1991 40HEO problem

[vinko]

Hi there
I have 1991 Yamaha 40HP autolube HEO..runs nice but recently when at full throttle makes some weird noise
you can hear that in my video I recorded yesterday
thanks
https://www.youtube.com/watch?v=llEtrgBFnac

 

[racerone]

Run with a timing light to see if you can determine a miss on one of the sparkplug leads.--------Perhaps run with the cover off.

 

[[email protected]]

Might be overheating when running at high revs.Did it shut down when you slowed down? check waterpump impeller.

 

[vinko]

impeler new, sparks new....runs nice, my boat is a 15 feet and makes at WOT 32mph which I think is very nice
perhaps it's from overheating but I don't rev it too much over 3000rpm

 

[racerone]

? are you planning to run with a timing light to observe spark behaviour ?

 

[vinko]

can you explain it how to run with timing light?