1989 Yamaha 40hp 40elf starts and idles but no power???

Adkmtnman

Recruit
Joined
Aug 30, 2015
Messages
2
Hello
I just bought a 14' Wahoo with a 1989 yamaha 40elf. I was told that one cylinder needed to be rebuilt cause a piston was hitting a plug. I've pulled all plugs and nothing seems to be out of the ordinary. I put water to it today and fired it up. Motor idles a lil rough but when I go past 1/4 throttle, its like its hitting a rev limiter? I'm new to outboards and really hoping this is an easy fix. No one wants to work on it :( Thanks in advance
 

mphelle8vld

Petty Officer 1st Class
Joined
Aug 17, 2005
Messages
321
I would start with a compression test, should be around 120psi in each cylinder.
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
Obviously the previous owner knew there were problems and even suggested it would need work. So I wouldn't be surprised to see low compression and a need for new parts to bring it back to life. As suggested, start with a compression test first and post the numbers back here...
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
For a piston to hit a plug it would have to come up higher than it should normally
or something was inside the combustion chamber that should not have been there hit the plug to close it
For that to happen a bearing,wrist pin, or piston itself has a problem.
or something else ended up on top of the piston
simple to look at top of piston to see if there are marks on it
 

gdpalumbo

Seaman
Joined
Mar 18, 2009
Messages
50
Let's start off by suggesting that if it had hit a plug, they could have been the wrong plugs, could be as simple as that. I have a yamaha v130 that had a similar problem to yours where It would start and idle fine and even rev fine, but when I went to apply power it would fall on it's face. It turned out to be the CDI unit. I guess the CDI units have an issue with a bad solder joint or joints inside and when I put pressure on the screws it would run fine, I got an extra two years out of that CDI. Try wedging a piece of folded up cardboard between the CDI screws and the bolt on cover and see if that helps. Could be a number of other things though. I would first check compression, spark and fuel pressure. Definitley check fuel pressure though, I think that motor should require somewhere around 7lbs or so and if it's pumping a little bit it maybe be enough for the engine to run but may not be able to supply enough fuel to go farther than that. You can take the mechanical pump off the motor and check for holes or dry rot in the rubber diaphram, I have an electric Holley pump on my V130 because the mechanical failed, the Holley was 180$ and the mechanical was 40$ but with the electric I never have to worry about priming or losing prime, the fuel is always right there the minute I turn on the pump. If that is all good I would check for some other simple things, if the prop was ever hit on a rock or other bottom structure, the flywheel key could be broke and the crank could have spun out of alignment and out of timing, if it hadn't moved much it would still run and idle but when you start dumping more fuel in and higher rpm's, the engine needs that advance to run correctly and "keep up" with itself. Honestly, until you get those basic tests done, then it's hard to say anything for certain without shooting in the dark and you don't want to start throwing outboard parts at a motor$$$$$$ my CDI was 450$. Outboards are very good motors hence their enormous cost so I would bet on it being something simple. Also, if it was a piston that came far enough to hit the correctly installed plug, it would have came up quite a bit farther and in this case you would FOR SURE hear a knocking noise coming from the engine from a bad wrist pin or a bad connecting rod bushing. Get a manual it will be the best thing you buy. If you think it did hit a piston like he said, buy a TDC dial indicator and find out what the spec for your motor is and you will be able to tell if the travel is not correct. If the other tests do show good, I would pull those carbs, buy a rebuild kit for 60$ with floats and clean and rebuild them, that will be great fro your motor no matter what. If all else fails, everything else is good and your not comfortable checking and adjusting timing, bring it in for a tune up that could be all it needs. Hope this helps and If you have any more questions feel free to post back. Have a good day.
 
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