Carb. paranoia -what to look for?

[d.boat]

I've read stories of engines damaged by poorly functioning carburetors. Some clean their carbs regularly, and it is often recommended to routinely clean carbs. when obtaining a used engine.

I've cleaned/rebuilt carbs, but only on my twin cylinder kicker. I did so not for general principles but specifically because it wasn't runnning perfectly.

Although it seems to be very routine for many of the more experienced posters here, it is not a trivial job for me, and certainly not somethng the most common outboard owner would even consider doing him/herself.

Along these lines, we amateurs could be well intentioned and really do our best to clean according to the service manual, but we could still end up with an imperfect job because we really don't know what is trivial contamination and what is not, or we really might not recognize that our cleaning job was imperfect because we never had any schooling on it by someone who knows.

In addition, sometimes the rebuild kits are expensive, $50+ each (which can add up for a larger engine). I can't imagine taking on the job for my big V6 both in terms of time and money... and would probably have it professionally done, making it more of a hassle (scheduling) and of course expense.

I would gladly pay if it were clear that it is necessary because it's so important.

So my questions are:

Is it possible for poor functioning carb to damage an engine with absolutely no signs that it's happening? I mean absolutely dead-on surprise w/o any warning.

If not - what exactly should one be looking for to assess the carbs? If the engine idles great, accellerates well and reaches appropriate WOT RPM's, does this absolutely mean the carbs are fine and don't need service?

Are there any tests that can be done, such as spraying pre-mix into the carbs while idling and/or WOT to see the response?

Thanks for any insight.

 

[Boss Hawg]

Re: Carb. paranoia -what to look for?

I'm in the "If It Ain't Broke Leave It Alone Club"

 

[Frank Acampora]

Re: Carb. paranoia -what to look for?

Typically, the damage done to outboard engines from malfunctioning carbs is from a lean run. This damage typically occurs at or near full throttle. It most often happens on multi carb engines although it can happen on single carb engines too, because, again, typically the cylinders serviced by one carb do not get an equally rich or lean mixture.

What happens in a multi carb situation is either one carb is set too lean or some junk gets into the carb, clogging or partially clogging the inlet needle. This restricts the flow of fuel into the carb. That cylinder now runs leaner than the prescribed (12 to 16) to one ratio. Because the other cylinders "carry" the engine, that cylinder goes into detonation and almost immediately, the piston melts, the rings break, and the cylinder is scored badly enough to need reboring.

Because outboards are relatively noisy in operation, the driver doesn't hear the detonation. However, even if he/she does hear it, the damage is done so quickly that by the time the driver reacts and throttles back, the engine needs rebuilding.

The best preventive measure is to set the low speed adjusting needles rich enough if the engine has them. The second best preventive measure is to be certain that a fuel filter is installed BETWEEN the fuel pump and carbs. Most larger late model OMC and Mercs do have the filter stock.

I find that with current TCW 3 oils, it is not necessary to drain the carbs from week to week, but it is a good varnish preventive measure for off season storage.

There is no need to be paranoid about damage: Most lean runs are the result of setting the carb too lean, because a lean running carb gives a beautiful idle on a two cycle engine. The mis-informed or under educated owner thinks he is doing something good when in actuality he is setting up the engine for harm.

With a modicum of care and a properly installed fuel filter, it is quite possible to spend your whole boating life without damaging an outboard due to detonation.

And, by the way: I am one of those few who believes that routine cleaning or rebuilding of carbs is, at minimum, a waste of time. As stated above: "Don't fix it if it aint broke!"

 

[Silvertip]

Re: Carb. paranoia -what to look for?

Spraying carb cleaner or any other snake oil through the carb is a waste of time and money since that mixture passes right through the throat of the carb and into the engine. Fuel system cleaners like SeaFoam must be added to the fuel that actually gets INSIDE the carb. The only way for that to happen is by adding it to the fuel supply. Fuel system additives are "preventive" measures and rarely solve an existing problem. Clean the carbs, THEN use a fuel system additive on a regular basis to prevent problems down the line.