1987 115hp Stalls in Idle

[rmart]

I have a 1987 115hp Yamaha on my 18' Boston Whaler that has run like a top until this weekend. After trailering our boat approximately 5 hours for a camping trip and then running the boat at 3/4 throttle for the 6 mile cruise to our island getaway the engine stalled the moment I backed off the throttle and reduced to idle speed. Then the engine was nearly impossible to start...and when I could start the engine I could only keep it running with a high choke. The moment I reduced the choke to shift into forward (or) reverse gear the engine stalled. A local mechanic looked very quickly at the engine for 15 minuted to see if this was as easy fix and he confirmed the following:

1. Fuel pump was delivering fuel as the plugs were wet and the carb had good clean fuel;

2. Plugs had good spark;

3. Engine had good compression at 117 in all cylinders;

4. Fuel filter on engine was clean;

5. Water separator (cannister style) was clean without any water.

What do you folks think is my problem? Carb problem? Fuel pump? Coil? CDI?,,,,?

The engine has been used a couple of times per week (2-3) alll summer without any problem and as a result this problem was a huge unexpected surprise.

Thanks in advance for any feedback or tips.

[Bluebird]

Get the boat to a dealer and have the carbs cleaned and rebuilt and at the same time have them clean the fuel tank. Make sure you have a new fuel water seperator and then watch it for water. Nice new YAMAHA only primer bulb, and all fuel lines checked for achohol intrusion (spongy).
New fuel pump then decarb. Now you get to learn how to adjust the pilot jet screws by reading the Clymer manual. Good Luck!

[rmart]

I checked the water separator tonight and no water was present. I also ran some Sea Foam Deep Creep in the carbs and while that helped get the engine to idle....it still sounded real rough.

One thing that surprised me was when I checked the fuel filter cup on the engine, there was no filter element inside (just the empty cup).

Bluebird, what do you figure the price to rebuild a carb, replace a fuel pump and clean a 63 gallon tank would run??

[Bluebird]

Carbs are 225.00 for both. Tank is done at time and Materials figure 100.00. Hope that helps.

[Bluebird]

Fuel pump 40.00 for parts should include that in the labor on the carbs.

[jb123]

D.I.Y. for a good lesson and the knowledge for next time.

[rmart]

While I consider myself pretty handy, I am intimidated by the thought of removing and rebuilding the carbs by myself even with my Clymer's manual.

I just dropped the boat off with my local mechanic yesterday and he while he hasn't looked at it or started the engine, his first comment was that my symptoms concerned him and the problem could be larger than just the carbs since I couldn't get the engine to idle or rev at high speed with the choke. His indication was normally you can get one of the two to sound relatively normal with a carb problem.

I was wondering, does this problem sound like a carb problem? Clogged jets?

If so, would a shock treatment Sea Foam or similar cleaner run through my fuel/water seperator filter be a potential solution? In another thread on this site it was mentioned that a shock treatment in this manner would get to the jets and potentially clean any restriction there.

I have sprayed Sea Foam into the carbs and that has helped the engine to idle, but it still is idling terribly rough.

Also, when I sprayed into the carbs I noticed (for the first time) that the in-line fuel filter under the engine cowling did not have a filter element installed. It was just an empty bowl that has had the fuel running unfiltered through it for the past 4 years I have owned the boat. I am a little upset with that since I had my carbs re-built when I purchased the boat 4 years ago and the mechanic didn't catch and install this missing filter element.

I assume this has not helped but I would have assumed that the water/fuel separator should have caught any significant debris that may have been in my fuel.

Any thoughts or recommendations is appreciated.

[Ken]

rmart,
I don't know how well that water/fuel separtor has filtered the fuel of small particles like dirt over the last four years. Anything that has gotten past the separator has gone right to your carbs since there was no element in the fuel filter.
While a shock treatment with Seafoam (see my post to Allan498) would not hurt (especially if the motor has not been decarbonized in the last three years), I don't think that Seafoam will dissolve any dirt particles like it will carbon, gum and varnish.
If a shock treatment doesn't help, then I would do a carb rebuild. If that doesn't fix the problem, then I would start suspecting ignition.
Good luck,
Ken K

[rmart]

Thanks for the help and advice Ken. I have not heard from the mechanic as he won't get a chance to look at the engine for 1-2 days. Does this overal problem and symptomology sound like carbs to you? Does this sound like a fuel pump problem? Thanks again.

[rmart]

Just got the boat back from my mechanic and am pleased to report it was clogged jets in the carbs. He rebuilt the carbs and installed a fuel filter element (finally will have one after several years) and the engine is running great again.

Thanks to all for the tips and the advice.

[Ken]

rmart,
Glad you got your problem fixed - and thanks for letting us know the solution - feedback like this helps us all to learn.
Now that you got those carbs cleaned, keep 'em cleaned - don't let that motor setup for more than two weeks at a time without running - preferably once a week is even better - slap on the ear muffs with water hose and run for at least ten minutes - runninn in lake/bay/river is preferred so that you can open the high speed jets, but this is not always practical.
If you have to store the boat in off season, follow the procedure in the owners manual to prevent fuel contamination and gum/varnish from forming in the carbs.
Good luck,
Ken K

[rmart]

Ken,
The surprising thing about the carbs getting clogged like this for me was that we have been using the boat all summer at least 2-3 times per week without a problem. Even in this instance the boat ran great for approximately 6 1/2 miles and then just completely stopped when we reduced to idle speed...then until I decarbed I couldn't even get it to run at all at idle speed.

I have heard different opinions on one way to avoid fuel gummin in the carbs:

That is, you remove the fuel line at the engine while running the engine on ear muffs. This will cause the engine and the carbs to burn any fuel left in the engine to avoid gumming/varnish problems. What do you think of this technique?

[Ken]

rmart,
Without an element in the fuel filter, debris goes right to the carbs and gets stuck in the jets.
I really think you are better off keeping fuel in the carbs/fuel system. If you run all the fuel out of the carbs, then you take a chance of gaskets and seals drying out and cracking. Best to run the motor in off season once every week or two, if that is practical.
Good luck,
Ken K