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Author Topic:   Outboard Running On Less Than All Cylinders

Mobjack posted 07-31-2006 09:00 AM ET (US)
Hey Guys--I have a 1983 Montauk with a 1985 Johnson 75-HP. Yes, it is an old motor, but it only had 342 hours on it when I bought it (same owner for twenty years), and I have put about 40 hours on it since then. It has been running like a top all summer, fires right up, no known problems.
Yesterday I took it out and as I left the creek where I live and started heading out into open water, I accelerated to my normal speed. The boat seemed sluggish. I checked the tach, and I was right around 4,500-RPM, which I would estimate gets me about 20- to 25-MPH. But I was nowhere near my normal speed. In fact, I was on the step, but just barely. I tried trimming out, accelerating, but something definitely seemed to be wrong. Problem is, the motor sounded totally normal. In my experience, outboards that are running on less than all cylinders run rough and have a noticeable change in sound and vibration. Now, I ran the boat twice more yesterday, and the problem seems to be resolved, normal speeds and RPM. I am wondering if I might have had a fouled plug, but I have yet to pop the cowling and see what's going on.
I guess the heart of my question is whether an outboard can run on less than all cylinders without presenting any noticeable change in engine sound or vibration?
brisboats posted 07-31-2006 10:38 AM ET (US)
When that motor is running on two cylinders you will be noticeably down on power. Could be a host of things that happened. You may have fouled the prop with grass/seaweed and it later cleared, you may have had some water in the fuel or a fouled plug as you mention. Check your throttle linkage those plastic grommets have a habit of cracking and throwing off the synch/linkage. The engine may run and sound normal when one of the throttle plates is partly closed but the boat will be sluggish. Hope this info helps.
Brian
andygere posted 07-31-2006 12:34 PM ET (US)
Check to see that all the plug wires are making good contact the spark plugs. A small zip tie fastened around the plug boot is a good way to be sure they don't vibrate off. This was a common problem on my '79 Johnson until I zip tied them on.
Mobjack posted 07-31-2006 01:29 PM ET (US)
Hey guys, thanks a lot, one more question, let us say that engine were running on two instead of three cylinders. What effect, if any, would that have on the fuel economy of the engine? Would the engine be less efficient running on two?
It sure seemed to chug down the gas yesterday, more than normal, or could be my imagination.
The Judge posted 07-31-2006 01:56 PM ET (US)
The engine will get great economy running on 2cyls because it will BLOW UP. You probably fouled a plug or a plug wire came loose. If that is the case, no biggie because fuel ( and oil) is still entering the cylinder If a carb was blocked and then cleared it could do MAJOR damage running it that way. If she runs fine now, change the plugs and fuel filter and call it a day unless it happens again.
The Judge posted 07-31-2006 01:57 PM ET (US)
PS...if it was a blocked carb and only running on 2cyls she will NOT plane. Hence why I think it was something else.
macfam posted 07-31-2006 08:32 PM ET (US)
If she was getting good rpm's and sounded fine, perhaps you have a prop with a slipping hub. Engine turns fine, but the prop is slipping and you won't get much speed. Just a thought.
jimh posted 07-31-2006 09:03 PM ET (US)
I have confirmed that my engine (a V6) has been running occasionally on only five cylinders. The fuel consumption rate increases noticeably, just about in proportion to the loss of power. With only 5/6-ths of the engine running, the MPG decreases about in the same proportion. Where I would normally get about 1.8-MPG, on five cylinders I get only 1.8 X 5/6 = 1.5-MPG. This shows up immediately on my fuel flow monitor.
BobL posted 07-31-2006 09:14 PM ET (US)
I think that Brisboats and macfam hit the nail on the head when they said that it was a prop problem. You would definitely hear a difference in engine sound with a cylinder misfiring and feel a noticeable vibration. You might have picked up a load of seaweed.
where2 posted 07-31-2006 11:20 PM ET (US)
I suspect it is ENTIRELY possible to run on 2 of the 3 cylinders on one of the 1985 OMC 3-cylinder Looper engines and not recognize it. They have a rather funny lope to them in the first place. It is also possible to have a fuel starvation problem which is not noticeable at lower RPM's where the carb is drawing through the idle circuit, but drops the cylinder out at high RPM's when it would rely on the high speed jet.
