1972 Merc 650E 3 CYL....fuel system Qs

[chipperstrauss]

I'm back after a couple year hiatus. Here's my story, it's sad but true... the last two cruises ended with engine problems. The first was a faulty ground connection on the battery terminal causing low voltage and a dead engine. I fixed that. The second time I was able to limp back to the launch ramp because the engine would abruptly stop while cruising. At that point, I chose to rebuild the carburators which took many months because life got in the way. I finally completed the carb rebuilds and went to the lake to adjust. I saw bubbly foamy stuff coming out the upper right engine mount. So, I chose to pull the power head (after fabricating a hoist in my garage now boat barn) thinking there was a gasket break. I also chose to rebuild the water pump. A couple months ago, the engine was finally back together. I have adjusted the carbs so it will idle but have not fine tuned the idle mixture. I did attempt to take a spin around the small bay in our lake... to my chagrin, that same stalling symptom remains. Here's a link to the video https://photos.app.goo.gl/foSKL7ZsRbw1sqWM7
I received a quick response from my mechanic who suspects a fuel issue of some kind. So, where to start. I reviewed several videos on fuel issues. One question I came up with is:
How many fuel filters are OK in the fuel line? Right now, I have a water separator filter close to the main tank, two in-line filters (one before the bulb and one just past the fuel line connection, and the fourth being the original filter just after the fuel pump. Could the issue be that the pump can't pull fuel through the 3 upstream filters and push it through the stock engine filter?
Another question I have is what mechanically stops the fuel flow when squeezing the bulb? I can't find an anser to that and assume it's the float valves inside the carbs. Am I right or is there something else?
My exposed fuel line is the gray hose but is new within the past two years. I plan to replace it with black fuel line which is more impervious to ethanol. I read a recommendation that one should use premium gas because it has a significantly lower ethanol percentage. Is that the consensus among you all?
I would like a procedure to trouble shoot the fuel issues prior to pulling the carbs off again. Doing that requires quite a bit of dissassembly.
I hope you all enjoy offerring online mechanic's advice as much as I enjoy the feeling of success when working these older outboards.

 

[jimmbo]

The number of Filters could be part of the Problem. Try removing the filters from the equation, Fuel Lines can break down internally act as Check Valves and Restrictionn. The bulb gets firm, when the Bowls fill up and the inlet valve(s) close. Sometimes, the valves can be forced off the Seats by very intense pressure on the bulb.

Have another person in the boat, with a Spray Bottle of Premix, and when the engine acts up, have them spray some fuel in the carbs and see what the outcome is

 

[Faztbullet]

It has an ignition miss just before it dies. This is either due to trigger fixing to fail(bad connections kill em) crumbling wiring to trigger loosing connection when advanced.

 

[chipperstrauss]

The number of Filters could be part of the Problem. Try removing the filters from the equation, Fuel Lines can break down internally act as Check Valves and Restrictionn. The bulb gets firm, when the Bowls fill up and the inlet valve(s) close. Sometimes, the valves can be forced off the Seats by very intense pressure on the bulb.

Have another person in the boat, with a Spray Bottle of Premix, and when the engine acts up, have them spray some fuel in the carbs and see what the outcome is

If the issue is fuel starvation, why would the engine start so easily post stalling? And, at the second stall in the video, the engine doesn't stall entirely. It kicks back in on its own. Seems there is sufficient fuel available at the time of stalling.

 

[chipperstrauss]

It has an ignition miss just before it dies. This is either due to trigger fixing to fail(bad connections kill em) crumbling wiring to trigger loosing connection when advanced.

Ah yes... the infamous trigger. I rebuilt the distributor a while back after finding it was the culprit for no spark. No spark was the main issue when I first became the owner. The support from CDI was terrific as well as support from the forums.
As I recall, the trigger components on the inside are encased in a waxy material. I'll double check the wires and connections but I believe the insulation is not brittle or cracked. What is the method to test the wires? At idle, if I wiggle the wires, should I be able to create the miss fire we see on the video?
If I'm reading you correctly, you are saying the issue is ignition; not fuel. I was thinking I would buy clear nylon tubing from the bulb to the fuel pump to eliminate two filters leaving only the water separator and the onboard filter just after the pump.

