Hi , new UK forum member,
I've had similar in the last months of ownership of my BF35 (second hand). I noticed engine oil increasing by 1/2" above max after a weekend of use, also not too strong of a tell tale water jet although pumping hard. New impellor fitted to water pump, no different, checked fuel pump by removing it and priming the bulb, no leak, recommendation from a handa service centre, and honda, probably the carbs, fitted new float jets but I didn't suspect them really, but done them anyway and checked float heights at same time. Ordered a stat also on reading these forums, found the stat to be siezed fully open!!!! Renewed stat, test run engine accross marina, engine now pumping like the other engines I've seen as there is now more internal cooling pressure due to a closed stat untill openning. Now engine up to temp and white smoke/steam coming from the exhaust port at rear under the top cowling line. Suspecting previous owner never looked at the engine running too hard with the siezed stat and just got away with being oblivious to its health. Now theres more pressure I'm now expecting to remove the head and hoping not to find also the heads cracked through uneven cooling. Hopefully just headgasket breached. Previously I noticed the lower sparkplug was running lean by the pale colour, this may have been from uneven cooling????? It's all ideas but untill I get my head off, Ill keep you all posted.
Trev, here's some info I got from some guys I know that deal with this and some few cures.
If the rings get carbon buildup and are not seated as a result you will get blowby fuel that ends up in the crankcase. Happened to me on a 4 stroke. Manual decarb knocked the problem right out. If it were water it would look milky and not have the fuel smell that he is getting.
If the engine is not above or the EMM "thinks" the engine is not above 105 degrees it continues to dump fuel into the engine like a choke. This not only can get passed the rings but builds up carbon which escalates the problem. If the T stat is stuck open there in lies your problem.
Generally operating temps are : 140-degrees-F to 160-degrees-F
Generally start with the least expensive or most likely culprit and move down the list. This is a well documented problem with folks that do a lot of drifting at idle or trolling. The engine doesn't get hot enough like this. If you do a lot of this it's best to run it hard on the way back in and get it hot.
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This is cut from another site. Not exactly the way I do it but easier and well written:
This works for Carbed, EFI, Ficht, HPDI, Optimax and even 4 strokes...
First you need a separate small fuel tank. One of those 3 gal red Tempos works great or an empty gal mike jug will also work, but might be a bit messier..
I use Seafoam over the OEM stuff like OMC Engine Tuner or Merc Power Tune because 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 you can buy from NAPA, CarQuest or other auto stores. Seafoam works in 15 mins.
You'll need 3/4 gal of gasoline and one 16oz can of seafoam for each engine. Don't forget to add 3oz of oil if you are premixing in a carbed engine. Use about 3 ft piece of fuel hose off the little tank. You connect this tank to your engine by pulling off the main tank fuel hose off the intake side of your water separating fuel filter and plug the hose off the small tank on to that fitting. Or you can separate the fuel line on the tank side primer ball, so you can still use your primer. If you have an engine that has fuel plug then you need a fuel plug on the little tanks 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 get loaded with the Seafoam. Run the engine 15 mins in the dock or just cruising around under 2500. Then shut it down and let it sit for 15 mins. Restart the engine, the smoke you see is the carbon burning off. Do the whole thing again and let her sit again for 15 mins. If she smokes after the second time do it again, but I've never seen one still smoke after three doses. The gallon mix should be enough to do this 3 times. You don't need any wide open throttle, you don't need to change the plugs. If it's cleaning the combustion chambers it's also cleaning the plugs, but every 50-60hrs is good time to change plugs in most engines.
I cleaned a antique evinrude one time that had a 1/4" of solid carbon on the exhaust chamber walls by running a 1/2 gal of the mix through it. Seafoam has been around since the 30's and it's what they used when they were burning straight 4 stroke 40SAE oils in outboards.
You guys with the 4 strokes think you are immune from this? Those engines work 10 times as hard as any auto engine ever will and they will carbon up. 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.
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 do 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. Says right on the can Oxygen Sensor Safe, for you Yam guys.
After that if your engine maunf recommends a daily additive treatment then do that in the mean time, but all 2 stroke outboard need decarboned every 50-60hrs. If I owned a 4 stroke I would do it the same. Once you are set up with the tank and hose the Seafoam is only 5-6 bucks can. It to easy not to do it.
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I'm going this route on Tuesday. seafoam shock, new T stat and hopefully that will cure it.
