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Author Topic:   Yamaha OX66 rough running

onlyawhaler posted 04-19-2008 08:30 PM ET (US)
I have a 2000 Yamaha OX66 that runs great at idle and the mid to upper end range just great
It however has a real rough spot about 1500-1700 rpms that I feel as I try to troll faster or get out of the harbor at slightly above wakeless speed or when I get up on plane. Once through this spot, it takes off just fine.
Is this charastic of this technology or has anyone with this vintage of Yamaha experienced this rough running spot in the RPM range?
Thanks
Onlyawhaler
TransAm posted 04-19-2008 08:38 PM ET (US)
I have owned several pair of v6 yamaha's of this vintage, both carb's and EFI. This is not normal as these engines should run and accelerate smooth through the RPM range. Many possibilities from O2 sensor to fuel delivery however I am not a mechanic so, unfortunately, cannot be more specific as to the cause.
timing posted 04-19-2008 11:19 PM ET (US)
Which horsepower / engine displacement OX66 do you have?
onlyawhaler posted 04-20-2008 07:49 PM ET (US)
It is a 2000 year model, 225hp.
I had read on another website that the 225 OX66 has the ability to drop off two cylinders from firing at low RPM speeds and that may be the rough running spot in the RPM range. It is, according to that article essential a V-4 until the RPMS reach a certain point and then the other two cylinders kick in and the smooth running comes back.
Has anyone heard of the dropping of two firing cylinders and rough running at 15-1800 rpms on a larger OX66?
I have called our local Yamaha dealer 40 miles north of us and he doesn't have any idea. He is newer and only has experience with 4 strokes and I am not confident in taking it in there.
Onlyawhaler
seabob4 posted 04-20-2008 08:48 PM ET (US)
Call Homosassa Marine at 352-628-2991, and ask for Vito. He was Yamahas OEM guy since as long as I can remember. He's now their service manager. He WILL know! I was hanging Yamahas back then and never heard of a shut down of 2 cylinders at low RPM, but I could be wrong. Give him a call.
timing posted 04-20-2008 10:48 PM ET (US)
Saltwater Series II big block (3130cc) OX66's have Yamaha's CCS (Controlled Combustion System). It drops up to 2 cylinders between 500 and 2000 RPM, resulting in a best case fuel savings of 36%.
I had a year 2000 250HP big block on my prior boat.
That big block was a solid work horse.
Did an admirable job pushing a 25 foot walkaround.
However, I do recall a slight out of balance feeling
in a couple of RPM ranges. I can't say if the balance condition was due to the CCS cylinder drop, or just
the nature of the big block's harmonics.
The small block OX66 on my current Outrage 21 is overall slightly smoother. I wouldn't hesitate at buying another boat with either engine. Oh and one more thing I recall on the big block regarding balance, I tried Penzoil full synthetic 2-stroke oil, and once in a while had a temporary rough idle right after warm start, went back to Yamalube and it eliminated that issue.
Peter posted 04-22-2008 09:08 AM ET (US)
I had a 2000 Yamaha Ox66 225. The Ox66 is programmed to run on 5 cylinders from idle to about 850 RPM, then on 4 cylinders from 850 RPM to approximately 2000 +/- 100 RPM (not sure exactly where the break point is) and then on all 6 cylinders above that.
On that motor, it is important to use the Yamaha RingFree or equivalent product in the gas to keep the O2 sensor clean. A dirty O2 sensor will cause the motor to run rough and foul plugs.
This V6 motor has an unusual angle of 76 degrees between the banks so it does seem to have some sound harmonics at certain engine speeds that I have not heard in either the 60 degree or 90 degree motors.

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Author	Topic: Yamaha OX66 rough running
onlyawhaler	posted 04-19-2008 08:30 PM ET (US) I have a 2000 Yamaha OX66 that runs great at idle and the mid to upper end range just great It however has a real rough spot about 1500-1700 rpms that I feel as I try to troll faster or get out of the harbor at slightly above wakeless speed or when I get up on plane. Once through this spot, it takes off just fine. Is this charastic of this technology or has anyone with this vintage of Yamaha experienced this rough running spot in the RPM range? Thanks Onlyawhaler
TransAm	posted 04-19-2008 08:38 PM ET (US) I have owned several pair of v6 yamaha's of this vintage, both carb's and EFI. This is not normal as these engines should run and accelerate smooth through the RPM range. Many possibilities from O2 sensor to fuel delivery however I am not a mechanic so, unfortunately, cannot be more specific as to the cause.
timing	posted 04-19-2008 11:19 PM ET (US) Which horsepower / engine displacement OX66 do you have?
onlyawhaler	posted 04-20-2008 07:49 PM ET (US) It is a 2000 year model, 225hp. I had read on another website that the 225 OX66 has the ability to drop off two cylinders from firing at low RPM speeds and that may be the rough running spot in the RPM range. It is, according to that article essential a V-4 until the RPMS reach a certain point and then the other two cylinders kick in and the smooth running comes back. Has anyone heard of the dropping of two firing cylinders and rough running at 15-1800 rpms on a larger OX66? I have called our local Yamaha dealer 40 miles north of us and he doesn't have any idea. He is newer and only has experience with 4 strokes and I am not confident in taking it in there. Onlyawhaler
seabob4	posted 04-20-2008 08:48 PM ET (US) Call Homosassa Marine at 352-628-2991, and ask for Vito. He was Yamahas OEM guy since as long as I can remember. He's now their service manager. He WILL know! I was hanging Yamahas back then and never heard of a shut down of 2 cylinders at low RPM, but I could be wrong. Give him a call.
timing	posted 04-20-2008 10:48 PM ET (US) Saltwater Series II big block (3130cc) OX66's have Yamaha's CCS (Controlled Combustion System). It drops up to 2 cylinders between 500 and 2000 RPM, resulting in a best case fuel savings of 36%. I had a year 2000 250HP big block on my prior boat. That big block was a solid work horse. Did an admirable job pushing a 25 foot walkaround. However, I do recall a slight out of balance feeling in a couple of RPM ranges. I can't say if the balance condition was due to the CCS cylinder drop, or just the nature of the big block's harmonics. The small block OX66 on my current Outrage 21 is overall slightly smoother. I wouldn't hesitate at buying another boat with either engine. Oh and one more thing I recall on the big block regarding balance, I tried Penzoil full synthetic 2-stroke oil, and once in a while had a temporary rough idle right after warm start, went back to Yamalube and it eliminated that issue.
Peter	posted 04-22-2008 09:08 AM ET (US) I had a 2000 Yamaha Ox66 225. The Ox66 is programmed to run on 5 cylinders from idle to about 850 RPM, then on 4 cylinders from 850 RPM to approximately 2000 +/- 100 RPM (not sure exactly where the break point is) and then on all 6 cylinders above that. On that motor, it is important to use the Yamaha RingFree or equivalent product in the gas to keep the O2 sensor clean. A dirty O2 sensor will cause the motor to run rough and foul plugs. This V6 motor has an unusual angle of 76 degrees between the banks so it does seem to have some sound harmonics at certain engine speeds that I have not heard in either the 60 degree or 90 degree motors.