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2010 8hp 4 Stroke Problem.

M

mikes1990

Member
hey all , having some trouble with my mercury 8hp 4 stroke. runs fine for first 30-45 minutes or so. if i shut it off to lets say do some fishing , when i go to crank it up , it turns on and when i hit the gas it slowy dies out like it isnt getting fuel. i cleaned the carb , gas vent is open on the tank. it has new gas lines with filter. so im running out of ideas. then after it dies it wont crank , i have to let it sit and sometimes it fires up and rides fine. i noticed the last time it happend i messed around with the fuel line going to the motor from the tank and it cured the problem but other times doing that hasnt. so im kind of stuck on this one. i would appreciate any help.
 
Did you change the quick disconnect coupler ? They sometimes leak air into the system. Dont reakky match your symptoms tho . Have you tried pumping bulb to see if you still have fuel pressure ? Did you disassemble carbs and thoroughly clean . I had all kinds of problems with my honda. Fuel passages are extremely small . I cleaned with a ultra sonic cleaner. Worked great. You can temporally by pass the quick disconnect by routing the fuel line directly to filter or pump (whichever is next in line)
 
i appreciate everyones input. dtoole , yes i bought the complete fuel line assembly it came with new quick disconnect coupler and prime bulb. i cleaned the carb very well, i took it completely apart. i mean wouldnt you think if it was the carb it would do it all the time? starts up on first pull when cold, rides good for a good 20-25 minutes, then boom.
 
when i hit the gas it slowy dies out like it isnt getting fuel
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I reread your comments. Did you replace the acellerator pump during the rebuild? Is the engine getting hot from a weak impeller? I never shut down my engine after a run w/o letting it idle for 5+ minutes.
 
well i didnt rebuild the carb , i just took it apart and cleaned everything. im starting to think it might be overheating? im not familiar with these engines as its my first outboard. when they overheat do they shut off ? more i think about it is it happens after running. so im leaning now to overheating. the guy i bought it from said it had a new lower unit? not sure what he meant? could it be he installed something incorrectly?
 
when i hit the gas it slowy dies out like it isnt getting fuel.
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Open the gas cap on the tank just a little...vent may not be working. If that does not help squeeze the primer ball when you increase the throttle.
im starting to think it might be overheating?
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I'm not familiar w/your engine but most outboards have a horn/alarm that sounds off when it overheats.
 
guyjg said:
Open the gas cap on the tank just a little...vent may not be working. If that does not help squeeze the primer ball when you increase the throttle. I'm not familiar w/your engine but most outboards have a horn/alarm that sounds off when it overheats.
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ok im going to try opening the gas cap a little and see if it changes anything. im not sure about it having any alarm or horn. its a 8hp not sure if they come equipped with one.
 
a little update. upon further looking into the fuel system , i checked the fuel filter and it looked as if it had some type of i wanna say brownish looking stuff inside. could a dirty or clogged fuel filter be the culprit?
 
That is granular fuel varnish. Using a fuel preservative can nearly prevent that fom forming.
well i didnt rebuild the carb , i just took it apart and cleaned everything
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I'm betting that crud is floating around inside your carb.
 
guyjg said:
That is granular fuel varnish. Using a fuel preservative can nearly prevent that fom forming. I'm betting that crud is floating around inside your carb.
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im going to replace the fuel filter and re clean the carb and see if it fixes the issue. the person that had it before me im guessing didnt use any type of fuel additive i have started using a ethanol treatment in the fuel so hopefully it shouldnt happen anymore.
 
Use compressed air to blow out the tiny fuel passages in the carb. Thanks to the EPA these carbs require super clean fuel. Change the fuel filter at least annually. Disconnect the fuel line when you are done boating for the day and let the engine run the carb dry.
 
after cleaning the carb today i noticed the bottom part of the carb where the prime bulb hose connects to , is leaking gas when i press the prime bulb. any ideas? i opened it cleaned it , and made sure the screws where tight , still shooting gas out.
 
mikes1990 said:
after cleaning the carb today i noticed the bottom part of the carb where the prime bulb hose connects to , is leaking gas when i press the prime bulb. any ideas? i opened it cleaned it , and made sure the screws where tight , still shooting gas out.
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anyone? its the bottom part of the carb that has 3 screws , where the prime bulb hose attaches to. well when the prime bulb is pumped gas it shooting from where the piece mates to the carb. there is no o ring or gasket , just the plunger as its called.
 
guyjg said:
This is your carb? It's leaking around #29? http://www.marineengine.com/parts/mercury-outboard-parts/8-4stroke209cc/0r042475-up-usa/carburetor No gasket or sealant between the parts? Strange...take it apart and check for warpage or debris...make a gasket if it won't stop seeping. You're sure it isn't coming from the nipple?
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yes from the area of 29. im positive its not coming from the nipple. i thought it was strange as well that there wasnt any gasket or anthing. i noticed that # 26 is rubber like and thought maybe thats what seals it?
 
Sorry, I don't know. Does the seal area look like it has a machined surface? No damage to it? Gasket material is available at any autoparts store. I have a roll in my shop and have used it on/off for years to make gaskets.
 
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