Half power during the first few minutes -- Am I missing a cylinder?

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Author Topic:   Half power during the first few minutes -- Am I missing a cylinder?

ShrimpBurrito posted 09-21-2003 12:17 AM ET (US)
I took the 15' Super Sport out today with its 1987 40 HP Johnson (2 cylinder). Top speed is ~38 MPH. As I was pulling away from the dock, I knew the engine wasn't operating at full capacity. I opened up the throttle, and I accelerated to a good 7-8 MPH. The engine noise was significantly different; it's hard to describe, but I'd say it was a much lower pitch, and a more "hollow" and full noise.
After about five minutes at slightly less than WOT (while underway @ 7 MPH), full power was miraculously restored and it was back to normal operation for the rest of the day. This identical sequence of events has happened a few times in the past, but I want to know what's going on and fix it.
Was one of the cylinders not firing? If so, what could be the cause? I replaced the plugs 6 months ago. I can't think of any spark or fuel problem off hand that would not have continued, or at least show its head periodically, after 5 minutes.
Any ideas?
pstollie posted 09-21-2003 09:20 AM ET (US)
I had this on a '86 40HP Evinrude. If I recall one of the carbs was fouled, no fuel going to one of the 2 cylinders. I think it was the lower carb, you may want to check and see if the lower spark plug is wet with fuel.
jimh posted 09-21-2003 10:35 AM ET (US)
If you have a two cylinder engine that normally goes 40-MPH and now can only make 8-MPH, I would suspect that it is operating on only one cylinder.
Try operating without the cowling. When the problem occurs, remove one spark plug lead. If the engine dies, replace that lead and try the other. This should help you identify the cylinder.
If your ignition system is sophisticated with electronics, etc., check for possible damage by removing high-tension lead without a load before trying the procedure I mention above. You could cause more problems, so be careful.
JBCornwell posted 09-21-2003 11:09 AM ET (US)
Howdy, SB.
I agree with JimH.
The cylinder that is dead on start-up may have a carb problem but I think it is more likely that you have a temperature related failure in the ingition for that cylinder. When it is warm, it works; cold, it doesn't.
Crank the engine and leave her at idle. Confirm that the dead cylinder is not making power by disabling spark temporarily. Then warm the associated electronics with a hair dryer. When/if the engine suddenly picks up rpm, you have just warmed a component that needs replacemdnt.
Good luck.
Red sky at night. . .
JB
ShrimpBurrito posted 09-23-2003 10:56 AM ET (US)
Thanks for the feedback, guys.
I'm not convinced that the problem is caused by gummed carbs simply because I had used the boat the week before. I've had the boat sitting for longer periods, on several occasions, and have not had this problem. I'll definitely check the carbs, though, as that's one possible source that's easy to eliminate. The problem doesn't happen very often (one every ~15 times I'm out), so that makes diagnosis more difficult.
I'm not sure pulling the spark plug cable while the engine running is a good idea. There is very high voltage at that terminal, and I don't want to get zapped. Secondly, as jimh eluded to, if I do get it off and remain conscious, excess voltage can build up on the coil and cause it, or some other part, to fail.
Some other causes I'm thinking of are a bad coil, or maybe excessive carbon buildup, causing one of the valves to stick. Unfortunately, determining which cylinder is the problem is going to be problematic. It doesn't happen very often, and when it does, I'm in the boat and the plugs are on the back side of the engine. Since the problem has already occured in one cylinder, it's probably not a bad idea to clean/fix/replace to both anyway.
SMLWhaler posted 09-23-2003 11:38 AM ET (US)
fouled plug for whatever reason.
Bigshot posted 09-23-2003 12:53 PM ET (US)
Twin cyl is easy to test. carry a spray bottle of gas or ether, spark plug wrench and spark plugs. Next time it acts up dp NOT run it hard, remove cowl and spray gas or ether into each carb. If it bogs then you are getting gas in that carb, if it pick up or does nothing then you found your bad cyl. i believe you have 2 carbs on that like my 60hp did. If it picks up then your float is sticking and shutting off ALL the fuel. Try "tapping" th float boawl with a screwdriver etc to break it lose if that is the case.
If nothing happens on 1 carb when you spray gas into it then you have a spark issue and I would again try tapping the coils and checking the connections but I doubt a coil. Coils usually cut out when they get hot, not when cold. My guess is a powerpack or a trigger not hitting the one cyl. If it is a carb problem, running it for 5 minutes without fuel/oil will do damage so don't do that. Also check your compression to make sure you did not do any damage. My $$$ is on a bottom float sticking, happened on my 60 a few times.
Gene in NC posted 09-26-2003 09:43 PM ET (US)
Shrimp Burrito, Took me a long time to fully respect the following advice. When you think there is a fuel problem, start with the ignition.
