ignition components and their purpose

my motor has this issue. cranks and idles great. but from half way to full throttle(say 45 degrees forward) to full throttle(say 90 degrees forward)
it only gets louder and runs at what seems to be a full bog condition. the carbs (3) "ARE" fully open when lever is pushed forward so i think fire. spark at all plugs determined by timing light. no way to know if its a weak spark though.
can someone quick explain all the parts to this ign system? im new to boats. posting pics in case it helps. one is of the distributor to hopefully help someone identify what type ign this is. the rest are components i dont know. one specific question i have is the pic with 2 vertical running wires. these go up and under the flywheel. definitely what are those? and i have never seen a dist run on a belt. whats with that?

sorry the pics are sideways guys. lucky i even got these on here.

Both Mercury and OMC used a belt-drive distributor on many models. Millions of 4-cylinder and 6-cylinder Mercs have been produced over the years with a belt and either magnetor or electronic-ignition-distributor.

It would help if you posted the HP of your engine and serial number so we could determine what year your Inline Six is.

The pictures show a 6-cylinder CDI system which has one coil, belt-driven distributor, with a switchbox.

Critical are the belt alignment and timing stop settings; if the engine is out-of-time it won't run correctly.

I can't tell what color those 2 wires are, but if they go up under the flywheel, they're for the stator (alternator). They have nothing to do with the ignition system, only for charging the battery.

On this motor, both the red terminal on the Stbd side of the switchbox, and the white terminal (same side) must be energized with +12V to get spark.

The belt drives the distributor rotor shaft, and there is a copper "chopper" disc down by the rotor end that uses the Hall magnetic effect to trigger a sensor which "fires" the switchbox. Note that the rotor is non-removable from its shaft and is quite expensive. Doesn't need to be replaced unless physically broker or shorted to ground (very rare).

The trigger assy is built into the body of the distributor and is non-replaceable. Also a very expensive part, so use great care not to damage if you pull the dist cap for servicing.

Since you say spark seems to be OK, and the carb butterflies are opening all the way, seems to me it might be a fuel-related problem.

Most of the time, the CDI system either sparks or it don't; so as long as the distributor is set up properly and timing advances to specifications, there shouldn't be any ign issues. I have seen 'em miss when there was crud/trash in the cap, but you don't mention any misfiring so probably not that.

Note that as you advance the throttle, the distributor rotates to advance timing from idle; at the specified degrees BTDC (usually around 21 deg), the distributor collar hits the "Spark Advance" stop screw and this is your maximum spark advance, checked with a timing light.

You can set this with all the plugs out except #1 cyl (top). Crank over the engine with the distributor against the spark advance stop, then adjust the screw to set max advance. You'll have to disconnect the throttle cable at the motor so you can move the distributor.

One effective way of diagnosing fuel issues is to have someone run the boat, then spray some pre-mix into each carb and see what happens. If it picks up when you do that, that carb isn't getting enough fuel. Don't run it long that way, 'cause those 2 cylinders aren't getting lubrication, either!

If the engine slows down, that carb is probably working and you just made those 2 cylinders too rich.

If no difference, those cylinders aren't kicking and need further investigation.

You can try the fuel spray trick at home, and you'll see better results if you idle the motor in a barrel instead of on a flusher. They all sound good on the flusher, there's no exhaust backpressure to drag the motor down. Any weakness will begin to show when run in a barrel.

A sometimes-useful test is to do a "spark drop" check. Pull one plug wire, stick a spare plug in it and lay the plug against the framework so it's grounded.

Then run the motor and see if rpm drops with that cylinder deactivated. If it does, you're good, if not, that's a problem cylinder.

Another tip, once you've run it for a bit, feel each spark plug on the metal body. They should be pretty warm and that's an indication that cyl is firing. If the plug is cold, no fire in that cylinder (for whatever reason).

If you can pinpoint the problem to one or more cylinders or sets of cylinders, it'll be easier to diagnose.

You might want to pick up a manual, this will help you with all the settings and troubleshoot info as well.

Post your serial # and hp, we'll figure out what you've got. HTH..........ed

sir, this is absolutely a stunning amount of information. I thank you deeply for taking the time to write this. to catch up the holes in the story.......I posted my number and pics of my motor in an alternate thread. no guarantees on my year as it didn't come up with a hit. therefore I still cant order parts with confidence. no shop around me will work on anything older than 1980 so that leads me to here. I will be very eager to try any and all of this probably today. I am very car saavy but this is different. it is going to be hard without having someone to ask in real time. please check back here periodically. I will post at every update on the situation. again....thank you. this is a 90 hp motor.

OK, analyzing your serial # 4603143, I can only conclude that the mid-section came from a 1977 115hp.

