Yamaha Outboard Only Two of Six are Firing

MKIV Surfer

Cadet
Joined
Apr 30, 2010
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I have came quite a long way since this thread:

http://forums.iboats.com/showthread.php?t=424302

Motor: 1986
Make: Yamaha 200HP

And was finally in the position to crank the motors last weekend. I searched the forum and could not find anybody that had the same problem that I am have. If you want the background, you can read the link above, but one of the motors ran fine (except needs a new water pump), and the other motor (the vandalized one), only the middle two cylinders are firing. The top two and bottom two cylinders are not firing (but suprisingly idles). Which led me to believe that it was a carbarator issue since each carb feeds two cylinders. And it would have made since that the top two and bottom two didn't work due to dirty carbs.

As it was running I shot carb cleaner in there and still nothing. So I took the top carb off and that thing seriously looked brand new, so I am beginning to think it is not the carbs. I checked the spark plugs while it was running to see if I am getting a spark and I was getting a spark in all of those cylinders from the plugs. So I am thinking that it might not be the spark plugs (I am going to replace them anyway just to make sure that the spark might just not be strong enough to ignite).

So now I am kind of at a loss here, don't know which step to take next. I am going to make sure the fuel pumps are OK. The only thing that is leading me to thinking that it might be the fuel pumps is that when I took the top carb off it was BONE DRY (and I took the carb off right after running the engine). So that is leading me to believe that either there is something in the fuel line blocking it from getting fuel, or the pump is bad (probably hasn't ever been changed).

I wanted to get any imput from you guys of what you might think it is or have any other suggestions. Thanks!
 
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