1993 175 Running really rich at idle

[xeenomorf]

I have a 1993 175hp Merc. It runs a little rough at idle but I take it to the canyons all the time and have never had a problem. After running it or anytime it is at idle there is a terribly strong odor of burnt gas (not the smell of leaking gas) I have rebuilt all the carbs and it made no difference. I have sync'd the carbs and checked the timing and everything seems ok. The all the plugs look very wet. Even the hub on the prop looks a little dark. The motor has about 75 hours on it. Is it possible to have a leak in the fuel pump causing this problem but still be able to run at high speeds? Is there a way to check the fuel pump without taking it apart? I have been throwing money into this problem but nothing seems to help. BTW the fumes are so bad that people notice it on shore as I drive by.

 

[gss036]

Re: 1993 175 Running really rich at idle

Maybe you should just rebuild the fuel pump w/ a diaphram kit. It is a cheap part, I just picked up one today, w/tax about $11.00. Looks to be a simple rebuild. <br />I think all the carbed engines run a little rough at idle. I know my 89 200hp does.<br />If you are turely running that rich, maybe the floats are too high on the carbs. How is the oil flow? or do you premix? What type of TCW3 oil are you burning? What does the engine look inside the cover(hood)? Black smoke is gas and blue is oil? What color is your exhaust? Should be blueish in color.<br />Just my opinion, I am not a mechanic by any means, just like doing my own repairs if possible.

 

[xeenomorf]

Re: 1993 175 Running really rich at idle

The engine looks brand new inside. I purchased the boat this year from a friend. The boat was used about 4 times since it was new and in storage until this year. The smoke is blueish but the fumes of burnt gas are much worse then they should be. I have owned many other outboards before and this is terrible. If I were to light a match behind the boat it would prob explode, it's that bad. But I don't see any black smoke like you would if a car was running rich. I use the oil pump in the motor and do not premix.

 

[KCLOST]

Re: 1993 175 Running really rich at idle

Have you checked the spark on all the cylinders?<br />And compression, while you are at it?

 

[xeenomorf]

Re: 1993 175 Running really rich at idle

Spark and compression are great

 

[MercNdude]

Re: 1993 175 Running really rich at idle

Could be one cylinder not firing and you're blowing fuel out the exhaust. The rough idle could be the telltale for that. At idle is when you're really going to notice one cylinder not sync'ing in.

 

[KCLOST]

Re: 1993 175 Running really rich at idle

Merc and I have a good point... When one of my switchboxes went bad, it was only firing on 3 cylinders and I could have burnt the neighborhood down if I lit a match while running on the muffs in the driveway... And it ran horrible at idle and required a signifigant advancement of the throttle to keep it running. <br />But only one, especially two cylinders not firing can cause a terrible idle condition.<br /><br />You need to use a spark gap tester to check the spark for sure... One of those pins with a light indicator will not work, they are too sensitive.

 

[xeenomorf]

Re: 1993 175 Running really rich at idle

Well, it's been another season and I still have this terrible fume problem. I installed a fuel pump kit for both engines and also rebuilt all the carbs and it's still there. I purchased an ignition tester last week, it gives voltage and spark duration of the spark fire. If we have a couple of warmer days I will test the spark and post the results.

 

[heybaylor]

Re: 1993 175 Running really rich at idle

Are you running at idle with the motor trimmed down?...<br />be sure and trim the motor up to clear the exhaust relief hole in the back of engine .<br />level to slightly tilted forward is best<br />if it is covered with water .you will get this loading up effect