Yamaha 50TLRD revs and bogs revs and bogs...

[Jim Hawkins]

This motor has given me no end of problems. Took it out today after rebuilding the carbs and replacing 3 coils. Before that work it would not get up on plane. It idled OK and ran smooth at low RPM but ran rough and bogged at full throttle moving at a steady crawl.
Now, after the work it takes off, sounds good like it wants to jump on plane but then bogs for a few seconds, goes back to an idle and then takes off again only to repeat the behavior without any adjustment to the throttle.
I pulled the fuel pump to look for any telltale pinholes or tears and nothing. Putting it back together and blowing through it, it makes the nice trumpet sound and seems fine.
My other suspicions are,
Could a low oil - RPM limiter make it run like that if the sensor was bad?
Could it be the CDI? I never had a bad one that acted like that.
I'm feeling pretty flummoxed

 

[99yam40]

test the buzzer to make sure it functions as it should.
if that works it should tell you low oil or overheat is not a possible problem if it does not buzz during the problem.

timing light will show if spark is steady and if timing is advancing as it should when the problem shows up. have to move the light to the different plug wire to test them all

does pumping primer bulb help when it has this problem?

 

[racerone]

Test run with another tank and hose.

 

[Jim Hawkins]

This just in!!! Dramatic footage of the issue. (for the full effect, turn up your volume.)
In this video you will hear the boat rev up and slow down 3 times without touching the throttle and it will just keep doing this forever.

 

[Jim Hawkins]

test the buzzer to make sure it functions as it should.
if that works it should tell you low oil or overheat is not a possible problem if it does not buzz during the problem.

timing light will show if spark is steady and if timing is advancing as it should when the problem shows up. have to move the light to the different plug wire to test them all

does pumping primer bulb help when it has this problem?

I'll check tomorrow.

 

[Jim Hawkins]

Test run with another tank and hose.

already tried that, thanks.

 

[racerone]

Use a timing light.----One cylinder at a time.----See if you are loosing spark on one.

 

[Sea Rider]

Electric components are not eternal, can go bad over time and use. Worse case escenario is having overheating intermitend behaviours which are the hardest to troubleshoot fast, unless having new extra CDI, coils, etc to swap and test....

Happy Boating
​

 

[Jim Hawkins]

Electric components are not eternal, can go bad over time and use. Worse case escenario is having overheating intermitend behaviours which are the hardest to troubleshoot fast, unless having new extra CDI, coils, etc to swap and test....

Happy Boating
​

My experience with bad fuel pumps, clogged filters, kinked hoses and all that rot is that it makes for much more sputtering and such. The way this cycles as if exactly timed makes me think it's electronic, like a capacitive circuit and as luck will have it, my girlfriends boat has the same motor. Oh Honey, can I borrow your CDI? What, huh, oh sure whatever

 

[99yam40]

or just follow the testing procedures for the ignition system in the service manual for your motor testing the inputs and outputs of the CDI

 

[Sea Rider]

Hey Jim, not a bad idea to test your girlfriend's motor CDI as a starter. Troubleshooting electrical components with Ohm, DVA testers is relative when cranking cold, if any with already hidden issues will miss when motor is at load...

Happy Boating​

 

[scout-j-m]

Maybe try running it with 1 plug wire pulled at a time to see if you can isolate it to one cylinder. Not sure if that would tell you much though since you already changed the coils. I guess from there you could trace it back to the CDI box and then to the pulser/trigger wire for that cylinder. Maybe then swap that pulser coil with another to see if the issue jumps to that cylinder? I do agree with Sea Rider though....if you can realistically swap out a CDI box to try, go for it.

Did you look at the plugs afterwards to see if they tell you anything? Just curious if they all appear to be evenly colored and wet or if one stands out somehow.

 

[Sea Rider]

Out of curiosity, the motor starts to miss right after is turned On or misses after some minutes while giving throttle ? When the motor is shut to cool while at rest, starts right up to miss again after some minutes, right ? If so, clear indication the motor is having intermitent electrical CDI, charger, pulser coils internal heat failures....

