1994 Yamaha 115 won't idle with cowling on

[Seadoomanls]

I have a 1994 Yamaha 115 V4 outboard that has ran flawlessly since I purchased it back in May 2013. About two months ago, I let the boat sit for 4-6 weeks. Before this, the boat was used at least once every week. When I went to use the boat, the motor fired up just fine, so I took it to the boat ramp and launched the boat. The boat is oil injected, and for the first time had a lot if visible white smoke. The boat idled and got on plane to my favorite hole for bait. I shut the motor down,caught my bait, then the problems started. The boat had a tough time idling and did not get back on plane.

Brought the boat home, changed all the fuel lines and fuel ball, water/fuel separator, cleaned and rebuilt the carbs, added 8 gallons of fresh gas to tank and tested the boat. Boat idled fine and I idled out to a lake for a test run... Ran good. On the way back in (about 20 min run time total) the boat stalled and had a rough time idling back to the dock.

I let the boat sit out of frustration and attempted to use it again yesterday. The boat will idle on muffs no problem. When I put the boat in the water, the boat will idle WITHOUT the cowling. Once I put the cowling on, the engine begins to sputter and dies out. This happens no matter how high i set the idle. Has anyone else had this problem? Also, when I added new gas, the old gas backsplashed out of the tank a little bit and was bright yellow...

I guess my main question is, has anybody had the same change of behavior from removing the cowling?

 

[dpoff]

Bee/wasps nest/ blockage in the intake of the cowling?

 

[Seadoomanls]

I should have mentioned... That is all clear, no debris on the inside of cowling to get sucked into carbs either.

 

[99yam40]

Adding new gas to old bad gas gives you more bad gas

Also If putting cowling on causes problems then I would be looking for exhaust leak under there starving the motor of O2

 

[Seadoomanls]

After reading a bit about it, this seems as if it could be the issue. How do I properly diagnose as an exhaust leak?

 

[steelespike]

Speaking generically look for a rubber connector that may vent exhaust and water.Otherwise look for gaskets/leaks in the exhaust components.

 

[jerryjerry05]

To help find the leak,
Mix some gas and oil heavy on the oil.
This should make it smoke a bit more.
Squirt it into the intake and see if the hoses or the base gasket leaks.

 

[slorole2000]

Though it's not good for it. I have sprayed starter fluid around intake's and Vac lines. if there is a leak it will rev up.
just never spray into carb or TBI.

 

[99yam40]

Though it's not good for it. I have sprayed starter fluid around intake's and Vac lines. if there is a leak it will rev up.
just never spray into carb or TBI.

Why you think an exhaust leak could be found that way is beyond me

 

[Capt Ken]

Take a small rubber hose, hold one end to your ear while moving the other around the base of the engine. If you have a leak you will hear it.

 

[Seadoomanls]

Thank you for the replies, I will investigate tomorrow. I suspect an exhaust leak because when I started the motor recently with the cowling off, I had white smoke coming from the below the power head. I assumed it was just exhaust smoke rising from the exhaust and just reminiscing under the power head. But, given the circumstances, it is definitely a place to start. Fingers crossed that I don't have to pull the power head

 

[slorole2000]

Why you think an exhaust leak could be found that way is beyond me

Sorry, I miss read. thought an intake leak mentioned in the post

 

[racerone]

Check for exhaust leaks.-------------Then do a check and see if possibly the plug wires are shorting to the brackets on the cowling.-------------------Do a compression test to see if motor is in good condition.

 

[Seadoomanls]

The compression on all cylinders is between 138 and 142.

 

[racerone]

What other testing and trouble shooting has been done today that is not yet mentioned ???

 

[Seadoomanls]

Let's see... I have tried an external gas tank, same problem. Rebuilt carburetors. Link n sync (however I am not sure I did that 100%, might hire mechanic)... I have a spark tester that checks all the spark at the same time, all cylinders had nice strong spark... New spark plugs (twice)... Compression test...

 

[Seadoomanls]

Can anybody touch on how I would use starting fluid to find an exhaust leak?

 

[99yam40]

as far as I know you cannot

 

[Seadoomanls]

Can any one tell me about the fuel pump? I did change the fuel pump, and I'm afraid maybe it's not tight enough letting some of the exhaust from that cylinder out? Or if any one has new suggestions how to test the exhaust gaskets under the cowling for leaks?

 

[racerone]

????????----------The fuel pump has nothing to do with the exhaust !!