 

[jimmbo]

Wires can break internally unseen. I would be very surprised to find the Insulation uncracked, on that motor, as Mercury had bought enough wire with an insulation that didn't age well, to go to the Moon and back severqal times.

 

[racerone]

Just one water separating filter is all you need.

 

[chipperstrauss]

Ah yes... the infamous trigger. I rebuilt the distributor a while back after finding it was the culprit for no spark. No spark was the main issue when I first became the owner. The support from CDI was terrific as well as support from the forums.
As I recall, the trigger components on the inside are encased in a waxy material. I'll double check the wires and connections but I believe the insulation is not brittle or cracked. What is the method to test the wires? At idle, if I wiggle the wires, should I be able to create the miss fire we see on the video?
If I'm reading you correctly, you are saying the issue is ignition; not fuel. I was thinking I would buy clear nylon tubing from the bulb to the fuel pump to eliminate two filters leaving only the water separator and the onboard filter just after the pump.

I changed out the fuel line from the port side connection directly to the fuel pump with clear vinyl tubing and a new bulb pump. No change to the performnace. I did notice fuel dripping out of the carbs when I tilted the engine up. It seems this happens when the bowls are full but the floats move off the valves when tilted up. Does this seem correct?
Anyway, I spoke to tech support at CDI Electronics about my high speed miss (I have a CDI Electronics switch box and coil). The tech guy suggested watching the voltage at and above 3,500 rpms to make sure it doesn't go over 16 volts and ideally stays under 14.6. He said some batteries are not compatible with these particular switch boxes. I have a basic NAPA Marine/RV dual purpose battery.
Here are my questions:
Does anyone have experience with this CDI switch box?
I don't understand why the battery would be the issue if the voltage exceeds 16 volts. It seems it would be the rectifier. Does anyone have experience with creating a simple voltage regulating circuit to keep the voltage from exceeding 16 volts.
Finally, can someone recommend a reasonably price laser tach to use? I have an ELECTRONIC SPECIALTIES 328 EZ TACH + which does not have a selection for a 2 stroke, 3 cyl engine. (I used it on my weed wacker and it worked well. But, I can't get it to display the correct rpms on my outboard.)

 

[merc850]

Fuel will drip out out of the carbs when the engine is tilted up and they have fuel in them. Why not buy an alternator tach and use it all the time - comes in handy for prop selection etc.

You can replace the rectifier with a rectifier/regulator; or get a regulator from Mercury and hook it up this way

 

[chipperstrauss]

Fuel will drip out out of the carbs when the engine is tilted up and they have fuel in them. Why not buy an alternator tach and use it all the time - comes in handy for prop selection etc.
View attachment 361142
You can replace the rectifier with a rectifier/regulator; or get a regulator from Mercury and hook it up this wayView attachment 361143

Thank you for your response. However, it is not clear to me that I could simply install a Mercury voltage regulator into the circuit. It did occur to me to install a voltage regulator but not that I could purchase one ready for installation. Nor do I know how to hook up an alternator/stator tach.
Are there specifications which need to be matched? Your diagram shows a 16amp stator. It also shows a cowl mounted tilt switch. I don't have a tilt switch (probably another safety item removed in a prior life) I don't know the amp spec for my stator. Does that matter? Adding a Mercury voltage regulator sounds like a good idea but does the voltage regulator need to be matched in some way to the amps of the stator?
Thanks again for your help.

 

[merc850]

All you do is hook it up to the red and yellow wires and bolt it to a grounded panel I did it to my 75 850 and its been working for 8 yrs. That diagram is for a V6 but it works on smaller motors; the alternator tach connects to one of the Yellow wires from the stator and +, - from the battery. All those switches and fuses are for the newer models.

 

[chipperstrauss]

Thank you for your response. However, it is not clear to me that I could simply install a Mercury voltage regulator into the circuit. It did occur to me to install a voltage regulator but not that I could purchase one ready for installation. Nor do I know how to hook up an alternator/stator tach.
Are there specifications which need to be matched? Your diagram shows a 16amp stator. It also shows a cowl mounted tilt switch. I don't have a tilt switch (probably another safety item removed in a prior life) I don't know the amp spec for my stator. Does that matter? Adding a Mercury voltage regulator sounds like a good idea but does the voltage regulator need to be matched in some way to the amps of the stator?
Thanks again for your help.

