25 hp mariner...... intermitently drops a cylinder??

mallard · #1 January 16th, 2007, 04:21 PM

I have been having problems with a 25 hp mariner......canadian production. Serial number 0A991090. It started by losing the bottom cylinder after around 10-15 minutes of running time. I replaced the coil, switchbox and trigger.....only to find the problem still there...but with no logic in its occurence. Sometimes it doesn't hit while it is cold....then starts to run fine......sometimes it runs fine....then drops the cylinder. I am running out of parts to replace. Any ideas or suggestions on things to check???

Laddies · #2 January 16th, 2007, 07:25 PM

If the engine seems to idle all right but the miss starts above 1500 it's probably the stator as it switches from low speed to high speed windings

mallard · #3 January 16th, 2007, 08:04 PM

Nope.........it just quits.... altogether. I have usually been at top speed when it quits......but have experienced it at idle. It sometimes hits a shot...then later fires back up.. Any good locations for a service manual.I was told it is covered by the mercury manual part number 90-43509-3

Laddies · #4 January 16th, 2007, 08:30 PM

Have you tried to disconnect the kill wire from the box(Blk/yellow) to see if there is a short some where other that ign componets. I have seen the wires that come from under the flywheel nicked causing a problem also

mallard · #5 January 17th, 2007, 12:03 PM

UPDATE --------->
I checked to see if there was any water in the fuel......just to rule it out. Not a drop. I changed the "dropping" cylinders spark plug only to discover heavy rust in the boot of the spark plug wire at the spark plug. I replaced the entire wire with a fresh one. As it is around 10 degrees today...I might have to wait untill the weekend to get it in the water for a test.That would be a good time to test the kill switch. Am I correct to understand that if I disconnect the (Blk/yellow) wire from the switchbox while it is running it should tell me what?

Laddies · #6 January 17th, 2007, 01:36 PM

The kill wire acts just as a kill wire on a magnetos it shorts the box to ground by disconnecting it you are checking all kill switches and connected wiring. Disconnect it with the engine off and reconnect to kill the engine use care it can poke you

mallard · #7 January 17th, 2007, 05:39 PM

Thank you so very much for your help........
Would a rusty spark plug wire boot potentially cause this kind of mess?

Laddies · #8 January 17th, 2007, 05:42 PM

Probably not, but a wire that is not pluged in the coil or on the plug all the way can give you a fit

merc.dog · #9 January 18th, 2007, 02:55 PM

Quote:

Originally Posted by mallard

I have been having problems with a 25 hp mariner......canadian production. Serial number 0A991090. It started by losing the bottom cylinder after around 10-15 minutes of running time. I replaced the coil, switchbox and trigger.....only to find the problem still there...but with no logic in its occurence. Sometimes it doesn't hit while it is cold....then starts to run fine......sometimes it runs fine....then drops the cylinder. I am running out of parts to replace. Any ideas or suggestions on things to check???

merc.dog · #10 January 18th, 2007, 03:09 PM

hey frist do a plug reading wet or dry when eng.drops out. you can use a timming light to see if you are loosing spark. if plug is wet ck. carb ball and spring on injector also powerhead mounting bolt stbd. side 2nd or3td back gose in intake port can leak add sealer to bolt thds. good luck. merc.dog!

mallard · #11 January 20th, 2007, 06:40 PM

Well.......I thought I had the problem solved......I launched the boat to goose hunt this morning....and it fired up and ran great!!!!!spent a 10 minute boat ride at full throttle and about 30 minutes putting out decoys at idle and it never dropped a cylinder. I parked the boat in the boat hide and it sat not running for around 5 hours. When I started it up to pick up decoys......it only hit on one cylinder. It continued missing for around 30 minutes untill it all of the sudden it hit a shot and fired back up. I disconnected the black/yellow wire and it ran fine.
I really appreciate the help you guys have shown....Is there a test to verify the switchbox is functioning correctly??

