1984 Mercury 150 - Starts from Cold great, then loses RPM/Power after short WOT run

[something2do]

Hello everyone,

I have posted about this motor before. Old 1984 Mercury 150 V6 that I resurrected from the dead and was running like a scalded dog once I replaced/restored most of the ignition, fuel system, and cooling system.

Late last year we were taking a family ride at WOT and the RPM's suddenly went from around 6,000 to 3,000-4,000 and the power cut back noticeably. From there, no more more hole shot and speed was limited to around 20-30mph (usually around 45mph) and degraded the longer I ran her.

I ran the boat yesterday after some updates and here is the exact scenario - Off the trailer cold, I can idle out, move to WOT and the boat roars out of the hole and gets up to about 45mph super quick. I ran it for just around a minute like this and then the cutback in rpm/power hits. After that, I go back to idle and if I try WOT anymore the boat just dogs like hell and won't get out of the hole. If I let the boat sit a long while, it will give me some power again. Something seems to give out after that initial cold run. Not sure if its heat or something else.

Here is what I have done so far:
I first thought fuel or stator so I put in all new fuel lines, filters, etc with no change. I then installed a new stator which seemed to help for a short while, (few runs) then same problem. I recently rebuilt the fuel pump will all new diaphragms and it still has not solved my problem.

I read through a few threads here and I am now thinking my switchboxes might be bad. The switchboxes are about the only ignition item I have not replaced on this motor other than the coils. I ordered a new set (2) of switchboxes that should be here in a few days.

Questions:
- Am I on the right track with the switchboxes, or do my symptoms point to something else?
- Should I assume the bad switchboxes burned out my new stator and should I go ahead and replace it with the switchboxes? Or should I install the new switchboxes, see how she runs first? I know bad switchboxes can burn out a stator but I am not sure if a bad stator can burn out some switchboxes and I hate to do that considering the $$ of buying them.
-The rectifier was new recently, but should I replace it with the switchboxes as well?


Here is the background on the motor and things I have done already for context:

Engine Background/Setup:


Mercury 150 V6 1984 - Serial Number: 6480926
unknown hours
on a 1996 ProCraft 18' dual console bass boat
no jack plate or set back
Cavitation plate even with the bottom of the hull
21 pitch aluminum prop (had a 19P, but prop guy told me to start with this one for testing)
No oil injection - mixing 50:1
Carbs are all 3: WH27-1

stock jets I think: .054 and .064 sized



Spark Plugs are BU8H NGK
added dual steering bracket (works good)
single piston trim style (re-built pump, works good)



Work Done so far:


New water pump
New thermostats
New poppet valve/kit
Rebuilt fuel pump
cleaned all 3 carbs and put in new kits

did not change floats, has plastic ones
did float test, floats are not holding water
Kit included all gaskets and needle/seat
set floats to be even with float bowel body when held upside down
Blew into fuel line to test needle seal when upside down, passed test



New Spark Plugs (BU8H NGK)
New Coil wires (checked firing order to wiring diagram - ok)
New Stator
New Rectifier
New Trigger
New Starter and wires
All new fuel lines, priming bulb, and water lines
Added a spin-on water separating filter between tank and motor
New cranking battery showing 12.90-13.4 volts (kept charged frequently)


I know if anyone can help it is the guys on this forum. I appreciate any advice you may have to offer.

[ahobbes]

Hi there,

I'm currently having the same symptoms (was just about to post about it when I saw yours). During my research I have considered the cause of the problem to be: 1) Clogged jets due to gunky/dirty fuel. 2) Water in the fuel. 3) Bad fuel (from the station). 3) Constricted fuel flow. 4) Bad coil pack.

Assuming you have good fuel pressure (is there a way to check this?), I would consider the coil packs to be just a likely culprit as the switch boxes. How does one test them?