I'd be going through those carburetors with a fine tooth comb (so to speak), and an air compressor. Rebuild kits are $16 per carburetor. A replacement engine is many times that cost.
In 26 years being around that particular OMC 3-cylinder engine, I have never seen the plastic carb synchronization linkage "let go". If it were a slipping hub, he could easily have punched the throttle to see whether the engine over-revved. In the 10 years I have owned my own 1985 70Hp Johnson, I have not yet had a spark plug wire become detached (although it is easy to check).
The Judge is correct, if it is a fuel related issue, you can certainly damage the engine by running it in a state where it is starving one cylinder for fuel and lubrication oil. Remember, the OMC VRO system (which may or may not be currently operational on this particular engine) combines the oil with the fuel prior to it entering the carburetors. If the carb is supplying less than adequate fuel supply the lubicating oil is also missing from that cylinder. Bad things can and will happen if operated for any great length of time in that state. (ring failure, followed shortly by the broken chunk of ring slipping into an intake or exhaust port, followed shortly by connecting rod failure...).
The 1985 motor is not an old motor, mine took me skiing over the weekend with three friends along, and my engine sees 99% salt water useage. Talk to me in another 9 years when the boat becomes an antique by Florida Statute standards.
brisboats posted 08-01-2006 08:59 AM ET (US)
The plastic parts of the carb linkage are now 21 years old and can become brittle they tend to crack and not "let go". If cracked they will rather open the throttle at first and then progressively slip as wide open is approached. Since the problem has disappeared I am guessing a fouled prop or plug.
Start with the easy stuff first, before tearing into the carbs. If you were running on 2 out of the 3 it would be more noticeable than what you describe and as Judge has stated the boat would probably not plane at all. If the synch and link is off it will produce the condition you described in your first post.
brian
Whaler_bob posted 08-01-2006 11:07 AM ET (US)

quote:
I guess the heart of my question is whether an outboard can run on less than all cylinders without presenting any noticeable change in engine sound or vibration?
Mobjack
If it's a boat/engine that you know well, you'd probably notice the difference. The more cylinders the less difference one dead one makes too.
My brother in-law bought his current boat in March of 2004.
He ran it all summer of 04 without any problems. We all thought maybe the boat was a little under powered cause with 4 people on board she was a little slow to plane. In mid summer of 2005 one of his power packs died so he replaced it. All of a sudden the engine hd new life, the boat had no problem planing and now had a top speed of 38 mph (instead of 32 mph)with 4 people on board. After a little bit of pulling spark plug wires to simulate one dead cylinder, it seems that one cylinder had been offline since he bought the boat a year and a half ago! The engine ran smooth, no heavy vibrations and fuel usage was ok on five cylinders.
The engine is a 8 year old V6 Mercury 150hp on a 21' Campion walk around cuddy (looks like a Grady).
The Judge posted 08-01-2006 12:08 PM ET (US)
Robbing spark and robbing fuel are 2 different things. Spark is bad performance, fuel is grenading a cyl. I did not notice my 225 was running lean in a cyl and blew the #2. Rebuilt engine and rebuilt carbs. Used it for 1.5 years flawlessly and let it sit for 8 months while I had a new dock & bulkhead rebuilt. Took her out for a test run and blew the #3 cyl. Ran fine until she started knocking. Do NOT mess with carbs on a 2 stroke. If you think they are messed up, rip them down. Running it and thinking it will "clear itself" will get you a quick trip to the engine store.
where2 posted 08-01-2006 01:00 PM ET (US)
On an '85 OMC 3 cylinder, tearing into the carbs IS easy stuff... A complete overhaul is what I consider moderately difficult. Broken bolts are what I consider difficult. When removing the carbs, the odds of breaking a bolt are similar to the odds of winning the lottery. (people may expect it, but it rarely ever happens).
I love to point out the fact that carburetor rebuild kits for the OMC 3 cylinder engine are $16 per kit. Three kits cost less than filling up the typical Montauk with a full load of fuel at $3/gallon.
Alternatively, you can make your own paperweight like this one: http://www.tfn.net/~wendtm/damaged_piston.jpg (paperweight removed from my 1995 115Hp Turbojet).
