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Mercury 50 1987 bogs down when full @ full throttle

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DennisCamps

New member
Hello,

My name is Dennis and iam living in the Netherlands.
Iam pretty new to boating but i have good technical understanding.

So iam running this new to me speedboat 4.5 meter with a mercury 50 hp from 1987.
I have to say it runs pretty good.

First it died at idle and it was very hard to get in to the harbour with engine quitting all the time.
What did i do,

I cleaned out the carbs and put new gaskets on.
I replaced all the internal parts of the fuel pump.
i replaced all gas lines. ( one note on this the gas filter on the engine is not installed in the correct way. fuel comes from ----> and filter says ----< but at this moment i dont think there is a problem with it.)

Now when i go at WOT the engine will bog down ( this happens after about 30 seconds of going WOT)
Then i go to near neutral and then i can go WOT again for about a minute. This is repeated all the time.

So what did i do, i took the engine cover off ( No noticeble problems anymore ) Put the cover on and moved the fuel line.
Now it still happens. but it takes longer to bog down on me like 1 minute.

What can this problem be. Can it be the fuel filter mounted incorrectly?
Can it harm to just remove it. i mean i have a filter between tank and motor aswell.

Regards,
Dennis
 
Three or four cylinder engine? Serial number is what? You can orient the filter correctly or just remove it for testing and insert a "T" to connect a pressure gauge in its place...fuel pump should show 4-6 psi. When you cleaned the carbs did you soak them in cleaner or just spray some into the openings and did you blow them out w/compressed air? How did you set the idle mixtures screws? Does the squeeze primer bulb go flat when it bogs? If you squeeze it when it bogs does it clear the bog issue and go to WOT?
 
Hello,

Its a three cyliner and the serial nr is 9651192
I used 400 ml brake cleaner fluid to flush all holes in the carb and no hole hesitated. I did not used compressed air to blow everything out.
The idle mixture screws are at like 1.25 uit from all in. i have set those so that it idles nicely.
I have the idea that squeezing the bulp does not make a difference.

i will buy a pressure gauge to check the psi on the fuel pump.

Regards and thanks for the awnsers
 
The idle mixture screws are at like 1.25 uit from all in. i have set those so that it idles nicely.
Click to expand...
You need to turn the mixture screws outward CCW an additional 1/4 to 1/2 turn to richen the mix of fuel/air to prevent the engine from running too lean at low speeds. You might have to reclean the high speed jets in the carbs. Your cleaning method may have just loosened hard varnish in the carbs that is now blocking the jets. Brake cleaner is just a degreaser. You need to use a solvent based cleaner for carbs. Soaking the carbs overnight will help and always finish w/compressed air. If you have access to lacquer thinner it is a strong cleaning solvent. Use it only on metal parts and use it outdoors.
 
Built in fuel tank or a portable?

You might have a vent issue on the tank (with either type) or a bad anti-siphon valve if it's built in.

As Guyjg suggests, definitely make sure that your carb was done properly and you have correctly adjusted. If nothing changes I would look to your fuel supply - if the vent is clogged (partially clogged) perhaps your motor pulls fuel until it can't suck anymore (quick enough to maintain WOT) - you go back to idle/neutral and the tank (sucks in a little air), works fine for a few seconds until it runs out again - on and on....
 
I have a portable tank and its new. vent is completely open.
I will take off the carbs again en let it soak over night.
So regarding the idle screw. when i turn it out counter clock wise it will run richer and dies when putting in gear.
how do i notice that it runs to lean at low speeds?
I have also read that when a fuel filter is mounted incorrectly it could end up in a lower fuel delivery.

Cheers,

Cheers,
Dennis
 
DennisCamps said:
I have a portable tank and its new. vent is completely open.
I will take off the carbs again en let it soak over night.
So regarding the idle screw. when i turn it out counter clock wise it will run richer and dies when putting in gear.
how do i notice that it runs to lean at low speeds?
I have also read that when a fuel filter is mounted incorrectly it could end up in a lower fuel delivery.

Cheers,

Cheers,
Dennis
Click to expand...

I guess you don't have access to compressed air. As a substitute we use a product: Berrymann's Chem Tool. It is an aerosol and has the same carburetor cleaning agents as does the can. You can have debris in your jets that require high pressure to remove. It's not as good as 100 psi compressed air, but better than just sloshing around in cleaner.

