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I have a 1987 15' O powered by a J50TLCUD engine. After

I have a 1987...

I have a 1987 15' Henry O powered by a Johnson J50TLCUD engine. After running at 3/4 throttle for 20 minutes or so, the engine bogs down, producing very little thrust. If I back off the throttle for a minute or so then throttle up again, everything is fine. I thought about the vent on the 6 gallon tank and it is open. I bought the boat at the end of last season and this is the first time I've used it. The tank is new and the fuel is fresh with SeaFoam in it. I'm thinking about pulling the carbs and rebuilding them. Do you think that will help?

Mechanic's Assistant: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else the Marine Mechanic should be aware of?

I think that covers all the facts.

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Answered in 1 minute by:
3/16/2018
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 18,179
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Hello my name is ***** ***** am I speaking with? I read what you wrote. When this problem happened, did you happen to try pumping the primer bulb over and over, or notice if the primer bulb had sucked itself flat?

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Customer reply replied 5 months ago
Hi Jason, Larry here. I didn't try pumping the primer bulb and the bulb didn't collapse.
Customer reply replied 5 months ago
I did ensure that the vent on the tank was open
Customer reply replied 5 months ago
The thing that concerns me is not knowing when the carbs were serviced and fuel filter was replaced.

Hi Larry. Will pulling the carbs help? Well, maybe.

The problem you are describing is fuel starvation, where fuel isn't making it's way to the carbs in the first place. If the vent was closed, if there was something in the fuel tank causing the tank pickup to clog, if the tank has a bad antisiphon valve on it (some tanks come with anti siphon valves, some do not), if there was pinched or collapsing fuel line, all of those items would cause a fuel starvation issue, and the fuel pump would struggle to draw fuel from the tank. If there is any kind of crack in the fuel pickup, or the fuel fittings, air can get into the system, and the fuel pump will suck in air through that leak instead of sucking fuel up from the tank.

At the same time, if the fuel pump is weak, or if it just happened to crap out on your maiden voyage, that would cause the same symptom.

Finally, there might very well be some debris in the carbs, or even a sticking float inside of one. Causing a lack of fuel to the engine.

If you actually wanted to get into testing things. What you would need is a vacuum gauge, a pressure gauge, a couple of T fittings, a double ended hose barb, and some clear nylon tubing. The fuel pump has an input and an output side. What you do is with the T fittings and you would splice in a pressure gauge on the output side of the pump. You would splice in a vacuum gauge on the input side of the pump, and you would also splice in some clear tubing on the input side of the pump. Once that is all done, you go run the boat, and duplicate the problem. What you are looking for is the relationship between pressure and vacuum, and if there are any air bubbles present in the clear tubing. Starting with the air bubbles, if there are any air bubbles in the tubing, then the boat has an air leak, and that needs to be found and corrected. Small bubbles here and there are not a problem, it is if you get a steady stream of bubbles that causes problems. (I am still here and typing away, stay tuned as there is more to come)

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Customer reply replied 5 months ago
It's a new tank with new fuel line running to the engine. I've already ensured all connections are tight.

A​fter that, you would have to look at the pressure and vacuum readings. Starting with vacuum. If the gauge shows more than 2.5 inches of mercury when running the engine, there is a blockage or restriction in the tank, fuel lines, or the primer bulb, and the engine is starving for fuel. That blockage/restriction will need to be found to correct the problem. If the vacuum reading is under 2.5, then you would need to look at pressure. Fuel pressure needs to be between 3 and 7 PSI at any RPM. If fuel pressure is below 3, the fuel pump is weak. Lastly, if there are no air bubbles, minimal vacuum, and fuel pressures look good, then at that point it would be safe to say the problem is in the carbs, and you can tear those off for rebuilding. Finally, realistically speaking it takes a lot of time to rig up those gauges and go run the boat. In most cases it is simply quicker and more time efficient to simply run through the entire fuel system on the boat and engine. Pull the carbs and rebuild them. rebuild or replace the fuel pump. Have a good look at all the fuel lines and make sure nothing is cracking and everything is properly clamped. Make sure the fuel tank fittings are not cracked or split either. In most cases it's simply quicker to do all that first, and then if it still gives you troubles, then go ahead and hook up all the gauges and test things by the book. Also, don't forget to change your spark plugs, misfiring plugs will make the engine run poorly as well. Does that all make sense to you. 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 or more specific 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.

Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.

Thank you
Jason

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Customer reply replied 5 months ago
This engine WAS using E10 fuel prior to me buying the boat. I'm now using marine (non E10) fuel. That's why I'm thinking carbs. Tank, primer bulb, fuel lines, and all fittings are new.
Customer reply replied 5 months ago
I may go ahead and rebuild the fuel pump just to be sure.

The on engine, the fuel system on that engine was never designed to run E10. E10 will rot the insides of the fuel lines (the ones on the engine) as well as rot the diaphragm out on the fuel pump itself. Most people do not replace the fuel lines on the engine unless there is a problem, but you definitely want to check them. What I do are 2 things. 1. Just bend it, if the lines are cracking on the outside then they are almost certainly cracking on the inside as well. 2. Stick a clean white paper towel on one side of the fuel line and blast compressed air through the other side. If any black bits come out then the fuel line is falling apart. Fuel lines on average last 10 to 12 years during regular usage. I wouldn't be surprised if the lines on your engine (the ones between the fuel pump and carbs) are all original. They usually are when the motors come into the shop. Was there anything else?

Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 18,179
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Customer reply replied 5 months ago
That tells me where to start. I'll replace the on-engine fuel lines, fuel filter, rebuild the fuel pump and carbs. That should take care of the problem. Thanks for the assistance, you'll get a 5 star rating.

You are very welcome and I was glad to help. Thanks again and good luck!

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