I have a Nissan/Tohatsu 8HP 2-stroke outboard for our dinghy. It was dying at idle, so I brought it home, replaced the fuel filter and cleaned out the whole carberator... almost. I replaced the float and pin, along with the gaskets. However, the slot on the slow jet wouldn't budge and stripped, so I crossed my fingers, got some new fuel, and tried to fire it up. Here's what happened: 1. Starts after many pulls with full choke and wide open throttle, but then have to go to half-choke to keep running. 2. Dies if throttle goes below half open. 3. Dies if choke shut off. I pulled the carb again and used a screw extractor to pull the slow jet. Blasted everything with carb cleaner. I'll order a new jet tomorrow. Is this my problem? This is my first bit of carb work, so I tried not to do too much. Consequently, I did not open the fuel pump. Am I missing something? Thanks. Harry
Outboard motor repair help!
- Thread starter Harry Greenspun
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Fuel pump?
Are you sure your 2-stroke Nissan has a fuel pump? Check to see where the hose from the tank leads. I am guessing straight to the carb if you have the top mounted integral fuel tank. If so and you are starving for fuel(from your description) then check fuel flow to the carb. Remove the hose from the shutoff valve and see if you have good flow. If we knew the exact year and model you might get more assistance since most engines and parts lists are on the web.
Are you sure your 2-stroke Nissan has a fuel pump? Check to see where the hose from the tank leads. I am guessing straight to the carb if you have the top mounted integral fuel tank. If so and you are starving for fuel(from your description) then check fuel flow to the carb. Remove the hose from the shutoff valve and see if you have good flow. If we knew the exact year and model you might get more assistance since most engines and parts lists are on the web.
Definitely has a fuel pump
Ed, Thanks for the reply. It is a 2003 model 8B. Definitely has a fuel pump (little black box on the side of the carb), as well as an external tank. It will keep running as long as I keep the the choke half open and the throttle at least half open. When I changed the spark plugs, they appeared to be oil-fouled, so I suspect between that and old gas, something in the carb was clogged up. Hary
Ed, Thanks for the reply. It is a 2003 model 8B. Definitely has a fuel pump (little black box on the side of the carb), as well as an external tank. It will keep running as long as I keep the the choke half open and the throttle at least half open. When I changed the spark plugs, they appeared to be oil-fouled, so I suspect between that and old gas, something in the carb was clogged up. Hary
When I have seen these running characteristics...
that is it only runs with the choke partially on and the throttle open, the problem has always been a clogged hi-speed jet or passage. My recollection is that the choke is only works with the low-speed jet to deliver more fuel and if the high speed jet is clogged, the only fuel must come from the low-speed jet. Partial choking increases the fuel from the low-speed jet, but the air/fuel mixture is wrong for hi-speed running. I would recheck the carb hi-speed fuel passages, looking for a clog. Spray carb cleaner thru all the passages. The hi-speed jet is probably a fixed jet on your small outboard. Just spraying carb cleaner into the air intake of the carb is generally ineffective. You need to get the cleaner thru the passages. A technique that *sometimes* works is to run the engine on a small quantity of fuel with a 20-40% mix of fresh carb cleaner. Back out the low-speed jet to allow a lot of fuel to flush thru the low-speed passages. Run the engine for 10-20 minutes while trying to increase the speed with the throttle. This will sometimes dissolve any deposits in the carb that are clogging the passages. This remedy works best on the low-speed passages and only works if the restrictions are due to gum and varnish and not a piece of foreign material. I am not directly familar with your engine. If by chance your engine does have a hi-speed mixture adjustment, then backing out that adjustment may allow the fuel and cleaner mix to get thru and clean the hi-speed passages as well. I have used this technique to clean a carb without dissembly.
