1985 Yamaha fuel leak help

[danjb]

I recently purchased a boat with a 1985 Yamaha 90 ETLK on it. The motor seems to function ok. I've cleaned up the fuel system (Drained, cleaned and put new gas in tank. Added fuel/water separator. Dis-assembled carbs and rebuilt w/ all new gaskets & floats.) I'm noticing a small fuel leak (while running) coming from beneath the lower cowling. As far as I can see, it looks as if it is coming from where the driveshaft enters the power-head. I did look over the carbs, fuel filter and fuel pump areas and did not notice any leaks. Also, looking from above, down into the lower cowling, there does not appear to be any sort of fuel gathering and running out from around the front of the motor. This leak is only visible from what is running down the outside of the motor and traced back up to the driveshaft entering the motor. On a side note, there is also a fairly distinct "puffing" noise coming from that same area. It cannot be heard from or around the power-head/carb area.. just seems to be coming from beneath the lower cowling where the driveshaft enters the motor. After rebuilding the carbs, I did run the boat in the water and did have to turn the fuel needles down to the lower end of Yamaha's recommended setting as it was idling a bit high. I'm not sure if they are still up too high and too much fuel is being sent through or not, but the "puffing" noise was definitely there before carbs were cleaned. Any suggestions or help is appreciated. I'm thinking it may be something to do with a crank seal, but may need to remove a few pieces of the housing to clearly see exactly where the fuel and puffing are coming from.

 

[danjb]

Re: 1985 Yamaha fuel leak help

So I took the outer cover off of this area and was able to get a closer picture. Circled in red seems to be where fuel, smoke and puffing sound are coming from. As far as I know, this is where the driveshaft would insert into the bottom of the crankshaft.

 

[robert graham]

Re: 1985 Yamaha fuel leak help

A lower crankshaft seal failure?....

 

[danjb]

Re: 1985 Yamaha fuel leak help

Could the fuel leak source possibly be the fuel pump? That's the only part of the fuel system I have not checked or replaced. Is there a way to check to see if the pulse valve is allowing fuel into the crank without taking apart the fuel pump? Either way, I will go ahead and get a new fuel pump on order and just replace it.
The leak coming out from below the lower cowling is a continuous slow flowing stream of fuel. You can see from the pics how much fuel has ran down the front of the motor leg over time. If there is an excess of fuel in the crank... where would it come out of? That entire upper casing area below where the drive shaft enters the powerhead is saturated with fuel. I am not familiar enough with outboards to know what seals if any may fail in this area causing unused fuel to flow from the power head at that location. (other than of course bad gaskets & seals) I'm not positive but thinking that the exhaust flow coming from the pistons would work its way through that upper casing and either out the back or down through the prop. If the fuel were working its way through the exhaust, it would be running down the back of the leg from the exhaust holes or out the prop. There is a little evidence that fluid is coming out of those holes and it's possibly fuel, but I cannot say for certain. I will mention that there is a minimal amount of smoke coming from around where the fuel is leaking out. This may be from the fuel heating up or could be from exhaust. This seems to correspond with the "puffing" noise I'm hearing. I'm thinking air in the system will cause this continuous "puffing", but am not sure why it would be coming out of that location (other than possibly a bad crank seal). If it helps... before cleaning the carbs, I was getting an occasional loud "chirp" with a puff of smoke coming out of that same general area. The upper 2 carbs looked fairly clean, but the lower 3rd carb had quite a bit of gunk and silt built up in it. Could this "chirp" possibly have been coming from a build up of pressure in that lower crank area and blown the bottom seal on the crank? I did happen to have the cowling off when one of these chirps occurred and want to say that it did not come from out the front of the carbs. And I've only had this boat on the water a couple of times... that much discoloration on the front of the motor leg is much more than anything I could have done in the past couple of months.
Hopefully this all is not too much information. Honestly, I started out with no idea what I'm doing and this is my first outboard. I've read through countless forums to get a better grasp, and do realize that I could just tear down the powerhead and replace all the gaskets and seals. It would be nice not to have to do that and to actually know what is failing between the gas entering the motor to the visible leak. I can follow the manual, but I'm sure the piston rings and crank rings are more particular than swapping out gaskets, O-rings and seals. As it is, the motor seems to start right up in & out of the water, idles fine and will get the boat on top of the water fairly easily. I would just rather not do that with the fuel leak issue as it could be a fire hazard.

 

[99yam40]

Re: 1985 Yamaha fuel leak help

unbolt the pump from the block, leave the hoses on,
and then pump the primer bulb to see if fuel flows out of the pulse port

Lean sneeze(chirp) can rupture the pump diaphragm if it happens on the one the pump is on.

