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engine runs worse after six hundred dollars worth of repairs

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wwolfe

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Thanks in advance for any advice I get. Here's the situation, I've got a 2000 Yamaha 40 horse. Although this used engine started, idled, and ran great, it always seemed to bog at wide open throttle. I put it in the shop and told them to go through the carburetors check out the rest of the motor, compression timing etc. Compression checked out at 130 pounds across the board. After they went to the carbs they called and told me that number 1 cylinder was not working. It does not suck any air through the carburetor at all. They felt as though the bottom ring was stuck and said the top ring was for compression the bottom line was for suction. They sold me a big bottle of hogwash which brought the bill to $600. It still ran worse tha when I brought it in and they wanted to t hn split the case which would bring the bill up close to a million dollars. I just towed it home and I'm trying to fix it myself. I've asked all along if it could be reeds and was assured that it could not be. Any thoughts men?
 
It could be reeds but you should see some pulse back at the carb if that is the case. It may also be a crankcase leak between cylinders at the crank seal. You would have a bad bearing as will if that was the case. Might also have nothing wrong other than imbalanced carbs or to much prop pitch.
 
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Thanks for responding PBR,
it makes sense that it would pulse at the carb and I've got to say I didn't really check for that yet. It took me a while to get it running at all and I've got it running in a drum of water so I could put a load on it and maybe unstick that ring they were taking about. Of course that only gives you a couple of minutes before the drum empties enough to where you need to shut it down and add more water. I'll check it some more without putting it in gear. That requires disconnecting the linkage so I can increase engine speed without engaging the drive. I don't think it is leaking between cylinders though because if you put your hand over either of the other two it sucks hard and shuts down immediately. Blocking off #1 however has no effect. I did work with the prop size back when it ran on all three cylinders and although I think it was initially overwheeled, I got to the point of seeing negligible results for substantial changes in pitch or even diameter. Correct my thinking if I'm off base. Also, would a reed issue be easy to see with the carbs off or do you have to dig a little deeper?
Thanks again.
 
Okay, thanks Chris. I'll keep plugging away at this. Does the stuck bottom ring theory sound even remotely plausible to you?
 
The compression values indicate that the #1 piston and rings are OK.-----------There are still shops that try to baffle the customer when they are baffled themselves, when they talk about compression rings and suction rings.-------Remove caruretor #1 and look at reeds.------------Carefully inspect crankcase #1 for a hole.
 
Thanks buddy, I'm on it. I'll keep you posted ... no pun intended.
P.S. I tried to fix some typos and ended up with duplicate posts. Can't figure out how to delete one.
 
racerone said:
The compression values indicate that the #1 piston and rings are OK.-----------There are still shops that try to baffle the customer when they are baffled themselves, when they talk about compression rings and suction rings.-------Remove caruretor #1 and look at reeds.------------Carefully inspect crankcase #1 for a hole.
Click to expand...

Ditto on this.

While you have the carbs pulled, Open them up, remove the float and put some carb cleaner followed with compressed air backwards through the needle seat. See if you can Catch what ever comes out in a clean cloth. Also roll up some emery paper and clean out the float seat, not where the rubber sits but the brass that guides the needle.

After this is all done, and it's back together, make sure you engine is reaching operating temps. Low operating temp will condensate water in the combustion chamber and put the spark out.
 
Still, you said there is no suction when you put your hand over the #1 carb intake? That is a serious mechanical issue. Did the shop actually check compression with a gauge? Was the shop actually a Yamaha dealer?
 
Thanks Chris. I sure will. My first instinct was to say "no, the shop went through the carbs " but all I know for sure is they went through my wallet.
 
To have good compression without suction at the carb sounds very strange. I would do a simple recheck on the compression in #1 just by removing all the plugs and putting a finger over the hole whilst someone hits the starter for a very short spin. You can at least get a basic idea of whether that cylinder is making compression like the others. If it is, you probably have some sort of leak in the intake prior to the carb (strange), and if it isn't you probably have reed or piston/ring issues.
 
Very strange indeed. Not only was the compression the same (within 2lbs) as the other two cylinders, but it took the same number of revolutions to get there. Thanks for responding. I'll get back to the motor on Tuesday and post what I find.
 
New poster here. some older yami triple snowmobile motors had crank issues with part of it slipping and being "out of phase" with the port timing. IDK if this could happen with outboards.
 
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