Mercury 500

[paparon]

Merc 500 Kiekhaefer Mercury 50HP Thunderbolt ignition. S/N2516773. Number on engine: 47904.
Please help since many marine shops cannot fix problem. When cold, motor starts and runs great but once you shut down motor and try to take off again, this is where the problem begins every time. Hot motor (normal temp after putting a running load on motor) starts and idles normal but as I give it throttle it "bogs" down and will not take the fuel, then dies. If someone with a precise pumping action works the fuel line squeeze bulb simultaneously as I precisely work the throttle to give the motor fuel, the motor will "take" or respond and run normal at all speeds until I shut down the engine again. Too much pumping of the squeeze bulb will flood the engine, too little is not good, must be precise squeezing rhythm. If motor cools down it will start (take throttle fuel) and will run normal everytime. Authorized Mercury repair shop (many visits) have replaced fuel pump diaphram, gaskets, rebuilt carb kit, fuel lines, fuel tank, fuel filter and connectors but problem persists.

[boats.net]

Try non-Ethanol gas or high test gas.

[paparon]

Merc 500 (fuel intake issue)

Thank you for your "gas" suggestion but this is not a type of gasoline issue. This motor is a 1977 model if I am reading the motor's serial number correctly and uses manufacturer recommended regular octane gasoline with Quick Silver 50:1 ratio 2 stroke oil. I have owned this bass boat and motor for over 30 years and except for this one mechanical issue it has always ran great. Always starting perfect when motor is cold or has time to cool down. I had a fuel pump rebuild kit recently installed to no avail. Should I try having a completely new fuel pump installed? If a fuel pump is bad could it malfunction when the motor is hot. Something is malfunctioning only when the motor is hot causing the motor to not get the proper amount of fuel? I need your help since my grandkids want to go fishing. Thank you

[Ski]

Trying a non-corn fuel with a higher octane is not a bad recommendation. If this was a fuel injected motor your description of what it takes to get moving would certainly sound like "Vapor Lock". It could be that somehow your motor is prone to the same thing, and changing the fuel might elevate that.

That being said, I would rule out the ignition. When the engine is up to temp pull the plug wires one at a time and force the coil to jump a 1/4" gap. You can do this with the engine running just use some insulated pliers clip leaded to ground and back the wire off of the plug and listen for the arcing, a slight further distance back and the engine should stumble. It could be that working the primer bulb is changing the mixture enough to get past the load and when the flywheel starts spinning it gets things cooled down enough to work. (or the wiggling of the wires is doing it)

It's all part of the trouble shooting, weak coils certainly look like poor fuel mixture. The highest demands on the motor is when it's trying to plane, the motor has high manifold pressure and is spinning slow. You need to rule it out, but I think it's vapor locking. Hope this helps

[paparon]

merc 500

Thanks for your reply Ski (member). Actually my motor was manufactured in 1969. I am taking my boat/motor(engine) to another boat/repair shop on Friday,10-04-13. The owner/mechanic over the phone thinks I have a bad fuel pump (the complete fuel pump needs to be replaced not just rebuilt) and once the engine is up to temp makes the fuel pump malfunction. I will pass on your suggestions to the mechanic regarding the possible ignition problem. The engine does not "bog" down, not take the throttle, when it is trying to plane but as soon as you give it a slight throttle out of the neutral throttle position. Starting and idling is fine but it will only take a very slight throttle. As soon as there is any load on the engine it "bogs down" and dies. After it dies sometimes I need to push the choke button on the throttle housing to get the engine to start. Once again it starts, engine idles, and runs (planes, etc) perfectly when engine cools down (approx 30-45 minutes after engine is up to temp then I turn it off). I appreciate your replies, thank you.

[paparon]

merc 500 50hp

Well I took my boat/motor to the boat shop last Friday, 10-04-13, and since my plastic type fuel tank was sucked in, the air vent on the fuel tank seemed to be malfunctioning, and my fuel line/squeeze bulb was old he said to replace all of that with new parts. I bought these parts and will install them tomorrow then on Monday the mechanic and I will take the boat to the lake and let the mechanic see what the motor does for himself. He said as simple as it sounds the air vent on the gas tank must be open and functioning properly or it can effect the fuel getting to the motor. I know others have posted the same problem I am experiencing with my motor so I will get back to you with my mechanics findings after we test drive my motor on the lake this coming Monday, 10-08-2013. If after installing a new fuel tank, fuel lines, sqeeze bulb, etc the motor still will not take fuel and "bogs" down on take off when up to running temp then the next step will be to install a new fuel pump since I have already had a new fuel pump rebuild kit installed to no avail. Please let me know if you think you may have a solution to my problem and I will pass your suggestions to my mechanic. Many minds are better than one.