I'll be keeping an eye on this thread. In the mean time I am going to do the cheapest thing possible before I delve into rebuilding carbs, etc.: drain the fuel out of my tank and stick to non-ethanol fuel from a reputable source (one guy also mentioned that he doesn't use fuel over a few days old, this might be paranoia but I'll try it and see if my problem is solved).

Thanks for a thorough post!

[something2do]

Hi there,

I'm currently having the same symptoms (was just about to post about it when I saw yours). During my research I have considered the cause of the problem to be: 1) Clogged jets due to gunky/dirty fuel. 2) Water in the fuel. 3) Bad fuel (from the station). 3) Constricted fuel flow. 4) Bad coil pack.

Assuming you have good fuel pressure (is there a way to check this?), I would consider the coil packs to be just a likely culprit as the switch boxes. How does one test them?

I'll be keeping an eye on this thread. In the mean time I am going to do the cheapest thing possible before I delve into rebuilding carbs, etc.: drain the fuel out of my tank and stick to non-ethanol fuel from a reputable source (one guy also mentioned that he doesn't use fuel over a few days old, this might be paranoia but I'll try it and see if my problem is solved).

Thanks for a thorough post!

I thought about fuel too, but I have ruled that out (not completely of course) because of the awesome performance I get from a cold start and run. I figured bad fuel, water in the fuel, or clogged jets/carb would give me consistently bad performance and would not improve just because the engine cooled down. I thought about fuel in the carbs running dry as well, but it seems like I could get another good quick run once they filled up and that doesn't seem to happen.

On the coils, maybe. They might be giving me some good power early, then failing after they get warmed up. Seems like it would be weird for enough of them to fail. I wonder how many would have to be bad for me to notice the power drop? I know I have spark on all cylinders on idle (cold) but I have not yet tested the coils after the initial run down the lack when they get warm to see if they continue to give me a good air gap spark after.

My current hypothesis is that the high speed windings on my stator have burned out due to a bad set of switchboxes. My guess is that someone here with more technical knowledge than me will second that idea and I will end up putting in a set of new switchboxes and a new stator to fix the issue.

However, could still be something else. Damn outboard engines are seriously picky and complicated in my experience so far.

Thanks for your post.

[ahobbes]

Maybe you've seen this website, it might help you to check your stator and ignition coils:

http://www.outboardignition.com/page39.asp

Browse around, some good tips.

[something2do]

Thank you,

Yes, I am very familiar with the document/site and it has saved my tail a time or two. In this case, I don't don't have the right equipment and setup to run the tests I really need to in order to really nail down my problem 100%.

Unless I get some feedback to the contrary here, I am going to switch out the switchboxes and give the boat a water test and see what happens. If that doesn't fix my issue, I will replace the stator again. Beyond that, I might look at coils (not sure how to tell which one(s) is/are bad). After that, If I am still out of luck, I will look at carbs/timing, etc. but will probably be fed up and take it to the mechanic. :)

Thank you everyone, stay tuned...

[j_martin]

On fuel pressure. Had trouble with an XR/4. The fuel to the carbs is railed through them. Usually there's a plug on the end of the rail. On mine is was bottom carb, port side 1/8" pipe plug. took it out and put in a hose barb and strung a hose to a 15 psi meter in my lap. With that I found the fuel pressure crashing at WOT.

The stock fuel filter is junk.
Someone had replaced the mercury barbed fuel fitting on the motor with a plastic Atwood fitting. It would not flow enough fuel.

Direct plumbed the fuel to the engine eliminating the connector. Tossed the stock fuel filter in the trash can. Put in a Racor fuel filter-water separator and a new fuel line and primer bulb. Offered to shoot anybody that put alcohol tainted fuel in the boat.

It's been screaming and flying for years that way.

[something2do]

On fuel pressure. Had trouble with an XR/4. The fuel to the carbs is railed through them. Usually there's a plug on the end of the rail. On mine is was bottom carb, port side 1/8" pipe plug. took it out and put in a hose barb and strung a hose to a 15 psi meter in my lap. With that I found the fuel pressure crashing at WOT.

