Fuel issue- 1999 Yamaha 40 hp 4 stroke

I hate seals

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Aug 24, 2004
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Bryan Z
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36' Hatteras
With our new boat came a 1999 Zodiac and 1999 Yamahe 4 stroke outboard.
The pervious owner did not care for it very well.
The motor starts first try, yet under load it won't go past 1200 rpm without bogging down and quitting.
At the dock, It has no issue going to 3000-4000 RPM, yet not under load.
I changed the main fuel filter.

I'm not an outboard guy, so any help would be appreciated.

Thanks, Bryan
 
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I hate seals

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Aug 24, 2004
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Maybe a dirty or clogged jet.
Is there an additive you would suggest?
Or should I remove the old fuel and start fresh?

Thanks
 
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Arima-bob

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Sea foam might help, but it doesn’t always do the job if the carb has been neglected. B-12 works too, but same results. Get the carb cleaned and use fresh gas.
 
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I hate seals

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Aug 24, 2004
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Sea foam might help, but it doesn’t always do the job if the carb has been neglected. B-12 works too, but same results. Get the carb cleaned and use fresh gas.
Roger, that is what we will do.
Thanks for the advice.
 
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I hate seals

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Aug 24, 2004
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It’ll be a happy engine after that. While you’re at it, I’d do a full service on it as well. Who knows when it’s had a fresh plugs, oil, etc...
While I’m sure with enough time I could probably do most myself, but seeing as we are starting to get busy, is there anyone you would recommend for mobile service in San Diego? Thanks
 
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Jul 24, 2017
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Change plugs, after gapping them, remove old fuel, change all fuel filters, add seafoam/lucas/b-12 to the new fuel. Is it injected or carb? If carb, remove, clean, remove jets and blow with compressed air. Looking inside the carb you will know if it was the issue. Resin is no good. Oil change would not hurt. Lower unit oil changed?
 
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Mike_I

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May 19, 2006
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Cabo 216 First Love
What size outboard? Are you running it on a portable gas tank? If so look it the tank to see if there's any crap floating around. Are there more than one fuel filter? If so replace them all. Try running the motor with the gas cap open.
 
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I hate seals

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Aug 24, 2004
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Bryan Z
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36' Hatteras
What size outboard? Are you running it on a portable gas tank? If so look it the tank to see if there's any crap floating around. Are there more than one fuel filter? If so replace them all. Try running the motor with the gas cap open.
In title. 40HP
Skiff has a built in tank.
I know maybe 3% if that about these motors or gas in general, been a diesel guy for the past 20 years.
I replaced the main in line filter.
I'll look for another asap.

Other than that, there are no service records for the skiff so I have no clue when anything was done.

Thanks for all the help guys.
We are running trips for a few days, I'll check everything listed here on Wednesday and report back.
 
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I hate seals

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Aug 24, 2004
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Bryan Z
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36' Hatteras
Change plugs, after gapping them, remove old fuel, change all fuel filters, add seafoam/lucas/b-12 to the new fuel. Is it injected or carb? If carb, remove, clean, remove jets and blow with compressed air. Looking inside the carb you will know if it was the issue. Resin is no good. Oil change would not hurt. Lower unit oil changed?
Thanks.
I'll check all that.
I know nothing about the skiff before we bought it, came with the boat. Owner kept great records on the big boat, nothing on the skiff.
 
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Arima-bob

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Mar 9, 2012
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There is a shop that was recommended to me, and I’ve done business with them before, called WOT marine. They’ll do ya right.
 
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dwaynesda

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Apr 27, 2003
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With our new boat came a 1999 Zodiac and 1999 Yamahe 4 stroke outboard.
The pervious owner did not care for it very well.
The motor starts first try, yet under load it won't go past 1200 rpm without bogging down and quitting.
At the dock, It has no issue going to 3000-4000 RPM, yet not under load.
I changed the main fuel filter.

I'm not an outboard guy, so any help would be appreciated.

Thanks, Bryan
The main jets are more than likely obstructed with old fuel that turns to a hard gel substance. When the boat sits long, the fuel in the bowls evaporate and any orifices that are normally submerged when the fuel bowl is full, are affected. The easiest and quickest solution is to use Seafoam . Go to their website and they have a lot of video tutorials on what to do.

In a nutshell you will be running a small tank of fuel mixed with concentrated Seafoam until the motor smokes, then stop the motor and let it sit so the Seafoam can dissolve the obstruction. Wait the allotted time, fire it up, (lots of smoke) and hope it works, Sometimes a second dose is needed. Seafoam is wonderful stuff and has saved a lot of outboards in your situation.

Last resort is to have the carbs disassembled, jets cleaned in a tank or on the bench and reassembled and installed.

For future reference, most small engines have a small fuel drain plug on the bottom of the fuel bowls for draining. Open and drain when the boat is going to be stored and it will save lots of time in the future.

A small engine mechanic once told me the reformulated gasoline now a days is a "full employment act" for people like him. It pays his mortgage and keeps the kids in college!
 
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I hate seals

Advertiser
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Aug 24, 2004
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Name
Bryan Z
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36' Hatteras
The main jets are more than likely obstructed with old fuel that turns to a hard gel substance. When the boat sits long, the fuel in the bowls evaporate and any orifices that are normally submerged when the fuel bowl is full, are affected. The easiest and quickest solution is to use Seafoam . Go to their website and they have a lot of video tutorials on what to do.

