Please explain the "Why" for DeCarb to a dumb newbie to this site

[Texasmark]

Help me understand this Roscoe and "gss036" if you see this, please, or anyone else who has the answer.<br /><br />This DeCarb thing is new to me. Till I popped onto this site a couple of weeks or so ago I never heard of it.<br /><br />On carbon, I always associated it with leaded fuel. When the lead left, that's when my engines cleaned up.<br /><br />Last 2 cycle engine I had apart was a '75 70 hp rude (in the late '80's) and the only reason I was into it was because it siezed up at WOT cause I had just bought it and it had no alarm and it had a frozen closed thermostat, and I had no way of knowing........they never stick open!!!! <br /><br />(On this site I noticed that some recommend you change them every 2 yrs. So I guess when you buy a used engine the first thing you do is to put in a new one......or trash the old one, like engines (Merc especially) ran for a lotta years "without one".)<br /><br />Anyway what am I fighting here? Is it gum and varnish in the fuel (carb innards particularly) caused by motors sitting alot, and/or built in fuel tanks that don't get fresh fuel cycled through them very often?<br /><br />The oils are supreme as compared to early boating years so they can't do anything but help the situation rather than hurt it. And with higher fuel oil ratio's there's less oil to burn up and clog passages.<br /><br />The fuel gets whacked all the time but I think fuel is just an excuse. Everything I have runs better on the fuel available today and when I can run a sparkplug 100,000 miles (Bosch platinum in GM), pull it out and have little or no buildup of whatever, that speaks pretty well for the cleaning ability of today's fuels. Also I don't remember the last time I stuck my nose in a can of gas over 6 months old and smelled varnish! <br /><br />My Dodge runs conventional Champions and I run them 40 or 50,000(with one gapping)...recommended to be changed at 30,000 but a waste of money... and they come out with minimum contaminants. I remember a '72 Chev wagon with a 402(396) big block that I had, and I would have to change them every 10,000 running leaded gas.<br /><br />So that leaves the EPA. I noticed the other day, a chart showing that they are requiring outboard motor emissions to drop about 10% per year and on my 2002 Merc, the chart was at about 60% of the emission level that existed when they went after outboards. <br /><br />So is there something in the engine that has drastically changed to cause "carbonization" requiring decarbonization caused by the EPA requirements?<br /><br />Would really like an answer?<br /><br />Now I assume if you troll a lot with a large engine, or run a big rig with a small engine where it is loaded heavily all the time, or a high performance rig run at WOT for long periods of time, or operate in a very cold climate, I could understand burnt oil in the explosion and exhaust chambers that may need removal.....after a long time running.<br /><br />Bet others would like to know also.<br /><br />Thanks,<br /><br />Mark

 

[Dhadley]

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

As for the carbon or coking, it all has to do with combustion temps and load in a 2 stroke outboard. We're not talking engine temps, but rather combustion temps. We're talking about an outboard, not a motor with very low and consistant exhaust restrictions like a motorcycle or a snowmobile or even a car.<br /><br />We're also talking about an engine that is always under a strain. Unlike a motorcycle or snowmobile or a car. An outboard must take off in high gear. Unlike other vehicles that have transmission that keep the motor "happy". Try that with your car. Outboards never coast. Would your car like that?<br /><br />Thru the years as the fuel changed we have seen this coking problem (carbon build up) get worse and then a bit better. It really seemed to help when the EPA removed MTBE from the fuel.<br /><br />Anyway, heres the results of some testing we did for OMC back in the mid 80's or so. It remains constant today.<br /><br />We used a V4 crossflow on a 16' boat. For the first part we loaded the motor up heavily -- dropped the X dimension and used a prop that would only allow a top rpm of 4800 with 2 people on board and 18 gal of gas. When it got light on fuel and only one person it would still only get to about 5200. Extreme? Yes, but it happens. Look on this board how many folks talk about their set up being close to this. <br /><br />At the time OMC was recommending that Engine Tune be used every 50 hours. We were still seeing coked up pistons and broken rings. <br /><br />On our test motor we coked up the pistons (starboard bank) in 12 hours of running. We broke rings at 19 1/2 hours. <br /><br />We rebuilt the motor and set it up on the same boat to turn 5800 with 2 people and 18 gal of fuel. We used no Engine Tune, no Carbon Guard or additives of any kind. Just OMC TCW II (I know, it was old school but thats what they wanted). After 500 hours there were no stuck rings or carbon issues of any kind. <br /><br />In both parts we ran the boat just as a pleasure boat. Cruising, idling, running flat out -- nothing special. The carbs were always clean, the water pressure was always correct, Champion plugs were always used as well as fresh 87 octane fuel.<br /><br />Now, if you look at combustion temps with that motor, the temps were much higher in the first test than the second test. High combustion temps promote coking. Coking leads to stuck rings. Eventually the rings break (more correctly the end is sheared off as the piston losses support).<br /><br />Hope that helps some.

 

[Chinewalker]

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Makes sense to me - I've got a 90hp in process of rebuilding that had EXACTLY that issue. The engine didn't even have 30 hours on it and the crosshatching from a previous rebuild was still perfectly evident on the three cylinders that didn't have a ring break. I had to find another block to rebuild...<br />- Scott

 

[DJ]

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Dhadley nailed it-as usual.<br /><br />Outboards are probably the most abused engines ever. <br /><br />An incorrectly propped engine is the norm, not the exception. That incorrect propping results in carbon build up. It has nothing to do with lead.<br /><br />Think about it. Some folks dole around at trolling speeds or non-planing speeds for hours. That leads to serious deposit build up. Add oil in the fuel and you get the problem described.<br /><br />Engines that run at high speeds for most of their lives may never have the issue.<br /><br />However, a decarb does NOT hurt anything, except maybe the plugs, and is a good preventive maintenance practice.<br /><br />BTW, the decarb. process has nothing to do with gunked up carburetors. That's a fuel storage issue best dealt with using fuel stabilizers.

 

[roscoe]

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Very nicely said guys. I added it to my decarb post in the FAQ forum. Now it is all nicely located in one place.

 

[Texasmark]

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Re: Please explain the "Why" for DeCarb to a dumb newbie to this sit

Thanks for the replies guys. Sorry for the delay in answering, but I just found it and I don't keep a list of my activity; probably should.<br /><br />Mark