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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Gas > Atomic 4
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Old 09-17-2014
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Carb Problem?

As part of a separate transmission cable replacement issue, I decided to hire a mechanic to rebuild my gunked up carburetor. In hindsight, I wish I had done it myself, but that is another story.
The engine now fires up on the first crank, but it wants to rev up high, and there is a lot of blue smoke coming out of the exhaust. There is also what appears to be a gas slick forming on the water behind the exhaust. And it sounds like it is spark knocking.
The oil pressure is 40 psi. No water in the oil, and the level hasn't dropped. The plugs look ok, except for two that are a bit black and dry(I am assuming from having to run it for an extended time with the choke, from a gunked up carb?).
Now the cabin of the boat smells like gas, and there appears to be a gas-like residue on the OUTSIDE of the carb and underneath it. The mechanic swears that there is a valve or piston problem and that the gas slick is an oil slick, but I know for a fact that it wasn't smoking/knocking/slicking before the repair.
I would greatly appreciate any insight on this problem. I will be checking the compression on the next trip down to the boat.
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Old 09-17-2014
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Re: Carb Problem?

burning rich, very rich. Float not set properly and idle/mixture not set properly. Don't waste your time on a compression check.

Be VERY careful with "the boat smells like gas" as vapors/fumes can cause problems.

Get it fixed, properly or do it yourself. At this point you would be better off ordering a new carb and replacing it yourself, than to give this person more money to "repair" what he has already broken. No more money for him, till it idles smoothly. He is not a mechanic.

While you may have a valve or piston problem, that is secondary to the carb getting repaired.
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Old 09-17-2014
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Re: Carb Problem?

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Originally Posted by kd3pc View Post
burning rich, very rich. Float not set properly and idle/mixture not set properly. Don't waste your time on a compression check.

Be VERY careful with "the boat smells like gas" as vapors/fumes can cause problems.

Get it fixed, properly or do it yourself. At this point you would be better off ordering a new carb and replacing it yourself, than to give this person more money to "repair" what he has already broken. No more money for him, till it idles smoothly. He is not a mechanic.

While you may have a valve or piston problem, that is secondary to the carb getting repaired.
To drain or not to drain

I also loaned him my 2HP Honda 4 stroke, same result. Even after I cleaned the carb twice, I could never get it to run spot on. A $100 new Honda carb did the trick.

Paul T
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Old 09-17-2014
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Re: Carb Problem?

Rebuilding a carb is more like watchmaking than general mechanic work. And even carb shops seem to screw them up more often than not. A whole new carb can be expensive, but if you can get a "major overhaul kit" for the carb, that's often ~$100 and with a gallon of gumout and an afternoon of patience you can put it back in new condition.

The overhaul kit usually includes detailed instructions, Some drill bits of wire gauges and a small steel ruler to make adjustments precisely are required, nothing exotic. Some needles or fine brushes to clean out the passages, all easily procured. The hardest part is just being patient and methodical. Take the phone off the hook, use some boxes or bags so the small parts can't run away, and take pix with a cell phone or digicam if there's any doubt about how a stack of things go together.

When it is done, if everything is rosy again, you keelhaul the alleged mechanic.
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Re: Carb Problem?

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Originally Posted by hellosailor View Post
Rebuilding a carb is more like watchmaking than general mechanic work. And even carb shops seem to screw them up more often than not. A whole new carb can be expensive, but if you can get a "major overhaul kit" for the carb, that's often ~$100 and with a gallon of gumout and an afternoon of patience you can put it back in new condition.

The overhaul kit usually includes detailed instructions, Some drill bits of wire gauges and a small steel ruler to make adjustments precisely are required, nothing exotic. Some needles or fine brushes to clean out the passages, all easily procured. The hardest part is just being patient and methodical. Take the phone off the hook, use some boxes or bags so the small parts can't run away, and take pix with a cell phone or digicam if there's any doubt about how a stack of things go together.

When it is done, if everything is rosy again, you keelhaul the alleged mechanic.
Good points. I have been successful at doing what you described many times.
Had I known the Evinrude carb was $400 I would have pulled the old carb & brought it home with me for a try. But, due to distance & logistics, I just bit the bullet & ordered a new one.

You really don't have much to lose by trying a re-build/cleaning first, except you won't know if it worked until you re-install & test it, which takes time.
A new carb should work properly right out of the box, needing only low speed mixture & idle speed adjustment, as compared to a couple of hours "cleaning" it.

I like to lay out the parts, "up" side up, in sequence from left to right, in order of dis-assembly, on a large, clean towel to be reversed on assembly. Even if you have a good parts diagram or a good shop manual, good, close up digital pictures would be a big help. Suggest you "go slow" & be gentle. Some carbs have small spring loaded "check balls" most difficult if they spring out onto the floor.

Paul T
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Old 09-18-2014
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Re: Carb Problem?

How could the machanic suggest that there is anything wrong with the carb, other that what he just did to it? It ran OK before, and crappy after. My best (very uneducated) guess is that it is the float. If you take the carb off (easy), and split it in two (easy), the only thing that may fly out is the float and float pin. The pin should have a rubber pointed end that seats into a hole. The hole needs to be free of crap. Also, as most A4 posts mention at some point, see moyer marine site.
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Re: Carb Problem?

"The hole needs to be free of crap. " And the pin needs to be "perfect" as well. If someone smashed up the tip (often "rubber") it usually needs a new one, which would be included in most overhaul kits. Or if the guy reamed out the hole with something too sharp, and it has been enlarged too much...that could ruin a carb and make it run rich forever.

You know boat projects, it rarely is over when you thought it would be.

Carbs are one reason that fuel-injected diesel engines became popular. (Until the owners get intimate with diesel and injection problems, anyway.(G)
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Old 09-18-2014
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Re: Carb Problem?

As a marine mechanic I would hazard that the mechanic you hired didn't either set the float correctly or didn't set the needles correctly the choke is sticking or some combination of all the above the problem is not due to the valves or pistons. M2cw
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Old 09-19-2014
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Re: Carb Problem?

Blue smoke indicates oil. Running fast is idle adjustment or vacuum leak. A float set extremely low can cause fast idle but not smoke too. I would also suggest, from your description, you have other issues. Is the base gasket on correctly, vacuum connections, breather?
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Old 09-20-2014
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Re: Carb Problem?

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Originally Posted by Marknid View Post
Blue smoke indicates oil. Running fast is idle adjustment or vacuum leak. A float set extremely low can cause fast idle but not smoke too. I would also suggest, from your description, you have other issues. Is the base gasket on correctly, vacuum connections, breather?
Actually when an engine is running extremely rich it will exhaust blue smoke with a distinct gas smell just like the op described
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