jun 2, 2014
Messages
11
99yam40 do you think that there is a possibility of a damaged/cracked reed valve causing this issue? Or maybe a piece of debris is holding open one of the reed valves?
 
S

schmidty25

Cadet
Joined
Jun 2, 2014
Messages
11
Just wanted to give an update that I had fixed the problem. Turned out that the idle jets had some debris/oil clogging them up. I am assuming from some of the old fuel lines. So I cleaned the jets and I replaced all the lines with tygon and had to bleed the oil injection system. What a pain in the ass that was to get all the air out...
 
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