Yamaha outboard engine running poor

[bolger]

Hi,
I have a 19 year old Yamaha 140,V4 ,1.7 ltr.Autolube,outboard.It runs reasonably well when ideling up to 2000 rpm but inbetween 2000 & 6000 it runs slugish & jumps from 6000 to 2.5.Sometimes it will all of a sudden run right up to the max. of 7000 rpm & stays there, running perfectly until I take it back down again,all with the idle throttle of course.I've tried to run it at sea & it cruises fine up to 2-2.5 rpm but anything higher than that it dies a death.
I've cleaned both carbs,replacing the rubber rings ion the jets,sprayed plenty of carb cleaner in there,checked the fuel,oil,petrol filter ect.,new plugs.The oil sensor is faulty (overflows if stays connected at the tank) but I've tried disconecting it at the engine & there is no difference,so it's not the low oil level engine cut-out.Sometimes it will go to max. revs. on it's own & won't switch off with the key or by pulling the cut-out cord,it only goes back to normal when I switch on the choke switch next to the throttle.
Any suggestions for a cure are very welcome please.

All the best
Steve.

[Nos4r2]

Originally Posted by bolger

Hi,
I have a 19 year old Yamaha 140,V4 ,1.7 ltr.Autolube,outboard.It runs reasonably well when ideling up to 2000 rpm but inbetween 2000 & 6000 it runs slugish & jumps from 6000 to 2.5.Sometimes it will all of a sudden run right up to the max. of 7000 rpm & stays there, running perfectly until I take it back down again,all with the idle throttle of course.I've tried to run it at sea & it cruises fine up to 2-2.5 rpm but anything higher than that it dies a death.
I've cleaned both carbs,replacing the rubber rings ion the jets,sprayed plenty of carb cleaner in there,checked the fuel,oil,petrol filter ect.,new plugs.The oil sensor is faulty (overflows if stays connected at the tank) but I've tried disconecting it at the engine & there is no difference,so it's not the low oil level engine cut-out.Sometimes it will go to max. revs. on it's own & won't switch off with the key or by pulling the cut-out cord,it only goes back to normal when I switch on the choke switch next to the throttle.
Any suggestions for a cure are very welcome please.

All the best
Steve.

Not what you'll want to hear but it sounds like you've got more than one problem there so very hard to diagnose. Take it to a dealer. It needs workshop facilities.

[MikeCC]

Could be the CDI - some of those symptoms are very similar to the ones I had on a Yam 115 V6 and that was the cause.

[9D280]

Originally Posted by bolger

Hi,
when ideling up to 2000 rpm but inbetween 2000 & 6000 it runs slugish & jumps from 6000 to 2.5.Sometimes it will all of a sudden run right up to the max. of 7000 rpm & stays there, running perfectly until I take it back down again,all with the idle throttle of course.
Steve.

DON'T run in neutral at that speed or you'll be adding to your problems......

Sounds electrical if it jumps. I had a similar thing on mine at load that got progressivley worse, then found one of the spark plugs was well on its way to being short circuit. (Megger proved that). Mine's 2 cyl and so it was quite obvious what was happening as one was cutting in & out like it was on a random switch. Pulsing high voltage does some funny things with semi short circuits, and spark plugs don't last forever......

I'd check & clean all the electrical connections in the engine first - it's amazing what 20 years of salt air can do to a bullet connector. If that doesn't cure it then change the plugs, it should be a cheap test. If that doesn't work, I'll echo NoS' comment & say go to a dealer.

Incidentally, does it do the same afloat and under load? (i.e. in gear)