ox66 250hp smoking

[Bevo]

I just bought a boat with 1999 ox66 yamaha 250. the hour meter on the speedo showed 115 hrs when purchased. The engine runs a bit rough at idle(about 700- 800rpm). Runs great @900 rpm and over in gear. Plenty of power and has not fouled a plug in 35 hrs of use. I have owned V6 excel, 200 Hp carb model as well as 90 hp carb model. They all smoked at start-up and would then calm down within a few minutes. This engine seems to smoke too much as soon as I shift into neutral. Anyone have any ideas???

[IFish4Tuna]

Potentially stuck (open) thermostat(s). May make the engine run a bit cooler and hence more fuel pushed in. When running at higher rpm in gear the engine is running hotter so the open therm is compensated for.

Does it shake a bit at idle also?

[jb123]

chech the oil pump linkage, make sure the linkage bottoms out on the stop pin.

[Bevo]

Yes, there is a noticeable shake @ idle and I suspect(hope)you are right, thermostats and gaskets on way. Also the pump linkage was not against the pin. I read in another thread where the actual link when screwed all the way down on the rod would bottom out - which is the case with mine as well. I'll report back this weekend and advise how I made out. Thanks for the quick replies.

[hooken203]

Check your fuel pumps. I just figured out the problem with my 225 vmax today. Hard start hot smokes alot miss at idle. Fuel pump leaking fuel into vacuum port causing 2 cylinders to flood. You have to remove the fuel pumps to find this. Remove pumps and squeeze bulb on fuel hose and fuel will leak out of the back of pump.

[IFish4Tuna]

But don't be fooled into thinking you have a leak because of the screw holes are leaking. It's a two person test. One to prime the bulb, one to watch for leak.

Ed

[bernieb]

That 250 has a slightly rough idle and thats normal,as it drops a cylinder at low rpm's.Buy some "Ring free" or buy some "sea Foam" and mix with the gas .I've only got 50 hours on my 250 and yes it smokes at start-up and idling,and shakes at idle.Since this pops up every other day on some board, try this method, I picked it up on another board and have been using it for awhile now,works great.
Tip for the Week
Do-It-Yourself Engine Tip; A Simple and Cost Effective Way to De-Carbon an Outboard
By Capt. Bob Dunkelberger dunk75@comcast.net
This works for Carbed, EFI, Ficht, HPDI, Opti-max and even 4-strokes... and should be administered after every 50-60 hours of use.
First you need a separate small fuel tank. One of those 3-gallon red Tempos works well or an empty gallon milk jug in a pinch, but it might be a bit messier.
I use Seafoam over the OEM (original equipment manufacturer) stuff like OMC Engine Tuner or Mercury Power Tune. Note: in the last few years they changed the formula and you have to let them sit up 12 hours. Who's got time for that? Seafoam does the job in 15 minutes and can be purchased from NAPA, Car Quest or other auto stores.
You'll need 3/4 gallon of gasoline and one 16oz can of Seafoam for each engine. Don't forget to add 3oz of oil if you are pre-mixing in a carbed engine. Use a 3 ft piece of fuel hose off the small tank. Connect this tank to your engine by pulling off the main tank fuel hose from the intake side of your water separating fuel filter and plug the hose off the small tank onto that fitting. Or you can separate the fuel line on the tank side primer ball, so you can still use your primer. If your engine has a fuel plug then you will also need a fuel plug on the smaller tank's hose.
Start the engine, let it warm up and start pulling the mix into the engine. You may have to increase the idle to keep it running once she gets loaded with the Seafoam. Run the engine 15 minutes at the dock or just cruising around under 2500 rpm's. Then shut it down and let it sit for another 15 minutes.
Restart the engine; the smoke you see is the carbon burning off. Do the whole thing again and let her sit again for 15 more minutes. If she smokes after the second time do it again.
I've never seen one still smoke after three doses. (I bought a Bronco two years ago that had 95,000 miles on it. When I used Seafoam on it I had the neighbors hanging out of their front doors looking for where the fire was after I started it the first time there so much smoke)
The gallon mix should be just enough to do this 3 times. You don't need a wide-open throttle and you don't need to change the plugs. The plugs are cleaned at the same time as the combustion chambers. My suggestion is that every 50-60hrs is the optimal time to change plugs in most engines.
I cleaned an antique Evinrude once that had a 1/4" of solid carbon on the exhaust chamber walls by running a 1/2 gal of the aforementioned mix through it. Seafoam, a great product, has been around since the 1930's and it's what they used when they were burning straight 4 stroke 40SAE oils in outboards.
For you guys with the 4 stroke outboards? Those engines work 10 times as hard as any auto engine ever will and they too will carbon up. Too many are under the assumption that it's totally the 2 stroke oil that causes the carbon, Wrong... it's also the additives they put in the fuels today. The carbon inhibitors in 2-stroke oil are there for this reason also. Remember when gasoline used to smell like gasoline, today it smells more like bad cologne.
For those guys that like to work the carbon treatment by spraying it down the carbs, Seafoam also comes in spray can called Deep Creep. It's the same stuff under pressure and notes on the can, "Oxygen Sensor Safe". After that, if your engine manufacturer recommends a daily additive treatment then do so. The tank and hose are a one-time purchase and the Seafoam is only costs $5-6.00 per can.

[Bevo]

Well, the problem has been solved... thanks everyone!!! Here's what I did.

1.) removed oxy sensor and housing. The spool going into the block had carbon/oil mix filling the inner land. The carbon looked like small smooth pebbles. The bore surrounding the sensor was filled almost solid with carbon. I cleaned these and the sensor and reinstalled.

Engine still smoked.

2.) Removed thermost housings and found the problem. One thermostat had the top valve sealing gasket partially extruded over the top of it. This put the thermost in open mode permanently. Thermost's & gaskets replaced.

Engine started to show signs of healing.

3.)Added Seafoam to tank... Engine runs awesome now, normal smoke at start up then settles right down.

4.) Gone fishin!

[IFish4Tuna]

Send me a check for $1500 dollars and 50 hours of your time.

[img]smile.gif[/img]

Thats what it cost me to diagnose those issues on my 1996 263 Chase a few years ago. 02 and thermostat. That was my first yamaha diagnosis a few years and tears ago.

Nothing like a good does of anguish relief.

Ed

[Wakeboard in North Wales]

I have a problem with a 115 misfiring at idle (on the lower 2 cylinders - se [post below) which causes it to stall below 2000 revs. I have replaced ht leads, connectors, stripped the carbs/rebuilt, also stripped the fuel pump again today re:advice about vacuum port.

On stripping the fuel pump I noticed that the gasket between the pump and engine had worn away on one side completely. On testing the pump (dismounted from the engine) I noticed that fuel leaks out of the bolt holes. In theory then could this cause my mis at idle due to fuel escaping into the vacuum whole and therefore flooding the lower 2 cylinders. Or could the associated air leak affect the pump at low revs.

I am going to replace the gasket and refit. If this does not do it, then I'll look at the lower carb, and check the needle valve (all jets are clear).

Anyone else got any bright ideas (I noticed the posted on this thread mentioning the thermostat, where is this on the engine, as it is not obvious on my factory manual as to where it is).

Cheers


James