You're right about burning out coil packs by running engine with ungrounded plugs.
Could also be a bad plug wire.
Sal DiMercurio posted 09-26-2003 09:59 PM ET (US)
Whens the last time you changed the plug wires ?
You might want to take the hood off & if you have the boat at home on the trailer, wait till it gets real dark & start her up, if the wires are bad or bad coil you will see a light show coming from the culprit.
By the way, there are no valves on a 2 stroke outboard.
Sal
MikeT posted 09-29-2003 03:16 PM ET (US)
I had a similar problem with my '79 70HP Mercury. Long story short my mechanic found a crack in one of the nipples that a bleeder hose fits on. It may not relate to your problem but it is one of those odd ball things that most folks don't think to check. You might also try posting in the appropriate section of the iboats.com repair forum. I have gotten a lot of good advice there in additions to this site.
Whalerdan posted 09-30-2003 07:22 AM ET (US)
Since it's intermittent, I'm guessing a power pack. If it was a coil, like BS says, it should do it when warm. I would also guess that if it was a spark plug wire the same thing, i.e. do it when warm. Doubt it has anything to do with the carbs since it comes and goes. If a carb where gummed up it should do it everytime.
Danny
ShrimpBurrito posted 10-01-2003 05:19 PM ET (US)
Thanks for all the informative suggestions, fellas. I expect to take a look at the engine this weekend, with your advice in hand, and will report back.
ShrimpBurrito posted 10-28-2003 05:57 PM ET (US)
Well, after a few more times on the water and a little tinkering around, I hope I have solved the problem.
The spark plug wires checked fine, but I changed them anyway because they had never been changed.
I checked the compression on both cylinders, and they are both at 120 psi. Sounds fine to me.
The next time "it" happened, I knocked on the carb bowl, but that didn't do anything. Like all the other times, it just "resolved" itself after about 5 minutes and then ran smooth for the rest of the day.
The last time "it" happened, I started knocking on several things, including the ignition coils. Knocking on the top one didn't do anything, but as soon as I knocked on the one to the bottom cylinder, the apparent slacking cylinder chimed in and the engine operated flawlessly with both cylinders for the rest of the day.
I just replaced the ignition coils to both cylinders, so I'm hoping that will take care of the problem. I'll report back after a few more times out on the water.
Thanks very much for all the helpful diagnostic tips. I appreciate it. I'll be saving this one in the notebooks for future reference.
Tom2697 posted 10-29-2003 11:05 AM ET (US)
An easy and safe way to check if all cylinders are firing is to connect an inductive timing light to each plug wire. These are available at almost any auto parts store for less than $25. They have the inductive pickup (clamps around the plug wire) that allows you to connect and disconnect to each wire without shutting off the motor. If the light is flashing, you have spark.
Frankenbrine posted 11-08-2003 10:41 PM ET (US)
Shrimpburrito-
I have an '85 Outrage powered by a 2.6 liter O.M.C. 2 cycle V-6(approx. 220 H.P. at the prop, so I'm told) and I've experienced the same problem you speak of, perhaps to a greater degree, for the last three years. I've replaced the flywheel and magnets, power packs (2), removed the anti-siphon valve at the fuel cell, rebuilt the carbs, and of course the plugs have been replaced multiple times (each mechanic I've consulted for a diagnosis has told me I had the incorrect plugs installed in that motor, and sold me the "updated" plugs recommended by the manufacturer, no two sets being the same, and no discernable difference in performance between them.). The first trip out after each service the engine would do "that" as I throttled up leaving the harbor (typical to this day----Thermostat?) then clean up and run fine the remainder of the day. The subsequent trips would become increasingly more frustrating as the frequency of this "intermittent" problem would increase, typically appearing after periods of trolling at relatively low r.p.m.'s., but also happening when we were wide open throttle, slowing us to about seven knots until it decided to straighten up and fly right (anywhere from thirty seconds to thirty minutes.).
I believe I have figured out my problem.
I now replace the plugs after each trip (sometimes two trips) with a cleaned up set, and the engine runs much more dependably, excepting the standard "leaving the harbour" bogdown, which still mystifies me, though I've come to accept it as s.o.p..
My engine smokes quite a bit at lower r.p.m.'s, which either fouls a plug right away, or just deposits so much carbon on and around the plug that a little vibration from the motor breaks chunks loose which foul the plug, and it is simply a matter of time until the chunks either dislodge themselves and leave the way the came, or are perhaps washed clear by the fuel in the cylinder, and we're off and running again.
On the other hand, she could have simply been jealous that I was spending more time with my wife than with her, and acting up a little was her way of saying "I need (DEMAND) a little more attention over here, honey".

Frankenbrine posted 11-08-2003 10:46 PM ET (US)
One more thing-
It is inadvisable to use ether starting fluid on a 2-cycle engine, as it will wash the oil off the cylinder walls, resulting in scuffing of the cylinder---that's a bad thing!