In a nutshell you will be running a small tank of fuel mixed with concentrated Seafoam until the motor smokes, then stop the motor and let it sit so the Seafoam can dissolve the obstruction. Wait the allotted time, fire it up, (lots of smoke) and hope it works, Sometimes a second dose is needed. Seafoam is wonderful stuff and has saved a lot of outboards in your situation.

Last resort is to have the carbs disassembled, jets cleaned in a tank or on the bench and reassembled and installed.

For future reference, most small engines have a small fuel drain plug on the bottom of the fuel bowls for draining. Open and drain when the boat is going to be stored and it will save lots of time in the future.

A small engine mechanic once told me the reformulated gasoline now a days is a "full employment act" for people like him. It pays his mortgage and keeps the kids in college!
That seems to be the easiest way to go to start, thanks.
I wish I had control over the skiff before we bought the Riv, but all I can do now is clean up the mess.
 
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Miss Fitz

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Mar 4, 2013
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All good stuff above. If the motor had old fuel, you likely have a combination of clogged injectors and possible clogged VST filter OR your VST pump may have failed. Since you can idle, I don’t think your low pressure fuel pump is misbehaving.

There are YouTube videos on injector cleaning which is really easy. You will need brake cleaner, a 9v battery, electrical tape and alligator clips to activate the injectors while you spray brake cleaner into them. protective glasses are a good idea too as the brake cleaner can get into your eyes if you’re unlucky.

If your high pressure fuel VST is clogged or quit working, they can be a little pricey to replace (>$350). If you run seafoam, clean your fuel system, plugs, injectors etc and still can’t get top end, I would look at the VST next. There is a small filter on the pump intake that can be cleaned or replaced if clogged. They are not fun to take apart or put back together but it definitely can be done. Replacing them is easy but $$$
 
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I hate seals

Advertiser
Advertiser
Aug 24, 2004
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761
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SD
Name
Bryan Z
Boat
36' Hatteras
All good stuff above. If the motor had old fuel, you likely have a combination of clogged injectors and possible clogged VST filter OR your VST pump may have failed. Since you can idle, I don’t think your low pressure fuel pump is misbehaving.

There are YouTube videos on injector cleaning which is really easy. You will need brake cleaner, a 9v battery, electrical tape and alligator clips to activate the injectors while you spray brake cleaner into them. protective glasses are a good idea too as the brake cleaner can get into your eyes if you’re unlucky.

If your high pressure fuel VST is clogged or quit working, they can be a little pricey to replace (>$350). If you run seafoam, clean your fuel system, plugs, injectors etc and still can’t get top end, I would look at the VST next. There is a small filter on the pump intake that can be cleaned or replaced if clogged. They are not fun to take apart or put back together but it definitely can be done. Replacing them is easy but $$$
Thanks so much for the insight and time you spent explaining. I'll get on it mid week and sure hoping it's I can fix it. Thanks!!
 
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dwaynesda

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I might be mistaken but, I don't think they introduced the F series (fuel injected) to the 40 HP until the late 2000's. Injectors and VST are part of the F series, not the carb motors.
 
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I hate seals

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Aug 24, 2004
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So I ran the Seafoam through the motor and it without a doubt runs smoother, but still stalls at 1200 rpm or more. So I pulled the carbs and will clean them tomorrow. Here is what they looked like. See anything wrong?
They don't look bad to me, but as I mentioned, not a gas outboard guy.

IMG_0908.jpg


IMG_0907.jpg


IMG_0906.jpg


IMG_0905.jpg


IMG_0904.jpg


IMG_0903.jpg
 
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Da Mad Anglah

Old fut who still misses home on da islands
Oct 21, 2020
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Chris
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'93 18' Weldcraft "Rod Rage"
The throat of those carbs won't be your problem, its the jets in the bowl. Pull 'em all out and take some electrical wire, or carefully use a welding tip cleaner, through each one of the jets. Don't run too big a tip cleaner through them or you may enlarge the jet! You can if you like, but too big a jet and you'll be replacing them!
In all honesty, its always the main jet that gets clogged with something hard similar to a grain of sand and no amount of chemicals will physically disintegrate it.
Make sure there's any other jets or metering tubes that's in there get cleaned the same way, and you'll find when you put it all back together that the engine runs like a champ!
Just did this to an old quad and a pressure washer in the past 2 months, both were barely able to run, after cleaning, they both start with zero effort and run high rpms just fine!
Tech tip! Those philips screws will most likely be a bitch to loosen! Take a well-fitting philips screwdriver or a long bit and whack each screw lightly with a hammer before taking them apart. Never a stripped screw if you do this before trying to remove them. Don't get friggin' crazy with the hammer, but don't be too soft with it either!
 
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dwaynesda

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So I ran the Seafoam through the motor and it without a doubt runs smoother, but still stalls at 1200 rpm or more. So I pulled the carbs and will clean them tomorrow. Here is what they looked like. See anything wrong?
They don't look bad to me, but as I mentioned, not a gas outboard guy.

View attachment 1280607

View attachment 1280608

View attachment 1280609

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You have 2 circuits in that carb. Low speed (idle) and High speed (main jets). The idle circuit sounds like it is fine. It is your main jet(s) that feed the high speed circuit that are clogged. Remove the fuel bowls and you will see the main jets. They are brass and they screw in. Screw them out and look through the orifice . They should be perfectly clean.
 
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