no fire on bottom cylinder

[MikeFaircloth]

My 90HP '02 Yamaha is not firing on the bottom cylinder. The spark plug is new. What should I check 1st, the ignition coil? Can the computer itself cause one cylinder to not fire? The motor cranks and runs with just the top two cylinders firing but obviously not very well.

Mike

[200090tlry]

How do you know

How does one check this with timing light?

[MikeFaircloth]

The motor starts and runs (poorly) with top two plugs connected but if I disconnect either of the top two it will not start. Also, fuel in the exhaust.

[200090tlry]

Well you should never run motor without having plug wires grounded

Never remove battery once motor is started. Even doing comp test you ground out plug wires to block while cranking. Maybe your cdi is fried from some feller messing around. I would also like to check spark but think best way is in water with running with test light maybe Rod will share his knowledge.

[jb123]

fuel in exhaust... have you checked low pressure pumps ?
you can swap coils see if issue "moves"

[99yam40]

Test spark with a spark tester to see if you have fire to bottom cylinder.

If you do have the proper spark then jb123 could be right with the fuel pump as that runs off of the bottom cylinder crankcaseand a leaking pump will flood #3

[200090tlry]

I had fuel in plastic carb cover

on bottom cyl, had to pour it out. I did replace the FP and checked it again and no fuel in cover. This is new motor to me so who knows how it got there. 2000 90hp

[99yam40]

on bottom cyl, had to pour it out. I did replace the FP and checked it again and no fuel in cover. This is new motor to me so who knows how it got there. 2000 90hp

200090tlry This thread was started by MikeFaircloth about not firing on the bottom cylinder. If you have a problem then start a thread on it, it is not proper and gets confusing if people start adding different questions to other peoples posts

[200090tlry]

My post was to show what might be wrong with his motor

He said he found fuel so must not be firing. I then posted how do you know for sure. Your right spark plug tester might be good check. Where can someone get one

[99yam40]

on bottom cyl, had to pour it out. I did replace the FP and checked it again and no fuel in cover. This is new motor to me so who knows how it got there. 2000 90hp

So what does this post have to do with his problem?

[200090tlry]

Lol

He assumes there is no spark without doing proper check. Just because he found fuel in the exhaust does not mean it's no fire situation. Do I have to spell it out lol.

[99yam40]

Maybe you need to spell it out, because stating you found fuel in a place that has nothing to do with the fuel pump,and have no idea how it got there,but replaced your fuel pump does not make any sense in my opinion and has nothing to do with his problem.

[ausnoelm]

gees, I am confused on this one, not too sure who has a problem, the oringinal poster or 200090, I'm with 99yam, spell out whatever you are trying to get across, also not sure where disconnecting the battery while running came from.