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Author Topic:   '84 merc 90 no power
newt posted 08-10-2002 10:54 PM ET (US)   Profile for newt   Send Email to newt  
OK folks,

I have put my new to me '84 Montauk with '84 Merc 90, inline 6 cyl in the water. The motor is not running well, and I could use a little advise.

The problem: Idles smooth at minimal RPM's, but rough at all other speeds. May cut out at any time. Under power, the engine seems to want to go, but alternately surges and bogs down. A more outboard savy friend says it sounds like it's not running on all cylinders. Lack of power. Top speed is 17 mph @ 3000 rpms. This is not a prop issue, there is definitely something wrong with the engine.

Here is what we have done:

Compression check, good.

All cylinders have spark.

All spark plugs are new.

New 6.5 gal fuel tank with fresh fuel.

Squeezing bulb has no effect either at idle or full power.

At idle, pulling any spark plug wire has a noticable effect (this test has not been performed at higher RPM's)', ie rpms drop. We could not isolate any cylinder as the culprit.

Fuel screen is clean.

Any thoughts? I would like to try any quick diagnostics before I get a mechanic involved.

- Nate

newt posted 08-11-2002 03:15 PM ET (US)     Profile for newt  Send Email to newt     

I have performed all the tests as outlined in the Seloc manual for the stator, trigger, and coils. All ohm readings check out OK.

What is next?

bsmotril posted 08-11-2002 09:53 PM ET (US)     Profile for bsmotril  Send Email to bsmotril     
Check for proper operation of the spark advance linkage. Then look for breaks in the wire that runs up to the moveable stator plate.
When the plate moves as activated by the advance linkage, the wire harness to the stator will sometimes flex or rub in the same spot causing it to ground out.
Also clean and retighten every single wire you can find under the cowl that is grounded to the block. Check where the wire terminal is crimped to the wire, tug on it to be sure it is not corroded. Especially check the coil or powerpack grounds. Lastly, eliminate your ignition switch and emergency stop switch from being intermittent by jumpering the switch pins on the back of the ignition, and unhooking the emergency stop switch wires.
A Li Volsi posted 08-12-2002 07:41 AM ET (US)     Profile for A Li Volsi  Send Email to A Li Volsi     
I ran into the same problem that you are currently having-check the fuel pump diaphram. My 6 cylinder is a 1986 version and Mercury had a replacement diaphram for the mid eighties 6'es. The original diaphram is prone to breaking down-and yes if it is found to be bad-replace the fuel lines and rebuild the carbs. Mine now runs like new.
Bigshot posted 08-12-2002 01:08 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
definately check the stator wires and ignition advancer. I think your problem lies there. To rule out carbs or fuel related issues. Remove cowl and flame arrestors(if they exist) on the carbs. Fill a spray bottle with 50:1 and while your bud is driving squirt gas in each carb. If it picks up, you have gas issues, if no difference or it ""bogs" when you add fuel, electrical. Cabeesh?
newt posted 08-12-2002 01:21 PM ET (US)     Profile for newt  Send Email to newt     
Bsmotril, Tonight I will check every wire I can find.

A Li Volsi, If squeezing the primer bulb makes no difference to the performance is it still possible that the pump diaphram is the culprit?

Bigshot, It may be a few days before I can get some on the water help. Would the fuel in the carb trick work under a no-load in the driveway scenario?

Bigshot posted 08-12-2002 03:27 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Nope! Squeezing bulb would rule out pump. Squeezing bulb would not rule out dirty carbs.
newt posted 08-12-2002 04:02 PM ET (US)     Profile for newt  Send Email to newt     

I think you have answered my question about the bulb, but I am not sure about the squirt of fuel in the carbs.

Can I try your trick with spraying fuel in the carbs with the muffs on? Or only on the water throttled up?

Salmon Tub posted 08-12-2002 09:21 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
I think you would want to do it on the water rather than on land simply because you need the load. Although, if it is that your timing is not advanceing, I beleive it would hesitate with or without the load. Check the timing (spark advance) linkages first. Also, it may be a choke issue. How does the choke work on those older Mercs? Is it operated by a selenoid, or a manual lever? If the choke vavles are stuck half open, they very well may cause such a problem.
newt posted 08-13-2002 08:18 AM ET (US)     Profile for newt  Send Email to newt     
Salmon tub,

I think (but am not entirely sure) that the choke is solenoid triggered, and since I do not see any butterflies on the carbs, I think I have the enrichment system, which pumps a little fuel directly into the carbs. Please dont quote me on that.

