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I just replaced the fuel tank, lines, added a water seperator/fuel filter, changed out the fuel filter on the engine and replaced the fuel pump. All were either bad from dirt or ethanol. The engine starts up but after a few minutes sounds like it's running out of fuel. I check the fuel bowl on the engine and it appears to be empty (even though there is a new fuel pump). The motor labors to stay running and if I apply some throttle the engine wants to cut out. I fear some how the carbs are plugged up. Before I go spending my kids college fund on the wrong thing, I figured I should get a few opinions. The engine is a 1986 Yamaha 90 with I have no idea hours. I haven't performed a Cly leak down test as I plan on buying the tool to conduct it. Was there a special way to install the fuel pump? Did it need to be primed? It would seem the fuel pump is not pumping. Too many thing to consider.....I need a drink. All opinions are welcome. :@

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well i feel your pain! my '91 90hp yamaha out of the blue just started belching smoke... its oil injection and has me bewildered.

goodluck
dana

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Did you replace or re-new the pump? Very easy to make a mistake as there are many gaskets and small check valves. I would only replace it not try to fix. I assume you checked for silly stuff like a closed vent on the tank?

Maybe you can get assistance form the Yamaha forum.

http://qs1272.pair.com/btsqs/bnetgrou...ay.php?f=2

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Hi Jon, Yeah that was the first thing I did was check the vent. I even took the gas cap off to make sure. I replaced the fuel pump with a brand new one from Yamaha.

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First off don't drink, nobody EVER made a good descision when drinking ! Is the arrow on the fuel line going in the right direction (Tank ---> To Engine) ? I only ask because, "I'VE DONE THAT" ! it's best to replace the whole pump, as stated above.

mw Try the Yammaha dealer in Island Park (K&K Outboard), "Dan" is the Tech, they're pretty good... 516-431-1865

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Same goes for the under cowling filter, there's an arrow on that too...

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I checked the direction, both good. Something I did notice though, there was no gasket between the engine block and fuel pump. Maybe air is getting sucked in through here??? Worth a try, I'll report back with findings today. :|

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Well here are my findings: Found out the little gasket between the engine block and fuel pump is a MUST HAVE! I went to Yamaha and for a whopping $1.11 I fixed my fuel problem. When I removed the old fuel pump I must have overlooked this important piece. FYI to anyone experiencing the same problem. Thanks to all for your help. :)

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A friend of mine had a fuel pump gasket leaking, he tried to slightly tighten it (I suggested that I would'nt touch that), he did, it leaked worse, he went through pretty much the same thing as you did. He was a mechanic, and spent the rest of the day re-building the fuel pump, and replacing the gasket.
mw

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Harley - I noticed you mentioned a cylinder leak down test in your first post - I believe all you can do with a 2 stroke is a compression test - at least that is what I am told. A cylinder leak down test is for a four stroke motor. I could be wrong - but I am going on what i have been told. If anyone here can confirm this that would be great.

Glad to hear you motor is up and running.

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Harley,

Glad to hear you are up and running. My 90hp yamaha is however still sick. I am wondering if you noticed leaking fuel or anything around your fuel pump due to the lack of seal?
Thanks,
dana

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Dana, the fuel pump was not leaking fuel. The gasket I replaced was between the outside of the pump and the engine block. There is a hole in the block that gets vacuum from the intake stroke. There is a similar hole in the back of the fuel pump that mates to this hole in the block. I had the vacuum leaking at this junction. The gasket mearly seals the connection.
Sraab, you are correct. the leak down test on a 2 stroke will tell you the cond of your rings. It is a little more accurate than a compression test. On a four stroke it will tell you the cond of valves and gaskets in addition to your rings.

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Harley - I had asked a dealer if a leak down test had been done on a used two stroke outboard I was looking at and they laughed at me. They said they only do them on 4 strokes - with a two stroke it will blow through the reeds or something. Not knowing any better I just apologized for my ignorance. But from what I am reading it still can be done to check the rings? Is this a good test to be performing on a 2 stroke? Sorry - I am just confused.
Thanks
Scott

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Well, when you do a leakdown test on a 4 stroke, you have to make sure the cylinder is on a stroke where the valves are closed (compression or power stroke) otherwise the compressed air is going to leak out an open valve and you'll be unable to test. I'd imagine the same holds true with a 2 stroke in that if the piston were at the bottom of the cylinder, the air would just go out the exhaust port. However, if the piston were high enough in the cylinder towards the head to have the exhaust port closed, you'd be able to manage pressure in the cylinder and test the rings and also the head gasket integrity... Never tried it but it seems logical.

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Scott,

I can hardly stay in my chair I am laughing so hard at the dealer you talked to.... It's a good thing they don't call themselves mechanics... However, they should probably talk to their mechanics if they have any good ones on the staff....

I call very few mechanics "Master Mechanics".... I have been using the same OMC/BRP mechanic for the last 19 years.... Ever since 1988.... He is in many people's opinion a "Master Mechanic"....
He no longer uses a compression test on 2 stroke engines. He uses only the leak down test... Yes, on 2 stroke engines. He says it is a much better way of diagnosing any problems even on 2 strokes.

So, the dealer you talked to must be living in the past or just doesn't know anything about outboard motors.... I would stay away from that dealer....

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Thanks for that clarification Joe. I did walk away from that outboard sale when they started questioning why I wanted to run a compression test.

If the leak down test is better maybe I should learn some more about it -(any links that anyone can provide to a tutorial would be great) All I do when I buy outboards and boats is a compression test. Up to this point its all I know. - Being a 4 boat owner now I should really get better versed on some of this stuff.

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Just did some reading and it seems like the leakdown test is very useful for 2 stroke engines. Couldn't find any tutorials to link to, but after reading different pages, seems the trick is to have the piston right at TDC and then check the leakdown rate. Once you have that number, you can then begin to slowly ease the piston down the cylinder by rotating the flywheel (carefully, with a large socket wrench I'd assume, as the cyl is under pressure) and watch the gauge for increased leakage, which would indicate an worn oval cylinder, or scoring, etc. Pretty useful. There are also many articles about how to build your own leakdown tester for short money. Thanks for bringing this up, very useful!

As an aside Scott, I have to say that I'm glad you walked on that engine. When anyone laughs at a legitimate question, especially a dealer, it reveals a lot about their character (or more accurately lack thereof). Given that, it's not surprising that they were wrong about their answer and I hope you can steer clear of them in the future.

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Thanks for the little background on the leak down - I will have to do some google searches myself and get set up. I am working on a 1991 Evinrude 225 right now and a leak down test would be a good indicator of block condition I guess. My compression #'s are in the High 80's low 90's which is supposed to be good for that vintage V6 Looper.

Im glad I walked too. It was the first time I had ever talked to that dealer. There are quite a few in the South Jersey area. Shopping for a used motor can be quite hard. I just have a hard time forking over the amount of money they want for new ones. Its often much more than I spend for my boats.

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I just bought a snap-on leak down tester for $49 on ebay. Just look under diagnostic tools in ebay motors. As far as the dealer laughing at you for asking that question, I'd steer clear of that place if they never heard of a leak down test. It works for 2 stroke (rings) and 4 stroke (valves and rings). It has been the real test over a compression test. Any GOOD mechanic knows the difference. Scott, those bozos at the marina had no clue. Don't feel bad. I have a great article i'll post.