Forget any pictures you may see of the fuel filter installation, in particular which end has the cap on it. On the side is an arrow and it shows the direction of fuel flow. My replacement has the arrow in the opposite direction to the original if you use the end cap as your metric. The only difference in having it on forward or backwards is the area of accumulation of crud. In the forward direction you have the outside of the filter media to trap particles. Installed in the reverse direction you only have the area of the center of the media and as crud builds up it makes a difference in how fast it clogs. If you use clean fuel and keep your system flushed out....aka running the engine, your filter will last for years. I changed mine after 10 years and could still blow freely through it.

Mark
 
Hello again,

So what did i do, i reversed the fuel filter and i looked to hold up better.
This morning i took the boat for a spin and even at half throttle the boat was bogging down. quick to neutral and wait a few second and i could rev up again. this repeats over and over again.
so i took the cover off of the engine and then no problems anymore.

What can this be ?

Regards,
Dennis
 
The only thing that changed by what you said was that you allowed the carburetors access to more air. Don't suppose dirt dobbers have clogged the air inlets which are usually at the top rear of the cover. Have to have air in a venturi carburetion system to pull the fuel out of the bowl. If it were the low speed jets too tight (1.25 turns you originally said....don't know what you did after given the advice to open them) you would think it would be the other way around, but maybe not. Did you open the jets as was suggested by Guyjg?

Mark
 
Hello,

I did not open the low speeds needles. Because if i do the engine lowers in rpm and when shifting in gear the engine quits.
What i also noticed and can maybe help, with the cowl on and my frend giving throttle til the point the engine starts to quit the ball on the fuel line stays hard. when bogging down and putting the throttle to neutral it became soft as in half hard.

Dennis
 
Interesting. Prior to running the engine, the ball fills the carb bowls and when full the needle valves close off the flow of fuel and continued pumping just pressurizes the whole fuel line from the bulb up. Once the engine runs, it obviously consumes fuel from the bowls and the fuel pump is supposed to be sucking on the fuel line and pressurizing (3-6 psig sort of thing) the fuel line from it to the carbs to move fuel fuel to keep the bowls full. That being the case, the normal thing is that the bulb will be softer as you mentioned, not collapsed like sucked flat which would reflect a lack of air to the fuel tank and the fuel pump was putting a vacuum on the fuel line.

When you replaced the internal parts to the fuel pump, what did you use for your instructions? Did you have any doubts that you didn't understand where everything went or any confusion that could indicate a problem with the pump? I still am confused about the relationship to removing the hood other than it may have been pinching the fuel line where the line enters the engine, or pinching the fuel line elsewhere. Have you checked that? I'd think that would be more of a possible smoking gun than the air inlet on the hood getting clogged.

Mark

 
I had no doubts when i redo the fuel pump. Also when i did something wrong there i think the issue would occur with the cowl off aswell.
I will make sure that the lines are not being pinched ow something. and will also check if the air inlet is clogged. Where is his air inlet located? is it in the back of the engine? I will have the boat in the water for another week untill storage.
So hopefully i get it sorted out. One other thing i might need to mention is that its only starting when pulling up the fast idle lever completely up for it to start. if i dont set it to fast idle it will not start.
This is with cold and warm engine. when this is done engine always start immidiately.

Thank you for your awnsers so far!

Dennis
 
DennisCamps said:
I had no doubts when i redo the fuel pump. Also when i did something wrong there i think the issue would occur with the cowl off aswell.
I will make sure that the lines are not being pinched ow something. and will also check if the air inlet is clogged. Where is his air inlet located? is it in the back of the engine? I will have the boat in the water for another week untill storage.
So hopefully i get it sorted out. One other thing i might need to mention is that its only starting when pulling up the fast idle lever completely up for it to start. if i dont set it to fast idle it will not start.
This is with cold and warm engine. when this is done engine always start immidiately.

Thank you for your awnsers so far!

Dennis
Click to expand...

Agree on fuel pump not problem due to cover on or off metric.

Most engines are sealed against sea water getting into the engine. Engine has to breathe. So air inlet is at the rear top of the cover sometimes in the middle, sometimes openings on each side. It's there somewhere.

Interesting on fast idle. Speaks again of jets too closed. I have had engines that had to be at fast idle to start regardless. My current 90 triple only needs it first start of the day but it has to have it and the enrichment.

Barring a blocked inlet, seems the only answer on the cover is pinching the fuel lines and on the other you might take another look at your low speed jet settings.

Mark
 
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