200 Black Max fouling/missing

[larsonblue]

I'm having a having a problem with my early vintage 200 Black Max running rough and gas fouling plugs.

I recently acquired a '78 Larson with this engine on it. I don't know the model year of the engine, but a couple of people who know boats said it is early vintage, probably no later than early 80's.

It had been sitting for a long time so I drained the tank and put Seafoam in it. It starts easily, but it misses a lot and gas fouls the plugs.

I took it out and it ran okay at first. I ran it up to about 40 without WOT. It fairly quickly started missing and got progressively worse until it fouled out all the plugs after an extended period of idling. I didn't have a spark plug wrench so I had to get a tow in. I'll be bringing one with me from now on.

I'm running the Quicksilver oil at about 35-40:1. It might be a little richer than that, but I don't think by much. I wanted to make sure it got plenty of lubrication after sitting so long.

I put new NGK BU8H plugs in and pulled the carbs and cleaned them and checked the floats. I expected varnish and crap but they were actually very clean. When I fired it up it still smoked and idled a little bit rough. Opening the throttle a bit, it smoked like crazy and missed badly at 3000 rpm. It took most of the throttle to get it up to 6000. I turned it off after about 60 seconds. All of the plugs were already gas fouled. I wiped the plugs off and tried it again, and they all fouled again. A third time and, as the engine started to get warm, 5 of the 6 plugs stayed dry, but it still smoked like crazy and missed badly with the throttle open.

Oddly enough, the last time I ran it the buzzer started going off. I went around back and noticed the water hookup had fallen off. The engine started to race before I could get back and shut it off. After I throttled it back it was still racing. I quickly shut it off and let it cool down.

I've checked the wires with an inductive spark tester and they all light up.

I looked for overflowing fuel coming out of the carbs and didn't find any. Once I prime it with the bulb, the pressure seems to stay in the line so I don't think it's the floats.

I'm close to sea level so altitude isn't an issue.

I don't have a compression tester so I haven't checked that. I know it might be low compression, but with it fouling this way, my first suspicion is too much fuel and oil and/or a weak spark.

Any ideas?

[sschefer]

Do a compression test and post that info. Sounds like it could be rings stuck but it's to hard to tell without a compression test and not being there to see and hear it.

[larsonblue]

Compression in firing order is:

113
115
115
125
115
125

The serial number on this engine is 6109533

[sschefer]

Compression in firing order is:

113
115
115
125
115
125

The serial number on this engine is 6109533

yep, looks like you've got a carbon'd up engine. Do seafoam decarb.

Mix 1 can of seafoam in 1-3/4 gals of 92 octane in a 2 gal gas can. Disconnect the engine from the main tank and pump out of the gas can.

Call you neighbors and tell them it's gonna get a little smokey. Take the laundry off the clothes line and put it away. Fold it and the wife won't complain about the smoke as much.

Run the engine on the mix for 15 minutes at varying speeds but no more than 2000 rpm. I try to not go over 1500. You will probably have to feather it to keep it running so you might want to disconnect the throttle cable so you can work nearer the engine. After 15 minutes shut it off and let it soak for 15 minutes. Repeat this two or three times or until you think you have it pretty clean. Your engine won't run all that great on that high of a concentration of seafoam so it'll hard to tell if it's done by listening to it.

Put the engine back on the main fuel tank and run it until it clears up.

Re-check your compression with the engine warm and the throttle wide open. You should come up to even around 125 on all.

[larsonblue]

I did notice a bunch of carbon buildup on the piston tops looking through the plug hole. Is there any other place it builds up?

One of the boat guys I know said these plugs arc to the piston and I should scrape any carbon off the piston top using something soft (so it won't scratch the piston and make a hotspot) through the plug hole.

I disregarded what he told me because I noticed these plugs are arcing to the side of the plug.

He also told me a lot of guys use plugs with ground electrodes. He thought they were using plugs for Mazda RX-3's. I haven't been able to find out which plugs to use.

[sschefer]

BU8H's are right you don't need to switch. Stick with what Merc and NGK both recommend.

You couldn't scrape enough off the piston through the plug hole to make any difference I don't think. The SeaFoam will do a much better job and keep it clean if you run it in your gas tank too. If SeaFoam doesn't do it then it's time to tear it down. Your compression isn't that bad so I don't see any reason why it won't help.

I think the guys on here running race engines try to get a nice even tan on the piston tops but that's running a little too lean for the average engine. Your piston tops should be darker but not built up.

As for other places carbon build up occurs. It builds up anywhere it can.. You'd be amazed. SeaFoam will get into all those places. The stuff is weird. You can soak a carbon covered piston in it for a week and it won't do nothing. But run it through your engine mixed with gas and add a little heat and shazam.. carbon's gone.

