9.9 intermittent loss of power

[imported_fisherdan]

Hello,
Great forum! I've learned some things by reading other threads, but hope to get some more direction with my particular problem...

For about a year now, my Mercury 9.9 from 1989 has been losing power at full throttle. When it happens, the more I open it up - the more it slows down. If I back off to less than full throttle (3/4 to 1/2) it usually will pick back up to that particular level, but opening back up to full will bog it down again. When its real bad, I end up limping around at barely more than idle speed; and when its not-so-bad it will correct itself when not running and act near normal upon start-up. The oddest thing is there seems to be no pattern to when it will happen. Like I said, its been about a year. At times, I've run two or three tanks of fuel (6-9 gal) through the motor over several trips (over 2-3 weeks) and never had a problem. And the next time I'm out it won't go more than half-speed. Sometimes it happens right at first start-up, and sometimes its not until several hours later. I've gone out on the water to try and replicate the operating conditions when I had problems only to have the motor perform flawlessly! My uneducated guess is that it seems like a fuel problem. I emptied my tank (no dirt or particles inside), the filter at the tank-side is clean, and the motor's fuel filter is clean. Also, after I squeeze the bulb, fuel squirts out when I depress the fitting so the hose assembly is good. I plan on borrowing another tank and hose to totally eliminate that area as the problem. I bought it about 18 months ago which would have been the last time it had any educated attention. I live in Florida and use the motor year-round. The most it has sat idle has been maybe a month and I usually add Sta-bil at every fill-up. The random nature of the problem has delayed me from getting it fixed. It seems to me that if the symptoms can't be replicated then I may be taking the motor to the doctor every two weeks for a new cure and spending a lot of $$$$ which I don't have. I have a repair manual (Seloc, I think) and some rudimentary skills and understanding, so I'm up for some basic tinkering or testing - but mainly I'm asking for some educated opinions. Thanks for reading this long post!

 

[Harker]

Re: 9.9 intermittent loss of power

Are you sure your tank is venting properly? I have one that has to have the vent screw almost totally out to vent reliably.

 

[imported_fisherdan]

Re: 9.9 intermittent loss of power

Harker,
I just checked how open the vent screw is from Saturday when I had some trouble. It was backed off 2 complete turns, with 5 1/2 turns screwing it out completely. I'll keep it set at about 5 turns to see if that makes a difference. Thanks for the input.

 

[imported_fisherdan]

Re: 9.9 intermittent loss of power

It's not the vent...
I've had the boat out twice since trying the vent screw nearly unscrewed approach. Unfortunately today I had the proof its not the vent. Motor was 99% normal running out to the fishing hole. Motor sat for four hours. On the way back it starting losing power and I unscrewed the filler cap to no avail. What could cause a problem like this?

 

[Harker]

Re: 9.9 intermittent loss of power

Hmmm..Make sure your fuel line isn't kinked and nothing is sitting on it..then when it acts up, pump the bulb to see if that helps. When was the last time it was tuned up and a carb re-build done? If pumping helps then rebuild it and the fuel pump. Make sure everything(linkage) is hooked up correctly and there is no water in your fuel. When it cuts out does it "sneeze" or just slowly lose rpms?

 

[imported_fisherdan]

Re: 9.9 intermittent loss of power

Thanks, Harker
I'm positive its not a fuel line obstruction or kink....I always squeeze the bulb and it has never helped...I am meticulous about keeping my fuel fresh...No sneezing - it just slows doowwwnnn... Since I've owned the motor (18 months) it hasn't had a tune-up, but I bought it from a guy who services Mercurys and he replaced the carb / fuel pump shortly after I bought it. I am contemplating my virgin carb / fuel pump rebuild, but since pumping the bulb doesn't help the problem would a rebuild simply be an exercise in futility?

 

[Harker]

Re: 9.9 intermittent loss of power

Do you notice exaust smoke coming from under the hood at all, if the exaust gasket is leaking it can choke out the motor ? Look over all the gaskets for signs of leakage and feel the cylinder heads when it happens to see if it may be overheating. You should be able to leave your hand on it for a bit..if it is too hot to touch, it is probably overheating. Check out "decarbing" on the site here and maybe do a good "decarb".Could be a number of things..sparkplugs look good right after it happens? You might have a spark tester in your tool kit so you could check the spark when it happens. Good luck.

 

[imported_fisherdan]

Re: 9.9 intermittent loss of power

I may have something here....a film of oil / fuel / dirt ? on the motor...