To ease and reduce the troubleshooting time have your girldriend lend her motor's CDI unit which currently costs $450 ouch price to swap and test. If the CDI is the culprit that 3 cylinder motor should run top with 3 new installed Ignition Coils. If not will need to troubleshoot the charge (exciter) coil and the 3 pack pulser coils outputs individually....

Happy Boating​

 

[Jim Hawkins]

Out of curiosity, the motor starts to miss right after is turned On or misses after some minutes while giving throttle ? When the motor is shut to cool while at rest, starts right up to miss again after some minutes, right ? If so, clear indication the motor is having intermitent electrical CDI, charger, pulser coils internal heat failures....

To ease and reduce the troubleshooting time have your girldriend lend her motor's CDI unit which currently costs $450 ouch price to swap and test. If the CDI is the culprit that 3 cylinder motor should run top with 3 new installed Ignition Coils. If not will need to troubleshoot the charge (exciter) coil and the 3 pack pulser coils outputs individually....

Happy Boating​

This motor on startup behaves just like any other 50HP 2 Stroke Yamaha that I have run, it starts right up, has a slight high idle for about 10 seconds then slows down to a smooth regular idle. Never a miss and never doesn't start. Idling down the canal and out onto the bay not the slightest hiccup. When I put the throttle forward the RPMs go up and the motor sounds like it wants to take on the world and then, like in the video the RPMs drop (smoothly) and then it repeats the cycle.
All 3 plugs are new.
All 3 coils are new, I only replaced them out of caution because when I pulled one wire off the spark plug the wire separated from the boot and I thought if they are old enough to do that they are old enough to change.
Fuel Pump - I kinda doubt it because of the smooth way it cycles no popping or sputtering (although occasionally when the RPMs drop there is a mild "lean sneeze")
Carbs - Just cleaned all 3 and tested them by covering the throat of each one to see how it affected the motor. All 3 acted the same but before cleaning covering #1 would stall the motor and covering #3 had no effect, #2 just slowed it down.
Fuel Lines and Filter - all new, I always replace them when I get a used motor
Pulser Coil - maybe, I dunno, maybe
Low Oil RPM Limiter - Can I test this by simply unplugging it?
CDI - being the most expensive naturally I suspect it!

I will swap the CDI this weekend and if thats not it, order a new fuel pump (ready for one anyway) as well as check the Low Oil thing and the Pulser Coil.

 

[racerone]

If you covered # 3 carburetor and nothing changed that certainly says something.------Find out why.-----Motor should behave the same with all 3 carburetors.----Should slow down ( too much fuel ) like it did covering #2 carburetor.

 

[Sea Rider]

An OEM CDI unit costs $ 450, 3 Pulser coil pack around $ 330, Charger Coil around $ 110.00 I'm always grateful to use portable motors whose parts only costs a fraction of a 50 HP motor, that's why can stock the 3 needed electrical parts for said motors to never let me down. Hope your bogging down issue it's a CDI related item to be back on water soon but at a horrible cost...

Happy Boating​

 

[Jim Hawkins]

If you covered # 3 carburetor and nothing changed that certainly says something.------Find out why.-----Motor should behave the same with all 3 carburetors.----Should slow down ( too much fuel ) like it did covering #2 carburetor.

thanks racer but that was before the carbs were rebuilt and afterwards I said all 3 acted exactly the same

 

[Jim Hawkins]

Ordered a new fuel pump, even though the old one is prob working ok I really didn't like the looks of the diaphragm so, like the coils, time for a new one anyway.

 

[racerone]

More trouble shooting needs to be done.--------Shine a STRONG flashlight into each carburetor bore and observe what is happening at full throttle.

 

[Jim Hawkins]

It was not the fuel pump.
It was the CDI.
So, for this motor I have bought,
Water Pump
Drive Shaft Seal
Carb Kits
Spark Plugs
Coils with Leads
Fuel Lines
Fuel Pump
and a CDI

About $700 Total but if I now have a motor that is trouble free for years I guess it was worth it.