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Carburetor Bummer

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jerlim
Master Marine Consultant

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USA
1484 Posts

Initially Posted - 08/28/2017 : 10:52:35

We've had a Merc 8hp for 11 years. Ran like the proverbial top for the first 8, the experienced stalling and starting issues. Apparently corrosion in the bowl from the water in the fuel...so OK...put in a new carburetor and for 2 1/2 years all is joy, but now the same old stalling in low RPM, and impossible to start issues are developing. I am told that the bowl (2.5 years old) is already staring to corrode and the particles are clogging the jet...

I use both Star Tron and Sta-Bil fuel additives and always buy fresh gas...so maybe, carburetors are just part of regular maintenance

Jerry

islander
Master Marine Consultant

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USA
4024 Posts

Response Posted - 08/28/2017 : 12:24:31

quote:

[quote]Originally posted by islander

If your sure the problem is water issues then put in a water separating fuel filter. That should keep the water from reaching the carb. Fresh gas is no garantee against water. Almost all stations and Marina's have water in their tanks.but our tiny engines are more affected by it than larger engines.
Short term solution is to remove the bowl drain screw and shoot carb cleaner in the bowl to rinse out any sediment and water.Also with the screw out pump the bulb until gas flows out the screw hole to flush the main jet. Hopefully you'll clear the obstruction without having to remove the carb. I'm not a big fan on additives being able to remove water as they claim. Lots of debate about it on the internet. Most are alcohol and very agressive cleaners like acetone that can do more harm than good to rubber parts. Hey if they worked you wouldn't have water in your carb. The water separating fuel filter is your best bet IMHO.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 08/28/2017 13:26:09

sethp001
Mainsheet C-25 Tech Editor

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814 Posts

Response Posted - 08/28/2017 : 16:51:18

For the future, another thing that you can do is disconnect the fuel line from the motor and let it run until it dies. This will evacuate all of the fuel (and theoretically the water) from your carburetor, which should prevent that corrosion.

I learned this from some old guys at the club who run very old outboards without problems. I only do this when I will not be using the boat for awhile because I am concerned about running the motor lean (and in my case, without lubrication because its a two stroke). So far, this has been better than removing my carburetor for cleaning every two years, despite buying ethanol-free gas and using fuel stabilizers.

Scott's idea for the water/fuel separator is good. However, I discovered that my old (2001 15hp Johnson) outboard's fuel pump cannot handle additional restriction to flow in the fuel line. On my motor, the fuel pump is a weak flapper valve actuated by pressure induced by one of the pistons moving. Your motor may have more robust fuel pump technology.

Seth
"Outlier" 1987 Catalina 25 SR/SK/Traditional Interior #5541
"Zoo" 1977 Morgan Out Island 30
"Nomad" 1980 Prindle 16
"Lost" 1988 Catalina Capri 14.2 (sold - yay!)
"Marine Tex 1" Unknown Origin POS 8' Fiberglass Dinghy
https://whichsailboat.com/2014/07/27/catalina-25-review/

Edited by - sethp001 on 08/28/2017 17:26:05

Voyager
Master Marine Consultant

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5376 Posts

Response Posted - 08/28/2017 : 19:37:58

I second Scott Islander's suggestion about the fuel-water separator. With ethanol in the fuel and with high humidity and variations in ambient temperature there's no doubt that water will find its way into the system. I drain my separator frequently during the season. I hadn't thought about running the bowl dry, but I'm going to start doing it whenever I return to the mooring. Having a four stroke engine, there's no worries about running the engine dry. If fuel pump suction is a concern, it might make sense to mount the fuel-water separator at the same height as the carburetor when the engine is deployed and running.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

hewebb
Admiral

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USA
761 Posts

Response Posted - 08/29/2017 : 04:18:43

I have most of the guys I know with outboards here using aviation fuel. That seemed to eliminate the issues with fuel problems. They get it at a self service pump at a small local airport. Also, if fuel is stored in a container that is not full it sometimes causes condensation to form.

