Yamaha 50 TLR Two Stroke

[steven85fish]

Hello,

I have a Yamaha 2 stroke carb'd motor that I'm trying to get back into running shape. Here is all the information I have.

1. Motor will not rev past 1/4 throttle
2. Changed lines, water fuel separator, the whole 9.
3. Cleaned/rebuilt carbs. Even fixed a slow gas leak due to a improperly seated gasket.
4. Checked hoses for vacuum leaks, didn't find any.
5. Pulled off airbox and put a rag on the cylinder to "choke" it, and each cylinder pulls fuel through.
6. Spark plugs are all firing

I'm stumped at this point. Anybody have any thoughts? My new concern is that the reed valve is bad.

[99yam40]

so does it idle well?
good compression, spark on all 3 cylinders, timing in spec and advancing as you open the throttle?
if so, maybe you have a main jet plugged up or at least partially plugged

[steven85fish]

so does it idle well?
good compression, spark on all 3 cylinders, timing in spec and advancing as you open the throttle?
if so, maybe you have a main jet plugged up or at least partially plugged

Would a clogged jet still pull fuel into the carb when I'm manually choking each cylinder?

and no, it doesn't idle particularly well.

[99yam40]

you did not answer my questions

[steven85fish]

you did not answer my questions

Hey 99yam40,

My mistake.

good compression - Yes, 110
spark on all 3 cylinders - Yes
timing in spec and advancing as you open the throttle? yes

[99yam40]

I am just guessing that it idles OK, also

so you are left with a fuel to air ratio that is a problem at higher RPM.
time to go thru the carbs

remember to follow the link and sync after putting the carbs back on after cleaning

would not hurt to check the fuel pump, no telling how old it is

choking air off will cause more fuel to flow for the air coming thru

[panasonic]

Put some premixed in a squirt bottle and have someone spray fuel into each carb as you are running boat in the water. If it picks up rpm you know you have lack of fuel.

Always good to post model and year of engine as well.

Link and sync carbs is a must to get a good idle as already mentioned

[FirstBoat50tlr]

There must be an illness going around with these 50tlr engines.
I’m having very similar issues w mine and I am under the belief I am running off only 1 or 2 cylinders when full throttle.

When you checked the water separator, was there any water found or any deposits in the fuel.

From my understanding, if it’s a reed valve it will spit it back out the carburetor when it’s running.

what are your max RPMs when in gear/throttling down.
Panasonic has a great idea, that’s one of the things I plan to do.
Also, how did you check timing and spark?

[steven85fish]

There must be an illness going around with these 50tlr engines.
I’m having very similar issues w mine and I am under the belief I am running off only 1 or 2 cylinders when full throttle.

When you checked the water separator, was there any water found or any deposits in the fuel.

From my understanding, if it’s a reed valve it will spit it back out the carburetor when it’s running.

what are your max RPMs when in gear/throttling down.
Panasonic has a great idea, that’s one of the things I plan to do.
Also, how did you check timing and spark?

Hey FirstBoat,

Thankfully, I was finally able to diagnose the problem with my motor, or at least narrow it down to 1 or 2 things. However, I'll get into that after I answer your questions.

There must be an illness going around with these 50tlr engines.
I’m having very similar issues w mine and I am under the belief I am running off only 1 or 2 cylinders when full throttle.

When you checked the water separator, was there any water found or any deposits in the fuel.

-- Water/Fuel Separator was clean, no deposits, no water. I purchased the boat a year ago and only use non-ethanol.

From my understanding, if it’s a reed valve it will spit it back out the carburetor when it’s running.

what are your max RPMs when in gear/throttling down.f

--Max RPM when in gear was around 2k rpm.

Panasonic has a great idea, that’s one of the things I plan to do.
Also, how did you check timing and spark?

--Timing light hooked up to spark plugs


I would do yourself a favor and check to see if it's something easy and simple. That's what fixed my initial spark firing problem.

There are three pulsar coils just under the flywheel. The piece just under the flywheel spins around telling the pulsar coils when to fire. The key here is that the coils themselves need to be grounded. I found that my number 2 cylinder wasn't firing, so I looked around and found that my ground had broken off, and therefore wasn't firing at all. Something to take a look at.

After I figured that piece out, I was still having the issues described above and took my carbs off, did a thorough cleaning of them with new parts and all, but when putting them back on, there is a small circular gasket with a little ear that fits inbetween the carb and the intake manifold. They get all stretched out and used up, so I replaced those as well it seems to have fixed my problem.

I hope my rant helped a little bit.

[FirstBoat50tlr]

2E4795FE-2655-4A2C-9F8F-B9A60CE9ED7E.jpeg Interesting. I checked my spark again today and I don’t think I have good spark on two cylinders. I took the coils off and am sending them back to Amazon to get replacements.

By “pulsar coil” under the flywheel, do you mean ignition coil? See image

[99yam40]

here is some good reading on CDI systems
FINAL_4-23-2014_Troubleshooting-Guide_6th-Edition.pdf (cdielectronics.com)

[FirstBoat50tlr]

99yam40
is he talking about the ignition coils?
I’m not sure what pulsar coils are.
steven85fish can you upload a photo?

[99yam40]

no the ignition coils attached to the spark plugs are not the pulser coils.
pulser coils send voltage to the CDI telling it when to fire the ignition coils