[wrechin2]

Serial is for a 82 engine. I agree, sea foam is some good stuff. I have built a few engines that the customers have used sea foam in and the ring grooves are a LOT cleaner. Makes it a lot easier to bead blast. If the rings grooves have carbon build up, then the carbon can be holding the rings. Sea foam can sometimes reverse the effects of carbon and sometimes only a rebuild can. JME.......

[wrechin2]

BU8H's are right you don't need to switch. Stick with what Merc and NGK both recommend.

Your piston tops should be darker but not built up.

.

:iagree: On the plugs.

Carbon is a byproduct that you can't get rid of. Some oils can lessen it.

I have a 2.5 that has 3 hours on it before I tore it down to do more mods to, and there was already a light coating of carbon starting to form on them. They were bead blasted and could pass as new when I put them in. After 28 years with no oil injection to even lessen the mix, I would say they would have alot of carbon on them. JMO....

[150aintenuff]

carboned up rings or not the compression isnt that far off... you have issues still.... regardless of how CLEAN carbs appear there are TINY air bleeds in several locations that assist in fuel atomization. and though things may look clean take and SCRUB every single orfice and part that can come apart in a bath of carb cleaner and a brass wire brush... you will be amaised at the CHIT that falls out of the old birds... also varify your timing, and an inductive timing tester aint chit.... you need to JUMP a open 3/8" gap to properly test the ignition system on a merc... 1/2" is better...


the fact you are fouling and it is loading HARD and taking WOT without load to get 6000 you have serious carb and ignition issues to address BEFORE you start looking deeper into the motor.... i have a 1978 175 that sat for 3 yrs... and had the dog snot ran out of it prior to storage and all it did was cough at idle due to varnish in the carbs.... clean that and even without a decarb it runs flawlessly solve all external problems BEFORE you dig deeper....


timing should be 18-22* max (WOT)

and carbs need to be basically FLAWLESS to operate as originally designed... start scraping inside the jets... ill bet you will be supprised just how cruddy they are..

[larsonblue]

carboned up rings or not the compression isnt that far off... you have issues still.... regardless of how CLEAN carbs appear there are TINY air bleeds in several locations that assist in fuel atomization. and though things may look clean take and SCRUB every single orfice and part that can come apart in a bath of carb cleaner and a brass wire brush... you will be amaised at the CHIT that falls out of the old birds... also varify your timing, and an inductive timing tester aint chit.... you need to JUMP a open 3/8" gap to properly test the ignition system on a merc... 1/2" is better...


the fact you are fouling and it is loading HARD and taking WOT without load to get 6000 you have serious carb and ignition issues to address BEFORE you start looking deeper into the motor.... i have a 1978 175 that sat for 3 yrs... and had the dog snot ran out of it prior to storage and all it did was cough at idle due to varnish in the carbs.... clean that and even without a decarb it runs flawlessly solve all external problems BEFORE you dig deeper....



Since even the good cylinders are loading up, I don't think it's sticking rings either. I've already run one can of Seafoam through and it got worse. I'm going to run the concentrated Seafoam as recommended just to make sure.

I don't know about varnish in the carbs. I didn't see ANY signs of varnish in the carbs. I pulled all the jets and eyeballed them in the light and I sprayed cleaner through every passage. I think the carbs are fine, but if they aren't I don't think they're bad enough to cause this problem. I've seen much dirtier carbs run better.

I'm with you on the spark. I'll check that next and do the Seafoam when I have the time.

[wrechin2]

Sorry long......

Don't take it as I meant it has internal problems. I was stating in general about a carboned up engine and what I have seen sea foam do. I corrected it not impose that I meant you have internal problems. I personally live by a leakdown test. I only do a compression test if I need to know what octane fuel to run. I couldn't tell you how many engines I have delt with with issues that other shops have looked at that found them to have good compression and say it is mechanically sound but I find them to have high leakage. They generally will have damage in cylinder or the rings are pinned in from carbon, but they passed a compression test. Compression test only tells you if it makes "PRESSURE" and a leakdown test tells you if it can "HOLD" it. In black and white, I have a factory OMC manuals that states.

IF the engine has equal compression, is hard to start, and operates poorly check for:
*scored cylinder walls
*Damaged pistons
*Stuck piston rings
*worn pistons rings

In the factory Mercury manuals I have, they only tell you what it should be. Myself and many other people have seen engines with good compression have issues though, again not saying your is one of those.
but a compression test is NOT the "BEST" way to determine the health of a engine. All of the faults listed above will show up with a leakage test 99% of the time. FYI only...........


