ignition components and their purpose

There, fixed 'em for ya! Sure doesn't look like 90hp ports to me! They are quite large.

Now, run the piston all the way down out of the cylinder and look straight thru the intake ports to the other side of the cylinder. You'll see the exhaust ports. Maybe you can get a pic of them. I expect they'll be large.

Last thing, with the piston at the bottom of its stroke, see if you can spy the power-port hole in the side of the piston. Should be there if it's a 150.

Attached is a pic of a power-ported piston for reference. Also attached is a pic of a block that has the power-port grooves machined into the cylinder bores. With the piston all the way up, you may be able to get a finger or bent piece of wire in there to feel the cylinder. If there's no groove it's gonna feel all smooth in there; the presence of the groove will be very distinct.

You cannot tell anything by looking they need to be measured(port timing) and run the piston UP so you can see side of piston , the boost port will be seen in the intake port.

ok guys. is this the power port hole? if so i apologize. the whole time i was thinking this was the wrist pin hole. i got my finger behind the piston wall where this hole would slide and i DID feel a dip where the cylinder is definitely not round.
as always.....gratefully waiting for your reply. but in the meantime can i get your best guess of which gasket to buy for the cover? does this gasket have to be 1 piece? i feel like i can cut the one section out of a new gasket where this plate goes and use it.

Looks like you have a 150 !!!! Just order the 2 cylinder gasket 27-55279-1 and wont need to cut anything

faztbullet said:

Looks like you have a 150 !!!! Just order the 2 cylinder gasket 27-55279-1 and wont need to cut anything

Click to expand...

Nice being able to use the single gasket from a Merc Twin! Good ol' Merc, again the Small Block Chevy of outboards!

http://www.marineengine.com/newparts/part_details.php?pnum=MER27-55279++1

Now that we know what it is, all we have to figure out is what's wrong with it!!

Too bad u can hook a wide band air/fuel to these motors like a car. Is this carb like a car? Idle circuit....throttle circuit? What is the little hose that crosses the top of the carb from one stem to the other? We ARE back to fuel or fire right? Possibly low compression?

Probably time for you to post a video of it running, after you get the transfer port cover reinstalled.

We'll need to see it idling in gear, and then throttle-up when it bogs.

Another thought I had, since you don't know what's been done to it by previous owners, is to check the firing order on the cap and make sure the plug wires are going to the correct cylinders. You might think it's idling OK, but with an Inline six it can be hard to tell unless you're experienced with them. A couple of swapped wires would royally mess things up. Easy to check, unto the clamp that holds the distributor cap in place then drop the cap down so you can see the numbers. Be aware that the plug wires screw into the cap (as does the coil wire, which does plug into the coil, however).

Also a good idea to inspect the cap for trash and clean out. Note the rotor doesn't come off the shaft, so don't try that, you'll ruin the $$$ rotor. The trigger assy can be fragile so take care while you're in there. Check out the carbon spring-loaded contact in the cap, it shouldn't be stuck but free to move a bit when you push on it.

Also need to know if when #1 (top) piston is at the top of its stroke (TDC), the plastic timing arrow lines up with the "TDC" or zero mark on the flywheel's timing-scale-decal. If that's off, you can't get the spark advance properly set.

BTW what spark plugs are in it? Champ L76V and NGK BUHW are commonly used.

What size/make of boat is the motor on? What's the pitch of the propeller? The part number on a Merc prop is typically stamped into the body of the prop, and has a "47-" prefix with a part number, followed by a "-##" for the pitch. i.e., "-17" would be a 17" pitch prop.

It'd be nice to have an O2 sensor on these but not a practical way to install one. I'm still not convinced of low compression, seen plenty of I-6's with readings like yours that run fine. If you're not having any trouble getting it started or idling in gear, it should still be able to get the boat on plane. Just have to go thru all the basics to pinpoint the problem.

IMHO it sounds to me like you're not getting spark advance when the carbs are fully opened. But these motors can have strange symptoms that mask the real problem, so we'll just have to keep working on it until we get to the root of the problem.