You wouldn't drain the oil out of your car and drive it around the block, yet I am amazed at the number of boaters who advocate pouring some potion in the fuel system and running the engine to "clear up" some gunk in the carburetor. Those stories generally end in "I found the problem, the engine seized up last Saturday. It must have been on it's last legs. Where can I find an affordable replacement?"
The Judge posted 08-01-2006 02:23 PM ET (US)
;)
I have NEVER broken a carb bolt. Only problem with removing the 2 V4 carbs is you have to remove the starter. If that was not the case you could drop those puppies in about 7 minutes instead of 20.
where2 posted 08-01-2006 09:36 PM ET (US)
I've never broken a bolt pulling carbs off an OMC engine. I think it takes me 15 minutes to pull all three of them on my 70Hp Johnson, if you count the time necessary to get out the tool box. Nick has it down to 7 minutes, but he has refinishing a 19 year old whaler down to 3 weeks.
whalerron posted 08-01-2006 11:00 PM ET (US)
Once the PowerPack on my Johnson 70hp partially died and left me with 2 running cylinders. In that state, the engine barely had enough power to push the boat at 6 knots. If your 75 drops a cylinder, you will definitely notice a difference.
About 3 years ago, I was moving at about 35 mph in my boat on the Delaware Bay when all of a sudden the engine became sluggish and had a lot less power. Even though the RPMs were fine, the engine simply wouldn't push the boat correctly. I thought about the spun-prop issue but this was a brand new outboard and it didn't seem very likely to me that a spun-prop would be the problem. So, I stopped the engine and tilted it up to see if I could see anything wrong. Unbelievably, there was a plastic milk bottle on the front of the lower unit. It had been split almost cleanly in half and it was draped over the front of the lower unit. I removed the bottle and the engine ran perfectly after that.
Sal DiMercurio posted 08-02-2006 12:22 AM ET (US)
My bet is a power pack going south.
Yes you still can get a 15' up on plane with a dead cylinder on a 70 or 75,...I just did it last week when I realized the reason this engine didn't have the guts to push me over 35 mph is because the power pack was not allowing all the cyliners to fire.
Once I changed the power pack she jumped up to 44 mph in 3 seconds from cruise speed.
As far as a spun prop hub, not even close.
When a hub gives up, the prop will still hang on at idle but once you give much more throttle, it totally breaks loose & just spins like it's in neutral.
Maximum speed you will get out of a prop with a spun hub is maybe 6 mph.
Once she breaks loose, you go absolutly no-where
with lots of rpms just like being in neutral.
Sal
Mobjack posted 08-02-2006 10:51 AM ET (US)
Hey guys,
Never thought this thread would get this big, but thanks for all the great advice. I took it out and ran it last night, I think it is definitely running on all cylinders. all the plugs are connected, did not pull them to see if they are fouled, but the fact remains that whether it be at idle or at full speed the engine is purring like a kitten. SOmeone on this thread mentioned that they thought it could be prop slippage, and that if it were, the engine would over rev. I think this is it: that engine is supposed to redline at 5500 or 5400 rpms and it went to 5650 when I tried it the other day. Is this what you meant?
Now its time to hijack the thread: If this is the cause, my prop is old anyway, and I have been thinking about updating my low time engine with a new prop and a Doel fin, for a 1985 Johnson 75 horse motor, on a boat that I want to acheive an acceptable top speed of 30-35 mph (it does not need to scream) and also be able to get out of the hole with a load. The boat is a Montauk, WHAT IS THE BEST PROP TO USE? STAINLESS OR ALUMINUM? PITCH AND SIZE? I know there are a bunch of guys on this site who know this stuff, and I am fairly ignorant about it. Please educate me so I dont get the wrong thing, or buy something I dont need to. Thanks again for your time everybody.
