I have a 1989 Yamaha 40hp 3 cylinder that came on a boat I purchased just recently. I went through rebuilding the carburetors, replacing the fuel filter, replacing plugs, etc. For some reason, it just doesn't want to idle.
As far as troubleshooting goes, I've made a few rounds. The bottom plug is cleaner than the top 2, but it seems to be making spark. I tested each cylinder for spark by disconnecting the other 2 plugs, leaving only 1 plug, and the motor would fire just fine and run on each cylinder just fine, even the bottom one with the cleaner plug. I also did a compression test and all 3 cylinders are on-spot. Basically what it does, is that it will crank and idle just fine, but just about every 20 seconds, it will all of a sudden want to die out (if it is running low enough RPM it will die out). If you bump the throttle up enough it will run, die down, then go back to normal and repeat the process over and over again. When it's on the higher RPM range, it seems to be fine; no hesitation or anything.
My guess is that it has something to do with the timing. Each cylinder has compression, spark, and fuel; and each cylinder is capable of running the motor on its own. The only thing I can guess is that the timing box is bad, and every 20 seconds it doesn't spark right or something, then it will go back to normal. The reason it runs fine at higher RPMs is because when it is almost near WOT, the spark is almost constant, so there wouldn't be a problem there. Does anyone else have any ideas? If it's timing, do I need to adjust that or do I need to replace some parts? Thanks in advance for your help!
I'm ready to unbolt this POS and put on a Johnson/Evinrude... (I'm an OMC guy at heart, don't hate me please)
Its like reading my own post. Have gone all the same rounds as you. Its not fuel starvation. Have been told that these 3 cylinders have an intermittent spark problem( CDI) I think. My engine(1986 50 HP Yamaha) is operatiing in a similar manner only at a higher RPM do the sympyoms show. Hope someone helps out here on ignition testing because that is probably where the problem lies. I have a manual but it will be a while before I understand the proper steps and specs to diagnose the coils and CDI unit.
I just tried some testing on my engine. I noted previously( or mabey I did not) that the spark from cylinder 2 appeared weak. It did not jump a gap as far as #1 and #3. All three cylinders have spark, all three on their own would run the engine. I switched the wires marked 2 and 3 from the CDI box to the coils.And then swithced the spark plug wires accrdingly. I then checked the spark on all three cylinders. Sure enough the #3 cylinder had weaker spark. I again switched them back and did the same procedure to #2 and #1. The #1 spark was now weak. This tells me that my coils are fine and the problem is the CDI. I was hoping for a bad coil ($75.00) vs a bad CDI ($275.00). I have not touched the timing ever it is still at the factory setting. If you are certain your timing is correct then I suspect you have a bad CDI. If any other person has an opinion here it would be appreciated. Hope I helped.
Yep, that helps. I'm just going to get my mechanic friend to come by and take a look at it. He knows how to test for timing to see if it is correct or not. Hopefully it's not an expensive part. If so, I'm going to unbolt this POS off the back of my boat and dump it in my lake...
Also, what do you guys think about a reed valve possibly causing this?
When I ran the motor on each cylinder one at a time I didn't let it run very long in fear of damaging anything. When it is running on all 3 cylinders (or 2?), when it goes to die out it will squeak once. It almost sounds like a bearing squeak or something, but that is definitely not the problem since I can run it all day wide open with no issues or noises.
What I figure, is that possibly one (or more?) of the reed valves are bad, starving one of the cylinders of gas/oil for a short moment, therefore causing one or more pistons to want to somewhat sieze (making a quick high-pitched squeak), then go back to normal and repeat the process. Running wide open the reeds are almost always open, so it has a constant supply of gas/oil, therefore not exhibiting the problem at the higher RPM range.
What I may do is just try and run it on one cylinder at a time and see if some can run longer than others. If one can run fine and another dies out systemically, then that cylinder's reed could possibly be bad. Thoughts???
But, would it happen systematically every 20ish seconds if it was the top seal? Also, remember that it doesn't make this squeal wide open and it has no issues running wide open for extended periods of time as far as I have observed.
On a side note, do outboards generally use the same steering connections? More specifically, would a newer 50hp Johnson bolt up to my Yamaha's steering?
Alright, I had a mechanic stop by and take a look at it today. He figured that it is not a bearing issue or leaking seal. He has it adjusted to the point where it cranks and runs smooth as silk (the jet on the middle cylinder was adjusted all the way in), but just every 20 seconds it dies down and cuts off. The carburetor isn't being starved of fuel because the bowls are all full, and they aren't getting overflowed because it's not shooting back out of the carbs. The timing seems to be fine, and all 3 cylinders are firing and getting correct spark. Any ideas?
I had a Yama 30 about the same year model. It gave me very good service for so many years. Then during last winter started having problems. Almost didnt make it back the landing.
Went home started calling for a motors. Liked the E Tec and the price.
I'm actually planning on upgrading to a 50/60hp E-tec over the winter. I've seen some leftover E-tecs about 1-2 years old but still new go for very cheap. As far as new outboards go, there's no reason not to buy an e-tec unless you just can't afford the price difference between a carb'd 2 stroke and the e-tec...
This is an interesting post as I have a '90 50Hp doing exactly the same thing. I had the motor rebuilt and since have encountered the squeak. I read a few other posts and have tried some of the suggestions with no success.
In case it is oil I have used 50:1 and 100:1 mix in the fuel with leaving the injection on - the engine smokes a bit but still squeaks so I don't think the oil is the cause.
I have played with the pilot adjustment but still get the squeak - I could not really get any difference on the pilot adjustment so I just set them as per the book.
I have also played with the synch linkage and still get the squeak - mine is also roughtly every 20sec.
I have cleaned the carbies and they look great but I have not replaced the needles - Could sticking cause this problem and how can I reliably check this?
I have a new fuel tank and fuel line but have not replaced any engine fuel lines - could an air leak before the fuel pump cause a squeak?
At the moment I just idle a bit higher but it would be nice to get a solution that doesn't involve replacing the motor
Yamaha 40hp 1989 not idling... timing?
Linear Mode