In my garage I took the lid off and noticed the dirtiness of the motor - definitely more than when I bought it. A film over the carburetor and covering the left side of the motor more than the right (carb is front-left). Also, small pools of what smells like fuel in the engine compartment floor that drains out, down the shaft, and has made a small greasy stain on the floor. I've always noticed the shaft being greasy - dirty, but thought it was normal and just wiped it off. I rigged up a test tank with a garbage can, started the engine, and watched for leaks - but saw none. But it only has the problem at full throttle and I could only just put the engine into gear in my test tank. Is it possible that I could have a sometimes - leaky gasket when the fuel demand is high?

In answer to your inquiries, I've never noticed smoke coming from under the cover, and haven't checked the spark plugs...

 

[Harker]

Re: 9.9 intermittent loss of power

Does gas spritz out of the front of your carb when it's running? Sounds like maybe you should take it to a good mechanic and have them do a check on it. If it was mine I would rebuild the carb and clean the snot out of it while dis assembled.

 

[imported_fisherdan]

Re: 9.9 intermittent loss of power

If you're meaning gas spritzing out of the air intake - no, I didn't see any during my garage testing, but then again, I couldn't open her up - and that's the only time I have problems. I'll check it out next time on the water.

Speaking of cleaning the carb, I'm having trouble identifying mine to order a rebuild kit. I know its a Walbro with integrated fuel pump and has "WMC" on it, but its number "3B" isn't even listed on the Mercury parts page when I type in my outboard's serial number....?

 

[Harker]

Re: 9.9 intermittent loss of power

Look on teh engine block for a quarter sized silver disc..it should be your motor number. I had a problem finding a carb kit for my 98 25 Mariner going off what I thought was the numbers on the transom tag..was mis-reading a letter in it because it was scratched a little. Just look up a carb kit for the year of your motor..should be correct and you may have a few parts left over that would be used on other models in the range of years the kit will fit..get the kit that has a float and fuelpump kit in it also.

 

[imported_fisherdan]

Re: 9.9 intermittent loss of power

Breakthrough!

I found the source of the leak. Gas bubbles coming from the lowest bolt securing the reed block assembly to the cylinder block. I took the carburetor and reed block off and now I need help interpreting what I am looking at...

I am expecting to find gaskets between the carburetor - reed block and reed block - cylinder block.... but the gaskets depicted in my Seloc manual and by the online Mercury parts blow-up are simply not there. (The gaskets I am expecting to see are thin, form-fitting, and paper like.) However, both sides of the reed block have a partially embedded (in the metal) rubber 0-ring-like border. Is this an updated version of the gaskets I am looking for? I am assuming that replacing the gaskets and / or resealing these parts will fix my problem.

 

[Harker]

Re: 9.9 intermittent loss of power

I would think if you got a new o-ring and torqued the reed block back on correctly, it would fix that problem. Was the bolt that was seeping loose? Does the re-assembly instructions say you need to put a "sealer" around it? If not, don't use any. You will probably have to get that o-ring from a dealer so you don't have to buy a complete powerhead gasket kit. Hope that solves your dillema.

 

[Harker]

Re: 9.9 intermittent loss of power

Just looked on Crowley marine's website and it shows a flat gasket that goes against the powerhead and an o-ring that fits on the center of the reed block. Check it out.

 

[imported_fisherdan]

Re: 9.9 intermittent loss of power

An easy fix!

Harker, thanks for the help - it certainly was useful to have someone give me leads.

The short of it is that the bleeder tube coming back into the carb was splitting and worn. Thats where I was leaking fuel / sucking air. Its right next to a bolt from the reed block and thats where I saw bubbles, but it was just collecting bubbles - not making them. I cut off the worn section and reattached it!

However (the long story), I took my reed block and carb into a shop before I had closely inspected the tube. The owner was perplexed because the reed block (where I thought the leak was) is under a vacuum and shouldn't leak. Lucky for me it was the day after Christmas and they were slow, so he disassembled my carb / fuel pump and everything was clean and functional and I learned a lot! At that time I didn't know the tube was worn, so we went with the old-style paper gaskets as a starting point. Ended up I didn't need them, but added them anyway. Great businessman, Steve I think, at Ahoy Marine in Sanford, Florida was very helpful.

Another lesson learned is that a previous owner had upgraded some parts (reed block among others) that makes a serial number search for parts with the Mercury system an exercise left to the professionals...