Keep in mind, that when you pull the plugs out after it has idled for a few second or minutes, they will be wet. THIS IS NORMAL on a 2 stroke outboard. If you pull one out and it is dry, that is not normal. You said 5 of the 6 plugs were dry after a high run... If it was cylinder 5 that is wet, I would look at my fuel pump diapram and see if it is ruptured pumping additional fuel into the intake.

Also remember you have a high and low side windings of the stator. I have had 2 that would drop 1 cylinder above 3K and turned out to be a bad stators. I would have bet money a stator couldn't do that, but I have seen 2 of them, so I keep a open mind about what can and can't happen. So the one may be wet due to loss of ignition also. Mercury are bad about the magnets breaking and dropping the voltage from the multiple magnetic fields that broken magnets cause. I like to see if they can jump at least a 7/16" gap. If not, the coil may be breaking down. Mercury just wants to make sure it is blue in color. It takes less voltage to fire a "rich" condition and more to fire a "normal" mix. As a engine goes up in RPM's the fuel mix starts to lean out. This takes more ignition voltage. I had a 2.4 175 that I found had 5 coils with cracked magnets on. Replaced all 6 coils and it picked up 400 RPM's. Just my experiences......

It may also be a carb issue still.



If I read your post right, you are running this at 6,000 for a few minutes on the hose??????? If so, it was racing because it was what is refered to as a runaway due to not enought load on the engine. I makes it worse when no water is being dumped into the exhaust, it actually offers a "LITTLE" back pressure, but not much.......

You may want try a remote tank with a 50:1 mix also. The heavy oil mix or quality of the fuel may be a issue. How did you drain the tank??? Most tanks will still have several gallons in them after no more fuel will come out with the primer hose. I remove the sending unit and have a fluid extractor that I get all of it out with. You may have some dead fuel causing the issues. Also remember if it had a set for a long time, the fuel evaporated leaving the oil behind. If you didn't get all of it out of the tank, along with your heavy mix, who knows what you are running. Just a thought....

IF interested, If you pm me your last name, I will send you a link to down load a manual covering this engine. I just finished it. It is a active PDF. It will have instructions on how to use it. I will encrypt it so that it requires a password to open it. I will use you last name or part of it for this.:cheers::cheers::cheers:

[pyro]

...I would look at my fuel pump diaphragm and see if it is ruptured pumping additional fuel into the intake...
I'd recommend replacing the fuel pump FIRST before you try to diagnose anything else. If the pump is original, it's VERY likely that the rubber diaphragm has a hole in it. This would definitely make it run pig-rich and consume lots of fuel.

Carb floats should be the next thing to check...

[150aintenuff]

ive taken carbs that people SWORE were totally clean and pulled corosion and varnish out that nobody knew was there.... ive personally watched a suzuki factory tech take a set of mikuni carbs off a 115, totally go through them and still have the original fuel lean condition the carbs came in with.... 15 min of SCRUBBING and holly cow... enough deposits that "werrent visible" to cause a .004 restriction in every jet... and enough deposits to completely cover a paper towel after draining off the dish full of carb cleaner used to reclean the carbs...

and this set of carbs LOOKED LIKE BRAND NEW!!! so its always good to double check.. especially if it was running better BEFORE you went through the carbs.


but as others have said.... there are other problems as well.. just saying just because it looks clean doenst necessarily mean it really is

[larsonblue]

Keep in mind, that when you pull the plugs out after it has idled for a few second or minutes, they will be wet. THIS IS NORMAL on a 2 stroke outboard. If you pull one out and it is dry, that is not normal. You said 5 of the 6 plugs were dry after a high run... If it was cylinder 5 that is wet, I would look at my fuel pump diapram and see if it is ruptured pumping additional fuel into the intake.

Also remember you have a high and low side windings of the stator. I have had 2 that would drop 1 cylinder above 3K and turned out to be a bad stators. I would have bet money a stator couldn't do that, but I have seen 2 of them, so I keep a open mind about what can and can't happen. So the one may be wet due to loss of ignition also. Mercury are bad about the magnets breaking and dropping the voltage from the multiple magnetic fields that broken magnets cause. I like to see if they can jump at least a 7/16" gap. If not, the coil may be breaking down. Mercury just wants to make sure it is blue in color. It takes less voltage to fire a "rich" condition and more to fire a "normal" mix. As a engine goes up in RPM's the fuel mix starts to lean out. This takes more ignition voltage. I had a 2.4 175 that I found had 5 coils with cracked magnets on. Replaced all 6 coils and it picked up 400 RPM's. Just my experiences......

It may also be a carb issue still.


You may want try a remote tank with a 50:1 mix also. The heavy oil mix or quality of the fuel may be a issue. How did you drain the tank??? Most tanks will still have several gallons in them after no more fuel will come out with the primer hose. I remove the sending unit and have a fluid extractor that I get all of it out with. You may have some dead fuel causing the issues. Also remember if it had a set for a long time, the fuel evaporated leaving the oil behind. If you didn't get all of it out of the tank, along with your heavy mix, who knows what you are running. Just a thought....



