Another OX66 issue

[TimC2520]

1999 S225TXRX

Thanks to many on this site, I was able to get her running pretty smoothly second half of last year. Swapped out the O2 sensor, vst filter, 3 low pressure fuel pumps and she ran as good as new. March 2008 did the t-stats and PCV valve.
I have about 50-60 hours on her since all of those things were done and she ran great all year...until yesterday. Grrrrrrrrrrr

Took the new wifey down to AC by boat and ran 4200 rpms the whole ride down..ran like a champ. Throttled around at an in-gear idle for awhile (30-45 minutes) through the different areas behind AC and all went well. Went to throttle up and she sounded like hell! Really rough, coughing, stalling, shaking excessively, like a fouled plug but 10x worse....
Pulled out of the channel, anchored and checked plugs..they were fine.
Checked water separator under the cowling, figuring if water got that far into the engine, it'd probably be visible under there instead of unscrewing and dumping the Yam big blue I have in-line.

The filter under the cowling looked fine. Put the plugs back in, started her up and still sounded bad...real bad. I kicked her in the butt, she coughed hard, darned near stalled again, shaked really bad then poof, hit 4200 RPM's and ran that # the whole ride home.. Sounded normal the rest of the day.

I did noticed 4500-4700 rpm's is the max I can get now but never really paid attention to what the max rpm's used to be ? ? ?
I'm spinning the original prop that came with the boat, 10 years ago, 15X17 Stainless, had it re-conditioned a year ago....still in great shape.
I ordered the TPS sensor from Andy at SIM and will check that this weekend. I am also considering decarb with Seafoam by filling the water sep filter 3/4 full and the rest with gas, putting that back on and proceeding with the de-carb procedure. Any suggestions ? I have never checked the TPS and the engine has never been de-carbed. Hours are 525+-. The engine has seen ring free from day 1, new...10 years.

Thanks,
Tim

 

[DaleH]

I did noticed 4500-4700 rpm's is the max I can get now but never really paid attention to what the max rpm's used to be ? ? ? I'm spinning the original prop that came with the boat, 10 years ago, 15X17 Stainless, had it re-conditioned a year ago....still in great shape.

You need to solve the motor issue first, but you seem to be WAY over-propped, which could be lugging the motor big-time. Yummiehas run best when propped to run within 200-300 RPMs off the MAX of the RPM range.

Sounds like your carbs need a rebuild, happened to a friend's similar vintage 175hp this year. I drained the bowls and then did a Seafom treatment via the pony or aux tank method, and while it made it better, he had to get the carbs cleaned out.

I am also considering decarb with Seafoam by filling the water sep filter 3/4 full and the rest with gas, putting that back on and proceeding with the de-carb procedure. Any suggestions?

I would NEVER do that! Motors run on fuel - NOT additives! I am not sure whomever first came up with that idea, but I think it is foolish at best. You're taking an engine running on an oil-injected FUEL mix and then slamming a large dose of a petroleum-based additive into it :shock: ?? The horror ...

Using the aux tank method ensures Seafoam is going through the inlet manifold and all small orifices in the carbs, but ... it ain't foolproof.

 

[TimC2520]

Hi Dale,

This engine is EFI, no carbs. I'll do the Seafoam this weekend off the aux tank idea and see what happens, although when I left yesterday, she seemed to be running fine.

Which props are you guys running on this 225 Yam attached to a 2520 MVSC ?

Tim

 

[cbigma]

Tim,

Deja Vu. I have the exact same model engine with loss of top-end RPMs dating back to 2005. It was so dramatic from one season to another that I thought my throttle cable had stretched!! :shock:

Is Cable Stretch Possible?

Tried everything, including the TPS. Had the YamaTech work on it for a couple of days. Their final response was that 4900 RPMs is still "In Spec". Lower end, but "In the range".

Have O2 and Decarb done annually. Still wearing the OEM 15X17 Stainless which is in excellent shape. Aside from the loss of top-end, she is bullet-proof. Always there and nary a sputter. I usually cruise at 4200 and rarely burst up to 4900.

Anyone else out there with a late 90's - early 00's OX66 that has lost top-end? :?:

 

[TimC2520]

I trimmed it up as far as it would go at those high RPM's and was able to hit 4800 area. Where I fish, along with the 14 degree hull, no wake zones and the ocean less than 10 minutes away, it's not often I can run 4200 for very long anyways....Usually 10 minutes or less then have to throttle back for a no wake zone or a 2-3 foot chop in the ocean so these rpms are fine for me.
Being able to run the 4200 for 30+- minutes on the trip to AC was nice though. The engine has never been decarbed, now having 525 hours on it. Maybe running it harder than I normally do for longer than usual loosened up some carbon somewhere inside. I am going to run the de-carb this weekend and I also ordered a TPS harness and O2 harness from Andy at SIM. The O2 was replaced 50 or so hours ago, the TPS has never been serviced. The boat ran fine after that slight hiccup so I'm hoping it was nothing serious. The vst was also changed 50 or so hours ago.

 

[Megabyte]

Throttled around at an in-gear idle for awhile (30-45 minutes) through the different areas behind AC and all went well.