The stock fuel filter is junk.
Someone had replaced the mercury barbed fuel fitting on the motor with a plastic Atwood fitting. It would not flow enough fuel.

Direct plumbed the fuel to the engine eliminating the connector. Tossed the stock fuel filter in the trash can. Put in a Racor fuel filter-water separator and a new fuel line and primer bulb. Offered to shoot anybody that put alcohol tainted fuel in the boat.

It's been screaming and flying for years that way.

Thank you J,

On your suggestion, I took a look at all my fuel plumbing just to be sure. It looks to me like I have sufficient flow and all my connectors are factory as far as I can tell. I am currently running a Racor fuel separating filter (no secondary inline filter right now) and I have all new lines between the tank, motor, and carbs. I also have a priming bulb between my motor and Racor. I like your suggestion on the fuel pressure gauge in the lap while running and may try that if I can't nail the issue down to ignition.

My thinking is that my fuel setup has not changed at all from when the boat ran great, and I still get the awesome cold shot and run so I am still not leaning towards a fuel issue. If it was a carb bowl refill issue - running the bowls empty before they could refill - I would think I could get another great hole shot and run after my initial one after idling around a while, but that doesn't seem to work.

Also, pumping the primer bulb, nor hitting the choke primer does anything in my situation while the boat is dogging.

Keep the suggestions coming.

[something2do]

I received the new switchboxes on Friday and installed them as soon as I could. Took the boat back out to the lake and it started up faster than it ever did before and seemed to idle better as well with less smoke.

Unfortunately, all the optimism faded after another short run. Same symptoms - after backing off the trailer, idling out in gear for about 3 minutes - great hole shot, up to about 45mph around 5500-6000 RPM, and then the power drop after about 10 seconds of a good run. The RPM's drop to 3500-4000 and the boat speed drops to around 30mph. From there, no hold shot anymore and can't get on plane so I put her back on the trailer.

Still sticking with my original hypothesis that my original switchbox(s) went bad and burned out my Stator. I then replaced the Stator and it proceeded to get burned out again due to the still bad switchbox setup. So, hopefully, now that I have replaced both switchboxes, I should be able to put in a new Stator and be good as new. I ordered a new one from CDI that should be in later this week.

If that new Stator and Switchbox setup does not fix my problem, then I have spent all the money and time for an ignition education only and I need to start looking at other causes.

Any advice from the pro's here is welcome. My only other guess right now is that I might be dropping some cylinders after a cold run due to some failing coil(s). Not sure how many cylinders/coils I would have to lose to experience a drop in power like I do. Also, my experience with coils was always that they failed completely, but maybe they are failing after a short run?

[ahobbes]

Bummer you still haven't solved your problem. I'm waiting for some parts to build a peak detector circuit for my multimeter then I'm going to test my stator. You can buy a meter ready to go for reading peak voltage:

http://www.iboats.com/Mariner-Multi-Meter-Dva-Tester/dm/cart_id.384118782--session_id.783503633--view_id.269012

Or just buy the adapter and use the meter you already have:

http://www.marineengine.com/products/accessory.php?in=1329773 (you can find them cheaper but this is from CDI).

You probably already know about all of that but I think it's a good way to check your stator's outputs before replacing it and it's not as complicated as it seems.

Also, you can do some simple checks on your coils as well as physically inspecting them. Are you seeing any difference in your spark plugs? If one is more sooty after a bad run then others you might be able to trace it back along that ignition circuit checking resistance and peak voltage along the way.

Like I said, I'm troubleshooting a similar problem so just bouncing ideas around. Hopefully I can pin it down with my meter checks.

Thanks for the updates, I'll let you know how my stator checks go.

[58Evinrude]

I'm not a Merc expert by any means, but I had a similar problem on my 1978 70 horse triple last year. Same thing, off the trailer it was good, after a short run it would die down to about 3000 rpm at WOT. I checked the plugs after it bogged out, and the top one was wet. I replaced the switchbox with a buddies, and no change. I replaced the coil for the top plug, and it's been fine ever since. On the bench the coil tested fine, but I guess when it warmed up it quit working.