I held several discussions with tech support at CDI Electronics. Those guys are terrific; very friendly and helpful. CDI makes and sells a rectifier/regulator originally developed for Evinrude engines but work well with old Mercs as well. It does need another hole drilled for mount the part. But, prior to buying it, I wanted to test the voltage when my high rpm failure takes place. The test happened earlier to day. The voltage never exceeded 14volts but the failure happened just as before. It happened three times and each time the engine kicked back on by itself. Then, the engine wouldn't restart. If I opened the throttle, it would start and then stop; like no fuel. I had to limp back to the dock with my trolling motor. I am really at a loss on next steps. The float on the lower carb fails to stop fuel flow. When I pump the bulb, I can see fuel coming out of the carburator. So, I can check that out but would too much fuel cause the high rpm failure? CDI has a trigger tester (~$100) but it seems to only check spark on each cylinder and not at high rpm. I'll speak with CDI about that tester. At low rpms, the engine runs fine.

 

[Faztbullet]

A timing light is your best friend right now......it will show you ignition drop outs at all rpms

 

[chipperstrauss]

A timing light is your best friend right now......it will show you ignition drop outs at all rpms

Thank you for the advice. Please share how you would go about using a timing light to identify the high rpm drop out problem.
Also, I placed a clear fuel filter between the connector and the fuel pump. You can see in this photo that the color of the fuel changes to yellowish from blueish.
Do you have an idea why this color change would happen? Should I be concerned that something is amiss inside the fuel pump like a torn gasket?
Thanks for your help and advice.

 

[jimmbo]

I can't see any colour shift, it all looks yellow with a very faint green to me, which isn't good as I haven't seen any TCW-3 that wasn't blue, blue-green, green, or red, and premix usually darker than what I see in the strainer. Fuel Filters should be placed after the Fuel Pump, as the fuel will be under pressure. Putting it prior to the Pump, can cause what is known as vapour lock, the Fuel vapourizing in the line due to the lower pressure when the Pump is trying suck it up.

 

[racerone]

I think the filter before the pump is just fine.----No issue with that on my boat.

 

[chipperstrauss]

I can't see any colour shift, it all looks yellow with a very faint green to me, which isn't good as I haven't seen any TCW-3 that wasn't blue, blue-green, green, or red, and premix usually darker than what I see in the strainer. Fuel Filters should be placed after the Fuel Pump, as the fuel will be under pressure. Putting it prior to the Pump, can cause what is known as vapour lock, the Fuel vapourizing in the line due to the lower pressure when the Pump is trying suck it up.

I'm sorry I wasn't clear in my previous post. In this photo one can clearly see the color change. the clear vinyl tubing (temporary, I will be changing it out with black fuel hose) holds the premix with the typical blue green tint.
I am curious what would cause the change to the yellowish in the previous photo.
I sort of agree with Racerone about the filter because there is a the large water separator filter up in front near the tank. I ran the vinyl tubing all the way to the fuel pump and that didn't seem to impact performance either better or worse. Once the system is closed, the fuel seems to flow just fine through the filter up to the pump. My concern is that the fuel pump gasket has a tear or hole which is creating the yellowish color of the fuel.

 

[jimmbo]

A very large filter is fine as it provides a very large area of Filtering media, which has little or no Pressure Differential, a smaller filter is more restrictive.

 

[racerone]

Simply ignore the color shift on this. fuel system !!!---Certainly not caused by a torn gasket either.--It is an optical thing.----My filters are spin on water separating filters.-----Right out of the tank before the fuel pumps.-----On a 235 HP 1982 Johnson.-----Fairly thirsty motors.-----No filter trouble at all here.------These 3 cylinder motors are not my favourite.----There are issues with top cylinder scoring and cracks near the sparkplug.-------Post the compression test values.

 

[racerone]

Hook up a timing light to #1 cylinder.----Lay the timing light on a seat or the floor.----Observe the flashing light when motor falters.------Intermittent flash / no flash means ignition issues.------Repeat with # 2 and #3 cylinder.-----I would carefully inspect all wiring on this motor.-----There are know issues with bad wiring in this Mercury era !!