Rough idling and sneezing of my 1996 Mercury 150 Offshore

[doyle007]

Guys,

I've had this motor for about three years now, and the entire time I've had an issue with the engine having a rough idle and "sneezing". Today I started the engine for the first time in about three weeks, since it's been impossible to make time for the boat with the holidays, rainy and windy weather, as well as the blizzard that we had last week.

Anyway, I started the boat, and ran it at a higher rpms (about 2,200) for about five minutes, and then backed the throttle down to the normal rpm range when the throttle "clicks" back into the middle position (ie....so that i could just push the throttle forward, and get into gear, or back, and get into reverse). As you can see from the attached video, the engine likes to sneeze and cough a lot. (Sorry that the video is sideways. For some reason, my cell phone makes the video fine when viewing it on the phone, but rotates the image 90 degrees for youtube).

http://www.youtube.com/watch?v=Ib8DfHe0KWU

This idling is the same whether it is warm or cold outside, and regardless if I've run the boat already that day, or the boat has been sitting for three weeks. Someone suggested a "lean idle sneeze", and someone else said that the fuel pump might not be supplying enough fuel at lower rpms.

I really appreciate anyone that watches the video, and let's me know what they think that it is. There are two other videos that I posted from today, but they may or may not be viewable on youtube. I had some issues, but was finally able to see them.

Thank you.

 

[Dukedog]

Re: Rough idling and sneezing of my 1996 Mercury 150 Offshore

If you have tha knowledge of how tha link n synk is done and can play with idle timing I'd start there. Mainly idle timing. Not all Mercs are "happy" with what tha "book" calls for at idle. Disconnect tha idle stabilizer module (you can throw it away if ya want to) and reset max timing to 22 degrees. Play with tha idle timing running at idle in gear. If it still persist, check reeds and bleed fittings/lines. This is just where I'd start but who knows with a Merc ...........D

 

[j_martin]

Re: Rough idling and sneezing of my 1996 Mercury 150 Offshore

If you have tha knowledge of how tha link n synk is done and can play with idle timing I'd start there. Mainly idle timing. Not all Mercs are "happy" with what tha "book" calls for at idle. Disconnect tha idle stabilizer module (you can throw it away if ya want to) and reset max timing to 22 degrees. Play with tha idle timing running at idle in gear. If it still persist, check reeds and bleed fittings/lines. This is just where I'd start but who knows with a Merc ...........D

Carb or EFI?

Sounds like what we call a lean sneeze. Bad reeds will usually miss every round. plugged bleed lines usually cause em to load up rather than sneeze.

Do a link n sync, then go from there. Next would probably be check fuel pressure at idle, and/or go through the carbs. Neither is very involved or expensive.

hope it helps
John

 

[King P.V.]

Re: Rough idling and sneezing of my 1996 Mercury 150 Offshore

There are a couple of things you should do prior to worrying too much about..... well. Here is what to do. 1st, compression check. Look for substancial differences between ajoining cylinders. Should be fairly close to each other. If you have bad compression, all other "repairs" will be for-not !!! 2nd, Spark on all cylinders. 3rd. If you don't have a factory manual, and they are fairly cheap,get one!! Don't bother with the generatic type of service manuals. Look at the specific mention of "sync and link" for carb "pick-up", which is when , at idle, all carb throttle plates are closed and , when advanced, start to open all carbs at the same time. This is crucial at idle for stable idling, throttle advancment and not having the engine "cough" or lean spitting. There are two phillip screws that adjust/tighten the linkages and one additional screw that tightens the roller that will open all the carb linkages. With all carbs closed, the engine should not spit! If it still does, then use your insulated spark plugs boots pliers and remove each spark plug boot and "drop" each cylinder untill you discover which cylinder is the affected one. Then, if it's still "lean cough", you can hopefully key in on a specific cylinder. Look for things like.... the fuel pump runs off that cylinder, or... the pulse line for the oil tank is off the block fitting... or...carb bowl drain plug is loose/fell out and that carb is dumping fuel all over the bottom of the pan. Anyways, start by taking off the motor cover.....

 

[doyle007]

Re: Rough idling and sneezing of my 1996 Mercury 150 Offshore

Guys, thank you very much for the feedback. I do have a Mercury Service Manual for my engine, and I just read thru it. It looks like there is a procedure to synchronize the carbs with the throttle adjustments under section 2 "Electrical - Timing, Synchronizing & Adjustng". I will try that, and let you know if there is any change.

I also plan to do a compression test. I believe that I read that I need to ground each of the wires in the spark plug boot to the engine block. Is this correct? If so, should i make up some wires with alligator clips on each side to make the connection? What gauge wire would I need for this?

 

[Dukedog]

Re: Rough idling and sneezing of my 1996 Mercury 150 Offshore

I also plan to do a compression test. I believe that I read that I need to ground each of the wires in the spark plug boot to the engine block. Is this correct? If so, should i make up some wires with alligator clips on each side to make the connection? What gauge wire would I need for this?

Yes ya do and 14 or bigger will work. Pull tha kill switch lanyard also just because............Just a suggestion, a remote starter button (comes in real handy doin' other things too) at tha solenoid works really well and ya don't hafta turn tha ign. switch on. Do it all at tha back of tha boat...........D

BTW, don't forget tha part 'bout tha "by the book" idle timing. May not hold true with your peticular motor..................I really think thats tha probem.

 

[j_martin]

Re: Rough idling and sneezing of my 1996 Mercury 150 Offshore

Guys, thank you very much for the feedback. I do have a Mercury Service Manual for my engine, and I just read thru it. It looks like there is a procedure to synchronize the carbs with the throttle adjustments under section 2 "Electrical - Timing, Synchronizing & Adjustng". I will try that, and let you know if there is any change.

I also plan to do a compression test. I believe that I read that I need to ground each of the wires in the spark plug boot to the engine block. Is this correct? If so, should i make up some wires with alligator clips on each side to make the connection? What gauge wire would I need for this?

I got a set of the nuts off the top of old spark plugs, and found 1 inch long screws that fit them. I put the nuts on the end of the screws with a hex jam nut, to fit up into the connector in the spark plug boots. On the other (head) end I have another nut, holding a wire. They are ganged together with wire and a single alligator clip grounds the whole schmear. The wire can be pretty light. I think I used 20g stranded. The current is measured in milliamps.

hope it helps
John