you will get ALL of this. video will be wednesday as the gasket doesnt arrive til tuesday. it does crank and idle every time but if it sits for more than 10 minutes i have to lift the throttle lever to get it to crank. once it fires it takes it 2 to 3 seconds for the throttle to make it way up to revved....just a bit slow getting its RPMs up...but i can immediately let the lever back down after it fires and move along. if it sits under 10 minutes it will fire up right off the key like clockwork. i never run the motor at full throttle because it wouldnt do anything anyway but i do run it for a mile at a time or so at half throttle. if i run it for say.....3 miles(or more than 6 or 7 minutes) back to the boatramp....tie the boat and go get my truck in the water...at that point it has a hard time running. cranks fine. but runs like running out of gas but you can always save it with a slight blip of the throttle. this is annoying approaching the trailer... this is its mannerisms. im making a list now of your post. you will have ALL this info by tomorrow night except the video.....AGAIN.....THANK YOU

things i know so far: plugs----L76V prop has a wierd run of number----48 773 1? A1 19
i went to check the cap wires and found that 2 were still connected but i could tell they had been pulled out without untwisting before. solder was still attaching it but was pulled out. i would happily buy a new cap and wires if i had (or you could tell me) a serial number or part # matching "now a 150?" pic of boat attached. small boat. very light. 15' 7" bow to stern.will check the rest tomorrow.

The dist. caps are expensive ($120) and unless it's broken or otherwise damaged you should be able to clean it up and re-use it. A good spritz on the inside of the cap with carb cleaner will wash any trash/debris right outa there.

This would be the serial # range for your 150: http://www.marineengine.com/parts/mercury-outboard-parts/1500/3502806-thru-4865677-usa

And yeah, it should really haul on that hull! Sounds like you have a 19" pitch prop which wouldn't be unreasonable for a 150.

The plug wires are quite stout and unless they are cracked, you should be able to re-make the end instead of spending $$$ on new wires. These plug wires are a solid-strand-type core and have improved insulation to hold up to the high-voltage of the CDI system.

Sierra makes a crimp-style screw-in plug wire terminal, P/N 18-5224. But you'll have to come up with a suitable means of crimping them, since these are brass and a lot harder/more brittle than a standard steel terminal. A crimper meant for automotive spark plug wires will probably break the brass terminal.

Maybe someone here that's had experience with making up a new set of wires can recommend a crimper. Otherwise I found a source of new yellow wires with pre-crimped screw-terminal end for about 6 bucks plus shipping. I don't want to post this openly & offend the site's moderators, 'cause it's the competition. But I will send you a P.M. if you'd like.

I did see a comment elsewhere that they used a set of Sears pliers that were meant to grip a busted bolt, and had (4) prongs that moved inwards to grip; something like that would grip the terminal evenly and wouldn't have such a tendency to break the brass. Another possibilty is a coax connector crimper, they have a 6-sided crimp that may work better. But you'd have to see if it's the right size for a brass terminal.

Obviously all the spark plug wires should be firmly screwed into the distributor cap. And since it sounds like they've been messed-with before, all the more reason to double-check the firing order in the cap. Those #'s are cast right in the cap as you're looking at the terminals.

Here's a good discussion at iboats regarding soldering the tips to the wires, that would work as well:

http://forums.iboats.com/forum/engi...-outboards/445697-plug-wires-for-115-evinrude

Sierra 18-5224 10-pack: http://www.marineengine.com/newparts/part_details.php?pnum=SIE18-5224

You can buy the Merc equivalent individually, if you don't need that many:

http://www.marineengine.com/newparts/part_details.php?pnum=MER8M0084600

HTH...........ef

ok guys....the thread is back with many answers i havent answered yet.
1. the firing order is correct. https://youtu.be/4wAnSk3Yi_8
2. cleaned the cap/rotor. pic included of cap just for reference.
3. my TDC is exactly on the zero....without me moving it.
4. i included 2 videos. they are from a phone so...theyre not hollywood quality.
one shows how hard it is to crank and an attempt to idle in gear. i think its getting worse because not at idle while moving (approaching the trailer) it
wants to go dead very bad. i have to play with the throttle blip blip blip all the way just to get it to stay alive.

I CANT GET THE VIDEOS TO LOAD. THEY ARE ON YOU TUBE TITLES: boat motor issues-1
boat motor issues-2 looks like the snippet.
IF YOU WOULD BE SO KIND AS TO LOOK FOR THEM.
the other shows the attmpt to showcase all speeds including . NOTE: this thing will no longer crank unless the thro ttle lever ishttps://youtu.be/9AiDdWIFbrs in full engage and you play with the choke button. it seems to be the standard now. this began after driving it at idle for a more frequent time. after i started running it for maybe 6 or 7 minutes it started doing that. also....every time i park it after the weekend....engine oil runs down my skeg. its NOT gear oil. its engine oil. should we go back to basics?

Guys as you probably already know...the video links are ok. It just wouldnt let me check and play them myself to make sure before posting.
Will stand by.

That motor don't sound like its running on all 6...its dull sounding. 1) compression test all 6 again 2) check that carbs are opening with throttle/distributor and post results

It's definitely not hitting on all 6. Need to do as suggested above then need to figure out which cylinders aren't running.