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Author	Topic: Half power during the first few minutes -- Am I missing a cylinder?
ShrimpBurrito	posted 09-21-2003 12:17 AM ET (US) I took the 15' Super Sport out today with its 1987 40 HP Johnson (2 cylinder). Top speed is ~38 MPH. As I was pulling away from the dock, I knew the engine wasn't operating at full capacity. I opened up the throttle, and I accelerated to a good 7-8 MPH. The engine noise was significantly different; it's hard to describe, but I'd say it was a much lower pitch, and a more "hollow" and full noise. After about five minutes at slightly less than WOT (while underway @ 7 MPH), full power was miraculously restored and it was back to normal operation for the rest of the day. This identical sequence of events has happened a few times in the past, but I want to know what's going on and fix it. Was one of the cylinders not firing? If so, what could be the cause? I replaced the plugs 6 months ago. I can't think of any spark or fuel problem off hand that would not have continued, or at least show its head periodically, after 5 minutes. Any ideas?
pstollie	posted 09-21-2003 09:20 AM ET (US) I had this on a '86 40HP Evinrude. If I recall one of the carbs was fouled, no fuel going to one of the 2 cylinders. I think it was the lower carb, you may want to check and see if the lower spark plug is wet with fuel.
jimh	posted 09-21-2003 10:35 AM ET (US) If you have a two cylinder engine that normally goes 40-MPH and now can only make 8-MPH, I would suspect that it is operating on only one cylinder. Try operating without the cowling. When the problem occurs, remove one spark plug lead. If the engine dies, replace that lead and try the other. This should help you identify the cylinder. If your ignition system is sophisticated with electronics, etc., check for possible damage by removing high-tension lead without a load before trying the procedure I mention above. You could cause more problems, so be careful.
JBCornwell	posted 09-21-2003 11:09 AM ET (US) Howdy, SB. I agree with JimH. The cylinder that is dead on start-up may have a carb problem but I think it is more likely that you have a temperature related failure in the ingition for that cylinder. When it is warm, it works; cold, it doesn't. Crank the engine and leave her at idle. Confirm that the dead cylinder is not making power by disabling spark temporarily. Then warm the associated electronics with a hair dryer. When/if the engine suddenly picks up rpm, you have just warmed a component that needs replacemdnt. Good luck. Red sky at night. . . JB
ShrimpBurrito	posted 09-23-2003 10:56 AM ET (US) Thanks for the feedback, guys. I'm not convinced that the problem is caused by gummed carbs simply because I had used the boat the week before. I've had the boat sitting for longer periods, on several occasions, and have not had this problem. I'll definitely check the carbs, though, as that's one possible source that's easy to eliminate. The problem doesn't happen very often (one every ~15 times I'm out), so that makes diagnosis more difficult. I'm not sure pulling the spark plug cable while the engine running is a good idea. There is very high voltage at that terminal, and I don't want to get zapped. Secondly, as jimh eluded to, if I do get it off and remain conscious, excess voltage can build up on the coil and cause it, or some other part, to fail. Some other causes I'm thinking of are a bad coil, or maybe excessive carbon buildup, causing one of the valves to stick. Unfortunately, determining which cylinder is the problem is going to be problematic. It doesn't happen very often, and when it does, I'm in the boat and the plugs are on the back side of the engine. Since the problem has already occured in one cylinder, it's probably not a bad idea to clean/fix/replace to both anyway.
SMLWhaler	posted 09-23-2003 11:38 AM ET (US) fouled plug for whatever reason.
Bigshot	posted 09-23-2003 12:53 PM ET (US) Twin cyl is easy to test. carry a spray bottle of gas or ether, spark plug wrench and spark plugs. Next time it acts up dp NOT run it hard, remove cowl and spray gas or ether into each carb. If it bogs then you are getting gas in that carb, if it pick up or does nothing then you found your bad cyl. i believe you have 2 carbs on that like my 60hp did. If it picks up then your float is sticking and shutting off ALL the fuel. Try "tapping" th float boawl with a screwdriver etc to break it lose if that is the case. If nothing happens on 1 carb when you spray gas into it then you have a spark issue and I would again try tapping the coils and checking the connections but I doubt a coil. Coils usually cut out when they get hot, not when cold. My guess is a powerpack or a trigger not hitting the one cyl. If it is a carb problem, running it for 5 minutes without fuel/oil will do damage so don't do that. Also check your compression to make sure you did not do any damage. My $$$ is on a bottom float sticking, happened on my 60 a few times.
Gene in NC	posted 09-26-2003 09:43 PM ET (US) Shrimp Burrito, Took me a long time to fully respect the following advice. When you think there is a fuel problem, start with the ignition. You're right about burning out coil packs by running engine with ungrounded plugs. Could also be a bad plug wire.
