2008 Yamaha 90 4 stroke running rough down on power

[crb478]

I just picked up an new boat with a 90hp Yamaha and took it out for the first time today. I left the ramp and got on plane and it was running great. I went through a no wake zone and got back on plane no problem. Went about 3 mile or so, turned around and went back through the no wake zone. I got back up on plane and it started running rough like it was dropping a cylinder or two. I nursed it back to my dock and made it there. I took the plugs out, which looked fine and cleaned them but it still ran rough and cut off. I then got a portable can of fresh gas with no change. I took the plugs out again and the top two were black, the bottom two looked fine. I got new plugs and no change. Tomorrow I plan to use an inductive timing light to see if I as getting spark to all cylinders, after that I am at a loss. Any ideas or help would be appreciated. The motor only has 42 hours on it. Luckily it is still under warrantee but I will have to find a Yamaha dealer if it gets that far. Thanks for any suggestions.

 

[Capt Ken]

Re: 2008 Yamaha 90 4 stroke running rough down on power

Ethanol fuel or non ethanol?

 

[crb478]

Re: 2008 Yamaha 90 4 stroke running rough down on power

Fresh fuel had ethanol in it, old fuel may have also and it was treated. Motor has run on ethanol mixed fuel since new and did fine. I don't know if this is a fuel delivery problem or if it is a spark problem yet. Ran great until it lost power, now it will barely idle, with the idle lever pulled up it will run at a higher rpm but still rough. Occasionally it will rev up towards wot but will then start running rough agan.

 

[crb478]

Re: 2008 Yamaha 90 4 stroke running rough down on power

Ok tried it out today and I have spark on all four, all inline filters look clean and blew the top one out, same result runs ruff then cuts off. There is fuel getting to the fuel line and to the fuel rail. I turned the motor over until the two arrows on top were pointed toward each other and the tdc mark on the front of the motor lined up. The TDC mark on the back was two teeth off from the rear arrow, but I have no idea if it is supposed to line up. At this point I have to believe that it might be something like injectors. Does anyone have any ideas before I take it to a Yamaha dealer? Will probably do that tomorrow if there is nothing else to look for, if I can get it in.

 

[esmatko]

Re: 2008 Yamaha 90 4 stroke running rough down on power

My 2008 75hp Yamaha had the same issue. When throttling down the engine would stall. Brought to a Yamaha dealer. Issue was bad TPS and IAC. I am by no means a mechanic but this seems to have been my issue.

 

[99yam40]

Re: 2008 Yamaha 90 4 stroke running rough down on power

Monitoring fuel pressure will tell you if there is a restriction.
If under warranty have it looked at, but if it is fuel contamination they probably not cover it

 

[crb478]

Re: 2008 Yamaha 90 4 stroke running rough down on power

Thanks 99yam40

To update the post, I took all the injectors out and sprayed card cleaner through them. Put them back in and fired the motor up on a fresh gas tank. I pulled the injectors again and sent them off to be professionally cleaned. Should be good to go when I get them back. It would run with just cleaning them, but I as sure that sooner rather than later they would clog again so I sent them out.