1988 WK/SR w/inboard diesel Joe Pool Lake
Hobie 18 Lake Worth

Life is not a dress rehearsal. You will not get another chance.

jerlim
Master Marine Consultant

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USA
1484 Posts

Response Posted - 08/29/2017 : 05:23:41

Many thanks for the great insights. As a matter of fact - I used to run the motor dry when securing the boat for a week, for about the first 8 years or so, but one of the mechanics advised that allows the gas to dry on the internal carb areas and cause a gunk build up, so I stopped that practive...just about the time I got the new carb, (which has lasted less than 3 years)...HEY WAIT A SECOND

Jerry

JohnP
Master Marine Consultant

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1520 Posts

Response Posted - 08/29/2017 : 05:24:24

After returning to the slip with my 15 year old Honda 9.9hp outboard I disconnect the fuel line and run the engine dry (for 2-4 minutes) while flushing the cooling system with fresh water through a hose connected to an adapter for the integral flush port on the engine. Rarely, and if I know I will not use the boat for a long time, I also drain the carb bowl by opening the drain screw and catching the gas in a paper towel.

This has solved 2 problems - salt crystals in the impeller of the sun-baked engine, and water separating over many days from the ethanol-gasoline mixture. Water in the gas in the fuel line, fuel intake, fuel filter, and carb stop the engine from firing up. New gas pumped into the engine allows starting on the first pull!

But each engine is different. Good luck!

JohnP
1978 C25 SR/FK "Gypsy"
Mill Creek off the Magothy River, Chesapeake Bay
Port Captain, northern Chesapeake Bay

Edited by - JohnP on 08/29/2017 05:25:16

jerlim
Master Marine Consultant

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USA
1484 Posts

Response Posted - 08/29/2017 : 08:25:48

We settled on a new carb, and incorporating the practice of adding 1/2 ounce/gallon of 2 stroke oil to the fuel tank. Am also going to run the motor dry at the end of the weekends...fingers crossed...

Jerry

islander
Master Marine Consultant

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4024 Posts

Response Posted - 08/29/2017 : 11:27:01

Just a thought, Since you said you use the fuel additives on a constant basis, Those harsh chemicals and the alcohol could be deteriorating the insides of your rubber fuel lines and a source of debris blocking the jets in your carb. Have you changed the fuel hose recently to the newer E10 compliant hose? The 2 stroke oil will give you some upper cyl. and valve lubrication but won't do anything for water. You can also use Marvel Mystery oil but don't over due it because you run the risk of fouling the plugs and carbon build up. More is not better in this case.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 08/29/2017 11:35:56

jerlim
Master Marine Consultant

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USA
1484 Posts

Response Posted - 08/30/2017 : 07:41:07

Yes, when we did the new carb, we replaced all the fuel system components; tank, lines, filters, etc...do you think that Marvel will be better than 2 stroke oil?

Jerry

islander
Master Marine Consultant

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USA
4024 Posts

Response Posted - 08/30/2017 : 09:28:58

Is it better, I couldn't say but if your adding a little oil to the gas for added lubrication, Well that's what it does. Probably costs less than 2 stroke oil.http://www.marvelmysteryoil.com/index.php/site/mmo/

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Dave5041
Former Mainsheet Editor

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3758 Posts

Response Posted - 08/30/2017 : 16:35:09

I really can't see how adding oil to your gas does anything beneficial. I know the list of claimed benefits, but nothing downstream of the carb needs oil. Valve stems are lubricated from the cam side; the valve seat doesn't benefit from miniscule amounts of oil. It just burns a little less efficiently in the cylinders and probably does no harm in small amounts.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

GaryB
Master Marine Consultant

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4304 Posts

Response Posted - 08/31/2017 : 19:09:31

quote:
Originally posted by Dave5041

I really can't see how adding oil to your gas does anything beneficial. I know the list of claimed benefits, but nothing downstream of the carb needs oil. Valve stems are lubricated from the cam side; the valve seat doesn't benefit from miniscule amounts of oil. It just burns a little less efficiently in the cylinders and probably does no harm in small amounts.

