Mercury 200 Carb - under power

[alessandro@manx.net]

Please help!<br /><br />I've recently completed a rebuild of my 1998 Mercury 200 v6 Carb outboard after a seizure including:<br /><br />- changing 1 piston plus relining<br />- all new rings<br />- all new big-end bearings<br />- oil-pump drive gear<br /><br />The engine runs fine but is not reaching full revs (about 3-400 rpm down prior to rebuild). After checking the ignition timing and making a few other checks, the engine is still not producing full power and seems a little (only a little!) lumpy at idle. There is a "boggy" feeling to the pick-up ...<br /><br />I have tried to adjust the carbs following a procedure in the maintenance manual but I have found it difficult to detect misfire between the max and min mixture positions on each carb. I'm putting this down to the fact that the engine has 6 cylinders and a slight misfire on one pot being difficult to detect (for me at least).<br /><br />The only thing I could put the problem down to is fuel starvation but I don't know how to check for this.<br /><br />One further point (although this may be a red herring), we were ploughing through some bad weather the other day and the fuel line took a big gulp of air (after jumping a pretty big wave) which stopped the engine. We had to re-prime before starting the engine. This has never happened to us before. Could it be related to the above problem?<br /><br />Anyway, please, please, please can anyone suggest anything?????<br /><br />Cheers from the Isle of Man.

 

[KCLOST]

Re: Mercury 200 Carb - under power

Have you "broke-in" the engine properly yet?

 

[alessandro@manx.net]

Re: Mercury 200 Carb - under power

Yeah, sorry, I forgot to mention ... I've run the engine in for about 15 hours. 5 hours with rich oil mixture.<br /><br />I have about 30 hours on the engine now.<br /><br /><br />

Originally posted by KCLOST:<br /> Have you "broke-in" the engine properly yet?

 

[KCLOST]

Re: Mercury 200 Carb - under power

What is the compression on each cylinder?

 

[alessandro@manx.net]

Re: Mercury 200 Carb - under power

I can remember the exact figures but well within spec and up from pre-seizure reading.<br /><br /><br />

Originally posted by KCLOST:<br /> What is the compression on each cylinder?

 

[KCLOST]

Re: Mercury 200 Carb - under power

Well, to eliminate the fuel starvation issue on the current tank, line, bulb and filter....<br />Run the engine on a remote tank with a new line/bulb and filter... That will determine or eliminate those from the starvation issue...<br /><br />I would also test the spark on each cylinder...While cranking... Look for a weak spark condition on any of the leads...<br />This could be electrical... a 400rpms loss is somewhat consistent with a possible loss of fire on one cylinder..

 

[alessandro@manx.net]

Re: Mercury 200 Carb - under power

I'll try that thank you.<br /><br />What does a weak sparl look like though?<br />I already checked that all cylinders were sparking but I didn't look for differences in the spark.<br /><br /><br />

Originally posted by KCLOST:<br /> Well, to eliminate the fuel starvation issue on the current tank, line, bulb and filter....<br />Run the engine on a remote tank with a new line/bulb and filter... That will determine or eliminate those from the starvation issue...<br /><br />I would also test the spark on each cylinder...While cranking... Look for a weak spark condition on any of the leads...<br />This could be electrical... a 400rpms loss is somewhat consistent with a possible loss of fire on one cylinder..

 

[KCLOST]

Re: Mercury 200 Carb - under power

If all the sparks look the same or close, you should be ok....Test the fuel first...<br /><br />Let us know!!!<br /><br />I'm sure someone else will forward some other suggestions... I'm hoping it's something simple... But with the rebuild comming into play, you never know????

 

[alessandro@manx.net]

Re: Mercury 200 Carb - under power

Excellent, cheers fella. I'll be trying this at the weekend and will let you know.<br /><br />Your comment about the rebuild worries me, what could I have done wrong? if there was anything serious it would have blown up by now surely?

 

[LubeDude]

Re: Mercury 200 Carb - under power

Did you ever find why it seized a piston to begin with?? Maybe you still have a lean condition in that cylinder. Did you go through the carbs before you started it again.

 

[KCLOST]

Re: Mercury 200 Carb - under power

A 400 rpm loss makes me wonder if you are loosing power from one cylinder.....<br />It could be fuel related, spark related, etc...<br /><br />But let's start with the basics to eliminate them...<br />If you think you have a fuel starvation issue, let's eliminate or identify it... If it's possibly electrical, target that....<br /><br />But Lube has a great point!!!! What was the previous culprit of the failure... A lean carb is a good possibility..<br /><br />And I appologize for not asking this earlier....

 

[alessandro@manx.net]

Re: Mercury 200 Carb - under power

KCLOST/Lube,<br /><br />The failure was due to a blocked oil line between the main oil tank and the header tank ... ie the engine ran dry. Unfortunately the alarm didn't sound (that problem has also been fixed now).<br /><br />I have been through the carb tune up procedure and have checked the reed-valves although I'm not convinced that I did the best job tuning the carbs.<br /><br />Cheers for all your help guys.