coil or fuel breaking down

[jlslavey]

Here's what I've learned so far, coil wires have spark going thru them when the engine slows down, fuel filter is clean, put a new fuel line and portable tank on today and the same problem, goes from 4500 down to 3000, I turned off the key each time and set for 15-20 seconds then started right back up, ran a few minutes then same thing. Must have turned the key on and off 10 times and each time the motor started I could run it at 4500 then slowed down again. Any way to check the fuel pump out or the cdi? thanks again for all the suggestions, I just haven't found the problem yet. I do know if I run it at 3000 I don't believe I've ever had the problem.

[DennisG01]

Just reiterating some things from above, but...

-- How do we know that there's ENOUGH juice flowing through the plug wires?
-- Did you check the entire length of the plug wire?
-- Have you checked into the winky blinky, yet?

You mentioned a few times that the issue happens "immediately" and we talked about how that indicates it's an electrical problem, not a fuel problem. Hence, it can't be your fuel pump if it's happening like you are saying it is. But, drain the carb bowls when the issue happens and compare if you want to see if there's enough fuel getting to the carbs.

[jlslavey]

Just reiterating some things from above, but...

-- How do we know that there's ENOUGH juice flowing through the plug wires?
-- Did you check the entire length of the plug wire?
-- Have you checked into the winky blinky, yet?

You mentioned a few times that the issue happens "immediately" and we talked about how that indicates it's an electrical problem, not a fuel problem. Hence, it can't be your fuel pump if it's happening like you are saying it is. But, drain the carb bowls when the issue happens and compare if you want to see if there's enough fuel getting to the carbs.

Thanks, no we only checked the middle of the plug wire with a tester and it showed current, I did pull the plugs and none were saturated with fuel, they all looked the same. The winky blinky no I have not, it looks to be a very very expensive item to buy. If one of the coil wires were breaking down would it show up in the plug itself ( lots of extra fuel )?

[DennisG01]

I'm not an expert in reading plugs, by any means, but I'm just kind of wondering outloud with the plug wire thoughts. Meaning, could it be sending some power through, but not enough to fire the plug under all circumstances - such as when the engine and everything start to heat up. That's what happened with my uncle's - although the culprit was the plug. But that's why I was wondering about the entire length of the plug wire... just trying to eliminate variables. I would agree with you, though, and "think" that the plug would be noticeably wetter then the others - but then it may depend on how quickly you pull the plug since the gas can evaporate quickly.

I think the winky blinky is only about $100? It's a diagnostic tool and can help point you in the right direction. If the CDI is seeing something it doesn't like, it may be able to tell you what circuit is causing fits. Note, that there is no memory to the CDI - you have monitor the winky blinky WHILE the issue is happening and note the code, then look in your service manual to see what the code is.

[99yam40]

a 50 2 stroke has no place to hook up a winkyblinky
we have no idea what year model this motor is because no one gave a complete model #

the CDI on newer models controls spark and timing to all 3 cylinders with the input from 3 pulser coils.
I believe overheat or low oil should reduce RPM to around 2000 not 3000 by misfiring cylinders, but I am not sure if it retards timing also.

OP said he sees spark when the problem occurs
I am not sure how he has done this, or if that was to all 3 plugs
but a timing light would be a good way, plus you can see if the timing is being retarted with that too

OP do you have gauges?
if not how are you reading RPM?

My C40TLRX had a high speed miss when I 1st got it.
turned out someone had drilled out the main jets.
I replaced all 3, it runs fine now.
my guess was a previous owner thought he could turn it into a 50HP by drilling them out to let more fuel in.
the proper amount of fuel and air is needed to burn properly

the service manual shows minimum specs for input to cdi and out puts of cdi.
need to proper peak reading voltmeter or a DVA adapter hooked to a regular meter

[DennisG01]

a 50 2 stroke has no place to hook up a winkyblinky
we have no idea what year model this motor is because no one gave a complete model #

My bad - didn't realize that. I had thought if it had a CDI, a Winky could be hooked up.

[jlslavey]

a 50 2 stroke has no place to hook up a winkyblinky
we have no idea what year model this motor is because no one gave a complete model #

the CDI on newer models controls spark and timing to all 3 cylinders with the input from 3 pulser coils.
I believe overheat or low oil should reduce RPM to around 2000 not 3000 by misfiring cylinders, but I am not sure if it retards timing also.

OP said he sees spark when the problem occurs
I am not sure how he has done this, or if that was to all 3 plugs
but a timing light would be a good way, plus you can see if the timing is being retarted with that too

OP do you have gauges?
if not how are you reading RPM?

My C40TLRX had a high speed miss when I 1st got it.
turned out someone had drilled out the main jets.
I replaced all 3, it runs fine now.
my guess was a previous owner thought he could turn it into a 50HP by drilling them out to let more fuel in.
the proper amount of fuel and air is needed to burn properly

the service manual shows minimum specs for input to cdi and out puts of cdi.
need to proper peak reading voltmeter or a DVA adapter hooked to a regular meter

The item used is a Calterm 66331 LED Indicator, you hold down a button and the red light flashes if there is spark going through the wire to the plug. NO rpm or anything, just a led light that senses current.