I have a portable tank too and there is no difference when I use it. The plug wires were dirty at the coils so I cleaned them and got a little improvement, but not much. The spark now jumps 1/2" so I don't think it's the spark. When I set the throttle around 3000 rpm it would run up and down several hundred rpm. I ran it up to around 5000 and it still misses a bit, but it doesn't need a lot of throttle. I think I'll check the fuel pump next. Is there anything I need to know about doing that?

[wrechin2]

Is there anything I need to know about doing that?

Process of elimimation. You will slowly rule things out.

PM me your last name or a SHORT password of your choosing, I will send you a manual on that engine.:cheers:

[pyro]

Take the pump apart, then replace the old diaphragm and gaskets. ;)

[TEXAS20225]

since you aint there:confused: but it sounds like a fuel issue to me Too i just today rebuilt a square fuel pump kit was 6.47 . but if i was making a guess i would say its the carbs aint clean 150 is right:iagree: there is a lot of small holes and places that are hard to get to, they got to be torn completely down to get it all out

[sschefer]

The full strenght decarb will go a long way in cleaning out the carbs. If there's a hole in the fuel pump diaphram you won't be pumping adequate fuel and you'll be pumping air into the fuel from the pulse port.

There are two check valves in the fuel pump that need to be changed also. They can be a little tricky if you just go at it so read the instructions. I use a finish nail to set them retaining pins.

Fuel pump is a good idea and a real carb cleaning with a 24 hours soak in gunk followed by a wash with a citrus based cleaner and a final blow down with compressed air is the routine. Have a good overhead light source and look closely at all those tiny holes in the throats. Brush them with a nylon brush until they're clear and you can see unobstructed light through them. Soak the jets too but keep them separated. I put down a piece of paper with some strips of double sided tape on it and stick them to it. The ones that are exactly the same can be soaked together but separate the others and keep track of where they came from so you can put them back exactly as your found them.

Set the floats according to spec's in the manual James is gonna send you. Don't backyard it, that's for when you don't have time to clean them properly and, by the way, it doesn't work.:D

You've got a ton of fantastic advice so you should have that thing up and running in no time.

Steve

[larsonblue]

Well, I pulled the fuel pump and it looks fine. Then I checked the spark on all 6. They're all jumping over 1/2" except one of them. Number 2 is weak and intermittent. I checked the wire on a different coil and it's not the wire. On another note, the buzzer went off on this last run and I noticed the cooling water wasn't squirting out the outlet at the top of the engine. It was squirting just fine earlier today. There was plenty of water flowing at the hookup so I don't think that's it. This thing has a new impeller so I don't think that's the problem either.

[silverbullet02]

If you're running high rpm on the hose, the water pump will starve for water as the hose can't flow enough. Just a thought.

[larsonblue]

If you're running high rpm on the hose, the water pump will starve for water as the hose can't flow enough. Just a thought.

I didn't take it out of idle this time.

[wrechin2]

There are two check valves in the fuel pump that need to be changed also. They can be a little tricky if you just go at it so read the instructions. I use a finish nail to set them retaining pins.


Steve

His is a TOTALLY different pump being a 82 from yours and Bobby's.

[TEXAS20225]

i did not think about the older style but according to his intermittent spark that sounds like a switch box or trigger maybe

[bigshrimpin]

make sure to remove those spark advance modules

[sschefer]

His is a TOTALLY different pump being a 82 from yours and Bobby's.

Oh yeah, your right I forgot. Sorry about that.

[sschefer]

i did not think about the older style but according to his intermittent spark that sounds like a switch box or trigger maybe

That's certainly a possibility. I'd like to see what the seafoam decarb does first.

[150aintenuff]

if you have intermintant spark... or WEAK spark... STOP.. get a DVA adaptor for your DVOM .. ( you do own a digi volt meter right.... ) and track the weak spark.... swappin wires on OB wont tell you a darn thing because unlike Automotive wires that are carbon/graphite based and high reisitance... the wires used on OB motors are of solid core IE all metal and at 45000-60000 volts arent going to show the deects a standard wire might... swap coils around... if it moves its a bad coil... if it stays weak on same hole its a switch box or trigger.


but carbs and pump NEED to be properly addressed



and finally.. i hate to say it.. but if you were sustaining 6K on the hose, your impeller is SHOT and will require both impeller and housing due to exhaust and friction heat damage.

i can get you a complete WP kit for under 35.00

[wrechin2]

PM'd you a link to the manual. IF you find any mistakes, let me know so I can correct them. Thanks.