Laddies · #12 January 20th, 2007, 07:04 PM

Mallard, are you saying that when the engine acted up you disconnected the blk/yellow wire and it ran alright or that it didn't help
A switch box is hard to test at times even with a DVA and can not be tested at all with a OHM meter as a repair shop if it tests alright but still acts up we change it and see if it repairs the problem.
The reason that a questioned the stator originally is we had a customer change his box himself a year ago this fall (a duck hunter like yourself) didn't want to take the time to bring it in when hunting and in the spring brought it in to have it tested because the box didn't fix it we tested it and ever thing tested OK, but when test running it would drop a cyl after 10 minutes or so of running, so we tried anouther box it did not help and I called rapair sevice and they said it was the stator, I said it checked OK even when the engine was acting up they said change and so we did, end of trouble. That can I say other than ever day is a learning experince--Bob

mallard · #13 January 20th, 2007, 08:23 PM

I disconnected the black/yellow wire after it re-fired up. Would it have helped if I would disconnect it while it is acting up? While it was running fine....disconnecting it did not change anything......I had to reconnect it to kill the engine.
Let me explain my switchbox dilemma..... just so I am not leaving any possible details out. I was told by a local mercury dealers mechanic that he guaranteed my 339-7452 A7 switchbox was the problem. He said they replaced it with an A!9 version that fixed some circuitry heat issues within the switchbox. I found another used A7 and tried it. He said when the motor/switchbox heated up....it would kick a cylinder out....when it cooled it would run fine untill at last it would no longer run normal. The 2nd A7 box didn't act like he explained........it would run fine sometimes while cold...and sometimes not........blowing that theory. I bid and purchased another switchbox........the current one that is installed....and it acts goofy too. The question would be.....is it possible that all 3 switchboxes are defective? or could another problem such as the stator be the problem? As I price these problems....it seems the stator is cheaper than the switchbox to replace.

Laddies · #14 January 20th, 2007, 10:04 PM

You need to disconnect the wire when the engine is acting up to ck for problems in the kill circurt wiring and switchs, I doubt that you have had 2 or 3 bad switch boxes all doing the same thing. We don't use mercury ign. componets as the stators on the larger engines are junk, I've never heard the story of switch boxes having heat problems, that is the problem with the potted stators on the larger engines though. Might be true or a inventive mechanic, gets to be more of them all the time

mallard · #15 January 22nd, 2007, 11:39 AM

UPDATE--------------> I launched onto the mississippi river for a goose hunt that was about 8 miles downstream.........the motor fired up and ran perfect all the way to the spot. On the first retrieve with the boat......it ran fine all the way to shutdown....around 10 minutes running time. On the second retrieve.....about 1 hour later.......it fired up with the dropped cylinder again. At that time I took the cover off and disconnected the black/yellow wire. It continued to run....on 1 cylinder....but kept running. I assume that I should rule out the killswitch circuit by this test. It eventually hit a shot and shortly thereafter.....fired up on both cylinders.
It seems to refire up better at lower rpm's...although it has regained the cylinder while at full throttle. Travelling upriver requires at least 1 cylinder at full throttle to outpace the current...hehehe:%
As I have been using the mercury express parts page....... I can see that the stator is broke into 2 pieces.....and while replacing the trigger recently I saw it for my own eyes. Does any of these details give some clue as to which piece or both need to be tried?

merc.dog

Quote:

hey frist do a plug reading wet or dry when eng.drops out

When in the "dropped cylinder" mode I did pull the affected plug out to find it moist....not dry.....not soaking wet....but just moist.

Also....if I have to replace the stator......my motor did not come with a charging feature that would be killer to replenish my battery......is it possible to add this feature which was once an option or feature? I think I was told that the stator is where it is located from. Would that require a different stator or am I confused?

Fellas......thanks for your help...... I love the motor........and I am confident that with as much appreciated knowledge you guys have....I can once again enjoy it's reliability.

Laddies · #16 January 22nd, 2007, 02:04 PM

Yes, the kill circruit is OK, On a 25 a seperate stator is used and can be added you will also need a rectifier to make it work, if you go to the BAM Marine site you can ck out the differances between the systems

Brochet99 · #17 July 29th, 2008, 01:49 PM

I have the same problem you had.
Motor starts fine and runs fine at full speed for a while. I stop fishing a while then as I start it up again it sometimes runs on only one cylinder. I play with it, clean the spark plugs, change them and after playing for a while, it suddenly goes back on 2 cylinders and is fine. Problem eventually comes back as I stop for another fishing spot.

Did you ever find your problem and resolved it?