1999 90 hp Merc Runs Rough on Water

[gbearden]

I have a 99 Merc that usually runs well; this summer had it on the lake and ran it all day. At the end of the day i idled it and it bogged down and I couldnt get it started. Took the carbs off; cleaned them up and replaced the gaskets. Took it back to the lake and it ran ok except it would surge at times at all speeds (but no too bad)

Anyways I ran it on the hose today and it idled ok; but if i fast idled and brought it back to idle (gave it just a little gas) it would bog down and pop a little and then smoke bad. After that it would idle fine. Plugs seem a little fouled.


Question is could this be a simple seafoam fix and new spark plugs or will it be more extensive?

 

[j_martin]

Re: 1999 90 hp Merc Runs Rough on Water

I have a 99 Merc that usually runs well; this summer had it on the lake and ran it all day. At the end of the day i idled it and it bogged down and I couldnt get it started. Took the carbs off; cleaned them up and replaced the gaskets. Took it back to the lake and it ran ok except it would surge at times at all speeds (but no too bad)

Anyways I ran it on the hose today and it idled ok; but if i fast idled and brought it back to idle (gave it just a little gas) it would bog down and pop a little and then smoke bad. After that it would idle fine. Plugs seem a little fouled.


Question is could this be a simple seafoam fix and new spark plugs or will it be more extensive?

Based on this information, it could be anything from a couple of dirty spark plugs, to stuck rings (sea-foam) to worn out rings (major overhaul)

 

[gbearden]

Re: 1999 90 hp Merc Runs Rough on Water

Thanks for your response; could the carbs also be out of adjustment? When i had them off i didnt mess with the jets so i didnt synch them either when i put them back on, just cleaned them and replaced the gaskets.

 

[gbearden]

Re: 1999 90 hp Merc Runs Rough on Water

Ran it again today and i pulled spark plug wires one by one while it was running. Didnt seem to make much of a difference although it was just idling. I touched the outside of #1 plug cap (rubber boot) and it shocked the crap out of my finger. Must be a crack in the rubber boot. Will that affect anything?

 

[ryanalaska1990]

Re: 1999 90 hp Merc Runs Rough on Water

Ran it again today and i pulled spark plug wires one by one while it was running. Didnt seem to make much of a difference although it was just idling. I touched the outside of #1 plug cap (rubber boot) and it shocked the crap out of my finger. Must be a crack in the rubber boot. Will that affect anything?

absolutly.it may be grounding out before it gets to the plug. that would just cause that cyclinder to misfire.

check all of your plug wires for cracks. if 1 wire is cracked theres a possibility that another couple may be doing the same thing!

 

[gbearden]

Re: 1999 90 hp Merc Runs Rough on Water

Thats what I thought. Can you replace just the rubber end or will the entire wire need to be replaced. If i replace one might as well replace them all.


Hopefully this will solve engine problems. I put electrical tape around the plug wire and it seemed to run a little better. Im planning on doing a comp check as well as soon as I get a comp kit.