coil or fuel breaking down

[99yam40]

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

well then how do you tell what RPM the motor is running at?

[99yam40]

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.

if you have to turn the prime start red switch to on, to start the motor then the carbs and the prime start system has some plugging going on and needs to be cleaned properly

[99yam40]

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.

most motors have a resistance measurement spec for the wires and caps

[jlslavey]

well then how do you tell what RPM the motor is running at?

The tester was for the spark, I have a tach on my console which shows rpm

[jlslavey]

if you have to turn the prime start red switch to on, to start the motor then the carbs and the prime start system has some plugging going on and needs to be cleaned properly

I never need to use the cold start switch, starts just fine without it, someone made reference to theirs and ask if I had one.

[panasonic]

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.

Plug caps are removable from the coil lead. Some have resistors in them, some don't. To check them you simply unscrew the cap and measure the resistance of them with your meter set to ohms...they all should read the same. Also you can inspect the connection between the cap and wire for corrosion. A bad cap can cause funny things to happen..work at some rpm and not at others. It is a simple easy thing to do and rule out...like changing spark plugs.

But trouble like you are having is hard to sort out because it is coming and going...not a hard fault that stays.

So is it fuel or spark? I would do like I suggested and run the engine with air box off and when it happens spray a bit of fuel in the carb(s) and see if it picks back up or not and go from there.

Do you see a year on the transom bracket?.it is important to answer the questions that are asked. We can only help effectively if we know what exact engine you have...otherwise it is a guessing ****.

Be safe.

[jlslavey]

As for the year I have it written on the front of the manual as a 2005, not sure where I got that but when it stops raining will look again, the boat is a 2006 Sun tracker

[99yam40]

The tester was for the spark, I have a tach on my console which shows rpm

well the tach would have lights for overheat and low oil if it is a Yamaha


your statement"

, I have to physically flip it down for cold start

" made it sound like you had to use it for cold start

[DennisG01]

The "cold start" question/confusion was my fault. When Panasonic mentioned squirting fuel into the carb, and if it works, then you know the problem isn't the plugs. And I would agree with that, except... I brought up the example of my uncle's engine (that exibited the EXACT same issue as jlslavey's) and messing with the engine mounted (under the hood) "extra" cold start lever whereby I could get the RPM's back. Doing that would ALSO lead me to believe that the issue wasn't spark related, except that the solution WAS to replace the plugs.

I was using my example to ask for clarification of how the spark plugs solved that problem when it seems like they should NOT have solved the problem. The reason for the slight diversion was maybe the answer could, in some way, help to fix/clarify things for jlslavey.

[jlslavey]

This is a reply to Panasonic with his suggestions below:


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.


Ok, today I took it out same problem, so I climbed on the back and sprayed fuel into the top carb, seemed to slow it down just a touch, same with the middle card, but when I sprayed into the bottom carb the rpm's increased and as long as I was spraying it would maintain the higher rpm's. Once I stopped dropped back down, tried several times with the same results. Stopped and tried to take off and it would die out at 1500, wasn't sure if maybe I flooded the thing or not, Would run in neutral to the max rpm but when I put a load kept wanting to die. Finally after several attempts took off but still would drop the rpm

[99yam40]

so what is that telling you?
bottom carb is not furnishing enough fuel.
keep running it like that and you can kiss that power head good by

[jlslavey]

so what is that telling you?
bottom carb is not furnishing enough fuel.
keep running it like that and you can kiss that power head good by

So does this mean it's not a supply issue but actually in the carb itself? it's time to rebuild carbs because it's not getting enough fuel through the bottom carb or would you try an additive to see if it will clean it first?

[99yam40]

as I said before,
keep running it lean and you can toast #3 piston
my brother sent a rod out of his 3 cylinder 2 stroke, but it was not a Yamaha.
anyway you look at it not enough fuel and oil is not good

[panasonic]

Time to take the carbs off.inspect and clean them. Bottom one is dirty and not supplying the correct amount of fuel. As 99yam40 already said....keep running it like that and you will burn up that cylinder.

Skip the additives....clean them properly.

[jlslavey]

Time to take the carbs off.inspect and clean them. Bottom one is dirty and not supplying the correct amount of fuel. As 99yam40 already said....keep running it like that and you will burn up that cylinder.

Skip the additives....clean them properly.

Is there a reason to buy a rebuild kit and replace everything or just a good cleaning? The motor probably has 300 hours on it maybe.