[something2do]

I'm not a Merc expert by any means, but I had a similar problem on my 1978 70 horse triple last year. Same thing, off the trailer it was good, after a short run it would die down to about 3000 rpm at WOT. I checked the plugs after it bogged out, and the top one was wet. I replaced the switchbox with a buddies, and no change. I replaced the coil for the top plug, and it's been fine ever since. On the bench the coil tested fine, but I guess when it warmed up it quit working.

I like that idea. I will pull my plugs and look for any bad/fouled/wet ones and try and replace that coil(s). If it is possible for a coil to work, then quit after warming up, then that definitely sounds like a possible solution.

Anyone know if just 1 bad coil would cause this kind of power loss? 2 maybe?

Thanks for the suggestion

[58Evinrude]

I'm thinking that just one bad one would do it. If you find a wet plug, you can always switch the coil to that plug with one of the other ones on your motor, and see if the bad plug follows the coil. That way you'll know for sure if the coil is bad before buying a new one.

[something2do]

I'm thinking that just one bad one would do it. If you find a wet plug, you can always switch the coil to that plug with one of the other ones on your motor, and see if the bad plug follows the coil. That way you'll know for sure if the coil is bad before buying a new one.

Thank you. Starting to think that this may be my issue. I have a very wet plug on number 3 so I will switch that one first. I ordered 2 new coils today for delivery tomorrow. Hoping to get a water test late tomorrow evening or the day after.

Thanks again

[58Evinrude]

Good luck, and I hope it works for you. Let us know if it does or doesn't work.

[ahobbes]

How did you do your wet spark plug test?

[mn808gade]

sounds like your running out of fuel on one carb.i'd say one needle/seat assy plugged with something small,or screen in one carb plugged.depends on which fuel system you have.after it sits carb refills and motor will run on all six. pull two plugs wires until you find which carb/or put timming lite into each carb till you stop seeing fuel flow.-th

[something2do]

sounds like your running out of fuel on one carb.i'd say one needle/seat assy plugged with something small,or screen in one carb plugged.depends on which fuel system you have.after it sits carb refills and motor will run on all six. pull two plugs wires until you find which carb/or put timming lite into each carb till you stop seeing fuel flow.-th

Thanks for the idea. This will be the first thing I check if the coils don't turn out to be the main problem. I received the new coils in the mail, but family stuff and work have me tied up for a while. It looks like I might be able to get them swapped out for a lake test next week.

Thanks

[89Talon18]

Im no expert but sounds like your running out of fuel. I thought I had seen in the first post that you set the floats level with the float bowl when you hold it upside down. I just cleaned and gasketed a set of wh22s a week ago and im thinking the merc manual said they are supposed to hang down 1/16"

[89Talon18]

Im no expert but sounds like your running out of fuel. I thought I had seen in the first post that you set the floats level with the float bowl when you hold it upside down. I just cleaned and gasketed a set of wh22s a week ago and im thinking the merc manual said they are supposed to hang down 1/16"

[sschefer]

I suspect it's heat related, not fuel. Run it at WOT and the second it begins to falter, shut it down and check the plugs. If one or more is wetter than all the others then trouble shoot the ignition coil and switch box. If there is no difference in wetness (either all wetter than normal or all normal) then I'd go after the stator. There is a low speed ignition coil and a high speed ignition coil in the stator. The low speed falls off around 2500-3000 RPM and the high speed takes over. If the high speed coil is failing your rpm will drop off until the low speed comes back on.

[something2do]

Well, it looks like the ignition is not likely my issue after all. I found the 2 blackest plugs and put new coils on those cylinders, but had the same results on the water.

This time out, I had my wife drive and I leaned back and pumped the priming bulb rapidly, and sure enough, the boat took off. So, the engine is not getting enough fuel for some reason.

