97 Yamaha Saltwater Series 150 losing power

"My Yamaha seems to lose power

"My Yamaha seems to lose power on one cylinder intermintenly after reaching operating temp. It is a V6 and it is very noticeable with a quick drop in RPM. Strange part is it cuts in and out as you drive. Can last a few seconds or maybe minutes. This started after 1 year of ownership back in 1998. I have been to several mechanics who can't diagnose the problem. I have also replaced fuel filter, separator, pump, wires, bacically everything. Can anyone help? I'm at my wit's end."

have you replaced all the fuel

have you replaced all the fuel pumps? or at least ispected diaphrams there are at least two fuel pumps on that engine if so check pulser coil output what is your wide open throttle rpm ?this may sound strange you could have an exaust gasket leak allowing water into engine will notice on lower spark plug one will be cleaner have you tride putting a timming light to each spark plug wire while having this problem look at light watch for loss of spark ? isolate cylinder! ispect all plugs closely

I have checked the diaprams an

I have checked the diaprams and are OK. Wide open throttle is around 5200 rpm. I will try and isolate cylinder. Thanks for the advice. Does the rpm at wot seem right?

I forgot to tell you that at w

I forgot to tell you that at wot it drops from 5200 to around 4600 when the power loss happens. It is immediate like cutiing a light switch on and off.

does sound like you are droppi

does sound like you are dropping one cyl you need to find out what is missing at that moment sounds like spark check and clean grounds on all 6 coils check and clean all grounds make shure batt conn are good at both ends no wing nuts use nylock nut s/s with a timming light you will be able to see if you are loosing spark check white wire in pan this is you kill wire. unplug and run motor. caution engine will not shut off with wire diconnected. this eliminates problems in safty switch and ignition switch have you run with hood off? 5200 is good

Great suggestions! Have not r

Great suggestions! Have not run with hood off but have always suspected electrical because of suddeness when happens. It can cut in and out 2 or 3 times in 10 to 20 seconds sometimes. It seems to correct when I back off the throttle some and open up again. Will let you know what I find. Thanks

"Hey Guys, just purchased a bo

"Hey Guys, just purchased a boat with this same engine and having the same problem. Has 850 hours with gas that hasn't been used in months. Runs great in idle, however, once a throw it into gear it just won't go. No matter how much throttle I give it, it just bogs down. Is this due to old gas? The compression is perfect. Having it serviced tomorrow, will this fix the problem?
Thanks"

"My 150 yamaha engine has this

"My 150 yamaha engine has this same problem where it drops a cylinder when going into heavy seas or just waves. The engine is a yamaha 150 ox66 saltwater seriesII from 2000. When it was new 7 years ago it ran fine. Does anyone know how I can get yamaha diagnostic software? Please email me at [email protected] if you know."