The only other Inline Six (besides 115hp) produced in '78-'79 was a 140 and the serial #'s don't coincide.

Small possibility it came from a '76 150XS but very slim since those would have been a short shaft. Not sure if any of 'em came in a long shaft configuration as they were a high-performance version of the 1500.

There's only one way to know for sure, if you can't find any numbers on the block. Usually there would be some sort of serial # and stampings on the Stbd side of the block, near the intake port covers.

Here's what you need to do: take the most convenient carburetor for you to get at (either top or middle); you'll see a hex-shaped brass-colored plug at the very bottom front of the carb. This takes a 7/16" wrench/socket. Use a rag or container to catch any fuel coming out of the carb (be sure the fuel supply hose is disconnected from the motor), and remove the brass main jet plug.

Within you'll see a slotted brass main jet, it'll have a hole in the middle. On the face of the jet is a stamped number. If you can't see it 'cause of residual fuel, blow a bit of air or carb cleaner in there until the jet is clearly visible. With a strong light (LED will do the trick), note the number on the main jet.

If it's a 90hp, it should have a .070 main jet. A 115 should have a .072 jet.

This is not absolutely conclusive, because the motor may have been messed with. Very possible it's a mix-match of 90hp and 115hp parts.

Since we have a pretty good idea it could be a "Frankenmerc", you're probably gonna have to do the on-water diagnosing since jetting and other carb problems like this won't show up at an idle in a bucket.

But if you spray fuel/oil mix in a carb when the engine is bogging, and it picks up, it's a sure sign you either have a fuel delivery problem with the carb, or it's been messed-with (i.e., wrong jets, etc).

Here's the good news, the distributor-fired Merc Inline Six is like the Small Block Chevy of outboards!

Most of the external parts are interchangeable, and the biggest differences lie within, in the way the blocks are ported and the piston configuration. Amazingly, the same basic block had a hp range of 90 to 155hp. And the racing version of the Inline Six produced well in excess of 200hp!!

So, for the most part you could flip a coin and look up parts for a '77 115 or a '79 90, they're gonna be really close.

115: http://www.marineengine.com/parts/mercury-outboard-parts/1150/3525441-thru-4855152-usa

90: http://www.marineengine.com/parts/mercury-outboard-parts/900-90/4845301-thru-5299505-usa

The nice thing about this site is, besides the diagrams, they have actual pictures for most parts. So if you eyeball a particular part you're looking for, and it's physically identical to the part on your engine, it's more-than-likely to fit. Note the ignition components on all of these 99-c.i. distributor-fired blocks are completely interchangeable.

Note the attached diagram, #28 is the main jet, #29 is the brass main jet plug, #30 is a little red or brown gas

updating: all cylinders compression between 117 and 122. i did this cold. should i do it hot?
also found another number about an inch below my middle cab. is this a serial number?(pic) and if i am not mistaken.....the jet i was supposed to find has 80 on it? (pic)

i am almost certain thAT these carbs are WMK-22 carbs. that jet number has me confused. if its not the jet that 90 or 115 hp models use then what is it? and is it the right carb/wrong jet? or wrong carb/ with tits normal jet?

Compression sounds ok for a cold engine. Those jets are the standard size for a 150hp motor, so the plot thickens! You really do have a Frankenmerc on your hands!!

Now I don't know what to think! The only other motor with a serial number range that falls within your ser & is a 1977 1500XS (starting #4602012) but again that's a short-shaft motor.

It's very possible that someone who didn't know what they were doing has messed with the carb jetting, thinking if they put a larger jet in, it'll go faster. Doesn't work that way!!!

So, we're back to guessing 'cause the only true way to tell for sure is to dismantle the powerhead and check the intake/exhaust ports, pistons and block! You probably don't want to do that so we'll have to be more clever!

It gets back to making it run right, regardless of what HP it really is. First you have to find out if it's running rich or running lean.

So we need to return to spraying fuel/oil mix into a carburetor, under load in the water, to see what it does. What I expect it'll do is fall flat on its face 'cause it's already running way too rich with bigger main jets. But you never know until you try.

The next thing to do after that is to disconnect the fuel line after the engine has been running, so everything is full of gas. Then take off real quick and see what happens when the engine starts to run out of fuel. It will, of course, lean itself out. So if all-of-a-sudden you get this serious leap of power right before it runs completely out of gas, that's an excellent indication of being way too rich.

You can also diagnose a blown fuel pump diaphragm with this technique. Oddly enough, it's a lot tougher to diagnose an outboard that's getting too much fuel, rather than too little.

