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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 16213
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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1988 Mercruiser 4.4 alpha one I changed out the throttle and

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1988 Mercruiser 4.4 alpha one I changed out the throttle and shift cables to mu control box... we took the boat out ran perfectly for about an hour opened it up to about 35 mph was running real good all of a sudden we let off the throttle went to throttle up again and once it hit 3000-3500 rpm the engine would bog down and have no acceleration and stall.... we started it back up will run perfevtlctky at lower rpms but give it more throttle and it dies the same and stall?
Customer: replied 30 days ago.
4.3 sorry

Good morning, my name is ***** ***** am I speaking with? I read what you wrote. Mercury engines are cataloged by serial number, do you happen to have that number handy so I can see exactly which version of the 4.3 you have? Next, is there a history to this engine, have you ever seen it run correctly?

Customer: replied 30 days ago.
I don't know the history of this boat I just bought it a few months ago... it was overheating when I bought it changed out the impeller and thermostat runs at 160* good now...

I can't make out the serial number in that picture. Are you able to make out what the numbers are?

Customer: replied 30 days ago.
No I'm sorry it's very blurry it's very hard to see the exact numbers

Is the engine carbureted or fuel injected?

Customer: replied 30 days ago.

Got it. Have you done anything on your own yet to troubleshoot the issue? Did you have questions that you specifically wanted me to answer, or would you prefer if I explained how we would approach this type of symptom in the shop?

Customer: replied 30 days ago.
This just happened last night I have it in a boat slip... I mean the first thing that came to my mind was plugs wires cap and rotor...

Is the engine actually stalling or is it just dropping power?

Customer: replied 30 days ago.
It would start to bog down at 3000-3500 rpm loose power then stall

Got it. Give me 10 minutes to get something typed up for you.

Customer: replied 30 days ago.
Ok great thanks
Customer: replied 30 days ago.
I'm at work now so I'm not at that boat till later

There definitely may be more than 1 thing wrong with the engine. But stalling typically means the engine is running out of fuel. And fuel is not getting from the tank to the inside of the engine. When the cap, rotor, plugs or plug wires go bad what will happen is those effected cylinders will either misfire or not fire. If the engine was running on say just 4 cylinders instead of all 6 because of a bad ignition component, it would still stay running as long as those firing cylinders were getting fuel. The engine might very well benefit from a tune up. But that by itself is not likely causing the stalling, The stalling is most likely because is the engine is simply running out of fuel. Here is what we would do in the shop.

1. Change all the fuel filters. If the filters are clogged then obviously fuel is not going to make it's way from the tank to the carb. Some models have filters inside the fuel pump as well as one in the carburetors fuel inlet.

2. As simple as this sounds you always start by running it off of a different fuel tank, like a small plastic portable tank. Half the time there isn't anything wrong the motor itself, but rather something wrong with the boats fuel system. This can be a pinched or collapsing fuel line, bad or old gas, or a bad anti siphon valve. Marine engines are very sensitive as to the quality of the fuel, and if any part of it is over 90 days, the fuel itself is always going to be suspect. This is a pass or fail test, and the engine is either going to run better or it is not. If it does run better, on this portable tank, first change the anti siphon valve and retest with the engine hooked back up to the boats fuel tank. If it goes back to running poor on the boats fuel tank, that tank will need to be pumped out. Bad anti siphon valves are a common problem, when they go back they create a blockage and restrict the amount of fuel that flows to the engine. If the engine does not get enough fuel it obviously will not make full power. Click this link, this explains more on the anti siphon valve and why they go bad. On this anti siphon valve there is an inlet side and an outlet side. The inlet side faces the fuel tank, the outlet side faces the fuel line. When the engine runs, the fuel pump creates suction. This suction pulls the check ball off of it's seat and fuel is allowed to flow around it. The problem with this is over time the spring in the valve will get weak or simply break. When that happens the check ball will be free to jump to the outlet side of the valve and create a blockage/restriction on the outlet side of the valve. If the spring is simply weak and not broken, this will more or less happen at random. Click this link for a picture, it will make more sense once you see it Http:// The anti siphon valve itself is located at the fuel tank, where the fuel line connects. If you pull the fuel line off the tank you will see a hose barb, that hose barb is the anti siphon valve.

3. Check the fuel pressure. Fuel pressure needs to be at least 3 psi at all speeds. This needs to be checked with the boat in the water and the boat going at full speed. If fuel pressure is below 3 psi then the fuel pump is weak. You want to make sure you test this after #2. If there is a bad fuel line or bad anti siphon valve will cause fuel starvation and low fuel pressure.

4. Finally. If all the filters are changed, and if there was no change when running it on the portable tank, and if the fuel pressure was good, then the problem is going to be inside the carb itself. The carb's internal fuel jets are going to be semi-clogged and not allowing fuel to make it's way from the carb and into the cylinders. Does that all make sense. That is where you stand on your end and what the problem is. I think that should do it but I work for tips so I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Please note that our question sessions never close out, so if you need to come back later down the road with follow up questions to the issue, you can do so at any time, even after putting through a rating.

Thanks in advance, and good luck

It took me a while to write all that for you. It looks like you read my answer and left without selecting a rating for my service, replying back, or simply thanking me. Was there something else?

Jason and other Boat Specialists are ready to help you
Customer: replied 30 days ago.
No sorry I read it quickly cause my boss called me I was gonna read it more clearly when I take break but I will rate it now
Customer: replied 27 days ago.
I changed out the fuel filters and the anti siphon valve took the boat out today same thing happened so I looked into the carberator and the valve that's on top of the carberator that allows air into the carb is not moving it was wide open allowing full air to enter the carb... i wire tied the arms on the side of the carb got my boat back to the slip as it was functioning normally with me wire Tyeing it... I have pictures of my carb am I missing a spring or something why that air valve on top is not moving with the throttle cable I can move the arms with my fingers and can move it no problem but seems like something may be missing why it is not moving with them throttle control..
Customer: replied 27 days ago.
I assume this is the choke but it's fully open does not move with throttle and stalls out the motor at higher rpms when I wire tied it so it would move the boat ran fine
Customer: replied 27 days ago.
The number listed on the carb is 9600s 2195

Good morning. Are you able to send a picture over of what you are looking at?

Customer: replied 27 days ago.

Okay I see it. That plate is the choke plate, and it's supposed to be open when the engine is above 75F degrees.

Customer: replied 27 days ago.
but in the side of the carb where the throttle cable is those arms that control the choke plate do not move with the throttle control like something is missing like a spring

I​s this choke plate closing on it's own when the engine is running?

Customer: replied 27 days ago.
No it does not move kind stays in the upright position

If it's not closing on it's own then it's not going to contribute to the problem. That would only be a problem if it actually was closing on its own.

Customer: replied 27 days ago.
Ok no prob I had read that the plate should be almost closed about an 1/8"-1/4 open in full throttle

The plate should be just very lightly closed when the engine temps are roughly 75F or lower, and more or less fully open when the engine is warmed up. As long as that plate isn't closed, it wouldn't be causing the problem.

Customer: replied 11 days ago.
Hey so I changed anti siphon valve, fuel pump, water fuel separator filter I even bought a new 4 barrel carb and changed that...I took it out today and I got to the entrance to the bay after say 2500 rpms for 1 minute and it started bogging down and stalled... I turned around and started heading back to my slip got half way through the lagoons and it stalled out at wake speed.. started it again same thing kept happening... a boat passsed us and towed us back to out slip...

Did you go through the entire list of things that I wrote to check? Did you run the engine off of a different fuel tank? Did you change all the fuel filters? Did you checked the fuel pressure?