rough idle

[luisdiaz]

Hi. Trying to help a friend with a Yamaha E75BMHD, 2006. It has a rough idle. When the spark plug of the bottom cylinder is taken out, the motor keep running the same. Unlike when the same thing is made with the other two sparks (get lot worst). It was made with a spark tester. The ignition is firing to the three sparks. The carburetor of the bottom cylinder was taken out and cleaned. Water and dirt was found on it as in the fuel tank. (They just bought this used boat). This boat was left like 5 months in the in salt water by the previous owner. We could not measure the pressure at this point.
Is it true that this motors has a sensor that will disable one of the cylinders, under certain circumstances?
Any remarks pinpointing possible work that will have to be done will be greatly appreciated.
Thanks

 

[Yamajoe]

Re: rough idle

Start with a removing all carbs and clean ( many posts here about carb cleaning). remove the tank, empty and clean, check ad clean the fuel pick up screens, install new water separator/filter. You have had water in the system which needs to be removed otherwise no amount of carb cleaning, electrical or timing work you do on this thing will solve the problem. Good time to get yourself a manual too.

 

[mnydvr]

Re: rough idle

I am under the assumtion from the amount of post relating to the same basic issue that this is a "common" problem?I have rebuilt the carbs myself and even had a dealer go through them again,it seems we have all done the same things to no avail.What is the fix?what do I tell my customer at this point?I'm starting to load up on labor and I don't blame him for wondering.

 

[luisdiaz]

Re: rough idle

Will let the friends know. Sure they will get a pressure reading tomorrow. If they get a low reading, I think they should take her to a pro. mech.
Thanks a lot

 

[luisdiaz]

Re: rough idle

You were right Yamajoe. Cleaning the carburetorss did make her to behave well. They need to do the fuel tank job.
Thanks for your post.
Luis.

 

[luisdiaz]

Re: rough idle

Forgot to say that pressure between cylinders was fine. Also to troubleshoot the problem, top and bottom carbs. were exchanged. This switch the symptom from bottom to top. For your info.

 

[mnydvr]

Re: rough idle

I don't have the carbs in front of me ,how involved is the linkage swap to switch them?

 

[luisdiaz]

Re: rough idle

To keep it simple, the choke link between carbs. was not connected. Did it manually. The throttle link, no big deal. Once the motor was on the spark plug from top and bottom cylinder was taken out (one at the time) the symptom switch cylinder, cause confirmed. I know it is been said by tons of people that taking the spark plug and starting the motor could kill the power pack if the spark has no way to discharge. But did see them doing it couple of times with the motor on and power pack still good. For my own pocket safety, I would not do it.
If need a picture let me know
Luis.