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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3980
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Year 2000 9.9 hp 2 stroke mercuy outboard. Starts great runs

Customer Question

year 2000 9.9 hp 2 stroke mercuy outboard.
Starts great runs great until top end. Then bogs down a bit.
It has new plugs, new carb (probably not needed).
It's not the fuel tank, filter or gas into the engine.
Last guess in reed valve block...I just took it apart and I see no gap or bro***** ***** valves. But it could be them. Being an old bike racer, I've had those problems.
Any idea??
It does have a lot of usage, but has good compression.
Submitted: 2 years ago.
Category: Boat
Expert:  Jason replied 2 years ago.
Hello, my name s Jason, whom am I speaking with? Is the engine bogging down a few hundred rpms at a time, or is it dropping a thousand or two rpms in the flick of a switch? What makes you say it's not the tank or gas to the engine issue, what did do there for testing?
Customer: replied 2 years ago.
It pumps up fine. No problem there. Cleaned it and took the lines apart. Pumped it to see if it flows good. It does.
I've tried pumping it with the throttle open. Nothing happens.
The engine runs up to a certain rpm and no higher...definitely not where it should go. Like when a fuel pump gets a little hole in it. But I put on a new carb. Fuel pump is part of it on this engine. No change. The filter is ok. Lines are open to the carb. Runs great up so far and then no more. Once in a while it may surge (very momentarily) like it's gonna rev up. It's just not getting the fuel into the engine is what it seems to me. I know on my old Johnson if the fuel pump was bad, I could pump the tank bulb and it would speed up. The vent is ok.. I tried loosening the cap to check that. No change there. I'm just at a loss on it. About ready to buy a new one, but this one shouldn't be worn out
Could it be weak coils? There is no misfiring that I can tell, so I don't think it's that. Just tell me what YOU think it could be.
Customer: replied 2 years ago.
By the way, my name is ***** ***** to race bikes, so am very familiar with engines. Overhauled several in my lifetime.
This just has me baffled. I know the back pressure from the engine operates the fuel pump. I was wondering about that. I've blown air thru the two openings the hoses are connected to in hopes that there could be a partial plug in them. Dang! Would fatiqued reed valves be the culprit?? It really has had a lot of running on it in Florida.
Expert:  Jason replied 2 years ago.
Hello. Has the engine ever run properly on the boat that it is mounted to now? What kind/size boat is the engine mounted to?
Customer: replied 2 years ago.
It's a lightweight vee bow 14' aluminum. The depth is ok. The planning fin about an inch below bottom of boat. Empty, the boat is light enough for this old man to pick up either end easily. Maybe 200 total weight. Yes, it pushed it very good.
Customer: replied 2 years ago.
The planing fin. Not planning Dam pc keeps trying to correct me when I'm already correct.
Customer: replied 2 years ago.
I bought it new in 2000, so I'm not a stranger to it. Lol!
Expert:  Jason replied 2 years ago.
So the engine has run differently in the past for you, is that correct?
Expert:  Jason replied 2 years ago.
Does the boat have a tachometer on it, if not, can you hook one up to the engine?
Customer: replied 2 years ago.
yes. it ran great.
No tach. just hand tiller.
Customer: replied 2 years ago.
It's well below top end tho. I can tell that easily.
Customer: replied 2 years ago.
The throttle opens completely.
Expert:  Jason replied 2 years ago.
Do you have a timing light to check for spark on both cylinders?
Customer: replied 2 years ago.
Customer: replied 2 years ago.
It fires and runs great up to maybe a thousand rpm (guessing here) from top end.
Expert:  Jason replied 2 years ago.
Have you tried running it on the lake with the engine cover off?
Customer: replied 2 years ago.
Oh, yes!
Customer: replied 2 years ago.
timing mechanism seems to open up ok..throttle, too!
Expert:  Jason replied 2 years ago.
You don't have any tools so there isn't much we can do. I don't think this is something I'm going to be able to help you solve without testing things the proper way.
Customer: replied 2 years ago.
Changed plugs, too.
Customer: replied 2 years ago.
Ok. I'll take it to a repairman and have him check out all electronics on it. Thanks anyway, Jason!
Expert:  Jason replied 2 years ago.
Your very welcome. Good luck
Expert:  Charles replied 2 years ago.
Hello, my name is***** have a few tests that you can do on the engine with out needing special tools, if you are interested in trying them.
Customer: replied 2 years ago.
if this is for the $5 charge, sure! I was notified by my credit union last night that I was charged 20 something dollars in addition to the $5. I DID NOT authorize that.
So, that said, sure!
Expert:  Charles replied 2 years ago.
Great. Start the engine on a hose. Allow it to warm for a min. Then bring in the RPM to about 3000. the with out slowing down the engine pull the kill cord. remoe the spark plugs and look for signs of water on them .Plesase let me know what you find.
Customer: replied 2 years ago.
Hope you're still on. Been busy. Fourth and also the wife is sick.
I pulled the engine off and have it on a stand. But I pulled both plugs and there is water on both. One plug is cleaner than it should be also. So I suppose that cylinder is taking on more than the other. Cracked head?? Blown gasket?? I'm pretty sure it didn't freeze up from the weather.
Worth fixing??
Expert:  Charles replied 2 years ago.
Welcome back,
Remove the exhaust plate from the left side of the engine. Look for signs of a broken gasket. If the exhaust looks normal, you have a failed powerhead gasket.
Customer: replied 2 years ago.
Gasket was blown up near the top cylinder. Also piston is scored. I ordered another two gaskets and will put them on anyway.
It may run good enough...and maybe not. I'll also check the plugs again after I've put it back together to see if that fixes it.
Meantime, I bought a new 15 hp Tohatsu four stroke.
Thanks for your help. You lead me to the cause.
Expert:  Charles replied 2 years ago.
I think that the engine will run good.
The Tohatsu is a good engine as well.