coil or fuel breaking down

[jlslavey]

I have a 50 hp 2 stroke Yamaha, running at 45 rpm and dropped suddenly to 3, left throttle in same place and went back to 45 then back to 3, got it to the dock and put 3 new plugs in today and within a minute or two done the same thing. How can I determine if I have a coil breaking down or fuel not getting to one of the carbs? thanks

[DennisG01]

I have a 50 hp 2 stroke Yamaha, running at 44 k rpm and dropped suddenly to 3, left throttle in same place and went back to 45 then back to 3, got it to the dock and put 3 new plugs in today and within a minute or two done the same thing. How can I determine if I have a coil breaking down or fuel not getting to one of the carbs? thanks

Well, there's your problem! You're running your engine at 44,000 RPM's!

I probably can't help as much as others, but since you used the word "suddenly" that sounds more electrical than fuel related. Fuel related issues will typically "slowly" cause RPM's to vary, where electrical issues are more like someone throwing a switch.

[jlslavey]

Sorry meant to say 4500 not 45000, big difference huh, thanks for the reply. Hoping a coil, lots easier than trying to find a blocked fuel line somewhere.

[rejesterd]

A fuel issue doesn't necessarily mean there's a blockage. Next time it happens, have someone pump the primer bulb and see if it stays running strong at 4400 rpm. If pumping the bulb prevents the issue from happening, I would say you need to replace your fuel pump. If it doesn't help at all, replace the fuel filter, then see if that helps. If it still occurs after that, then I would say your carb jets are getting clogged.

If it's a bad coil, then one of the plug tips would look very different from the others.

[99yam40]

I have a 50 hp 2 stroke Yamaha, running at 45 rpm and dropped suddenly to 3, left throttle in same place and went back to 45 then back to 3, got it to the dock and put 3 new plugs in today and within a minute or two done the same thing. How can I determine if I have a coil breaking down or fuel not getting to one of the carbs? thanks

I would not think a motor could run at 45rpm much less at 3 rpm.

I would be looking to see if an overheat or low oil level is limiting RPM after running for a little while

since we have no idea what motor this is, it is hard to tell much.
could be oil level if it is oil injected, could be a tiller modle without a buzzer/alarm.
but might be a remote and have gauges to tell if and alarm is happening.

also a bad fuel pump could dump extra fuel into #3 cutting out that cylinder

[jlslavey]

Here's what I found out so far, took it out ran it at 4500 rpm and ran for a few minutes then slowed downed to 3000, kept it running at this speed, climbed over and put a test on each of the 3 coil wires and all 3 were firing, let it run full throttle at 3000 rpm and then it all of a sudden took off and went back to 4500. So I think I can rule out the coils or coil breaking down. Starts fine , idles fine, just once in a while bogs down from 4500 to 3000. I took a man with me and I ran it full throttle setting still and it started cutting out, he says this is a safety feature on this particular motor. The motor is a 50hp TLR 2 stroke with oil injection.

[99yam40]

does the alarm(Buzzer) in the remote work when low oil or overheat happens?
I believe you can test the buzzer itself by pulling the kill switch and then hitting the start switch.

grounding the over temp switch with the key in the on positions should set the alarm.
draining the oil tank and then turning the key on should set the alarm also .
do you have gauges to show these alarms also?

did you try pumping the bulb to see if more fuel would help?
and I think

[jlslavey]

does the alarm(Buzzer) in the remote work when low oil or overheat happens?
I believe you can test the buzzer itself by pulling the kill switch and then hitting the start switch.

grounding the over temp switch with the key in the on positions should set the alarm.
draining the oil tank and then turning the key on should set the alarm also .
do you have gauges to show these alarms also?

did you try pumping the bulb to see if more fuel would help?
and I think

I tried everything that was mentioned above, pumped the bulb but it took about 30-45 seconds to kick back in ( not sure if the bulb was the answer) , tried opening gas cap to make sure had plenty of vent, checked the 3 coil wires with a tester while bogged down but all 3 showed firing. Anyone else have any ideas I might try? Ran it one day full speed no problem, today bogged down after a couple minutes at full throttle.

[jlslavey]

Thanks to everyone, maybe someone else can come up with an idea.

[DennisG01]

Can you verify... in your first post you mentioned "suddenly dropped", but at other times you mentioned "bogs". Those sound like two different things in relation to how quickly the RPM's drop.

If it's NOT like someone flipping a switch... then try running the engine on a portable tank connected right to the engine (pre-mix, if needed). That will eliminate the entire boat-side fuel system. For example, a fuel line could be failing internally, making a check valve, of sorts.

[ausnoelm]

Very first check, remove the plugs after it's dropped RPM and see if they all look the same, that can at least narrow it down to a cylinder, is this a three cylinder model?

[rejesterd]

I tried everything that was mentioned above, pumped the bulb but it took about 30-45 seconds to kick back in ( not sure if the bulb was the answer) , tried opening gas cap to make sure had plenty of vent, checked the 3 coil wires with a tester while bogged down but all 3 showed firing. Anyone else have any ideas I might try? Ran it one day full speed no problem, today bogged down after a couple minutes at full throttle.

Did you try replacing the fuel filter? If that doesn't make a difference, I would start taking the carbs apart and making sure they're clean. If pumping the bulb didn't help, then I would say the fuel pump is ok.. and it doesn't seem spark related based on other tests you've done.

[99yam40]

still no info given on the alarm system working as it should.


running at high RPM for a few minutes can cause an overheat where lower RPM will not.
burning more fuel creates more heat

[jlslavey]

Can you verify... in your first post you mentioned "suddenly dropped", but at other times you mentioned "bogs". Those sound like two different things in relation to how quickly the RPM's drop.

If it's NOT like someone flipping a switch... then try running the engine on a portable tank connected right to the engine (pre-mix, if needed). That will eliminate the entire boat-side fuel system. For example, a fuel line could be failing internally, making a check valve, of sorts.

I call it bogging down, I can be running full throttle at 4500 and it will instantly drop down to 3000 and maintain there. Sometimes after a minute or two it will then go back up to the original 4500, but sometimes not.

[jlslavey]

Very first check, remove the plugs after it's dropped RPM and see if they all look the same, that can at least narrow it down to a cylinder, is this a three cylinder model?

Pulled the 3 plugs out and all were clean and dry.