Questions, if pumping the bulb is getting the engine going again (bearing in mind that I just rebuilt the fuel pump diaphragms a few weeks ago), then does that mean that I have a restriction ahead of the bulb or I have some fuel line collapsing somewhere? Or, does this pumping action force fuel into the float bowls and it means that I have a faulty/stuck needle/seat and need to clean the carbs?

My plan right now is to replace all my fuel lines and spin on a new racor fuel/water separator. I also plan on replacing all the fuel lines in the motor as well. I had some crappy attwood fuel line in the past that had a liner that was collapsing on me so I might have some of that somewhere else in the motor to replace.

[53w]

I had similar thing happen. I put new fuel lines on and after was starving for fuel. When I pushed barbed end of the fuel filter or primer bulb into fuel line it rolled the inside of the fuel line up and blocked the barb hole. That was a crazy too find it, drove me nuts for 2 days of trouble shooting.

[ahobbes]

Something2do,

I've solved my problem, there was a section of the fuel line (from tank to primer bulb) that was older than the next section (from primer bulb to engine/bayonet connector) and so not ethanol tolerant. The lining of this part of the fuel line was disintegrating. I was out on a boat camping trip a couple of weeks ago and my boat stalled after about ten minutes of mid-high throttle (because I had to keep it under 4500 RPM otherwise I would experience bogging around 4800 RPM, as observed on the previous 3 boating runs). I was able to restart but idle was not able to be maintained. I took the cover off and started up again then noticed fuel flowing out of the vent jet/overflow on the bottom most carburetor. My friend and I decided the float must be stuck high, blocking fuel and redirecting to the vent jet. We removed the float chamber cover and fuel hoses then blew through the fuel inlet while actuating the float levers to determine the valve was in fact closing. Upon close inspection of the levers and valve opening; I noticed a very small, semi-transparent piece of hard and flaky, plastic-like material. We reassembled the carburetor, neglected to prime the bulb then started the motor. The motor seemed to run fine, the problem was fixed in that the float was no longer sticking. Over the next 2 days, I ran the motor at mid-range throttle for a number of hours without any problems. When I got back I decided to search for the cause of my WOT bogging problem starting with the screen in my fuel pump which was surprisingly clean. The factory manual instructed me to remove the bayonet connector (fuel inlet on lower cow/body area) prior to rebuilding the fuel pump. I noticed a very similar looking debris stuck to the metal ball on the inside of the bayonet connector. I did a google image search and saw exactly what I was expecting:

http://forum.gon.com/showpost.php?p=6051899&postcount=10

I removed the bayonet connector and cut off the fuel line. The inlet side of the bayonet connector was clogged with the same debris. The fuel line itself was visibly "peeling" from the inside inward just like in the above photo.

I'm in the process of replacing my fuel line, cleaning out my bayonet connector (perhaps removing it and just direct plumbing as I've seen others do) and rebuilding my fuel pump to remove the last of the disintegrating fuel line debris.

[ahobbes]

After reviewing your first post I see you already replaced the fuel line. I suggest rigging up a fuel-pressure gauge after the fuel pump, I'm not sure what fuel pressure to expect but I'm in the process of confirming from my manual. I'm working on a little monitoring system to constantly monitor and compare fuel pressure and RPM. Hope I didn't mess up your thread here, just trying to eliminate possible causes.

[Magcat 62]

I DID my carbs 3 times about togive up. it was the stupid azz plug in connector o ring desinagrating every time ide plug in pieces of rubber would contaminate whole system. took weeks to figure problem.

[Magcat 62]

attwood makes the most inferior products on the market IMO

[ahobbes]

Hmm, I saw that o-ring on mine and it looks to be in-tact. Mine is metal and seems to be of good quality but if I have to replace it in the future i'll be sure to avoid attwood.

So where is the best place to put an in-line fuel filter, or perhaps use more than one, between the primer bulb and quick-disconnect/bayonet connector, between the quick-disconnect and fuel pump and/or between the fuel pump and carburetor?