2003 Yamaha 90 HP 4 stroke missing #2 cyl

[Robert63]

Hi I am having trouble with my 2003 Yamaha 90 HP 4 stroke missing #2 cyl I swapped out coils problem stayed on #2 I used a timing light on all 4 cylinders all are firing except #2 it is interment I also changed out plug and wire on # 2 still same problem can anyone help me thanks in advance.

[rodbolt17]

make sure the coil ground is good.
make sure the plug is not fouled.
that is a waste spark system.
anytime #1 fires so does #4.
same with 2&3, anytime 2 or 3 fires the other does as well.

[Robert63]

I am confused if 2 and 3 fire at the same time wouldn't my timing light show a miss on both and I swapped both coils so if it were a bad ground wouldn't it follow the coil to 1 or 4 I did not remove the grounds when swapping thanks again

[rodbolt17]

its called a "waste spark" system.
both 1 and 4 are always at TDC at the same time.
one is on a compression stroke and the other is on an ex stroke.
same with 1 and 3, they always hit TDC at the same time.
typically if you lose spark on 2 you lost it on 3.
same for 1&4.

[boscoe99]

I am confused if 2 and 3 fire at the same time wouldn't my timing light show a miss on both and I swapped both coils so if it were a bad ground wouldn't it follow the coil to 1 or 4 I did not remove the grounds when swapping thanks again

Clean the grounds. Grounds cause many big troubles and almost always over looked.

https://www.google.com/search?q=wast...DWbM4uivhYM%3A

https://www.google.com/search?q=wast...QsXrlpoHsrM%3A

[Robert63]

Hi again thanks for the advice I checked all the grounds took all plastic covers off all grounds are spotless I also cleaned the battery terminals this is a fresh water boat and looks like it came out of a showroom and I was wrong it is skipping on 1 and 2 any help is appreciated

[TownsendsFJR1300]

Did you physically pull the grounds off, inspect/clean re-tighten (NOT just look at it)?

[Robert63]

Yes all grounds removed and cleaned with wire brush there was nothing to clean but did it anyway I was hopping for a bad ground

[rodbolt17]

how are you doing this "spark" test?

while it is possible to lose 1 cyl on a waste spark system, it is very rare.
which is why under normal operation if you remove a plug wire and do not allow it to ground(spark) you lose both sparks.
two cylinders.

[Robert63]

I am using a timing light while it is running on each cylinder and you can see 1 and 2 missing 3 and 4 flash constant I do not remove the wires wile it is running I also replaced # 2 wire and plug and it made no differance

[rodbolt17]

your not understanding.
and your not testing it correctly.
if #1 fires SO DOES #4.
if #2 fires SO DOES #3.
that is why the CDI only has two outputs.
on for coil 1&4 and the other for coil 2&3.

make a homemade spark tester,make the gap 1/2-7/16ths.
google it if nessasary.
then you MUST test 1&4 and 2 &3 simultaneously.

an over rich OR lean fuel mix can put out the flame rendering the timing lamp test useless.

a Kv tester would show the same results.

my guess is your chasing a ghost and it is not spark related but fuel related.

[Robert63]

Thank you now I have to check my carbs and they were rebuilt by a yamaha dealer and charged 1400 nice I am glad you are steering me in the right direction I appreciate all your help Thank you.

[rodbolt17]

correctly test the spark.
correctly test that the cylinder can seal.
then fight fuel.