Carbon build up in 1 cylinder

[kapaafire]

First off I'd like to thank everyone on this forum. With your advice I've sucessfully got my 83' 115 hp evinrude up and running. Kids had a great time on the water.

Took it out the other day and it ran fine. However, I later checked the plugs and noticed that 1 plug had a lot of carbon build up compared to the others. Quite a bit of a difference.

What could be the cause of this? Just changed the head gaskets, deflectors, ignition coil, plugs, and water cover gaskets. The compression on this cylinder was 120 psi.

Could I continue to run it this way without any problems?

 

[OBJ]

Re: Carbon build up in 1 cylinder

Check your spark to that cylinder kapa. Should jump a 1/2" gap with a hot lighting like spark. If it dosen't, swap coils and check again. If the poor spark still remains, swap the power packs and see if the problem follows.

 

[reeldutch]

Re: Carbon build up in 1 cylinder

and you also might want to check the float level.
it could be running rich. float to high?

wich cylinder are we talking about?

is your fuel pump getting crankcase pulses from that cylinder?

 

[kapaafire]

Re: Carbon build up in 1 cylinder

OBJ,

I recently changed the coil to that cylinder. How would I test the spark gap? Would I remove the plug and crank the engine to see if spark present?

Reeldutch,

It is the lower starboard cylinder. Could the float level affect only that cylinder? Because there doesn't seem to be carbon build up in the other cylinders.

How do I check if the fuel pump is getting crankcase pulses from that cylinder?

Thanks guys in advance

 

[reeldutch]

Re: Carbon build up in 1 cylinder

the lower starboard cylinder is where the oil pump gets its pulses from.
if your fuel pump diaphrams are broken you could leak fuel into the crankcase and cause a rich condition only on that cylinder and create more carbon buildup.

its a regular fuel pump and it isnt so hard to check it out.

i dont think its the carb because i do think you have only 1 float serving 2 cylinders.
so that would have to be rich on both bottem cylinders.

good luck

 

[Walker]

Re: Carbon build up in 1 cylinder

Do a compression test. Which plug is carboned up??

 

[kapaafire]

Re: Carbon build up in 1 cylinder

The lower starboard plug is carboned up. Compression on that cylinder was 120. Others were 120, 110, and 95.

Reeldutch,

Thanks for the info, that could explain why only lower starboard plug carboned up. I will check fuel pump this week. Any suggestions on the best method to check diaphrams?

Thanks Again in advance

 

[reeldutch]

Re: Carbon build up in 1 cylinder

get the manual out and follow the instructions.
just take it apart and look for any cracks or damage.

i would get a rebuild kit or a new fuel pump if its bad.
the pumps are not so expensive.

 

[Walker]

Re: Carbon build up in 1 cylinder

Check the recirculation valves

 

[Dhadley]

Re: Carbon build up in 1 cylinder

On a crossflow I think the fuel pump pulse line is on #4 cylinder which is the bottom port cylinder. The bottom starboard cylinder is #3.

 

[flabum]

Re: Carbon build up in 1 cylinder

95#'s on the low cylinder...... that is beyond the 10% limit. sounds like the 120# cylinder is carrying most of the weight causing the carbon build up.