Yamaha 150 TXRY not firing in 2 cylinders

[Williamalvin4]

I have a 2000 150hp TXRY Yamaha set up as twins. The port engine works great and will get up to 4000rpm without the starboard, but the starboard engine would not power up under load. I first thought it might be fuel, but wanted to eliminate spark. I took all the spark plugs out and checked them while the engine was cranking. I notice that the bottom right cylinder and top left cylinder were not firing. I though it was the coil packs since it was only 2 cylinders, but I bought 2 new ones and the cylinders are still not firing. I did all the continuity checks and I dont believe it is the stator since it is only 2 cylinders. I am going to swap CDI boxes from the other motor to see if it will fire, but dont know why only 2 would not be hitting. Also dont know if this is a safety feature that is locked out since it is 2 opposite cylinders. Does anyone have any advice?

[99yam40]

when you say they are not firing, does that mean they do not get spark or is there spark but the cylinders are not igniting the fuel in the cylinders(firing) to produce power.

It is easy to check voltage output of the CDI at different RPMs to see if it meets spec, but you do need to use the proper test equipment.
Even a timing light should tell you if it is getting spark.

Most motor problems are fuel related but there are simple ways to test compression,spark, and timing to make sure all of that is good and then chase the fuel problem

[rodbolt17]

port bank,top to bottom, numbered 2,4 and 6.
stbd side,top to bottom, numbered1,3 and 6.
which are you missing.
we dont use left and right on engines.

[99yam40]

port bank,top to bottom, numbered 2,4 and 6.
stbd side,top to bottom, numbered1,3 and 6.
which are you missing.
we dont use left and right on engines.

you have too many #6s Rod

But I am sure he can figure out the odd and even part

[Williamalvin4]

Yeah the #2 and # 5 cylinder are not getting spark. Weird I took the cdi off the good motor and put it on the bad motor same cylinders were not getting spark. Then I put the cdi from the bad motor on the good motor. I got spark out of # 5 cylinder , but not # . Cdi could clear up #5 issue but not #2.

[rodbolt17]

you really really wanna know why its not a CDI issue?
cause its a crank position sensor issue.
cylinders 1and 4 fire from a pulser.
cylinders 1 and 6 fire from the other.
cylinders 2 and five are made up by the CPS signal.
carefully test the sensor output and air gap.
make sure the sensor face is clean. test the wiring back to the CDI.
quit parts swapping before you have technician induced failures.

[Williamalvin4]

Rod,
I do appreciate all the help. I will be testing the CPS, but this is the crank position sender or is it sensor. Just want to make sure there is no sensor that I am not seeing. You say "carefully" test. Is there specifically something to look out for?

[99yam40]

Are you using your Yamaha service manual for any of this troubleshooting?
It should have the steps and specs.
And tell you what equipment to use, along with what wires to hook to.

well worth the price to save time and frustration

[rodbolt17]

the CPS is that little two wire dohickey thangy on the std top of the block about .020" from the flywheel teeth.
bad sensor OR poor connections OR dirty sensor can dump two cylinders that just happen to be 2 and 5.
need a peak reading type meter to correctly test voltage output.

[Williamalvin4]

Thank You

I appreciate it guys. Replaced the CPS and both cylinders are firing. This is a great thing you guys do on here.