The Judge posted 08-02-2006 01:53 PM ET (US)
13.25x17 alum or 13 3/8x17 SST is the best to use on that boat. cratch the doel fi umless you like to drive at 12mph. I never found a need for them on 15-19' whalers. I usually have a few 17" props laying arund but have recently liquidated. Should be able to pick one up on e-bay cheap being it is a VERY popular sized prop. A good SST should fetch under $150 delivered. You can sometimes rob one for cheap but beware of condition, you don't want some worn down nub, you already have one of those ;)

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Author	Topic: Outboard Running On Less Than All Cylinders
Mobjack	posted 07-31-2006 09:00 AM ET (US) Hey Guys--I have a 1983 Montauk with a 1985 Johnson 75-HP. Yes, it is an old motor, but it only had 342 hours on it when I bought it (same owner for twenty years), and I have put about 40 hours on it since then. It has been running like a top all summer, fires right up, no known problems. Yesterday I took it out and as I left the creek where I live and started heading out into open water, I accelerated to my normal speed. The boat seemed sluggish. I checked the tach, and I was right around 4,500-RPM, which I would estimate gets me about 20- to 25-MPH. But I was nowhere near my normal speed. In fact, I was on the step, but just barely. I tried trimming out, accelerating, but something definitely seemed to be wrong. Problem is, the motor sounded totally normal. In my experience, outboards that are running on less than all cylinders run rough and have a noticeable change in sound and vibration. Now, I ran the boat twice more yesterday, and the problem seems to be resolved, normal speeds and RPM. I am wondering if I might have had a fouled plug, but I have yet to pop the cowling and see what's going on. I guess the heart of my question is whether an outboard can run on less than all cylinders without presenting any noticeable change in engine sound or vibration?
brisboats	posted 07-31-2006 10:38 AM ET (US) When that motor is running on two cylinders you will be noticeably down on power. Could be a host of things that happened. You may have fouled the prop with grass/seaweed and it later cleared, you may have had some water in the fuel or a fouled plug as you mention. Check your throttle linkage those plastic grommets have a habit of cracking and throwing off the synch/linkage. The engine may run and sound normal when one of the throttle plates is partly closed but the boat will be sluggish. Hope this info helps. Brian
andygere	posted 07-31-2006 12:34 PM ET (US) Check to see that all the plug wires are making good contact the spark plugs. A small zip tie fastened around the plug boot is a good way to be sure they don't vibrate off. This was a common problem on my '79 Johnson until I zip tied them on.
Mobjack	posted 07-31-2006 01:29 PM ET (US) Hey guys, thanks a lot, one more question, let us say that engine were running on two instead of three cylinders. What effect, if any, would that have on the fuel economy of the engine? Would the engine be less efficient running on two? It sure seemed to chug down the gas yesterday, more than normal, or could be my imagination.
The Judge	posted 07-31-2006 01:56 PM ET (US) The engine will get great economy running on 2cyls because it will BLOW UP. You probably fouled a plug or a plug wire came loose. If that is the case, no biggie because fuel ( and oil) is still entering the cylinder If a carb was blocked and then cleared it could do MAJOR damage running it that way. If she runs fine now, change the plugs and fuel filter and call it a day unless it happens again.
The Judge	posted 07-31-2006 01:57 PM ET (US) PS...if it was a blocked carb and only running on 2cyls she will NOT plane. Hence why I think it was something else.
macfam	posted 07-31-2006 08:32 PM ET (US) If she was getting good rpm's and sounded fine, perhaps you have a prop with a slipping hub. Engine turns fine, but the prop is slipping and you won't get much speed. Just a thought.
jimh	posted 07-31-2006 09:03 PM ET (US) I have confirmed that my engine (a V6) has been running occasionally on only five cylinders. The fuel consumption rate increases noticeably, just about in proportion to the loss of power. With only 5/6-ths of the engine running, the MPG decreases about in the same proportion. Where I would normally get about 1.8-MPG, on five cylinders I get only 1.8 X 5/6 = 1.5-MPG. This shows up immediately on my fuel flow monitor.
BobL	posted 07-31-2006 09:14 PM ET (US) I think that Brisboats and macfam hit the nail on the head when they said that it was a prop problem. You would definitely hear a difference in engine sound with a cylinder misfiring and feel a noticeable vibration. You might have picked up a load of seaweed.
