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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14579
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have a 1996 25 HP 2 stroke outboard Model 1-025211SD S/N

Customer Question

I have a 1996 25 HP 2 stroke outboard Model 1-025211SD S/N 0G409321. This outboard went unused for 2 seasons and then would not start. I have replaced the fuel line (concerns with ethanol fuel damage), fuel filter and installed a Carburetor Repair Kit (P/N 1395-823707-2). I have added fresh fuel to the tank and made sure that the filter in the tank pick is clean. The engine starts easily and idles well but will not power up under load (in gear). It revs to high RPMs in neuteral but when in gear if I turn the throttle just beyond a fast idle the engine bogs and dies. It feels as if the engine is being starved of the fuel needed to run beyond idle speed. I have checked the engine timing and the spark advances as expected so it does appear to be an ignition problem. The spark plugs are also new. What would you suggest I do next?
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.
Hello my name is ***** ***** am I speaking with? Couple of things. But the first thing always starts with spark output and compression testing before digging into the fuel side of things. Has that been done yet?
Expert:  Jason replied 1 year ago.
Also, you said you added fresh fuel to the tank. Was the tank empty before hand, or was there old gas in it?
Customer: replied 1 year ago.
My name is***** was about a gallon of gas in the tank that was new last fall and had appropriate amount of stabalizer added. The compression has not been tested.
Customer: replied 1 year ago.
I added the additional fuel in case the fuel in the tank had lost some of its octane over the winter.
Expert:  Jason replied 1 year ago.
Gotcha, now what would you like to do? Would you like me to explain how I troubleshoot these engines in the shop and you can go through that explaination and do what you have the tools for, or what works best for you?
Customer: replied 1 year ago.
Yes please explain how you would troubleshoot this engine.
Expert:  Jason replied 1 year ago.
All engines need 3 things to run properly. Compression, spark, and fuel. The problem with a lack of power situation is you have to do some troubleshooting to figure out which of the 3 the engine is missing, giving you that bog.If you brought this to me here is how I would go about troubleshooting it. 1. Compression test. Your results should be about 90psi or better on that engine, all cylinders should be within 10-15% of eachother. If you get much below 90, then the engine is worn out or has mechanical problems, and you might as well stop your troubleshooting here, as there is nothing you can do to an engine with low compression to make it run better. 2. Spark test. These are the testers we use in the industry. you can also get cheap spark checkers at most good autoparts stores.You need to hook the spark tool up and set the gap to 7/16ths of an inch. The spark should easily jump that gap, be hot and blue in color, and be consistant with engine rpms. Weak looking yellow spark will not cut it. If you find no or weak spark on any cylinder, the ignition systems individual components will need more troubleshooting. You can also use a timing light. Click this link below to watch a video explaining how compresison and spark testing is done. - Next is fuel quality. You do have old fuel in that tank, and that old fuel can contaminate the entire tank. What you would do here is either get another tank and run the engine off of an alternative fuel supply. Or, dump out your tank and flush it . If still has the lack of power after all this. Try pumping the primer bulb over and over to force fuel to the engine. If the engine picks up, the fuel pump is bad. If you try to pump the bulb and the bulb sucks flat, or does not reinflate. The fuel tank is either not venting or has a clog in the pickup tube. If still nothing even after all this. The problem is going to be back in the carb. Either you didn't get it cleaned properly the first time. Or, you did but contamination from the tank got back into the engine. And that is how you go about troubleshooting it. Does that all make sense to you? Did you have any further questions on the issue?
Customer: replied 1 year ago.
I purchased this engine new and over the past 19 years it has less that 200 hours of operation. I don't run the pi$$ out of it and I maintain it carefully. It sat for 2 years just because I was busy with life and I was running my other boats. Since the engine will rev to full throttle in neatural, I doubt that the compression isway off but I won't rule it out until I test it.
When the engine bogs while attemting to plane, if I back off of the throttle the engine continues to run. If I don't back off quickly, the moor stalls and conks out but is easy to restart. I have tried squezzing the primer bulb while advancing the throttle but that had no effect.
I disconnected the fuel line where it meets the carb and squezzed the primer bulb to test for fuel flow
from the tank. I get about two onces of fuel per squezze so the fuel deliver system to the carb seems to be OK. BTW, I did make sure that the tank was venting.
My top suspect is the fuel pump is not delivering enough fuel to run the engine under load. Can you you point me to some information on the theory of operation for this type of fuel pump.? My second suspect would be the main jet. But I did remove nd inspect it again and it looks fine.
Expert:  Jason replied 1 year ago.
If it was the fuel pump then pumping the bulb would force though through the pump, and the engine would pick up. If there is no improvement when pumping that bulb over and over, then it would not be a fuel pump issue. Does that make sense?
Customer: replied 1 year ago.
You seem conviced so I defer to your expertise since I don't understand how this pump moves the fuel without any apparent moving parts. I understand how a mechanical and electric fuel pump move fuel but it is not obvious how this pump works based on a spring and a button against a diaphram. Is it somehow vacuum based caused by the air flow through the carberator. Is it a reasonable assumption then that if the fuel pump can fuel the engine for extended periods in neuteral at both open and WOT then it is not likely to cause the problem that I am having with getting the engine to power up and get my boat onto plane?
I am still stumped as to why the motor will run well in neuteral but not when in gear.
Expert:  Jason replied 1 year ago.
It's the actual diaphram that moves, thats how it pumps fuel. I am still stumped as to why the motor will run well in neuteral but not when in gear. That is because in neutral the engine is simply spinning. Not making any power. Just spinning it's own weight. It will spin it's own weight pretty much no matter what is wrong with it.
Customer: replied 1 year ago.
I still don't understand what causes the diaphram to move. If it is vacuum based are there multiple airways to the throttle body to push more fuel when the engine is under load and/or higher RPMs? I might have miseed something when I cleaned the caruretor.
Thanks for the clarification that no load operation does not correlate directly to under load performance.
Expert:  Jason replied 1 year ago.
It's crankcase pulses that cause the diaphragm to move. The fuel pump is plumbed into the lower crankcase via a passageway in the carb. When the piston goes up, it creates low pressure/vacuum and the diaphragm gets sucked in. When the piston comes back down it creates pressure, and that pushes the diapghram back out. It is this in/out with every stroke of the engine that allows the fuel pump to draw fuel in from the tank and then push it out into the carb. Does that make sense/
Expert:  Jason replied 1 year ago.
Hello, just checking in. No rating has been put through yet so I wanted to see if you had any more questions on the issue? -Jason

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