rough idle

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rplas48

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I have a 2005 F150 with 1000 hrs on it. It starts up quickly and idles smoothly at 700 rpm for a minute or two an then the rpm starts to drop to 400 rpm with the engine starting to shake. If I increase the rpm to 700 while in neutral using the lever on the remote throttle and gear module at the helm the engine smooths right out. I checked the throttle linkage at the engine and it had a slight play in it. Started the engine again and the same thing occured ie. at 700 rpm smooth and then dropping to 400 rpm and rough. This time I slightly pushed on the throttle linkage at the engine and the rpm increased and the engine smoothed out. I am thinking the linkages have to be adjusted. But for the life of me can't figure out what would cause the linkages to change.

The engine operates perfectly in all other respects. Your thoughts would be appreciated.

Ray
 
sounds like a lean running condition not linkage. You should probably pull your spark plugs and give them a good look. You may have a clogged injector.
 
First thing I checked were the plugs . Gap was ok with a slight light tan on the ceramic. Runs great otherwise with no hesitation. Wouldn't lean affect performance at other conditions? Thanks for your thoughts.

Ray
 
filter in front of the engine looked good and the racor fuel water separator was changed in the spring,no water in the see thru bowel. I kind of ruled out fuel filters including the VST as the performance is great with no hesitation other than at idle.
I went over the linkages today per the service manual and tightened one linkage 1 turn. That removed the slight "play" I had. I have my fingers crossed but don't think that's going to do it. Any additional thoughts are welcomed.

Thanks all

Ray
 
rplas48":yvnasu0g said:
First thing I checked were the plugs . Gap was ok with a slight light tan on the ceramic. Runs great otherwise with no hesitation. Wouldn't lean affect performance at other conditions? Thanks for your thoughts.

Ray
Click to expand...

I still would be suspicious of the injectors. Im not well versed in the cold/choke operation of Yamaha; but, it sounds like it cold starts with fuel enrichment and idles ok. When the enrichment goes a way, it drops the rpm to 400 which again sounds like a lean condition. You may want to check any vacuum lines on the motor. They could also be causing the lean condition at idle.

When you move the throttles up the motor will run off the knock sensor and enriched the mixture preventing the lean mixture and preventing damage to the motor. This also can mask the original problem of a vacuum leak or partially clogged injector(s).
 
well the linkage adjustment didn't work. I took the boat out and was able to get the rpms to 5500. Which is what it was when the engine was new with no hesitation at all. Back at the dock the idle was 700 for a minute an then dropped to 400. So hot or cold didn't matter. Have to get someone to look at it and will let you know. Thanks for your comments

Ray
 
How old is the primer bullb? They can go bad and leak and need to be mounted verticially to work correctly .... arrow to the sky. Gas filters like Racor can leak around the filter head or gasket is bad

If replacing buy a brand name like Yamaha bulb or search the archives for other brands
 
checked that there were no fuel leaks and after 2 or 3 squeezes the primer bulb is hard and fuel lines are not hard or brittle. Hooked up a small tank with seafoam and followed Dale's post on how to use it. There was with no change and I didn't notice any smoking so I assume the engine was pretty clean with little carbon build. I always use ringfree which is also suppose to keep injectors clean.
Trying to get my mechanic down but they are backed up.
Any thoughts are welcomed

Ray
 
I have a bigger problem which may be related to the rough idle. I checked the PCV valve and it looked good. Ran the engine to check for leaks and found water slightly spraying up from below . Put my hand down as far as I could and felt a hole where the water was coming from. Hopefully the mechanic will get to look at the engine soon. Must have corroded out somewhere. Any body have similar problem ?

Ray
 
I am now thinking the spray and vapor is coming from the very bottom or the exhaust cover. Hopefully from the gasket. The exhaust cover has both the thermostat (water) and PCF valve (vapor). Mechanics looking at it thursday.

Ray
 
I have heard of a couple of the 150 four strokes rotting out. Hope that's not the case for your motor.
 
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