[paparon]

merc 500 50hp

Well I took my boat/motor to the boat shop last Friday, 10-04-13, and since my plastic type fuel tank was sucked in, the air vent on the fuel tank seemed to be malfunctioning, and my fuel line/squeeze bulb was old he said to replace all of that with new parts. I bought these parts and will install them tomorrow then on Monday the mechanic and I will take the boat to the lake and let the mechanic see what the motor does for himself. He said as simple as it sounds the air vent on the gas tank must be open and functioning properly or it can effect the fuel getting to the motor. I know others have posted the same problem I am experiencing with my motor so I will get back to you with my mechanics findings after we test drive my motor on the lake this coming Monday, 10-08-2013. If after installing a new fuel tank, fuel lines, sqeeze bulb, etc the motor still will not take fuel and "bogs" down on take off when up to running temp then the next step will be to install a new fuel pump since I have already had a new fuel pump rebuild kit installed to no avail. Please let me know if you think you may have a solution to my problem and I will pass your suggestions to my mechanic. Many minds are better than one.

[JUST-IN-TIME]

You had vapor lock from the vent

[paparon]

Merc 500

Met my marine shop mechanic at the lake on Monday, 10-07-13, with new gas tank, fuel line, squeeze bulb, fittings, etc installed to eliminate the possibility of vapor lock. Fully pumped up the squeeze bulb. Cold motor started perfect and ran good. The mechanic was impressed how the motor ran and sound for an older 1969 Mercury 50hp.Took right off from a standstill with no hesitation (good compression) and all normal. Ran the motor 15 minutes or so so it was definitely up to running temp, shut off the the motor, immediately started it back up/all is normal with take off, etc. Now we turn off the motor again and wait 15 minutes or so. NOW MY PROBLEM ONCE AGAIN OCCURS. We start the motor, slowly engage the throttle and the motor "bogs" down same exact symptoms as my previous threads. Then motor becomes hard to start. We make sure the squeeze bulb is fully pumped up and it still won't start. We engage the manual choke, the motor starts, takes the fuel/throttle and off we go. DO YOU HAVE ANY POSSIBLE SOLUTIONS? The bottom line, with vapor lock ruled out, good compression, and the fuel pump working properly what would cause the fuel to siphon back and the motor be starved for fuel? From a laymen's (my) perspective does the carburetor need to be rebuilt to keep the gas where it belongs (in the carb or ??) so the motor isn't starved for fuel upon initial take off and to prevent the gas from siphoning/draining backward or running forward (or where ever the fuel needed for start up/take off is going)? P.S. In the meantime I will make sure all fuel line fittings on the motor are tight and rewiring old/frayed ignition wiring (my son is an electrician and will help me). Thanks for your input, Papa Ron

[Ski]

did we check the ignition.....?

[paparon]

merc 500

When I met my mechanic I took a copy of your reply to my posting and had him read it. He said an ignition problem is a possibility and did not bring it up again. I don't know if he mentally ruled it out but he never mentioned it again. Then we made plans to meet at the lake and after experiencing the problem firsthand on the lake he didn't mention a possible ignition problem. I will talk to a guy that lives down the street from me and ask him to check my ignition per your instructions. This guy knows alot about marine motors and rebuilds his as needed. So Ski, or anyone else after reading my postings do you think it could possibly be the carburetor malfunctioning or is the ignition the first thing to check? Also Ski, I'm definitely not a mechanic but will try to check the ignition myself if I can't get anyone else to do it so would you clarify as simple as possible and step by step how to check the ignition again for me. Please start by telling me to remove one sparkplug and tell me exactly what to do next. Thanks for your patience. I appreciate your input.

[Ski]

The easiest thing to do is clamp a timing light on the wires and drive around. The light see's the spark and the strobe fires accordingly. Or....

Pull the wires off of the plugs and put them back on so they are toughing but not snapped tight. (makes it easier later) Find a pair of pliers that seem to have good insulation and a piece of wire preferably "test/clip leads". Connect the pliers to the engine block with the wire. This serves two purposes 1) If (or when) you go too far back during the test and the coil is good the arc will jump through the boot and have some place to go, (motor ground) other than through you. It will still "smart" if your toughing metal 2) When you drop the pliers after getting shocked you won't lose them in the lake.