where2	posted 07-31-2006 11:20 PM ET (US) I suspect it is ENTIRELY possible to run on 2 of the 3 cylinders on one of the 1985 OMC 3-cylinder Looper engines and not recognize it. They have a rather funny lope to them in the first place. It is also possible to have a fuel starvation problem which is not noticeable at lower RPM's where the carb is drawing through the idle circuit, but drops the cylinder out at high RPM's when it would rely on the high speed jet. I'd be going through those carburetors with a fine tooth comb (so to speak), and an air compressor. Rebuild kits are $16 per carburetor. A replacement engine is many times that cost. In 26 years being around that particular OMC 3-cylinder engine, I have never seen the plastic carb synchronization linkage "let go". If it were a slipping hub, he could easily have punched the throttle to see whether the engine over-revved. In the 10 years I have owned my own 1985 70Hp Johnson, I have not yet had a spark plug wire become detached (although it is easy to check). The Judge is correct, if it is a fuel related issue, you can certainly damage the engine by running it in a state where it is starving one cylinder for fuel and lubrication oil. Remember, the OMC VRO system (which may or may not be currently operational on this particular engine) combines the oil with the fuel prior to it entering the carburetors. If the carb is supplying less than adequate fuel supply the lubicating oil is also missing from that cylinder. Bad things can and will happen if operated for any great length of time in that state. (ring failure, followed shortly by the broken chunk of ring slipping into an intake or exhaust port, followed shortly by connecting rod failure...). The 1985 motor is not an old motor, mine took me skiing over the weekend with three friends along, and my engine sees 99% salt water useage. Talk to me in another 9 years when the boat becomes an antique by Florida Statute standards.
brisboats	posted 08-01-2006 08:59 AM ET (US) The plastic parts of the carb linkage are now 21 years old and can become brittle they tend to crack and not "let go". If cracked they will rather open the throttle at first and then progressively slip as wide open is approached. Since the problem has disappeared I am guessing a fouled prop or plug. Start with the easy stuff first, before tearing into the carbs. If you were running on 2 out of the 3 it would be more noticeable than what you describe and as Judge has stated the boat would probably not plane at all. If the synch and link is off it will produce the condition you described in your first post. brian
Whaler_bob	posted 08-01-2006 11:07 AM ET (US) quote: I guess the heart of my question is whether an outboard can run on less than all cylinders without presenting any noticeable change in engine sound or vibration? Mobjack If it's a boat/engine that you know well, you'd probably notice the difference. The more cylinders the less difference one dead one makes too. My brother in-law bought his current boat in March of 2004. He ran it all summer of 04 without any problems. We all thought maybe the boat was a little under powered cause with 4 people on board she was a little slow to plane. In mid summer of 2005 one of his power packs died so he replaced it. All of a sudden the engine hd new life, the boat had no problem planing and now had a top speed of 38 mph (instead of 32 mph)with 4 people on board. After a little bit of pulling spark plug wires to simulate one dead cylinder, it seems that one cylinder had been offline since he bought the boat a year and a half ago! The engine ran smooth, no heavy vibrations and fuel usage was ok on five cylinders. The engine is a 8 year old V6 Mercury 150hp on a 21' Campion walk around cuddy (looks like a Grady).
The Judge	posted 08-01-2006 12:08 PM ET (US) Robbing spark and robbing fuel are 2 different things. Spark is bad performance, fuel is grenading a cyl. I did not notice my 225 was running lean in a cyl and blew the #2. Rebuilt engine and rebuilt carbs. Used it for 1.5 years flawlessly and let it sit for 8 months while I had a new dock & bulkhead rebuilt. Took her out for a test run and blew the #3 cyl. Ran fine until she started knocking. Do NOT mess with carbs on a 2 stroke. If you think they are messed up, rip them down. Running it and thinking it will "clear itself" will get you a quick trip to the engine store.
where2	posted 08-01-2006 01:00 PM ET (US) On an '85 OMC 3 cylinder, tearing into the carbs IS easy stuff... A complete overhaul is what I consider moderately difficult. Broken bolts are what I consider difficult. When removing the carbs, the odds of breaking a bolt are similar to the odds of winning the lottery. (people may expect it, but it rarely ever happens). I love to point out the fact that carburetor rebuild kits for the OMC 3 cylinder engine are $16 per kit. Three kits cost less than filling up the typical Montauk with a full load of fuel at $3/gallon. Alternatively, you can make your own paperweight like this one: http://www.tfn.net/~wendtm/damaged_piston.jpg (paperweight removed from my 1995 115Hp Turbojet). You wouldn't drain the oil out of your car and drive it around the block, yet I am amazed at the number of boaters who advocate pouring some potion in the fuel system and running the engine to "clear up" some gunk in the carburetor. Those stories generally end in "I found the problem, the engine seized up last Saturday. It must have been on it's last legs. Where can I find an affordable replacement?"