Two things:

1. When I was a kid we had a 100HP Evinrude that we used during the summer and then it sat for 8 or 9 months. We ALWAYS ran the carbs dry and over the course of 10 years that motor never saw the inside of a shop or the hand of a mechanic.

My 8HP Suzuki has always had the same treatment over the past 10 years and it always starts on the 2 or 3rd pull.

2. My guess is the suggestion of using a slight amount of oil in the fuel was to prevent corrosion in the carb. The oil would add a slight protective coating to the fuel bowl.

Association Member

GaryB
Andiamo
'89 SR/WK #5862
Kemah,TX

Edited by - GaryB on 08/31/2017 19:09:45

Stinkpotter
Master Marine Consultant

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Djibouti
9080 Posts

Response Posted - 09/01/2017 : 06:52:20

quote:
Originally posted by GaryB

[quote]Originally posted by Dave5041

... 2. My guess is the suggestion of using a slight amount of oil in the fuel was to prevent corrosion in the carb. The oil would add a slight protective coating to the fuel bowl.

...and gum up the idle jet, which is the first to gum up.

Dave Bristle
Association "Port Captain" for Mystic/Stonington CT
PO of 1985 C-25 SR/FK #5032 Passage, USCG "sixpack" (expired),
Now on Eastern 27 $+!nkp*+ Sarge

Lee Panza
Captain

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USA
468 Posts

Response Posted - 09/01/2017 : 07:13:19

The carburetor on my Tohatsu 9.8 has to be cleaned-out periodically, when the motor begins to idle poorly. In very short order after first noticing the idling problem the motor will refuse to idle at all. It starts right up, and it runs fine with the throttle open, but no idle. The culprit, of course, is clogging of the idle jet, and it takes surprisingly little to cause the problem. This requires the tiny ports in the jet to be cleared with a fine copper wire (softer metal than the brass jet) and compressed air. It also requires completely cleaning the carb, not just the bowl but the passages throughout. When the bowl is removed I usually (though not always) find small amounts of residue inside and around the edges of the gasket between the top and the bottom of the carb. This deposit drys to a white powdery material.

I have become resigned to having to do this periodically, so I always have a spare carb, which was cleaned after the previous episode, ready to install while I clean the one I just removed.

I have tried several brands of automotive gasoline (here in California it's all oxygenated - primarily with ethanol and MTBE) and none eliminate the problem entirely.

Removing and disassembling the carb is easy, as is putting it back together with new gaskets (I haven't found it necessary yet to replace the float or the intake needle valve, although I've had to on automotive carbs over the years, so I keep a spare of each onboard). The idle jet is a long, thin tube with ports on its side as well as the bottom end, and if even one of those side ports is clogged it affects the idle performance. Or, as I mentioned, the small passages and ports in the carburetor body can become partially obstructed and need to be cleared by flushing with carburetor cleaner and compressed air.

So, Jerry, in response to your original post, I have found that carburetor maintenance is, indeed, part of regular maintenance. At least out here where the CARB reigns.

The trouble with a destination - any destination, really - is that it interrupts The Journey.

Lee Panza
SR/SK #2134
San Francisco Bay
(Brisbane, CA)

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 09/02/2017 : 22:10:15

I have occasional carb problems, twice on my 8-9 year old mercury and more frequently with my old 9.9 2 stroke Johnson. I have alway had complete success by disassembling the carb and cleaning with spray can of carb cleaner. I have never had to resort to wires, but I generally use most of a can for one cleaning.

edit: I usually forget to add fuel stabilizer, burn E-10, and have a Sierra water separator/filter that gets a new cartridge every year.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

Edited by - Dave5041 on 09/02/2017 22:15:56

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