That's the reason for all the excess "mung" coming out of your motor, it's not getting burned in the cylinders.

ABSOLUTELY. on a car.....you check the compression then squirt a little oil in there and see how it leaks over a small amount of time. is there specifics to checking these boat motors? i want to do it exactly as needed so we can rule in/rule out.

Plugs out for compression test,fully charged battery, 200-300 rpms while cranking. When engine is running pull one plug wire at a time with plastic pliers,listen for rpm drop!

guys......here is a video of a test of each c https://youtu.be/Ek56gQx-D-c WATCHED
ylinder in order. is this sufficient?

Compression Rooks marvelous.I just went thru entire thread and there's no mention of an open gap spark test being performed, Your thread reads" so i think fire.Spark at all plugs,determined by timing light,no way to know if it's weak spark though". basic troubleshooting was not followed

ok. today I will pull each plug individually and note any differences. is there a confirmed way (official way) to check the spark strength? where we can rule this out? I know there is a tool on e bay where you set a gap and see if it will jump it but I just cant wait til next Monday which is when 90 % of everything I order arrives.

Portis Left said:

ok. today I will pull each plug individually and note any differences. is there a confirmed way (official way) to check the spark strength? where we can rule this out? I know there is a tool on e bay where you set a gap and see if it will jump it but I just cant wait til next Monday which is when 90 % of everything I order arrives.

Click to expand...

..........................................Try the local Auto Zone near you. they may have a tester you can borrow or rent.

That thing does show spark. But does it show strength? The one I can't buy at a store grounds to block and u dial in the gap to jump. But it will take past the weekend.

You can make your own do-it-yourself spark tester using an old non-resistor, extended-tip spark plug. Take the ground electrode and bend it way back or cut it off. If you want to get fancy, tap a threaded hole in the side of the plug body (on the hex part would be best), then attach a big spring-loaded clamp to hold it to the framework of the motor. Or use a double-ended clamp which can hold a spark plug, then you don't have to drill holes.

But you don't even really need to do that, just make sure the plug body is laid firmly to the block so the plug is grounded. When you do the spark test, have all the plugs out. Stick all the plugs in and ground against the frame, it's not good to let the ignition system spark without a load.

Then stuff the "test plug" in the plug wire you're testing, and crank away. It should jump the large gap like nobody's business, and will probably be a bluish or purplish, hot spark. If it'll jump that much of a gap, then it should be strong enough to fire under combustion pressure.

If you want to get really really fancy, built yourself a test board with (6) spark plugs fastened to the board. Drill/tap each plug to hold a screw then jumper them all together with #12 wire. With a long #12 wire going to the motor to attach with an alligator clip to ground.

There's your 6-at-once spark plug tester, for the price of (6) cheap spark plugs and some wire! But one-at-a-time gets the job done, as well.

BTW I searched for a cheap, non-resistor extended-tip plug, and it looks like the Autolite #16 fits the bill. But whatever you have that works for ya.

Go forth & prosper........ed

will test today. let me get a couple questions ahead. if it indeed does have a weak spark what component will be at fault? what size gap should this engine be capable of jumping? and finally...is there a tried and true method someone can give me to assure the timing is on point? I do understand timing on a car so I should follow the steps fairly well. THANK YOU GUYS THAT HANG IN HERE. I didn't think it would be this drawn out. boat motors. gotta love em right?

Well, it beats making payments on a new boat/motor, and the troubleshooting is an excellent learning experience. Plus the satisfaction of doing your own work and enjoying the benefits of such!

Here's a good Link and Synch writeup at iboats:

http://forums.iboats.com/forum/engi...ing-and-sync-of-merc-inlines-to-1988?t=168855

Set the max spark advance to 21 deg BTDC.

For your spark test, the CDI system should be able to jump at least a 3/8" gap with a strong, snappy spark. Depending on what you get for every plug wire, it'll lead us to some sort of conclusion, but until we hear the results I won't speculate.

ok guys.....here is a video of the sparks one by one starting at 1. somehow i messed up and deleted #4 video when deleting the garbage videos off my phone. i do believe this "was" a resistor spark plug. it was an AC DELCO 12. the sparks looked weaker in person than the video. do i need to do it again? my initial thought is that spark is fine? especially if they are better with a non resistor plug. will do the link and sync tomorrow.. STANDING BY....

P.S. it ran about the same on all plug pulls except the lowest one. number 6. it really made it mad when i went to do 6. wouldnt crank or stay running without
th throttle lever pulled up at least half. other than that it cranked beautifully every time. what about the exhaust "leaving" the motor. do these things have problems with that?