The Judge	posted 08-01-2006 02:23 PM ET (US) ;) I have NEVER broken a carb bolt. Only problem with removing the 2 V4 carbs is you have to remove the starter. If that was not the case you could drop those puppies in about 7 minutes instead of 20.
where2	posted 08-01-2006 09:36 PM ET (US) I've never broken a bolt pulling carbs off an OMC engine. I think it takes me 15 minutes to pull all three of them on my 70Hp Johnson, if you count the time necessary to get out the tool box. Nick has it down to 7 minutes, but he has refinishing a 19 year old whaler down to 3 weeks.
whalerron	posted 08-01-2006 11:00 PM ET (US) Once the PowerPack on my Johnson 70hp partially died and left me with 2 running cylinders. In that state, the engine barely had enough power to push the boat at 6 knots. If your 75 drops a cylinder, you will definitely notice a difference. About 3 years ago, I was moving at about 35 mph in my boat on the Delaware Bay when all of a sudden the engine became sluggish and had a lot less power. Even though the RPMs were fine, the engine simply wouldn't push the boat correctly. I thought about the spun-prop issue but this was a brand new outboard and it didn't seem very likely to me that a spun-prop would be the problem. So, I stopped the engine and tilted it up to see if I could see anything wrong. Unbelievably, there was a plastic milk bottle on the front of the lower unit. It had been split almost cleanly in half and it was draped over the front of the lower unit. I removed the bottle and the engine ran perfectly after that.
Sal DiMercurio	posted 08-02-2006 12:22 AM ET (US) My bet is a power pack going south. Yes you still can get a 15' up on plane with a dead cylinder on a 70 or 75,...I just did it last week when I realized the reason this engine didn't have the guts to push me over 35 mph is because the power pack was not allowing all the cyliners to fire. Once I changed the power pack she jumped up to 44 mph in 3 seconds from cruise speed. As far as a spun prop hub, not even close. When a hub gives up, the prop will still hang on at idle but once you give much more throttle, it totally breaks loose & just spins like it's in neutral. Maximum speed you will get out of a prop with a spun hub is maybe 6 mph. Once she breaks loose, you go absolutly no-where with lots of rpms just like being in neutral. Sal
Mobjack	posted 08-02-2006 10:51 AM ET (US) Hey guys, Never thought this thread would get this big, but thanks for all the great advice. I took it out and ran it last night, I think it is definitely running on all cylinders. all the plugs are connected, did not pull them to see if they are fouled, but the fact remains that whether it be at idle or at full speed the engine is purring like a kitten. SOmeone on this thread mentioned that they thought it could be prop slippage, and that if it were, the engine would over rev. I think this is it: that engine is supposed to redline at 5500 or 5400 rpms and it went to 5650 when I tried it the other day. Is this what you meant? Now its time to hijack the thread: If this is the cause, my prop is old anyway, and I have been thinking about updating my low time engine with a new prop and a Doel fin, for a 1985 Johnson 75 horse motor, on a boat that I want to acheive an acceptable top speed of 30-35 mph (it does not need to scream) and also be able to get out of the hole with a load. The boat is a Montauk, WHAT IS THE BEST PROP TO USE? STAINLESS OR ALUMINUM? PITCH AND SIZE? I know there are a bunch of guys on this site who know this stuff, and I am fairly ignorant about it. Please educate me so I dont get the wrong thing, or buy something I dont need to. Thanks again for your time everybody.
The Judge	posted 08-02-2006 01:53 PM ET (US) 13.25x17 alum or 13 3/8x17 SST is the best to use on that boat. cratch the doel fi umless you like to drive at 12mph. I never found a need for them on 15-19' whalers. I usually have a few 17" props laying arund but have recently liquidated. Should be able to pick one up on e-bay cheap being it is a VERY popular sized prop. A good SST should fetch under $150 delivered. You can sometimes rob one for cheap but beware of condition, you don't want some worn down nub, you already have one of those ;)