OX66 frustrating issue

[Gill7858]

Hello all, I've been having a very frustrating time with my Yamaha 2002 OX66 250 HP 2 stroke. All last summer it was running just fine except that towards the end of summer I notice that if I was running open throttle it would start slowly dropping RPM's on its own. If I came off of plane and shut it down for a few minutes, once I started back up it would run normal for the rest of the day. So a few months back I decided to do all of the maintenance and try to fix this issue, so I went to the dealership and they advised me that I should use Ringfree to clean the combustion chamber (which has never been done before). So since I added it (small bottle to about 75 gallons of Ethynol gas) my problem got worse, much worse. Now my plugs appear to get fouled up and the last two times I've taken her out I've barely been able to get up on plane. I've replaced the spark plugs about 5 times and no real fix. I can start the engine and she'll fire up however now it idles at like 400-500 rpms for the first couple of minutes then all of a sudden wakes up and idles between 700-800 or so. I notice that at times the engine shoots out exhaust (not really smokey) and then the engine shakes (rough idle). At times its even made a loud backfire sound then either shut off or idled slightly better. I'm assuming that maybe the ringfree broke some gunk loose and that's the engine shooting it out. However I'm being told that it should cause all of the failure i'm experiencing. Also if I start to accelerate it in neutral (not under load) it'll surge from 1000 to 2200 rpm's or so and eventually shut off.

Here's what I've done so far:
Had injectors cleaner (at a professional shop), replaced VST filter, replaced the 3 low pressure fuel pumps, replaced engine fuel filter (including the cup, spring and O-rings), cleaned O2 sensor and holder (contained lots of carbon buildup), replaced fuel/water separator filter and cup, replaced primer bulb with Yamaha bulb, and had a professional flush and condition my tank. Now the engine is only running Ethynol free gas.

I'd appreciate whatever advice anyone can give, cause I really don't know what else I can do. Thanks in advance

[ausnoelm]

Wait for someone to reply, posting again a couple of hours later will not help.

[Gill7858]

Yeah that was by mistake. I posted it before and couldn't see it on the new threads, I though it didn't post. I tried to delete the new one but couldn't figure out how to do that. Any ideas?

[ttles714]

just a shot !!

Interesting situation .. i have same engines and it seams like you have covered all the bases ... Just a couple of thoughts... First I hope that maybe Rodbolt Boscoe, or someone of their skill and knowledge level can help ... but in the meantime, Did you do a compression test ? Is it possible that you have a vapor lock caused by a bad gas tank vent .. maybe run with filler cap loose and see if that helps ..Did you install OEM pumps ??

[TownsendsFJR1300]

The RF, especially mixed that light, won't cause all the issues your having.

I run it at 2-3x's the recommended amount with very good results.

I suspect you have another issue elsewhere..

I'd start by draining and catching (in a super clean container) what comes out of your VST tank
looking for water, crap, etc.

Hooking the engine up to a puter (YDS) and checking the perimeters of it running should show something too

[Gill7858]

Interesting situation .. i have same engines and it seams like you have covered all the bases ... Just a couple of thoughts... First I hope that maybe Rodbolt Boscoe, or someone of their skill and knowledge level can help ... but in the meantime, Did you do a compression test ? Is it possible that you have a vapor lock caused by a bad gas tank vent .. maybe run with filler cap loose and see if that helps ..Did you install OEM pumps ??

When the gentlemen flushed and conditioned my tank, he replaced the gas tank vent hose and vent. Today I went to fill the tank with rec 90 and vent is working fine plenty of fumes exiting the vent while filling up. Also all three pumps installed were all original new Yamaha pumps purchased at the dealer.

Townsend, when I cleaned out the VST tank and replaced the filter all appeared good in there. Just a couple of very small particles in the filter but the VST tank itself was clean with normal green gas.

[formula29]

No YDS for an ox66, Have you tried running it on a portable test tank to eliminate your fuel tank pick-up, check valve, ect. I think I would run it with a fuel pressure gauge connected above the vst and see what the fuel pressure is doing, I think it should be around 40psi or so,

[Gill7858]

Formula, I haven't tried that but sounds like a good idea. I'll have to give that a shot.

