mercury 200hp running on 2 cylindars only

mmaxey

Cadet
Joined
Aug 10, 2004
Messages
7
Hi, i have a 1978 mercury 200hp, it was just rebuilt before i bought the boat. <br />Here is what i have checked.<br />Stator, trigger coils, main coils, timing adjustment, carbs, compression.<br /><br />it only runs on #1 and #4 cylindars out of 6<br /><br />new reeds were just installed.<br />the carbs were just rebuilt at the marina.<br />it has new cdi ignition boxes. wiring is correct.<br /><br />spark is fantastic at all cylindars, jumps at least and inch, and is bright blue.<br /><br />i tried spraying gas into the cabs of the cylindars that were not firing and it did nothing.<br /><br />am at a loss of what can cause this since the spark, fuel and compression seem to check ok. 125lbs/cylindar when warm.<br /><br />have never had this much trouble fixing any motor before. please help if you can thanks
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: mercury 200hp running on 2 cylindars only

Why post this in a non-repair forum, MM??<br /><br />Moving to Merc Troubles.
 

DHPMARINE

Captain
Joined
Dec 16, 2003
Messages
3,688
Re: mercury 200hp running on 2 cylindars only

MM Motor ran okay when you got it?No work performed since?You say wiring is OK.Do the wires with the yellow band go to the same switchbox?<br />Also fuel sample good?<br />DHP
 

2springers26

Seaman
Joined
May 18, 2004
Messages
63
Re: mercury 200hp running on 2 cylindars only

Make sure the pistons are in correct... starboard & port.... it will not run if they are missmatched.... since it was just rebuilt!!!
 

mmaxey

Cadet
Joined
Aug 10, 2004
Messages
7
Re: mercury 200hp running on 2 cylindars only

yeah i know i didnt realize i was in the wrong catagory sorry.<br /><br />no the motor hasnt ran correctly since it has been rebuilt.<br /><br />i was thinking the same thing on the pistons so i will dissaseble it and check it this weekend.<br /><br />yes the blue/yel and red/yel wires are on the same switchbox.
 

mmaxey

Cadet
Joined
Aug 10, 2004
Messages
7
Re: mercury 200hp running on 2 cylindars only

i havent taken a fuel sample, but i just filled it up, it was empty when i got it.<br /><br />also i ran it off a mixed fuel gas can i had in the garage and it didnt change anything.
 

mmaxey

Cadet
Joined
Aug 10, 2004
Messages
7
Re: mercury 200hp running on 2 cylindars only

one question i did have is the seals in the crankcase, if they are bad could it cause this??
 

2springers26

Seaman
Joined
May 18, 2004
Messages
63
Re: mercury 200hp running on 2 cylindars only

bad seals... i don't think so.. seals would only effect #1 & 6.. because of the sealing rings.... just pull the heads to verify piston location... port & star are marked with a up & a p or s!!!
 

mmaxey

Cadet
Joined
Aug 10, 2004
Messages
7
Re: mercury 200hp running on 2 cylindars only

Ok thanks for the help fellas. I will check the pistons this weekend. I will let you know next week if thats it or not, but i bet thats it.<br />thanks again
 

mmaxey

Cadet
Joined
Aug 10, 2004
Messages
7
Re: mercury 200hp running on 2 cylindars only

yup thats it, running fine now. thanks for the help i appreciate it.
 
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