Anyway, I want to thank all of you for trying to help me out. I have decided to bite the bullet, stop trying to be a penny pinching hero, and bring the boat in to a mechanic. After countless phone calls, I found someone local who has only a 3-4 day backlog.

My wife is about to kill me. When she agreed that life was too short to not own a Whaler, the one requirement she had was that I buy a boat that did not need a lot of work. She was actually pissed off when I came home with a boat for $4-6k less than the average. I bought the boat fully expecting to throw the motor away, and repower. So now, I am sending it to a mechanic so I can finish painting the fence, cleaning the yard, drafting plans for an addition, etc, etc.

I will send a case of your favorite beer to whomever diagnosed my problem the closest.

Thanks again.

Bigshot posted 08-13-2002 02:21 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     

Like I said has to be done on water. My inline ran great in neutral but sucked butt under load. I spent more time working on that POS than I care to remember and I still have no idea what was it's deal. I am NOT bashing Mercs or inline 6's just saying that when they do act up they can be a bitch to fix.

newt posted 08-15-2002 02:25 PM ET (US)     Profile for newt  Send Email to newt     
OK, the mechanic called and....

Motor is only running on 3 cylinders.

He recommends replacing both switch boxes and stator, and do a rebuild on carbs. Also says that head gasket should be replaced every few years and judging from the rusted out head bolts this one has not been done in the last decade.

All said and done $1500 bucks.

Forget head gasket do carbs and ignition for 6-800, but no guarentee how well it will run.

The big question is how much money does one spend on a motor that is only worth $1000 when its running?

I think I need to find a good deal on new power!

So, who gets the beer?

Bigshot posted 08-15-2002 03:52 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Hold up....switch boxes run 3cyls at a clip. either top 3 or bottom 3. Should be easy to tell which one needs replacing. Leave stator alone, leave carbs alone and just replace 1 switch box. For 4200+/- you should have an idea if she runs to your satisfaction, etc. You can always run some techron in the tank and clean up the carbs if they are not perfect. If it is not getting gas from one carb then it would have blown up on you by now from lack of oil, etc.

Nutshell. Replace the switchbox and let her rip.

Bigshot posted 08-15-2002 03:58 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I was the closest but not worthy of beer being my first post just said check stator, etc. You also stated that all cyls had spark. Did they or did'nt they? If so then you might have stator issues, not switchbox. Depends on what 3 cyls are not firing. Talk to mechanic again about the switchbox. If he says he just likes to replace both because of blah blah blah. You tell him you'll take your chances because of blah blah blah. Find out why he wants to change stator. i replaced everything electrical on mine and it did little, I think I had a bad reedvalve which unfortunately can't be replaced without splitting engine in half. What I am saying is replacing all electronics won't do shit unless all are bad. You don't swap out your alternator on your car just because the tires are worn....cabeesh?
lhg posted 08-15-2002 04:05 PM ET (US)     Profile for lhg    
A friend had your exact same set up. Running properly, you should get about 46-47mph of her. That's what his would do.

I'd fix it up if paint and other components are good. It will still be you best buy for the money.

newt posted 08-15-2002 04:38 PM ET (US)     Profile for newt  Send Email to newt     
Yeah, I am a little confused myself. I think the guy may just want to sell me a new motor.

I just spoke with him again. He said he found 1 switch box was bad and thinks that the stator is what caused the switch box to go bad. So, he wants to replace all three (2 boxes and one stator). He also said the middle carb was puking gas so it needs a re-build and if he rebuilds one he might as well rebuild all of them.

I know for a fact that all six cylinders have spark, and told him such. He said that doesnt mean they spark all the time and at the right time.

My impression is that he is not 100% about what is wrong and wants to replace all the ignition and rebuilt carbs to cover himself.

A Li Volsi posted 08-15-2002 09:23 PM ET (US)     Profile for A Li Volsi  Send Email to A Li Volsi     
I'm not going to say that any of the info that you have been given here is incorrect-but I went through the whole process you described-2 fishing seasons lost and about $1000.00 in electronics and carb rebuilds.
Pumping the primer will not rule out a bad pump. The primer pushes fuel up to the fuel pump and if the diaphram is bad it will not be able to push the fuel up to the carbs. I've been there and done that.
In my Mercury shop manual, there is a note about replacing the gray pump diaphram gasket with a new black one part # 27-75360A1. The earlier gray gaskets "have shown a tendency to decompose and contaminate the fuel system."
And because the engine was painted black after being built originally-you cannot tell if yours is gray until you open it up.
All I'm saying is that I wish I would have followed the "K.I.S.S" method before.
The gasket is simple, cheap ($13.00) and easily replaced (four exposed bolts).
Good luck.
Bigshot posted 08-16-2002 01:04 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Al that is why I told him to squirt gas into each carb while under load. that will determine fuel or electrical issues.

