1977 85 horse Merc power problem

[McMudpuddle]

Is it possible to have spark during a spark test and no spark while under way?

The problem seems to be with the lower two cylinders or the bottom carb. I can disconnect the rod that connects the upper carb to the lower carb and the motor runs the same? The butterfly is closed and when opened nothing changes, I can see fuel getting pulled though the lower carb via the venturi. But it seems to just run straight through and not really burn. Inspection of the plugs shows the upper plugs, #1 &2, burning well and the lower plugs look as if they just came off the shelf, polished clean and not a bit of carbon/soot. When performing a spark test all four have nice bright blue spark. #1,2, & 3 cylinders have good compression, can't get a gage on 4 but when you stick your thumb over the hole it feels the same as the rest. The motor seems to start fine and idle fine, it's just running on two cylinders when you give it the gas.I am completely mystified? Any help is appreciated.

 

[MercFan]

Re: 1977 85 horse Merc power problem

What I always do to check for actual spark is use a timing light. I get the old man to cruise the boat around the river, throttle up, down, hole shot, full throttle, idle, cruise, with the main engine cover off. And the whole time I'm changing the timing light pick-up from wire to wire while looking into the light, with my shades on.

Some older timing lights require you to unplug the spark plug, but most have an induction pick-up that you simply clamp over the plug wire insulation.

Very simple.

I'm glad you confirmed that you do have fuel going to the bottom cylinders. It's easy to forget that a 2 stroke will seize if some of the cyliners are running without fuel.

 

[Chris1956]

Re: 1977 85 horse Merc power problem

McMud, it the bottom two plugs are real clean amd do not smell of fuel, you likely have water intrusion into those two cylinders.

On those inlines the exhaust baffle or the inner exhaust cover will corrode thru and this allows water to enter the cylinder. the cure is to replace the rotted out parts.

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

Both replies are greatly appreciated! As long as I have spark, which now I can test, and the water in the hole idea seems like a real legitimate candidate.
I have direction!! I hate going in circles!
Thanks again.

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

Spark has been confirmed at all throttle positions.
The plugs do not smell of gas, but they are wet, not dripping wet, just wet.
How far into the motor would I find the potentially corroded parts? I know on a car it would be a head or head gasket, is it that far in, or further? How long can I run this out of the water without causing a problem with the water pump or other components? It would seem a simple "test" to see if it ran on all four while out of the water and then lost two when dipped in the water at the ramp. It is a pump/jet drive, if that matters.
Thanks again.

 

[Chris1956]

Re: 1977 85 horse Merc power problem

Running the motor without water is not feasible, since you will destroy your waterpump impeller, and possibly damage the good parts of the motor during the test.

Try this test instead. Remove all of the spark plugs. Fuel line should be connected. Put the flusher on the motor and turn on the water. Now crank the motor by jumpering the solenoid. Hold a rag over the spark plug holes for #3 and #4. You will see a mist being expelled. if it beads on the rag, it is water. If it soaks in, it is gas/oil.

If it is water, you need to pull the powerhead and remove the exhaust cover (port side of motor). The trick is to not break the bolts that hold it on.

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

Sounds like a good plan, thanks. I will have to run it back down to the ramp for the test. I run a jet pump on this one, & I have yet to figure out a way to deliver water to it with out having the pump/shoe submerged.

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

Rigged up a swimming pool I stole form the kids and cut a bucket to divert the water from the jet. worked like a charm! I couldn't give it much throttle, but was able to get water to the motor. Ran it for about 15 minutes at a 1/4 throttle or so. Took out the plugs and spun the motor over. Nothing came out, not water/ fuel, nothing. The lower two plugs where cool in comparison to the upper two. I thought maybe spark was being delivered at the wrong time? By watching the mark on the flywheel, and marking where in the rotation of the flywheel the spark appears it would seem to be firing 1-4-2-3.
I also have swithched the upper and lower carbs just to confirm that it really isn't a fuel problem.

How much evidence of water intrusion would/should their be in order to cause the lower two cylinders to be completely dead? Should water be on the spark plugs?
Thanks again!