I think there's enough spark! Jumps a pretty large gap for sure.

Do you have a barrel you can stick the motor in? It would be easier to tune in water and with a bit of exhaust backpressure, any running issues will be more pronounced.

Take a look at how far out each idle mixture needle is set. Turn each needle clockwise until lightly seated then notice the turns. Normally about 1-1/2 to 2 turns is what it takes.

You can get a good read on whether there's a set of cylinders pulling the load or not by slowly turning the idle screw in while the motor's idling. It's either gonna speed up, or eventually slow down and stall.

If there's no change at all, the 2 cylinders being fed by that particular carb aren't combusting for whatever reason.

Ideally, you should adjust each carb's mixture needle for fastest idle speed, then turn it rich (CCW) about 1/8 turn. That's good enough for a rough adjustment.

Do one carb at-a-time and see what you get. Should be interesting!

ok guys.....just like every other problem i had in life....ill never know the answer.
the good news is this thing is fixed. dont know how. did the timing sync stuff attached in this thread. was perfect..made zero changes... got to the lake this morning, pushed it forward almost all the way which gives me 4 miles an hour, stood up to stow my dock rope and it just exploded into power. runs hard now. WATCHED

idle is pretty good(not perfect) and full throttle is excellent.
bad news.......in between isnt so hot. and i found that if i go hole shot to full throttle and back off at any point, (say i approach a boat and want to slow down a hair just to be cautious) then push it back to full throttle it doesnt want to run back at full. if i stop, go back to idle, then just floor it, RIGHT BACK TO POWER. this thing is so strange. but its working now and i thank each and every member who commented from my heart. i have a track record of dying threads on most of my forums but you guys stuck with me. thank you. i will let this thread die now and do some of my own research on getting it to run right but i cant guarantee i wont make another thread for help. FINAL QUESTION......MY BOAT WEIGHS ABOUT 3 POUNDS AND WE AGREED THAT THIS WAS A 150 HORSE ENGINE. I MAXED OUT AT 42. DOES THAT SOUND RIGHT?

Well, isn't that just Crazy! She's running pretty healthy, too.

Far as speed goes, now you're into fine-tuning. It sounds like it's revving up quite a bit and you may be able to increase the prop pitch to gain more speed.

You really need a tach to let you know how fast the motor's turning. For speed purposes, it should be pulling at least 5500 rpm at WOT (Wide Open Throttle) with just you in the boat. 1500's will not hesitate to rev to 6000 BTW and will still be making power.

So, just don't change the prop without knowing what the engine's doing; if you put too large of a prop on 'er you may lug the engine and destroy it from detonation.

Another issue is how the boat is riding, if it's trimmed up you will have less wetted hull and it'll go faster. There are of course limits to trimming and you can lose your hole shot and have lots of porpoising if the motor is trimmed-out too far.

Something else that will affect boat speed is transom height. You can safely run the anti-ventilation plate about 3/4" above the keel. I did this on my old Sidewinder 16' SS; with spacer sticks. If you get higher than that, and depending on the hull and prop design, it can ventilate the prop upon takeoff, and possibly in turns.

A prop with more "rake" will give you more bow lift while increasing steering torque a bit. You'd have to install a different trim tab 'cause the prop blades are raked-back and interfere with the stock item.

A stainless prop will perform better than aluminum. But you should optimize your existing setup before spending a ton of $$ on an expensive prop.

BTW your issue with dodgy throttle control might come from worn-out parts in the control box. The motor doesn't have to be running to check this out. With the cover off, slowly advance the throttle and see if the distributor turns smoothly and hits its "spark advance" stop, then as you advance the throttle more, the carbs should open fully at WOT. Go back to Neutral and it should shut down smoothly, back to the idle stop. Repeat a few more times to see if it does anything strange.

I've seen plenty of worn-out parts in the old rectangular-style control box, so you may need to inspect the innards if you find the throttle operation notchy.

If you have the rectangular control box, it'll probably have a 4-pin connector in the front of the box. Here's a really really cheap 4-pin wiring harness on eBay, this is an excellent deal for one of these and you might want to snap it up if you think you might want to install a tach:

http://www.ebay.com/itm/Mercury-Out...ash=item5b2b03bbd7:g:Uu4AAOSw4shX3ABq&vxp=mtr

Enter this search string into the eBay Motors query box to find tons of marine tach stuff: (outboard, marine, teleflex) (tach, tachometer)

Glad to see it's running that well, now the fun really begins! Cheers........ed