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1990 Merc 25hp dies trying to get up to full speed

I try to avoid those plastic fittings, good call, brother. Aftermarket fuel lines, tanks, and bulbs can be substandard as well. Many aftermarket items are fine and with some even an improvement. Gotta use your knowledge and experience as well as good advice to make that choice. On line purchasing can be risky because you can't get it in your hands and check the items thoughtfully.
 
FishinLite said:
This may not be a help, but here is a some insight from my experience. I have a '85 - 60hp 2 stroke. It was dripping gas at the motor from the gas line quick connect after I disconnected the the tank fuel line.

I went out on e-bay and purchased a aftermarket replacement check valve/quick connect fitting.

The aftermarket fitting went in smoothly appeared to worked well, eliminated the drip I was trying to correct, my thoughts great.

Went to the lake, boat started fine, throttled up fine, and then after a short time the motor appeared to starve and die.

If I throttled back it would continue to run just fine at about 1/2 throttle.

I had just thoroughly cleaned the carbs and the motor had run fine prior to changing the quick connect fitting.

The aftermarket fitting was plastic, the original oem fitting was metal, they looked the same, the fuel line connected properly.
Pumping the bulb didn't help. But it was the only think I had changed.

I finally stopped by the marina and purchased the oem parts at four time the price of the aftermarket fitting.

The motor has run fine ever since.

My conclusion was that there was some restriction in the aftermarket part that was not there in the oem version
or the aftermarket part was not the perfect replacement for my particular motor model even though it looked the same from the outside.

Think, what have you changed?
Click to expand...

Thanks for the reply.

I like the thought. I have done the thinking on that as well. Here is where I am on that line of thought. The only thing I had replaced before the problem was found was electrical-trying to get spark back. Once I got spark and took back to water the problem with fuel started. Did not start messing with carb or fuel lines until after the problem was discovered.

So logical question I asked myself, could one of the electrical changes caused, it? Well while trying to problem shoot while on water, the motor would run while pumping the bulb.

So, with that, I assume that if it was something from the electrical replacements, the pumping of the bulb would not have worked. Is there any thoughts on this being an incorrect way of thinking?
 
Yes, but you mean sucking air under vacuum. You will notice it better while applying bulb pressure with motor in all normal operating positions.....look for leaks. In other words, don't simply look for a leak while nothing is moving. Turn the motor left and right....you get the idea.
 
timguy said:
Yes, but you mean sucking air under vacuum. You will notice it better while applying bulb pressure with motor in all normal operating positions.....look for leaks. In other words, don't simply look for a leak while nothing is moving. Turn the motor left and right....you get the idea.
Click to expand...


Tried the bulb pressure test this weekend. No leaks. there...
 
Okay, next question, have you replaced the fuel lines IN the motor? Sometimes they can delaminate internally, creating a blockage under certain flow direction or pressure. It's entirely possible that during the course of repair, the line was moved and began this delamination. This is more common with ethanol use. (I avoid ethanol in all my equipment). This photo shows a hose that failed me last October......some hose I got with a used outboard purchase. Granted it's the supply line from the fuel tank it, however, shows what I'm talking about. Your problem is maybe at the lines up in the motor. You may have a partial restriction.
 

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timguy said:
Okay, next question, have you replaced the fuel lines IN the motor? Sometimes they can delaminate internally, creating a blockage under certain flow direction or pressure. It's entirely possible that during the course of repair, the line was moved and began this delamination. This is more common with ethanol use. (I avoid ethanol in all my equipment). This photo shows a hose that failed me last October......some hose I got with a used outboard purchase. Granted it's the supply line from the fuel tank it, however, shows what I'm talking about. Your problem is maybe at the lines up in the motor. You may have a partial restriction.
Click to expand...


I did replace both the line that goes from external connection to the fuel filter (also new filter), as well as the line going from filter to carb. I have been studying the parts schematic after looking at motor again this weekend. One part that did not get replaced during carb rebuild is the plastic "fuel pump body" that is in with diaphragm. Could that have a hair line crack or other issue?
 
Do you have a new one? Might be warped too. I would replace it, you've about run to the end of your rope. Also, make sure that the crankcase pulse port is open and not blocked by the gasket.
 
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timguy said:
Do you have a new one? Might be warped too. I would replace it, you've about run to the end of your rope. Also, make sure that the crankcase pulse port is open and not blocked by the gasket.
Click to expand...
Sorry it's been a while, finally got decent weather on a day I had time to work on motor. So I put a new fuel pump kit and new fuel connector at the motor on. Did not help anything. I did pay more attention to the fuel filter as I ran it to see if it was getting drained when trying to idle up. It stayed full through all RPMs. Was not able to get passed about 1/3 speed before it would try to die. Pumping the bulb did nothing to help it out. All the ports in carb seem clean and clear. Obviously I am missing something, so I guess I will be calling some mechanics and see if I can get into the shop.
 
You are leading us to a carb problem. It really HAS to be. If the float level is too low, the needle may be not opening enough allowing adequate fuel at full or near full power. Or is it possible that there is a partial restriction in fuel flow between the fuel filter and float chamber?
 
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timguy said:
I think a vent problem would result in an empty fuel filter and collapsed primer bulb.
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So here is the latest, and it's actually good news, for a change. I finally gave up and took it into a shop. Turned out to be the wires going into the trigger. They were wrapped in insulation and had a zip tie on it. When cut zip tie off and pulled insulation off, the wires under the zip tie had some how got pinched apart. Suppose to be all fixed up. Pick it up Saturday and plan to head straight to some water to try it out...fingers crossed...
 
timguy said:
So how did it run, Rando?
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Sorry been a while. Went ahead and replaced throttle linkage at mechanics recommendation due to it being worn. Once I got that on and adjusted, the motor is running as good as ever!

And yes, you did mention the possibility of trigger, but was left to believe it was fine from the first mechanic. Because he never put the motor under load like the last mechanic did, he really never gave it a true look. Also, I don't have access to a timing light, so I was not able to do it myself...

Thanks for all the helpful suggestions. Motor will hopefully good for another 10 years with all the new parts...
 
Great job and hope you didn't have to take out another mortgage on your house. Its always nice when we hear back from the customers. This is a great service and the techs, like me, enjoy to learn as we go. One of our top techs bailed out on this post "Flyingscott" I miss him and wonder if his disagreements with me had anything to do with it. Thankfully we have some bright newer techs coming up, they are doing a great job.
 
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Hi, I'm a new member.

Just wanted to say, this post caused me to signup and was an amazing read. Rando71 threw his entire tool box at this issue and never once broke. Timguy patiently stood by methodically offering possible solutions until a solution was discovered. Pretty Awesome indeed!

oh, also have a 1989 mercury suffering the same symptoms and was an internet search that led me here. I hope to start my own thread on that matter soon. Will be using this post as a benchmark starting point

Thanks Everyone!
 
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