Re: need help with rough idle Yamaha 115 4-stroke
Found this March 09 forum question on a search that seems eerily similar to my problem. I probably over stated the cough in my original post, it's really just a rough, oscillating idle that when it falls to 600 it stalls unless I give it some gas. Does the t-stat replacement really make sense for a rough,oscillating idle?
During my de-winterization and on my first run of this season, I noted the engine idle would cycle down to 7K then up to 9K and then go back to 8k. It occurred every 30-45 seconds at idle. Normal idle is 8k on digital Yamaha tach.
The idle fluctuation occurred on both the muffs and on the water when in neutral idle. No other problems at other RPM's.
Background:
Prior to starting the engine for the first time, I replaced the fuel/water separator cartridge and engine filter. I purged the fuel from the separator to the engine.
Fuel tank full of non-ethanol fuel treated with Stabil from October.
Engine run on muffs 20 minutes.
Engine run on the water for 3+ hrs without any other issue.
Last March, I had clogged VST, injectors that was resolved by dealer. See Issue with Fuel System thread
Boat ran ~ 60 hours last season without any signs of a problem.
Engine has 142 hrs.
Resolution
It appears the problem is fixed.
The thermostat was changed and the motor is now idling at 7 and there is no intermittent fluctuation. An in the water test will be done to confirm.
There was some salt globs that appear to be keeping the old thermostat from closing completely. I would hazard a guess this part was original (2003).
Thanks to Sdsaw, Rodbolt and Jay. I really appreciate your help.
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