1987 mercury not firing on all cylinders

[mtjesse]

When I first start my boat it only fires on 2 of the 3 cylinders. Once its warmed up after about 15 minutes the third one kicks in. Ive checked the plug wires and coils and they are good. What should I check next? Any ideas what might be wrong?

 

[ONERCBOATER]

Re: 1987 mercury not firing on all cylinders

thinking you need to do a compression check on all three cylinders... and should provide a bit more info... such as HP of engine. and which of the two cyclinders are functioning and which isnt as you can learn alot by that info. since the 3rd one (is this the bottom one?) kicks in once warm i am leaning twards compression issue or fuel mix I assume you have more than one carb with 3 cylinders and that may be the issue as well... less likely I would think but that one may be running out of spec.. and until engine warm less likely to fire.
I would say do compression check cold, then warm... then we will have more info to work with

 

[BatDaddy1887]

Re: 1987 mercury not firing on all cylinders

...at the very least try a cup of Seafoam or Quickleen in the gas tank to help clean out the fuel delivery system, maybe check the fuel filter, or old hoses sucking air....it's a good start. Also, search the forum for the decarb instructions.

 

[mtjesse]

Re: 1987 mercury not firing on all cylinders

The engine is a 60hp. I have already used the seafoam and it worked great. Its the top cylinder that is not firing. Compression is about 130 on all three cylinders. After running the engine pulling a tube around the lake for 30 or 40 minutes it losses spark on that cylinder again. The next day same thing takes about 15 minutes before the top cylinder kicks in and then its good to go. I can troll around the lake all day at idle speed when fishing and engine runs mint.

 

[ONERCBOATER]

Re: 1987 mercury not firing on all cylinders

check your coils when hot.... or the issue occurs... they can test good when cool or warm... and fail on the other end of temp spectrum... also check all connections that you can... esp the ground cable... I have found that the simple act of cleaning connections when everything else checks fine can make gremlins disappear sometimes.

Sean

 

[mtjesse]

Re: 1987 mercury not firing on all cylinders

I have switched the coils around and still no spark on top cylinder. The wires are all in real good shape.

 

[ONERCBOATER]

Re: 1987 mercury not firing on all cylinders

maybe switch box?

 

[aussieflash]

Re: 1987 mercury not firing on all cylinders

Definitely check switch box output.

 

[mtjesse]

Re: 1987 mercury not firing on all cylinders

What exactaly does the swith box do and how do I check the out put.

 

[Coloradolakeboy]

Re: 1987 mercury not firing on all cylinders

Here are the tests you can do for your motor. Look at pages 80-81. Look at " No spark on any cylinder" and "No spark or intermittent spark on one or more cylinders" You will need a DVA, the diagnostics will tell you the condition of your power pack (switchbox), trigger and stator.

http://issuu.com/cdielectronics/doc...t.xml&backgroundColor=000000&showFlipBtn=true

 

[mtjesse]

Re: 1987 mercury not firing on all cylinders

Thanks to all that helped. I replaced the switchbox and boats running great.