Sal DiMercurio	posted 09-26-2003 09:59 PM ET (US) Whens the last time you changed the plug wires ? You might want to take the hood off & if you have the boat at home on the trailer, wait till it gets real dark & start her up, if the wires are bad or bad coil you will see a light show coming from the culprit. By the way, there are no valves on a 2 stroke outboard. Sal
MikeT	posted 09-29-2003 03:16 PM ET (US) I had a similar problem with my '79 70HP Mercury. Long story short my mechanic found a crack in one of the nipples that a bleeder hose fits on. It may not relate to your problem but it is one of those odd ball things that most folks don't think to check. You might also try posting in the appropriate section of the iboats.com repair forum. I have gotten a lot of good advice there in additions to this site.
Whalerdan	posted 09-30-2003 07:22 AM ET (US) Since it's intermittent, I'm guessing a power pack. If it was a coil, like BS says, it should do it when warm. I would also guess that if it was a spark plug wire the same thing, i.e. do it when warm. Doubt it has anything to do with the carbs since it comes and goes. If a carb where gummed up it should do it everytime. Danny
ShrimpBurrito	posted 10-01-2003 05:19 PM ET (US) Thanks for all the informative suggestions, fellas. I expect to take a look at the engine this weekend, with your advice in hand, and will report back.
ShrimpBurrito	posted 10-28-2003 05:57 PM ET (US) Well, after a few more times on the water and a little tinkering around, I hope I have solved the problem. The spark plug wires checked fine, but I changed them anyway because they had never been changed. I checked the compression on both cylinders, and they are both at 120 psi. Sounds fine to me. The next time "it" happened, I knocked on the carb bowl, but that didn't do anything. Like all the other times, it just "resolved" itself after about 5 minutes and then ran smooth for the rest of the day. The last time "it" happened, I started knocking on several things, including the ignition coils. Knocking on the top one didn't do anything, but as soon as I knocked on the one to the bottom cylinder, the apparent slacking cylinder chimed in and the engine operated flawlessly with both cylinders for the rest of the day. I just replaced the ignition coils to both cylinders, so I'm hoping that will take care of the problem. I'll report back after a few more times out on the water. Thanks very much for all the helpful diagnostic tips. I appreciate it. I'll be saving this one in the notebooks for future reference.
Tom2697	posted 10-29-2003 11:05 AM ET (US) An easy and safe way to check if all cylinders are firing is to connect an inductive timing light to each plug wire. These are available at almost any auto parts store for less than $25. They have the inductive pickup (clamps around the plug wire) that allows you to connect and disconnect to each wire without shutting off the motor. If the light is flashing, you have spark.
Frankenbrine	posted 11-08-2003 10:41 PM ET (US) Shrimpburrito- I have an '85 Outrage powered by a 2.6 liter O.M.C. 2 cycle V-6(approx. 220 H.P. at the prop, so I'm told) and I've experienced the same problem you speak of, perhaps to a greater degree, for the last three years. I've replaced the flywheel and magnets, power packs (2), removed the anti-siphon valve at the fuel cell, rebuilt the carbs, and of course the plugs have been replaced multiple times (each mechanic I've consulted for a diagnosis has told me I had the incorrect plugs installed in that motor, and sold me the "updated" plugs recommended by the manufacturer, no two sets being the same, and no discernable difference in performance between them.). The first trip out after each service the engine would do "that" as I throttled up leaving the harbor (typical to this day----Thermostat?) then clean up and run fine the remainder of the day. The subsequent trips would become increasingly more frustrating as the frequency of this "intermittent" problem would increase, typically appearing after periods of trolling at relatively low r.p.m.'s., but also happening when we were wide open throttle, slowing us to about seven knots until it decided to straighten up and fly right (anywhere from thirty seconds to thirty minutes.). I believe I have figured out my problem. I now replace the plugs after each trip (sometimes two trips) with a cleaned up set, and the engine runs much more dependably, excepting the standard "leaving the harbour" bogdown, which still mystifies me, though I've come to accept it as s.o.p.. My engine smokes quite a bit at lower r.p.m.'s, which either fouls a plug right away, or just deposits so much carbon on and around the plug that a little vibration from the motor breaks chunks loose which foul the plug, and it is simply a matter of time until the chunks either dislodge themselves and leave the way the came, or are perhaps washed clear by the fuel in the cylinder, and we're off and running again. On the other hand, she could have simply been jealous that I was spending more time with my wife than with her, and acting up a little was her way of saying "I need (DEMAND) a little more attention over here, honey".
Frankenbrine	posted 11-08-2003 10:46 PM ET (US) One more thing- It is inadvisable to use ether starting fluid on a 2-cycle engine, as it will wash the oil off the cylinder walls, resulting in scuffing of the cylinder---that's a bad thing!