85' 150 mercury v-6 excessive smoke and roughness at low rpm

68drummer

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Hey guys! I finally bit the bullet and joined the forum in hopes of gaining more outboard knowledge. I hope someone can help me with this one. I've been fiddlin' with this 85' 150 Mercury 2 stroke trying to figure out whats wrong with it, to no avail. It runs really rough and smokes excessively at idle, and lo-rpm (sometimes even skips off idle for a bit at times). Seems to be too rich and loading-up the engine. The carbs are non-adjustable. It also has new plugs, decent Compression around 95-100 on all cyls, carbs are spotless inside with new seats and needles that i just installed just a few days ago along with new fuel lines. Nothing helps! Any thoughts on what could be the issue? Thanks in advance for any info.!
 

68drummer

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Thanks for the response guys! Went to the Pennzoil 100% low-ash synthetic a couple tanks ago to see if it would help. Didnt seem to make a difference. The Spark seems strong. But i'll recheck this weekend and look closer to see how far. Could it be a weak ignition component somewhere? It runs like a BOH at mid-range and hi-rpm. Its just seems to be an idle to off-idle low rpm thing. Shakes like a beast too! Really rough at low rpm.
 

Dukedog

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do you know how to check and/or adjust idle timing, bleed system?
 

68drummer

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No. I don't know much in that area. I was trying to do as much of the little things that i knew about in hopes of resolving the problem.
It kinda seems like it could be a retarded timing thing hence the bottom end being sluggish. What do you mean when you say "Bleed the system"?
 

Chris1956

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Duke means "check the bleed system".

First of all, did you set the float heights to the given specification? Are the floats in good shape?

Next I would check the idle pickup timing and max spark advance. A service manual is best to help with that.

I would then check the bleed system to make sure all the hoses are good and the valves are working.
 

68drummer

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Chris, the floats seemed almost perfectly level when i pulled the carbs off, broke them down and flipped the bowls upside down, and they seemed to be in pretty good shape too. The bleed lines seemed ok. But admittedly i just gave them a look -over. Seems that things are getting over my head on this thing so i probably need to just take it to someone more qualified to work on it. I've just had too many bad past experiences where it cost me a wad$$$$, never got fixed right, and in the end if it got fixed right i had research info. and just do it myself! LOL!
 

Dukedog

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try ta find yourself a manual for it... makes guiding ya thru different procedures a lot easier on tha computor.. as for tha "idle timing" there are several steps involved that can't be missed.. some exactly by tha book and some justa tad different...... manual doesn't need ta be "motor specific" for your motor, justa oem for tha pre '91 carb V6.. basics for those all are justa 'bout tha same...
 

68drummer

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Thanks Duke. I'll see if i cant get my hands on one somewhere and see what i can learn, check over, and get back to ya'll. Thanks to everyone for all the help!
 

achris

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You also need to check that all the bleed hoses go to the right places.

I would also do a spark plug test. That may help determine which cylinders are causing problems. With the engine running and using insulated pliers or an HRC fuse puller, pull the lead of each spark plug one at a time. You will then know which cylinders are not running.

Chris. ....
 

Chris1956

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Check or rebuild the fuel pump. If the diaghram leaks, raw fuel will get into the crankcase causing smoke and rough idle.
 

Dukedog

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this also one place ta look.... gettin' old n forgetful.

Check or rebuild the fuel pump. If the diaghram leaks, raw fuel will get into the crankcase causing smoke and rough idle.


merc850..
wh's are non-adjustable anything.... jettin' controls all mixtures... idle timin' controls idle rpm and speed on tha wh v6 motors.
 

Whaler672

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Carbon buildup. Pick up a can of sea foam. Mix up a gallon of fresh fuel and the required amount of oil and pour in the sea foam. Connect the gallon can to the engine. Start it, let it run or idle for about 10 minutes. Shut off the engine and let it sit for a half hour (hot soak). Start it back up and she will smoke heavily for awhile burning off all the carbon. You can repeat this procedure until she stops smoking at startup. I give all my two cycles a steady diet of seafoam. Keeps them running clean.
 
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