Do you recall what engine rpm's you were turning at idle and in gear?

My 1997 225 OX66 runs at about 600 in gear, and at idle.
BUT... if I try doing that for too long, I will get an overheat alarm - a fact I discovered back when I bought the boat.

My dealer told me they like to see 700 to 800 rpms, because lower than that, they said that big block OX66's do not pump enough water to cool properly. Don't know about that as I've got 4 additional seasons on her now with 2 sets of water pumps, t-stats, poppits, and new fuel pumps cycled through her since that issue occurred.

My habit these days is to always limit my idle/in-gear time around the docks, and I try to stay at a minimum of 800 rpm if I'm sightseeing or transiting a no-wake area.

This March, with a fresh tune-up, cool water, full of fuel, and a clean bottom, my boat ran 35 kts @ 5300 rpm WOT.
Today, she will run 5000 rpm @ 32.7 kts WOT, full of fuel and with a 'summer bottom'.

My motor is wearing a 17p Mirage plus prop that I bought used, and might have been tweeked by the previous owner, so I'm not certain she is a box stock 17p.

Hope some of this helps.

 

[TimC2520]

Kevin,

She has always idled in gear or neutral somewhere in the area of 600-800.

Somedays 600, somedays 800 so those would have been the rpms while we crawled around the bay behind AC. I never did hear any alarms going off so I didn't bother to look at the gauge which I believe would visually show a temp problem. I would think there would also be an audible alarm, no? If not, I guess it could have been the problem, will never know unless it happens again.

 

[DaleH]

I would think there would also be an audible alarm, no?

Do you hear the audible alarm being sounded/tested when you first go to turn the ignition on?

FWIW here's how you can test the audible alarm circuitry for an overheat alarm yourself ...

* Key off
* On top of each powerhead, find the pull-apart connector that had a lead coming out of the head
* On Yummies this is a pink wire, it is tan on most other OB makes
* Pull aprt connector carefully
* Take 6" piece of odd 16awg or so wire, stripped on each end
* Insert one end into the connector side AWAY from or not now connected to the block
* Turn ignition on to RUN, but do not crank/start the motor
* Touch other end of short wire to the block, grounding it out
* Your audible alarm should sound

 

[TimC2520]

I would think there would also be an audible alarm, no?

Do you hear the audible alarm being sounded/tested when you first go to turn the ignition on?


You know, I bought the boat new and the alarm has never sounded when I first turn the key on. I always wondered why because I assumed most do sound an alarm with the key just to let you know it's working. I never did get around to asking the dealer why it doesn't. I guess if that's the case, I'll just get a "throttle back" during an incident, without a warning buzzer.

Maybe it did over heat. There is an "icon" for temp on the gauge, but I do not know what or how it shows an overheat incident. As I mentioned, I never thought to look at the gauge when this happened. I have fouled a plug or two over the years with this engine, but it never behaved like that before.

I installed the poppit valve and thermos myself back in March. I'm sure if it was something I did wrong I would have found out about it sooner so I'm pretty sure that's not it. I'm assuming if it did overheat, the rpms would just drop below a certain spot but would it also run extremely rough ?

 

[John_Madison CT]

Single OB Yamaha 0x66's will not sound an alarm when you first turn the key. Dual OB ones will.

To test the horn, disconnect the "kill switch" lanyard, then turn the key. You should then hear the alarm.

 

[Harpoon]

you may have issues ...

 

[TimC2520]

Since I ran that decarb, she developed what people were telling me was a "lean sneeze"....I worked on it this weekend and this is what I found.

I had some time this past weekend to do some investigating.
I fished on Saturday, most of the day, and she was sneezing and stalling often at idle but ran fine at all other rpms.
I fished it anyway with the intention of trouble shooting it on Sunday.

On Sunday, I first checked the plugs, trying to keep it simple.
Look at the photos attached. These were pulled from the port side, middle and bottom plugs.
Looks like one wasn't firing often, if at all? And how in the world could the tips on these things bend like that?
The only thing I could think of was (1) the cowling cover could have hit those when I was putting it back on
at some point in the past? Or (2) I did notice that when the cover is off, the port stern line does rub against those plug caps
pretty severely. I guess if I wasn't paying attention at some point, that could have caused it. I am hoping there was no damage to the inside
of those plug caps. They looked ok to the naked eye, but it's tough to see in there.

I swapped out all 6 with new plugs and fired her up....she still sneezed so that didn't solve that problem, but I did notice
I was able to achieve a much higher RPM than before, Lately, it'd top out at 4800 rpms, now there is no problem getting into the low 5's and
still wasn't wide open.

A few weeks ago I did a de-carb but never cleaned the O2 sensor after that and that's when this sneeze showed up.
When I took the cover off the sensor, I immediately noticed a problem. There was this brown, very oily substance leaking
from where the sensor screws into the mounting block. I guess I did not tighten it down enough last year and it vibrated back off a bit.
I took the whole thing apart, draw tube was clogged, mounting block was full of carbon, cleaned it all up.
Re-assembled and so far, so good. Fished it for 4-5 hours yesterday and she only sneezed once during warm up,
but never again the rest of the day.