yamaha dies when bottom plug wire is removed

[twc033]

my 40 hp yamaha will run with the top plug wire removed, but it dies immediately when the bottom plug wire is removed. is this normal. any problems to look for.

 

[jim dozier]

Re: yamaha dies when bottom plug wire is removed

This indicates that the top cylinder isn't pulling its weight and has a problem. Check spark and fuel for that cylinder.

 

[twc033]

Re: yamaha dies when bottom plug wire is removed

if i pull the bottom plug wire and ground it to the block the top cylinder will run. if i pull the top plug wire i do not have to ground it for the bottom cylinder to keep running. it this the way it is supposed to operate. it is a 1995 yahama c40.

 

[rodbolt]

Re: yamaha dies when bottom plug wire is removed

Hello<br /> I believe that ign is a waste spark type. as with most it was not designed to operate with one plug wire off. why are you pulling plug wires? do you suspect a problem or are you trying to create one? when you pull a plug wire the secondary ign voltage will instanly try to spike aboive 30kv. sometimes it can actually arc through a coil or plug wire or try to burn the coil primarys. better to use a spark tester. but from your description it ispossible that you have a weak ign and need to check it further. good luck and keep posting

 

[mrn714]

Re: yamaha dies when bottom plug wire is removed

Agree with rod, why are you trying to create a problem. The question is not why will it not work, it is why are you trying it in the first place. You got a starting, running, power or other problems?<br /><br />

 

[twc033]

Re: yamaha dies when bottom plug wire is removed

thanks for the info guys. i didn't not know this could cause so much damage. just got this boat and motor and was trying to see if both cyliners were firing ok. pulled the top wire at first and realized that it did not make a difference in the running of the motor. top carb float was stuck. i thought that when i pulled the bottom wire and motor died, that the top cylinder was still not right, but motor seems to be running ok. i read another posting on here were someone was checking out a 1996 yamaha 40 to buy, and a gentleman told the man to check each cylinder by pulling each wire and shorting it to ground. so i tried it and it kept the top cylinder running. thought i was a doing right. and i am still wondering do i have a problem.