Mercury 8hp smoky phuts

[KevO]

A new to us 2002 Mercury 8hp 2 stroke with tiller gear change arrangement. It was a real pig to start but we got there eventually and used it on the tender for a few short trips to and from shore over a weekend. Occasionally, and it seems fine at first, it has a slight change in rhythm then a distinct ‘phut’ with a puff of white smoke seemingly through the exhaust then recovers. Then it does it again shortly after, and again etc. Not just at idle, does it while under load too. Fresh E5 Shell supreme (?) fuel, correct 50:1 mix. All hoses and connections seem fine, no visible air or fuel leaks.

So… brought it home and changed to new plugs although they seemed absolutely fine, good spark. Checked timing with strobe, idle timing was a bit ahead of spec and is now correct at 8 degrees BTDC. Cannot check WOT timing until back afloat because it blows all the water out of the drum . Carb settings checked and adjusted, seemed largely correct but tweaked them a bit. Seemed to run fine and I thought hey ho, sorted, but then ‘phut’ and then again every 40 secs - min or so. Stripped cleaned and rebuilt the carb and fuel pump. Nothing noticeably dirty but primer assembly (maybe) a little sticky?. All thoroughly cleaned and rebuilt with new gaskets etc. Fuel filter also stripped and a little bit of white waxy (?) crud in there but nothing major. New filter arriving today anyway.

So, will try and get it run up over the next few days to reset the carb settings after the rebuild. Anything I still might be missing? (excuse the pun).

 

[Anibal]

Not an expert but white smoke sounds like oil being burned. Your oil/petrol ratio is correct but once in a while a white/blueish cloud may indicate a head gasket issue or even a block or cylinder issues. Have you checked your oil levels?

 

[wallacebob]

Not an expert but white smoke sounds like oil being burned. Your oil/petrol ratio is correct but once in a while a white/blueish cloud may indicate a head gasket issue or even a block or cylinder issues. Have you checked your oil levels?

It’s a 2T.

 

[Anibal]

I gathered that and by default they are smokier than 4T, specially when cold. But a white plum of smoke here and there should not happen.

 

[KevO]

Have run a few 2Ts over the year, they all smoked, particularly when cold - our Merc 5 is prob the worst. They never ‘phutted’. I’m hoping it’s just a mixture issue and can be adjusted away but wanted to know if there is something else to rule out first.

 

[VicS]

A new to us 2002 Mercury 8hp 2 stroke with tiller gear change arrangement. It was a real pig to start but we got there eventually and used it on the tender for a few short trips to and from shore over a weekend. Occasionally, and it seems fine at first, it has a slight change in rhythm then a distinct ‘phut’ with a puff of white smoke seemingly through the exhaust then recovers. Then it does it again shortly after, and again etc. Not just at idle, does it while under load too. Fresh E5 Shell supreme (?) fuel, correct 50:1 mix. All hoses and connections seem fine, no visible air or fuel leaks.

So… brought it home and changed to new plugs although they seemed absolutely fine, good spark. Checked timing with strobe, idle timing was a bit ahead of spec and is now correct at 8 degrees BTDC. Cannot check WOT timing until back afloat because it blows all the water out of the drum . Carb settings checked and adjusted, seemed largely correct but tweaked them a bit. Seemed to run fine and I thought hey ho, sorted, but then ‘phut’ and then again every 40 secs - min or so. Stripped cleaned and rebuilt the carb and fuel pump. Nothing noticeably dirty but primer assembly (maybe) a little sticky?. All thoroughly cleaned and rebuilt with new gaskets etc. Fuel filter also stripped and a little bit of white waxy (?) crud in there but nothing major. New filter arriving today anyway.

So, will try and get it run up over the next few days to reset the carb settings after the rebuild. Anything I still might be missing? (excuse the pun).

You say the sparks are good but how good? Will they jump 9/16" in free air or an adjustable gap spark tester?

Is the phut a "lean sneeze"? Maybe your carb settings are a bit on the lean side or the carb needs further cleaning. Clean all jets with a soft copper wire or nylon fishing line

 

[KevO]

The awaited fuel filter arrived yesterday - Evri had it for over a week but at least it arrived in the end. Finally got he chance to fit it this morning. No leaks from the rebuilt carb or fuel filter housing which is good. Ran up the motor and it started more easily - another win. When well warmed up confirmed the idle timing is spot on, the idle rpm in neutral and in gear is also as the manual specifies. Then had a phut or 2 but riching up the mix incrementally killed them off so as suggested, it probably was lean sneezing. When back afloat I'll have to check the WOT timing but so far so good. Thanks for the advice provided.