 

[Chris1956]

Re: 1977 85 horse Merc power problem

McMud, Your issue is a bit baffeling! Spray some 50::1 fuel mix into the lower carb while the motor runs to see if it starts to fire. It would be unusual if the reed valves were bad, but it happens rarely.

I still think it is ignition or ignition timing, or water!

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

I hear you man, I am truly baffled! I tried the fuel squirt thing earlier, it did not change a thing. Did not accel or bog down, I could pour gravy in there and I don't think anything would change. It seems to be crating vacuum, I can see fuel being pulled in from the float bowl through the venturi. I can disconnect the plug wires on 3 and 4 and it runs the same. It is like no body is home on 3 and 4. I guess I would expect to see fuel or water or something on the plugs after I run it and take them out to inspect them, yet they are not dripping with fuel or water.
I am about ready to tear the thing down, but not sure enough on the diagnosis or my ability to tell what is bad once I get it apart.

 

[emckelvy]

Re: 1977 85 horse Merc power problem

Maybe too much fuel. Does the primer bulb get hard when you pump it up? If not, check the fuel pump diaphragm for rupture, typically if it does it'll suck excess fuel into the bottom cyl's. Then they won't run at all.

BTW if there's enough water entering both cyl's to 'wash' them out, you'd see it all over the spark plugs. Since it doesn't seem that you're getting that, I'd bet more on the fuel issue.

And if the lower crankshaft seals were bad, you wouldn't see #3 dropping out, just #4, and probably drops of water in #4 only.

HTH..........ed

 

[ricksrster]

Re: 1977 85 horse Merc power problem

"http://www.homestead.com/dolphinmarineservice/Ign5.html"

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

Thanks again for the support. I have ruled out the water intrusion problem. Took the jet/lower unit off and ran it with out water, (only for a short time). The problem remained the same. Thanks for the link to the trouble shooting guide on the ignition system. That sounds like a good next step. It says to "check the DVA voltage of the stator" what does DVA stand for?

 

[ricksrster]

Re: 1977 85 horse Merc power problem

Direct Voltage Adapter.
http://www.iboats.com/Multi_Meter_D...5488651--list_time.1191770137--view_id.271177

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

Well the test results indicate a trigger. Can a trigger really cause this type of problem?

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

Anybody ever have this kind of problem caused by a faulty trigger?
Thanks

 

[SeaKaye12]

Re: 1977 85 horse Merc power problem

Hmmm...

I've been following this post because I also have a 85...

Originally you said that you have a nice blue spark on all cylinders. Is that possible with a bad trigger?

Maybe the spark is timed wrong because of the trigger?

Anxiously awaiting the pro's reply to this one...I might be in your shoes someday...

Chuck

 

[Chris1956]

Re: 1977 85 horse Merc power problem

Here is the troubleshooting procedure for your issue. Courtesy Dolphin Marine services.

7. Engine runs rough on top or bottom two cylinders (4 cylinder engines): Check DVA voltage of the stator between blue wires and to ground. Readings to ground should be fairly equal, If unequal, swap stator leads (blue with blue/white, red with red/white) and see if the problem moves with the stator leads. If it does, replace the stator. Check trigger resistance between #1 & #2, compare to resistance between #3 and #4. The readings should be approximately 850 to 1250 ohm for OEM (950 ohm for CDI & Repair). For test purposes only, swap trigger leads I & 3, and 2 & 4. If the problem moves, replace the trigger. If it does not move, swap coil primary wires, and replace the pack if the problem remains on the same terminals.

 

[McMudpuddle]

Re: 1977 85 horse Merc power problem

That is the test I have followed. I just have a hard time understanding how the trigger can work to make spark and be sending it at the wrong time. Just looking for someone who has had this same problem and it was fixed by replacing the trigger.
Thanks agian!

 

[rick48cj2a]

Re: 1977 85 horse Merc power problem

Did you swap the leads and did the problem change to the top cylinders? If so I think you've got it solved. From what I understand the trigger tells it when to fire. If it is bad it either won't fire or will fire at the wrong time.