that is it only runs with the choke partially on and the throttle open, the problem has always been a clogged hi-speed jet or passage. My recollection is that the choke is only works with the low-speed jet to deliver more fuel and if the high speed jet is clogged, the only fuel must come from the low-speed jet. Partial choking increases the fuel from the low-speed jet, but the air/fuel mixture is wrong for hi-speed running. I would recheck the carb hi-speed fuel passages, looking for a clog. Spray carb cleaner thru all the passages. The hi-speed jet is probably a fixed jet on your small outboard. Just spraying carb cleaner into the air intake of the carb is generally ineffective. You need to get the cleaner thru the passages. A technique that *sometimes* works is to run the engine on a small quantity of fuel with a 20-40% mix of fresh carb cleaner. Back out the low-speed jet to allow a lot of fuel to flush thru the low-speed passages. Run the engine for 10-20 minutes while trying to increase the speed with the throttle. This will sometimes dissolve any deposits in the carb that are clogging the passages. This remedy works best on the low-speed passages and only works if the restrictions are due to gum and varnish and not a piece of foreign material. I am not directly familar with your engine. If by chance your engine does have a hi-speed mixture adjustment, then backing out that adjustment may allow the fuel and cleaner mix to get thru and clean the hi-speed passages as well. I have used this technique to clean a carb without dissembly.
Could be a vacuum leak
Two strokes have reed plate gasket and carb throat gasket. If it was a fuel pump it would run at slow speed then run out of gas. Spray WD-40 around the carb...not in the throat but around the carb and reed plate to seal any leaks. If it runs as you douse the outside with WD-40 you have a vacuum leak. Replace any gaskets. It could also be a chipped reed. A vacuum leak allows too much air so choking it adds more fuel to even the mixture. Careful about using carb cleaner and such in the fuel mixture. Remember, the oil and gas lubricate your bearings and rings. Compromising the lubrication can cause galling and internal bearing damage. Running it lean (like with a vacuum leak) can do the same damage. Run it only long enough to diagnose the problem. It sounds like a vacuum leak to me.
Two strokes have reed plate gasket and carb throat gasket. If it was a fuel pump it would run at slow speed then run out of gas. Spray WD-40 around the carb...not in the throat but around the carb and reed plate to seal any leaks. If it runs as you douse the outside with WD-40 you have a vacuum leak. Replace any gaskets. It could also be a chipped reed. A vacuum leak allows too much air so choking it adds more fuel to even the mixture. Careful about using carb cleaner and such in the fuel mixture. Remember, the oil and gas lubricate your bearings and rings. Compromising the lubrication can cause galling and internal bearing damage. Running it lean (like with a vacuum leak) can do the same damage. Run it only long enough to diagnose the problem. It sounds like a vacuum leak to me.
fuel it self
While I agree that it is most likely a carburetor problem it most likely was CAUSED by bad gas. The new ethanol added gas is junk. It has about a 30 day useful like if not treated with stabilizer. Even then you should keep the gas "fresh" by using it or just buy what you will use in the short term future. Any gas more then thirty days old put in your car and use right away. Also depending on age of motor you may need to replace the fuel line from the tank and on the engine itself. If older then a 2000 year of manufacture the fuel lines themselves can cause problems. I also use "gumout" carburetor cleaner in my gas all the time to help keep the carb clean. Thanks to the new ethanol fuel carburetor work will be something you will need to do unless you turn the fuel over very quickly. Just wait until they replace the "E 10" gas that is common now with the "new and improved" "E 20" as you will be more familiar with your carburetor !!.
While I agree that it is most likely a carburetor problem it most likely was CAUSED by bad gas. The new ethanol added gas is junk. It has about a 30 day useful like if not treated with stabilizer. Even then you should keep the gas "fresh" by using it or just buy what you will use in the short term future. Any gas more then thirty days old put in your car and use right away. Also depending on age of motor you may need to replace the fuel line from the tank and on the engine itself. If older then a 2000 year of manufacture the fuel lines themselves can cause problems. I also use "gumout" carburetor cleaner in my gas all the time to help keep the carb clean. Thanks to the new ethanol fuel carburetor work will be something you will need to do unless you turn the fuel over very quickly. Just wait until they replace the "E 10" gas that is common now with the "new and improved" "E 20" as you will be more familiar with your carburetor !!.
Tank vent
My outboard was having a running problem friday, and it turned out that my tank vent was clogged. opening the cap a tiny bit allowed the engine to run for now, I'll need to fix the problem soon The tank vent prevents a vacuum from being pulled as fuel is extracted.
My outboard was having a running problem friday, and it turned out that my tank vent was clogged. opening the cap a tiny bit allowed the engine to run for now, I'll need to fix the problem soon The tank vent prevents a vacuum from being pulled as fuel is extracted.
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