I can tell you from experience that even one jet size too-large may make the motor un-runnable. Years ago I rebuild my 1350 Merc and put larger jets in it. Well, it ran great in cold November salt water. But next summer when I fired 'er up, she wouldn't even throttle up. The 70-80 degree warm air was way too thin for the extra fuel. Whereas the cold, dense air of late fall made the perfect air/fuel mixture. I reinstalled the correct-sized jets and next time at the lake she ran perfectly.

So, looks like you might have a bit of troubleshooting to do! Fortunately replacement main jets are available and not extremely expensive, if that turns out to be the problem.

Let us know what happens..........ed

Saturday morning I will do this. please check back in Saturday later half of the day. grateful for your help.

UPDATE: When spraying mix in the carbs is tried to kill the motor. So.....rich issues? Also now after that it tries to die when slow idling like the trailering approach. Never did that before. Is there harm in running too rich? At least we can be pretty sure I haven't run it lean right? Please advise. And thank you.

Are you second owner of this engine? Is motor being used at sea level or at what altitude. where are you at? Running too rich will foul plugs constantly and waste fuel and pollute the environment !

Portis Left said:

UPDATE: When spraying mix in the carbs is tried to kill the motor. So.....rich issues? Also now after that it tries to die when slow idling like the trailering approach. Never did that before. Is there harm in running too rich? At least we can be pretty sure I haven't run it lean right? Please advise. And thank you.

Click to expand...

OK, so did you spray in one-carb-at-a-time, under load? If so, sounds like you're pretty rich if they all died when you sprayed. And of course it's gonna run even richer with more fuel sprayed in the engine, until that fuel is burnt up.

Did you try the unplugging-the-fuel-line trick to see if rpm picks up as it's running out of fuel? That's gonna be a critical part of this troubleshooting. Because if the engine does not start to run better right before it runs completely out of fuel, there may be other problems we haven't figured out yet.

UPDATE: yes. I sprayed them at the fullest load I could put on it....in 30 feet of lake....the top carb wasn't so bad. It changed the tone of the motor but not noticeably the running. The middle carb affected and made it stumbly. The bottom carb tried to take it all the way out. I just sprayed enough in them to get a result. Not to try to kill it. Went back today just to do this part cause I forgot. Pulled the motor gas line at full load....same water. It ran itself out of gas pretty much like a car. No surge of power that I felt. Took it longer than I thought. Where do we go? I'll do whatever you can think of. Should I buy some jets anyway? I'm not above spending useless money (at least some) to get somewhere.

WMK-22 carb where used on the 1975/76 150 I6 motors along with the .080 jet. If its a 150 the compression readings are low as it came from factory with 145+psi cranking an will suffer idle and low end problems when below 125psi. The front casting number is common to all the I6 motors 90-150hp and the only way to be sure is to pull transfer port cover and see it piston has boost port as a 90/115 will not.

Did you find the "WMK-22" number on one or more of the carbs?

Does each spark plug seem like it's getting warm/hot, or do some stay cold (indicating that cylinder isn't firing)?

Have you checked the max spark advance and what is it set at?

Re: compression readings, I've never found a worn-out engine to have all cylinders so evenly worn that they have almost-identical low readings. Usually all over the map. Variances with compression gauges can give results different from factory specs. So can cranking speed. And an engine that's more radically ported may have lower compression at cranking speed than a mildly-ported engine.

Might need to pull a transfer port as suggested, if you find a power-ported piston in there it'd most-likely be a 150 block, especially considering the serial number. Of course, if it doesn't have power-ported pistons, I dunno if there's any way to tell the distinction between a 90 and 115 without tearing the powerhead apart. But at least you'd narrow-down the possibilities for the price of a gasket.

Yes. I think the carb had 22 on it. I will pull one tomorrow and confirm. I will see if I can check this port tomorrow. Not sure what it is but can't be hard to google. I don't really care about hat the motor is. I think 90 is more than enough. The size only matters so I can order parts hopefully. My goal is all "make it run". Will opening this port require a gasket? I don't know about advance stuff. I know cars so this can't be different right? But it was different. I did a link and sync off a you tube video by a guy named cturboaddict. My motor needed only minuscule adjustments to be correct with this guys instructions. I can do anything. But I will need instructions.

I found a halfway-decent pic of a 90hp block on ebay, which shows the intake port cover side. Note that each one covers 2 cylinders.

The gasket is one-piece, so once you pull one cover you're gonna have to pull the others anyway, unless by some miracle the gasket doesn't tear. Which ain't likely and it'd be better to install a new gasket anyhow.

The 90hp does have pretty small ports, especially on the exhaust side. And with a piston down, you can look thru the cylinder and see the size of the exhaust ports. If it is a 90, this would be a good way to verify. And I think we actually can tell if it's a 115, too. It'll have larger ports but no power-ported piston or the power-port in the block.