You can not diagnose an engine all at once. you need to eliminate one thing at a time. Eliminating the carbs will make electrical diagnosing easier. Replace the switchbox and let her rip. Puking gas can mean many different things. It could be the carb needs rebuilding or lack of spark is making it puke. Could mean the reedvalves are bad and crankcase pressure is spitting it back out. Could mean crank seal is bad and crankcase pressure is spitting it back out. The latter 2 mean total engine rebuild so you must eliminate one thing at a clip. If it runs good after the switchbox is replaced but still pukes gas, a rebuild is in order.

newt posted 09-27-2002 05:27 PM ET (US)     Profile for newt  Send Email to newt     
Follow up:

This motor is now for sale - see marketplace. I repowered (which was my intent at the time I bought the boat)

The problem is not either of the switchboxes. The mechanic tried swapping them from another motor he had, and still got bad readings. The carb thing turned out to be minor.

Most likely it is the stator.

Clark Roberts posted 09-28-2002 07:38 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
Newt, if your mechanic suggested replacing head gasket then he doesn't know what he's talking about as the 6cyl in-line (and most mercs except the V6's have no head gaskets (no removable head!) as they are of "blind bore" design. The gasket that looks like a head gasket is the water jacket cover gasket. ... happy Whalin'.. Clark... SCN
Bigshot posted 09-30-2002 09:35 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
If you got it that far...why not drop $200 ona stator?
newt posted 09-30-2002 10:14 AM ET (US)     Profile for newt  Send Email to newt     
I now have a shiny new '03 motor sitting on the back of my Montauk.

I have no interest in playing around with the old motor. While shopping for a Montauk, my primary goal was to find one for short money that I could re-power. Be it intuition, instinct, gut feeling, stubborness,or even stupidity, I was intent on having a new motor.

Now I have the new motor, and no desire to do anything with the old one except get it out of my garage.

If I had more confidence in the mechanic, I may have spent the $200 for the stator, but with the season getting short, I opted to go with the sure thing - brand new.

newt posted 03-03-2003 10:26 AM ET (US)     Profile for newt  Send Email to newt     
Update: I sold this motor to the local Harbormaster a few months ago. He called me recently to give me an update.

His mechanic replaced the stator, and another unknown electrical part (I say unknown because the guy did not remember what the mechanic told him it was). Bottom line: $700+ bucks for new stator, other electrical part, prop, o-ring on trim cylinder, and the engine screams in the tank.

With controls, battery cables, purchase price, and mechanical work listed above, he will end up spending $1300 +/- for the engine and installation, and his mechanic tells him he will be very pleased.

NOTE: The unidentified electrical part must have been related to the charging circuit, since his mechanic diagnosed low voltage. After replacing the unidentified part, the voltage increased some, and then with the stator, the voltage was normal.

Just thought you shade tree mechanics would like to know the outcome.

BQUICK posted 03-05-2003 10:41 AM ET (US)     Profile for BQUICK  Send Email to BQUICK     
Thanks for the update!
I have a 1980 90 Merc. Runs real well but hard to start cold. Usually end up having to hold the throttle way open and when it starts it ROARS and you have to pull it back fast. Until that point no willingness to fire at all. Runs fantastic all day long after that.....
Choke issue? I try not to choke it too much since it seems flooded when it does start.
Any ideas?


newt posted 03-05-2003 01:36 PM ET (US)     Profile for newt  Send Email to newt     
Bquick, it was the exact same procedure with my old merc. I only fired it up 6-8 times before I took it off, but same thing: lots of throttle and then pull it back quick.
weekendwarrior posted 03-05-2003 02:12 PM ET (US)     Profile for weekendwarrior  Send Email to weekendwarrior     
This may not help but here goes; A few years ago a friend had an old Mercury 150 V6 on a 16' bass boat. It sat for some time and when we tried to use it, it would idle OK but didn't have enough power to get on plane. If we ran to the front to help the boat get on plane then it would get on plane and run better, but definitely not 150HP better. At the end of the day, the problem was the carbs. All carbs were rebuilt and it ran like an animal. Night and day difference.

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