115 idles rough over 4mph

[Parker]

Hi Ken, I am back working on that 115. I received your latest update and have been checking over the fuel system once again. Gas is flowing through the fuel filter and fuel pump when I squeeze the fuel ball. I am figuring that they are both operating fine. Is that assumption correct? I did notice when I took the cover off of the carberators, oil was colleccted in the cover and the water collection/filter tube on the bottom of the oil tank was overflowing. I emptied the small collector tube and reassembled it. I will run those compression tests later today and will let you know what happens. Thanks a lot Ken, Hope you had a great New Years! -Parker

Have a couple of questions before I run the compression tests too. The manual says to disconnect lanyard plate of the engine stop switch, is that the same as a lock plate the manual refers too?

Just to confirm: I take out all the sparks plugs, connect the pressure tester to one, turn the engine over for about 3 seconds and then take reading? Just want to make sure.
Thanks again Ken

[Hamfisted]

The manual may be refering to the kill switch lanyard, pulled to make sure there's no spark. Warm the motor on the garden hose, pull the kill switch lanyard, pull all the sparkplugs out, open the throttle plates full open, and test one cylinder at a time. 110-120 psi is a good reading per cylinder.


Mike

[Ken]

Parker,
You still may have a weak fuel pump (a split diaphram) that just won't deliver enough fuel at the higher speeds. As a routine maintenance, some owners replace the fuel pump on a regular basis, depending on hours used, like every four years.
I agree with Hamfisted on the lanyard switch - just pull it before you do the compression test to kill the ignition.
Also agree with Mike on the compression test procedure - he has done more than I and knows his stuff.
Do you have a fuel filter/water separater between the fuel tank and the motor? I'm talking about one other than the little local one mounted on the motor. Considering where you are, I think that would be a good idea (cold weather and condisation). Racor makes a really good one with a see-thru bowl at the bottom - you can look at it and quickly determine if there is water in the fuel.
Let us know how you progress - and a Happy New Year to you [img]smile.gif[/img] ,
Ken K

[Parker]

I ran the compression tests and they read from 131 psi to 135psi.

I pulled apart the fuel pump and wondering what I am looking for. There seems to be 2 openings through the gasket and the bottom one is covered with a rubber (diaphram?) It doesn't seem to be broken but I will check the second one too.

I read something about a throttle sensor, not sure if that could be the problem?

Again, thanks for your help.

[malcolm]

I have had a similar problem, what kind of ignition system do you have. have you changed the fuel filter lately.

[Ken]

Parker,
Well, you are making progress, and that's good news on the compression.
You and I have very similiar motors - mine is a 2000 C115 - I reviewed the manual last nite - took a look at the fuel pump diagram. The "active" parts of the fuel pump are the two diaphrams and four valves. Upon inspection, you are just looking for splits in the diaphrams and distorted/split valves. When you reassemble the pump, you should be able to blow thru in one direction, but not the other - there are arrows on the side of pump to indicate fuel flow.
Take your boat for a test run, and get it to act up. Check the primer bulb - if it is collapsed, then there is a restriction from there back to the tank. If not collapsed, then try pumping the bulb to see if the motor responds. If it does, then the fuel pump is bad.
I don't think our little 115s have "throttle sensors". What we do have is a magneto control arm that moves the stator when the throttle is opened - this gives the spark advance. Look in the front of your manual, and there is a procedure for checking spark advance. I don't think you need to go thru the entire procedure just yet - but you need to take a look at the control arm and see that it is connected to the stator and moves it when you go forward with the throttle.
I don't remember - did you do anything with the carbs? You might try removing the high speed jets and squirting carb cleaner into the orifices.
Inspect the ends of the jets - if the o-rings are distorted or cracked, they need to be replaced.
You may just have clogged carbs from gum and varnish buildup. Have you done a shock treatment with SeaFoam or RingFree? If none of this works, may have to remove carbs and install a carb kit.
I'm hoping you have something simple that is causing the problem - you're just eliminating the "easy and inexpensive" things first. The CDI will be the last thing - and Yamaha is real proud of their CDIs ($$$$).
Good luck, and let us know how you come out.
Ken K [img]smile.gif[/img]