Another unburned fuel question

[Oh Snap!]

I have a 1985 Yamaha 40ELK that I recently purchased. The motor was in poor shape and needed some work. Below is a list of the work I've done to it:

• cleaned carbs, checked floats, replaced float bowl gaskets
• replaced fuel lines,fuel filter, and cleaned out fuel tank
• replaced spark plugs (previous owner was using the wrong type plug)
• replaced lower gear lube, replaced O-rings on drain and check plug
• replaced prop

The motor now runs great. It starts up on the first try, sounds great, and really gets my boat across the water in a hurry.

Here is the problem. Fuel is coming out of the lower unit. When I run it on the muffs I can see a rainbow colored oil slick running down the driveway. I can even smell the fuel in the water. I've narrowed the source down to the two holes in the picture. One hole is a small weep hole where water is pumped out and the other is where a shifter rod goes thru. I've attached pics of what I'm describing.

Any ideas on what is causing this??

 

[rodbolt]

Re: Another unburned fuel question

most likly a bad fuel pump diaphram.

 

[Oh Snap!]

Re: Another unburned fuel question

Thanks for the response Rodbolt. I replaced the old fuel pump with a new about a month ago, but I'm going to check to make sure it didn't rupture since then.

 

[Oh Snap!]

Re: Another unburned fuel question

Yesterday I checked the new fuel pump to see if it was ruptured and everything appeared fine. I pulled the lower unit off to find the source of the fuel coming out of the weep holes and talk about a mess. The front half of the lower unit was filled with carbon deposits. It almost looked like flakes of coal. I cleaned it all up and replaced the lower unit. Fired motor up and noticed immediatly that i had a much better water flow from those small holes.

Now back to the origianal problem. I still have a high volume of unburned fuel coming from those little weep holes. Any other causes besides bad fuel pump?

Thanks again.

 

[99yam40]

Re: Another unburned fuel question

Sounds like it is running too rich.

I had a similar problem with mine, it had a WOT miss and had unburned oil/fuel residue dripped out of lower unit after being parked in the driveway.
I finally found out that one of the previous owners apparently drilled out the jets. I put in new main jets and have not had a problem since.

You may need to run some Seafoam or a Yamaha product Ring free to decarbon the motor, but after finding what is causing the excess fuel.The plugs should tell you which cylinder is having a carb problem.
If they are all the same you may need to look at the jets.
Are you running the prime start red lever in normal position?
That system could be dumping extra fuel also if diaphragm has a rupture or it is turned to the open position.

 

[Oh Snap!]

Re: Another unburned fuel question

I checked around the carbs and air box and couldn't find a prime start lever so I'm assuming my engine model didn't come with one. Ordering new jets tomorrow along with an owners manual to hopefully solve the case.

While I'm at it, is there a possibility I need new shaft seals? Someone mentioned that excess fuel/oil is sometime used to lubricate the shaft bearings in the upper unit. Maybe the seals are bad allowing fuel to leak into the lower unit. Any truth to this? If so I will order new seals the same time I order the jets.

 

[99yam40]

Re: Another unburned fuel question

Owners manual will not give you much info on motor ,You need a service/repair manual.

Does your motor have a choke and not the prime start enrichment system?
Make sure it is not partially closed off while running

 

[99yam40]

Re: Another unburned fuel question

http://forums.iboats.com/showthread.php?t=144019

Here is a thread that may help it was at the bottom of your thread in the similar posts

 

[Oh Snap!]

Re: Another unburned fuel question

Started the motor up today with the airfilter off. The choke plates are staying open like they should. The attached post has some good info in it. Not sure if I have a recirculating valve on my model outboard but I will know for sure once my service manual comes in. I will be sure to follow up with the results after I get my parts and manual. Thanks again for the help!