Yamaha f115 4 stroke rough idle and stall

My 2002 f115 stalls when throttling back to idle.
It starts fine and runs fine at any rpm above idle. The engine will will run 5600 rpms wot and has plenty of power.
problem is intermittent.
Sometimes it will do this when I start it and as it warms up at idle it will stall.
I bought the boat and motor used so no experience with Yamaha.
Any ideas ?

Re: Yamaha f115 4 stroke rough idle and stall

I had the same issue with my F115 4 stroke and also had the "making oil" issue... you can search this forum for some good reading about that. Anyway, the problem I had was with the mechanical fuel pump with the diaphragm sticking and causing fuel to leak into the crankcase. Once the fuel pump was changed, I no longer have the rough idle and stall after throttle back.

I hope this helps you out a bit!

Re: Yamaha f115 4 stroke rough idle and stall

Thanks for tyhe quick reply.
I checked the water separator filter and it was clean , oil level was good.
Going to replace plugs before I take it in to a mechanic.

Re:02 Yamaha f115 tlra 4 stroke rough idle and stall

Re:02 Yamaha f115 tlra 4 stroke rough idle and stall

I am still trying to figure this out. I taped the primer bulb in a almost vertical position and the engine will not even plane the boat it is running so bad, When i lay it down horizontal in the well it runs fine but will still stall at idle more often than not.
The plugs are new since posting this and the old ones were light brown on one side of the electrode and white on the other side. I gained less than 2 mph top end after replacing the plugs ( 1750 crestliner sc)( 42.5 mph at 5800.
I suspect it might be a weak lift pump and /or primer and fuel lines.
The plugs would seem to indicate a slightly lean condition.
I know I should be taking it to a good mech but I have a daughter getting married in a month and just had my roof and my truck damaged in a hail storm.
I am replacing the the primer bulb and fuel lines and I feel capable enough to replace the diaphram in the lift pump. The engine oil level is the same as when I changed it this spring.
I would appreciate any ideas ?

Re: Yamaha f115 4 stroke rough idle and stall

I'm thinking that your problem may be with either your IAC valve or possibly dirty injectors or high pressure pump filter which is in the VST.
I've heard it suggested to check your fuel pressure at the problem RPM.

This is worth a try
IAC on my Yamaha powerhead Merc 115


Clean the center plunger with carb cleaner.
Let the cleaner seep down and soak around the tabs, then blow out.
This has helped my idle over the years.


Maybe this will help

Re: Yamaha f115 4 stroke rough idle and stall

One more thing to carefully check:
If and when you have the injectors out, carefully check all the seals for damage or tears... for myself, they seem to get damaged fairly easily

Re: Yamaha f115 4 stroke rough idle and stall

Thanks for the pictures..I will give all your ideas a shot. I am not at the lake now but when I return this week i will be replacing the primer bulb and lines as well as any filters and the tstat. I am retired on fixed income so got to wait til the eagle flies over.
I will check my tank for an anti-siphon valve and take a look at the injectors.
The guy I got it from used it mostly on lake michigan with down riggers and probably did a lot of trolling. I can't picture the injectors being dirty as all the plugs were burning exactly identical. Very clean and a light milk chocolate brown on one side of the electrode and white on the other side. Possibly slightly lean but without any experience with yamaha i can only judge by my 2000 90 honda that burned almost identical to the yammmie plugs.
He gave me all his service records but nothing in them for any repairs just annual maint.
I also read rodbolts comments about the idle problem and checking the tstat , IAC (like you suggesred) and the tps altho I am at a loss to know how to check the tps.
Thanks again
****

Re: Yamaha f115 4 stroke rough idle and stall

Many thanks to Eagle 180 and Sdsaw for the help and photos.

I replaced the primer bulb and lines with the new Merc bulb.
The old bulb was bad.
I removed and tested the thermostat, removed and sprayed the connectors for the tps and iac with contact cleaner.
I removed the iac and cleaned it with carb cleaner,
The IAC was the culprit. The engine is running at about 800-850 in neutral and around 750 in gear.

Re: Yamaha f115 4 stroke rough idle and stall

cleaning the ISC valve is needed at least once per year, I use the yamaha combustion chamber cleaner.
if the valve sticks mechanically it can and will take out the ECU.

Re: Yamaha f115 4 stroke rough idle and stall

Ok after cleaning the iac valve, testing the tstat, replacing the plugs, and installing new fuel lines and primer bulb.
The motor ran at 850-900 in neutral at first but after running it for awhile it would still miss and die when coming back to idle like coming to the dock.
After a lot of reading on the forum I decided to try the air screw on the throttle body.
I turned it clockwise 1/2 turn and idle went up to 1000 rpm and backing it out about 1/4 turn settled it down to about 775 in gear and in neutral.
I didn't adjust the throttle screw at all.
The motor seems to run perfect at this setting and I have trolled for hours and quite a few times in and out of my boat lift without any stalls.
My question is should I have left it at 1000 rpms and adjusted the throttle screw to the correct idle.
Generally with carbs you adjust for highest idle and back it off 1/4 turn to fatten it up a bit and then adjust throttle screw to correct idle.
I see that yamaha has tried to keep the air screw away from my pudgy fingers and favorite screwdriver so If I got it coming I'll take it like a man.

Re: Yamaha f115 4 stroke rough idle and stall

only way to correctly set the shutters is by the book and with a manometer.
the ISC does the rest of the air metering.
however we do occasionally have to fake out the ecu.
what you did was allow more air than the ECU knows about.

Re: Yamaha f115 4 stroke rough idle and stall

rodbolt said:

cleaning the ISC valve is needed at least once per year, I use the yamaha combustion chamber cleaner.
if the valve sticks mechanically it can and will take out the ECU.

Click to expand...

What is the difference between an IAC and an ISC? Are they the same thing? I am having the same problem and had a yamaha mechanic tell me he suspected the cdi unit so I am trying to do a few maintenance steps myself before I dump a grand on a new cdi unit. I know my boat is running rich, my altitude here in Idaho is 4200 feet. Can I safely adjust the air intake screw to lean it out or is that a no no? I am used to having to tune sleds for higher mountain altitudes but this 4 stroke boat thing is new to me. Any help or past experiences would be greatly appreciated