Warm up your motor to the where it's faulting and while it's running pull the wires back off of the plug (one at a time) about 1/4" you should hear the spark arcing. If not, back it off more and see if there is any change in motor speed. no noise and no change in speed and you found your smoking gun.

I find myself doing the latter because out on the lake I didn't have a timing light handy. In the shop when doing compression test I have a tool that holds a set gap (around 1/4") and I check to see if it has a good spark. If it can't jump it it's a sign of a bad coil.

When the engine is running the voltage needed to jump the plug changes with engine load. Resistance of air changes with pressure and voltage need to jump the gap at idle is considerably less than under load. That is why it can be suspected as a fuel problem. I hope this helps

[paparon]

merc 500

Ski, member, I greatly appreciate you giving me your time and patience to thoroughly, step by step, explain how to check to see if it is an ignition problem. Rest assure, after reading many other postings on this forum, that you are helping many more people than just me. I have a further question, in your last reply posting you stated "In the shop when doing compression test I have a tool that holds a set gap (around 1/4") and I check to see if it has a good spark", so CAN I USE A "FLUSHER" TO SUPPLY WATER TO MY MOTOR without actually taking it to the lake or does it need to be under a load (like in the lake) to do the ignition test you are prescribing? I can get one of my mechanic friends with timing lights, etc, and use a flusher on the motor, much easier than getting somebody to spent half a day or more to do it on the lake (our nearest lake is at some distance from our homes). Also WHAT IS THE NAME OF THE TOOL that holds a set gap (around 1/4") that you use to see if it has a good spark (my head post office mechanic relative may also have this tool at his disposal). This is the mechanic that I will ask first to help me. Please note when I take my boat (motor) to the marine shop they say the motor does not "bog" down when they test it with a flusher. I don't know if it is because the load on the motor isn't great enough or if they don't get it up to running temperature (hot enough) to cause the motor to bog down? Ski, once again, thanks so much for your input. Papa Ron

[Ski]

This the tool I use to check the coils. It can be used with the muffs in the shop. You need to make the spark jump the 1/4", to simulate the load. Just watching the spark jump the plug is too narrow. If all is well, then pull the wires back off of the plugs as it's running to check for a bad plug. (I just did this today and found a bad plug) If all seems well then try the timing light on the water. Do this when the engine is warm to simulate your problem.

All your hoping to do is rule out the ignition, these checks are quick and aid in trouble shooting. Running the engine on the muffs and spooling it up will not duplicate "load" and it's small wonder your dealer hasn't been able to duplicate the problem. (fuel or spark) Forcing the ignition to work harder with a gap usually gets it to show up. Heat soaked problems in components like switch boxes are easier to see with the light on the water.

Don't forget to bring a six pack of your mechanics favorite beer

[paparon]

Merc 500

Ski, member, I am so thankful that you will take the time out of your schedule to help me and others on this mercury forum. It sounds like you are a marine motor mechanic with a heart for helping people. Two last questions: 1. I have been running Champion sparkplugs L76V and now I referred to my Seloc Publications, Mercury 1965-1983 Outboard Tune-up and Repair Manual, by Clarence W. Coles and Howard U. Young (copyright 1983) and it shows to use a Champion sparkplug L19V. I believe either Autozone parts store or my previous marine mechanic recommended the L76V sparkplugs. Can you tell me which plug is best for my application? 2. When I previously (Aug 2010) took my motor in to another marine shop with my existing "bogging down" problem they rebuilt the fuel pump and I also had all my old 1/4" marine fuel lines replaced. Well, the fuel line directly to the fuel pump was attached to a 1/4" hose mender elbow fitting and because of the angle of the elbow and the motor once the fuel line was attached they could not properly tighten down the elbow so they left the fitting very loose and used neoprene on the threads. I replaced the loose elbow with a straight 1/4" hose barb (barbed on one end and threaded on the other end), tightened it down into the fuel pump and added a new piece of fuel line on the barbed in. Since the other end of the existing fuel line was way down in the motor I used a 1/4" (barbed on both ends) hose mender (made by X.tra seal p/n: 15-5754) to splice the two fuel lines together. MY SECOND QUESTION: Will using this brass looking barbed hose mender/splicer reduce my fuel rate to my fuel pump (to my motor) so my motor runs improperly? Of course there is an obvious diameter size difference/reduction between the fuel line and the barbed on both ends slicer/mender(since it fits into the fuel line). The parts house employee said the motor would run fine but I want to make sure it will. Thanks again for your advice, Papa Ron