The complete mode is a 50 tlr 6H5KL-1008850 2 stroke oil injection. The rpm is on my gauge which reads around 4500 at max throttle under load on the water, drops to 3000 and stays there . I have the boat 2 yrs and this is the first time this problem has occurred.

[DennisG01]

Just a side note, 4500 is on the extreme low end of the range for that motor. Ideally, you'd want to be at or close to 5,500 with a normal load. This could be improper trimming or even just the wrong prop. But that's a thread for another day.

[DennisG01]

Oh... just for giggles... the next time you're out and this happens, double check that the throttle linkages on the engine aren't buggered and falling back. It's a long shot, but...

[99yam40]

The item used is a Calterm 66331 LED Indicator, you hold down a button and the red light flashes if there is spark going through the wire to the plug. NO rpm or anything, just a led light that senses current.

The complete mode is a 50 tlr 6H5KL-1008850 2 stroke oil injection. The rpm is on my gauge which reads around 4500 at max throttle under load on the water, drops to 3000 and stays there . I have the boat 2 yrs and this is the first time this problem has occurred.

so , you do have a gauge.
Is it a Yamaha one?
does it have the lights to indicate overheat and low oil?
I asked that a long time ago, but you never answered that.

I agree with Dennis that 4500 is a low WOT RPM.
If it has spark on all cylinders when the rpm drops, check to make sure timing is correct at that time also.
If that is all good it has to be fuel problems.
too much or too little fuel dropping a cylinder
I think this is a motor from a different area than USA, maybe Boscoe can tell us what year it was produced,
or the op can get that off of his transom bracket also

[panasonic]

First thing we need to know is the year of the engine...please provide that, it is on the transom bracket where you got the serial number.

Still don't know for sure if it is a fuel or spark problem.


Take off the cowl and airbox and go for a another run. With a little squirt bottle of gas mix spray some fuel in the suspected carb(s) and see if the cylinder(s) picks back up. If it doesn't...it's a spark problem.

Did you check your plug caps?????

[DennisG01]

Take off the cowl and airbox and go for a another run. With a little squirt bottle of gas mix spray some fuel in the suspected carb(s) and see if the cylinder(s) picks back up. If it doesn't...it's a spark problem.

Question.. for clarification. In the case of my uncle's 50HP, carb'd - this past summer. The EXACT same thing was happening. His engine has some type of "extra" choke for really cold starts. It's a small lever on the side of the engine. When the RPM's dropped down, I was able to get them back up by manually adjusting that choke lever a bit while the engine was running. Which would lead one to believe that the problem was a fuel problem. HOWEVER, simply putting in new spark plugs 100% solved the issue. ???

Edit: Oh, not that it likely matters, but my uncle's engine is a 2-stroke Evinrude.

[jlslavey]

so , you do have a gauge.
Is it a Yamaha one?
does it have the lights to indicate overheat and low oil?
I asked that a long time ago, but you never answered that.

I agree with Dennis that 4500 is a low WOT RPM.
If it has spark on all cylinders when the rpm drops, check to make sure timing is correct at that time also.
If that is all good it has to be fuel problems.
too much or too little fuel dropping a cylinder
I think this is a motor from a different area than USA, maybe Boscoe can tell us what year it was produced,
or the op can get that off of his transom bracket also

I only have the hand held led voltage tester, nothing directly tied into the motor, no overheat or low oil, just the alarm.

[jlslavey]

Question.. for clarification. In the case of my uncle's 50HP, carb'd - this past summer. The EXACT same thing was happening. His engine has some type of "extra" choke for really cold starts. It's a small lever on the side of the engine. When the RPM's dropped down, I was able to get them back up by manually adjusting that choke lever a bit while the engine was running. Which would lead one to believe that the problem was a fuel problem. HOWEVER, simply putting in new spark plugs 100% solved the issue. ???

Edit: Oh, not that it likely matters, but my uncle's engine is a 2-stroke Evinrude.

Mine has a "cold start" switch located on the front but it is in the "run" position, I have to physically flip it down for cold start which take a little bit of pressure ( I believe it is on a cam like plate). So I don't think it is moving on it's own.

[jlslavey]

First thing we need to know is the year of the engine...please provide that, it is on the transom bracket where you got the serial number.

Still don't know for sure if it is a fuel or spark problem.


Take off the cowl and airbox and go for a another run. With a little squirt bottle of gas mix spray some fuel in the suspected carb(s) and see if the cylinder(s) picks back up. If it doesn't...it's a spark problem.

Did you check your plug caps?????

Will take it out for the run as suggested. As for the plug caps not sure what to check, they all fit tight on the plug, gap is set accordingly , might have to run it at night and see if I might have a spark jumping which I don't think is the problem, starts great, idles great, runs at a slower rpm without dropping.