Yamaha 200 carb 2 cylinders not firing

[windknotnc]

Ran the boat yesterday with a Yamaha 1999 200hp SWII carbed engine and the # 2 & #5 cylinders are not firing. My tach also stopped working. I rebuilt my carbs a couple months ago and all seemed fine when I cranked it after this. Today it cranked and idled fine just would not turn up nor plane the boat. Not real sure what the connection to the tach is. Tach is new and has worked fine until today. Any help appreciated.

 

[DaleH]

I wouldn't run it, but would get it checked out pronto. VERY odd a differen location cylinder on each bank isn't firing, which that and the tach, leads me to believe it could be your stator. With motor off, look under the flywheel, if you see black gop dripping down around the wirngs, that's not good.

Also please tell me you do not have wing nuts on your battery cable connections, as loose connectors cause intermittant issue you won't notice, but that can kill the stator wiring. Also put a SS lock washer down on any battery post BEFORE adding the cable connections.

Stators run the high voltage windings that fire the coils and run the tach signal.

 

[windknotnc]

All battery cables are tight with nylon lock nuts...I definitely have no spark at all in #2 and #5. I just checked these out this afternoon.

 

[DaleH]

Have never seen 2 coils go together in my life ...

 

[windknotnc]

That is why I am wigged out. Is it possible the CDI unit could be causing this? All I see is this could get real expensive real quick. Obviously I am capable of replacing the parts, but trial and error at the price of even used parts is crazy. Anyone got any sure fire ways of diagnosing the problem?

 

[camron]

Yea that seems odd 2 at the same time maybe swap coils around and see if the problem follows them

 

[windknotnc]

I have already swapped coils and no change so it is obviously something that is not generating a spark to these 2 cylinders. I am hoping someone with much 2 stroke V6 Yamaha experience can tell me the connection between #2 and #5. The fact that the tach has quit also makes it interesting.

 

[camron]

Yea seems like an odd problem i would like to see what the issue is found this on another forum about no tach and 2+5 cyl no spark


http://forums.iboats.com/showthread.php?t=489066

 

[charlesretired]

Check out if this is one of the motors that when at low rpm the ignition system cuts out 2 cylinders for fuel savings as when trolling ?????????

 

[windknotnc]

That is only in the HPDI engines not the carbed ones. I have been told to look at the Crank Position Sensor. A piece of me wants to just take it to the shop, but the fear of $1000 in parts drives me nuts.

 

[DaleH]

I have been told to look at the Crank Position Sensor. A piece of me wants to just take it to the shop, but the fear of $1000 in parts drives me nuts.

In the article Camron posted it was the CPS at fault, taking out the EXACT cylinders (2 & 5) and tach. But even there, you could still end up throwing $$ at a symptom and not the real root cause problem. This is most likely one area where an experienced mechanic can be worth their weight in gold.

 

[windknotnc]

I read that post also and "Rodbolt" is a pretty sharp mechanic. Sadly he does not post on any sites anymore. I think he got blasted by either his employer or Yamaha for providing too much assistance. I have been temped to buy a CPS and putting it on to see if the problem is solved. My usual mechanic is 2 weeks out right now.

 

[windknotnc]

Problem solved...This is bizarre. My tech guy checked all electric components and all were fine. He disconnected the tach and the #2 & #5 started firing. Seems there is some sort of issue or back feed through the key switch and tach. He has never seen this before. I decided to replace the wiring harness and key switch with new stuff and hope that resolves all issues. Since I will be replacing the engine with a Yamaha in the future it is not a waste of money.