Not sure about the lower seal though

too much fuel in crank case and cylinder can wash the oil off the places it is really needed
Bearings and pistons will suffer

 

[danjb]

Re: 1985 Yamaha fuel leak help

Pulled fuel pump off and pumped primer as mentioned. Nothing from pulse pump. However, did get fuel out the side of fuel pump. This does not happen when motor is running. Block bolts may be contributing to keeping it tightly sealed. New pump should be here tomorrow. Will be able to eliminate flooding due to pulse pump or any part of a faulty fuel pump.

BTW. compression and spark are both ok.

One thing I also checked was the idle pilot screw. Seloc manual says it should be from 1 5/8 to 2 1/8 turns out. I turned all three down to just over 3/4 and it seems to run much more smoothly with much less vibration at low idle and with just a bit of idle up. Not sure if having them that low will have any adverse effects..? This is with muffs on.. will check boat on water next week and make adjustments if necessary. Is there a way to fine tune the three carbs individually? All the fins in carbs are in sync as well.

I did also notice by looking at both motor and manual that there is no recirc line coming from the bottom of the crank and/or the lowest part of the crank cylinders. So I'm assuming that there is no good place for unburned fuel to exit the bottom of the crank... out the piston or out a blown seal.

Double checked inside of motor. No visible fuel leaks. So, everything is checking out good so far. Only problem is that I still have a slow flow of fuel out from beneath the lower cowling approx. where the driveshaft goes into the crankshaft. Not as bad with the needles turned down this low, but still there. Also took a look at reeds when I had the carbs off for rebuild. Not a complete inspection, but the looked good w/ flashlight from where carbs bolt on.

Beyond the fuel pump, the only other next step I can think would be to pull the powerhead off and replace those lower crank seals... looks like it's just a few screws to get to them without pulling apart the entire powerhead. Is there anything else I should replace just to do it when I take that step? Suggestions..?

I've also found similar motors on craigslist with the same sort of fuel staining on the front of the leg as mine has. It doesn't seem correct to have more than a drip of fuel coming out, but maybe it's common to have a slow stream..? The ones I was able to get a look at are Yamaha's fairly close in hp and year. Not too many people have pictures of that part of the motor.. I'm sure especially not if they've noticed it.


Is there anything else I should be looking at as to why there would be so much unburnt fuel in that area?

 

[danjb]

Re: 1985 Yamaha fuel leak help

Problem fixed... oil seals at the bottom of the crankcase were damaged over time from pulling the lower unit on and off for impeller changes. Wasn't too big of a task. Pulled the head off and replaced all the exhaust and leg gaskets while I was at it. So, to all those "do it yourselfers".. be very careful when sliding that driveshaft back into the crank after changing the water pump.

 

[robert graham]

Re: 1985 Yamaha fuel leak help

I'm glad you found it and fixed it....thanks for sharing the good advice regarding carefully installing crankshaft....

 

[99yam40]

Re: 1985 Yamaha fuel leak help

Sorry, but I do not see how installing drive shaft from lower unit into the crank shaft splined hole could affect the lower crank shaft seals

 

[danjb]

Re: 1985 Yamaha fuel leak help

Sorry, but I do not see how installing drive shaft from lower unit into the crank shaft splined hole could affect the lower crank shaft seals

My observation while completing this task is that when re-installing the lower unit after removal for servicing, is that the driveshaft (splined tip) slides through the 2 oil seals in the oil seal housing and then continues to insert into the crank (splined hole). There is no guide of any sort (other than whoever is putting it back together) that lines the driveshaft up to insert straight into the crank.. it hits the seals first, then the splined hole. In this case, the lip on the seals was folded over, gas was running out and there was a distinct air "puffing" noise. I'm not an outboard mechanic, but the problem is now fixed and it is my assumption that the failure was from inserting the driveshaft into those seals at a slight angle... repeatedly or once... I'm just saying that I personally, after seeing the condition the seals were in, will make sure that I take extra care putting the lower unit back on.

 

[99yam40]

Re: 1985 Yamaha fuel leak help

Well, you can tell how many times I have ripped one apart.
Seems you are correct.

For some reason I expected the seals to be riding on the crank shaft not the drive shaft.

But I am amazed that there was enough liquid fuel in the crankcase to be running out like that

 

[danjb]

Re: 1985 Yamaha fuel leak help

The amount of fuel kind of baffles me as well. It was not a huge amount, but enough to be a slow steady flow out through those seals. I'm guessing that maybe instead shooting like aerosol into the piston, the air leak pulled it down and turned it back to liquid before it made it all the way back. And there is no recirc line on that bottom crank cylinder to recycle it back up.
Compression is good across the board at approx 116. Spark looks good. No audible signs of any bogging down or misfiring. I plan on calling it done, and will use the motor as it is with normal maintenance. Maybe I'll double check timing later on when I feel like figuring out how to do all that.
If I should be concerned or digging deeper, someone please do let me know.