[ttles714]

pick up in tank

Do you have access to remove the fuel pick up ?? I like the Idea of running on a portable tank that would confirm any issues that could be in the fuel tank

[Gill7858]

No. When the guy opened up the sender in the tank, I saw the pick up which is a metal tube so I won't be able to remove it from the take without cutting into the deck. If it is the pick up then I'll have to cut into the floor and install a larger hatch.

[ttles714]

Pick up

I had a brand new boat once doing almost the same.. (Johnson Motor) When they opened the Tank and pulled the tube, the screen on the end of the tube was clogged with metal shavings and carpet fibers. The good part was there was a removable tank cover . No cutting the deck .. That was on a Grady White.. They got sloppy somewhere on the build of this boat, but at least they had the smarts to allow tank access without cutting up the deck.

[Gill7858]

Actually the guy that cleaned the tank remove a couple of pieces of aluminum which he called "slag". He told me that 99% of tanks have that it there and that was completely normal. I really hope I don't have to cut into the deck, that would suck.

[cpostis]

Gill, reminds me when I first got my used 2001 OX 66 150. So here's a few things I did on top of what you have to solve my "Mystery Problem". I did have white powdery residue on my VST filter. I first thought it was fuel related to begin with.

1.) Checked O2 sensor output (Found barely out of spec) and replaced
2.) Checked oil pump output and adjusted link (was way out of spec).
3.) Disconnected any electrical connectors (including grounds) cleaned with electro contact cleaner, lubricated with CRC 656 (Good electrical connections free of corrosion are a must), and reconnected.
4.) Checked throttle and crankcase position sensors (Were OK)

My conclusion is that I did have fuel, oil pump, and O2 sensor issues. I addressed the fuel and oil pump issues first with improvement. Once I replaced the O2 sensor, everything came together. That was back in 2010. Since, I have made it a maintenance task to remove/clean the O2 Sensor at least bi-annually.

One more unrelated item. I recently had my first overheat problem and found cooling passages clogged throughout heads and many deposits on block. I run in strictly salt water. I wound up doing a complete teardown of the engine, replacing heads, and cleaning the block. I no longer use the fresh water flush connection (Useless). I now always flush my cooling passages in a tank ($65 @ Tractor Supply), motor running until after about 5 minutes from thermostats opening. See the video link. The motor is running on 50:1 portable tank and oil from the pump during the start-up; thus the extra smoke. Always use non-ethanol gasoline.https://www.facebook.com/chuck.posti...d=350685531728

Good luck!

[TownsendsFJR1300]

RUNNING on muffs will work as well as tank flushing.

The key is to RUN the engine so the thermostat OPENS and your fresh water gets everywhere..

Religiously flushing after saltwater use is also CRITICAL..

I usually, as the boats lifting (4 post lift), use the hose adapter at the power head. Once its up, the muffs for at least 15 minutes running.

I just invested in the "Salt Away" tool and product and introduced that into my engine. I can run my F150, with the Salt Away tool attached W/O overheating.

Then, no more than 30 seconds of adjusting the valve to apply Salt Away and your done. Don't flush with fresh water, leave it in to continue working..

You'll see like a liquid soapy solution come out. Doesn't take much...


Re the tank, can you disconnect the primer bulb from the engine, add a short piece of 3/8" hose. Then, with a fuel tank lower than the main tank, prime and see what flow you get with gravity. You'll get a GOOD IDEA of / if the inside tank filter is clogged and how bad.

Simply blowing air BACK thru the fuel hose (not thru the primer bulb) may help clean the filter. Weather the filter stays clear or not (depending on the height of the filter in the tank) is unknown... Might need a re-flush / vacuum...

[cpostis]

Matter of opinion. With muffs only, you will not get enough back pressure on either the exhaust or cooling passages to do what I want to accomplish. Also, when run in a tank the cooling water temperature will rise about 20 degrees and help dissolve any deposits (Especially salt) stuck on surfaces. I do run on muffs after my tank flush.
Please realize, people that know me say I do sometimes go overboard