Note there are 2 styles of intake port cover gaskets, one has provisions for fuel pumps and one doesn't. Most likely your motor will have fuel pumps mounted on the block and not the lower cowl.

http://www.marineengine.com/newparts/part_details.php?pnum=MER27-64941

http://www.marineengine.com/newparts/part_details.php?pnum=MER27-856730

I have questions. What is a power port in the block? How can I tell the size of the exhaust ports? Will posting pics enable you to determine? And in theory....because I don't know the size of the motor...just wait and see what the old one looks like before ordering? Pics to follow. Which is the fuel pump?

and the carbs ARE 22s i found a pic from when i rebuilt them

I can't make out any carb # in the pic but that doesn't really matter, long as you can see it!

So your motor has a fuel pump mounted on the lower cowl and and you can also see the fuel pump's vaccum line going to the bottom intake port (aka "transfer port) cover.

If you look at the first gasket I posted you'll see how the gasket has 3 triangle-shaped areas which cover the shape of your transfer port covers. In older motors, one or more fuel pumps were actually bolted-up to the triangle-shaped areas. After that Merc moved to a single fuel pump, mounted off the lower cowl. The vacuum line between the engine and pump provides pressure pulses to the fuel pump diaphragm.

Check out the pics of a 90hp block from the exhaust side. You'll note the quite large "square" exhaust ports cast into the block, but check out how the smaller ports of the 90hp were made by drilling holes thru the wall of the raw casting (and the steel cylinder sleeve).

You obviously won't see this view when looking in the cylinder from the intake side, but the round exhaust ports are very distinct and will be clearly visible when viewed thru the intake ports, if yours is a 90hp. Otherwise you'll see the larger, square exhaust ports and then it's either a 115 or 150 depending on the piston & block configuration.

And you'll be able to see whether the piston has a power-port hole in it. As I recall, the hole would be visible when the piston is at the bottom of its stroke. Where you'd want it to be so you could look thru the intake ports, as well.

Post some pictures when you get a cover pulled and we'll see what we can see!

Sorry for the confusion. I didn't post the carb # pic. Was just stating it. I will remove this and we will see what we can see. Will update tomorrow night around 8. I can't thank you enough.

Found a pic of an older 115 block that shows the huge difference in size of ports from the '78-'79 90hp.

All the cylinders wear evenly on a engine unless there is a mechanical or lubrication problem with a cylinder....

?????

Re: compression readings, I've never found a worn-out engine to have all cylinders so evenly worn that they have almost-identical low readings. Usually all over the map

Click to expand...

Above was my reply

fellas.......its going to be another day before i get a result. i took the starboard side middle cover screws out but its stuck in place. its too dark to assure i have an adequate place to get leverage. these come off in twos right? if i have to replace the gasket i realize how hard the bottom one will be. i am fully willing but let me ask.
am i just trying to see what size this motor is or is this the path to make it run ? you guys are really all i got and i fear the thread will grow cold if we wait a week or so to get a new gasket and install it....

You can use a suitable prying instrument to leverage the middle port cover off, against either the bottom of the top cover, or the top of the bottom cover. They're strong enough to stand up to the prying.

When you get around to needing to pull the top and bottom covers, just bolt up the middle cover with enough bolts to hold it firmly in place, and pry away! Works like a charm, and this way you're not inserting prying tools between the cover and the block, and potentially damaging one or both surfaces.

I've done this dozens of times and it works Slick.

To answer your other question, not knowing the correct hp of your motor will make it extremely difficult to troubleshoot. If it had never been messed with, it wouldn't be much of an issue. But at this point with the mish-mash of cowlings and serial number, there's no way to tell if the jets in the carb are correct or not. A set of jets isn't extremely expensive, but it's a fair amount of trouble to change the jets and you don't want to waste $$$ ordering 2 sets of jets, then installing the 1st set to find out they're not the right ones.

And if it is indeed a 150, then there are other things we've gotta look at besides carb jetting.

IMHO better to know and then we can help you better. Chances are it could be a 150, but I wouldn't stake my life on it!

ok guys.....the cover literally is bending out of the way of the tire iron i used to pry. maybe someone glued it. ill try a different one tomorrow. i keep running out of light. sorry guys.... i promise i am committed to this. i wish i had someone to look at it. i live near lake allatoona in georgia and STILL nobody wants to do this old of a motor.

Make sure all the 1/4 -20 bolts are out!!!!

guys i got em. this is the right panel correct? i dont know what you could possibly tell from this but...let me know..sorry theyre sideways