1999 Yamaha 4 stroke F50TLRX running rich

[ChuckB1954]

Choke lever pulled when it shouldn't be?

IE, butterfly's CLOSED?

Is the system working correct now?

3 of 4 carbs , must be talking about a link and sync problem

The prime start is working like it should. The device works like a timed plunger or solenoid. When power is dropped, when the engine is shut off, the carbs slowly becomes choked as the prime start cools down. When you start the choked engine, the prime start slowly releases the choke and within a minute or so the choke butter flies are wide open. Turn the engine off and the prime start slowly chokes the carbs again. The temperature of the engine has no affect, although once the prime start warms up, the cycle is a little faster. Kind of a wacky setup, but my spark plugs are now burning clean after checking them following numerous cycles. You would think the unnecessary choking of an already warm engine would fowl them, but it is not the case.

Now an answer to my question in my previous post.. If you notice, the spring that keeps the choke open is in the wrong position! Three carbs were like this. In the picture, the little loop of that spring is at about 5 o'clock. As I mentioned quite a few post back, the choke linkage was "flapping in the breeze" when it should have been under spring tension in the open position. Initially when I hooked everything up, the prime start held the choke closed firmly. I could not move the linkage. Once the engine began running and the prime start released the choke linkage, I noticed the linkage was loose again and gravity held the linkage down keeping the carbs choked.. I looked at my new set of carbs that I purchased, which are still assembled, and I saw the problem. On that set of carbs the small shaft springs were holding the chokes wide open. I corrected the springs on three carbs, turning that little loop counter clockwise and hooked it to the 7 o' clock position and now, all is good.

[ChuckB1954]

f50 choke.JPG




But that makes no sense (thinking out loud) because the thermo switch 2 appears to be "normally open" and closes when warmed up.

You have anymore information on this?

The thermo switch 2 on my engine is a closed circuit when the engine is cold. I need to test it to when the engine warms up to see if it changes state. The wiring diagram clearly shows it open, but without an explanation whether the engine is cold or warm. I would assume that it is open when the engine is warm. As you can see by the diagram, the solenoid only engages when the starter is engaged.

[ChuckB1954]

I figured out how the choke solenoid works..It will only activate the choke under two conditions.. 1: Engine must be cool enough for thermal switch 2 to be closed..2: Prime start must have the choke released. These 2 conditions are almost impossible to exist at the same time. By the time the prime starter has released the choke, the engine is warm enough to disable switch two, disabling the choke solenoid. In turn by the time the engine has cooled down long enough for switch 2 to be closed, the prime start has already cooled down long enough to close the choke. Apparently the designer of this system wanted to ensure that this engine is choked when started, no matter what, whether the engine is hot or cold. Looks like the solenoid choke would never be used in South Florida, but this system may be useful is freezing weather.

[TownsendsFJR1300]

Excellent, glad to hear.

Years of previous owners putzing with the engine (choke springs) / removing parts, just added to your issue....



*BTW, Kohler and some B&S engines have automatic chokes that activate whether the engine is hot or cold. Some black smoke on initial start up, but clears out immediately..

[boscoe99]

This note is repeated 4 or maybe 5 times in the service manual. As in, "if it ain't broke, don't be fixing it".

[ChuckB1954]

This note is repeated 4 or maybe 5 times in the service manual. As in, "if it ain't broke, don't be fixing it".

Oh yeah.. I'm not touching them babies.. seems to be running great. I plan on eventually checking adjustments on the choke linkage per the manual. Someone was struggling with this choke system, explaining the debauchery and the missing parts.

[ChuckB1954]

I took the boat out today to do some fishing and also to see how it runs. As seen in the photo, it is no longer running rich. I was a little disappointed as it seemed to be down on power. It would not even plane off with two of us in the back. It only did so when my friend moved to the front. Before, when it was running rough and rich, it would run 32MPH and had little trouble reaching plane. Now, top speed is 29MPH. Perhaps it could stand to run a little richer. Also Idled a little poorly. I checked the idle mixture screws and all of them are turned exactly 2 1/2 turns out. Any opinions?



btw, hardly got any strikes let alone catching any fish.

20190602_121603_small.JPG

[99yam40]

MPH means little,
need to know what RPM it gets to WOT

also need to make sure the carbs are clean, and have the proper jets in them.
need to make sure it is propped correctly.

no telling what may have been done to this motor.

My C40 had mains that were drill out to larger holes, took me a long time to find that out.

need a 4 channel manometer to set carbs properly

[ChuckB1954]

MPH means little,
need to know what RPM it gets to WOT

also need to make sure the carbs are clean, and have the proper jets in them.
need to make sure it is propped correctly.

no telling what may have been done to this motor.

My C40 had mains that were drill out to larger holes, took me a long time to find that out.

need a 4 channel manometer to set carbs properly

Wide open is slightly over 5000 RPM's I would say 5200 RPM's.

I agree.. I would not to attempt to adjust these 4 carbs without that tool.

[TownsendsFJR1300]

Don't know what YOUR particular engine is spec'ed at for WOT but many 4 strokes are 5,000 to 6,000.

My F150, (after being installed) was propped INCORRECTLY with a prop that MAX RPMs was 5,000 .

Performance was HORRIBLE. it would barely get on plane, nor PU a skier.

Once re-propped to get to 6,000 Max, it's a whole different engine... Would now easily jump on plane, darn near as fast as the 150 V6 Evinrude it replaced.


Once someone posts for certain, your recommended RPM range, time to get the correct prop for the max RPM...

[walleye1]

It is 5000 to 6000 rpm.

[ChuckB1954]

Don't know what YOUR particular engine is spec'ed at for WOT but many 4 strokes are 5,000 to 6,000.

My F150, (after being installed) was propped INCORRECTLY with a prop that MAX RPMs was 5,000 .

Performance was HORRIBLE. it would barely get on plane, nor PU a skier.

Once re-propped to get to 6,000 Max, it's a whole different engine... Would now easily jump on plane, darn near as fast as the 150 V6 Evinrude it replaced.


Once someone posts for certain, your recommended RPM range, time to get the correct prop for the max RPM...

That's how I would describe the performance of this motor, Horrible! Might not even reach plane unless someone is up front. First time I took it out, with all 4 carb bolts loose on one side (unknown to me at the time) and the choke randomly opening and closing due to un-sprung choke linkage (also unknown to me at the time), it had no trouble planing even with two people in the back. The RPMS were slightly higher and the top speed was 63 MPH. One I discovered the bolts were loose and correct it, It struggled to plane. (this was before I corrected the choke issue.) Now that the choke issue is resolved, no real difference except I lost a few MPH's and the plugs run quite normal (if anything maybe a little lean).

Don't know if this comes into play, but this engine had a hydrofoil on it at one time, but was taken off. The seller gave it to me when I bought the boat. Maybe I should put it back on?

Wide open, this engine only makes it to 5200 RPMS @ 29MPH

[ChuckB1954]

It is 5000 to 6000 rpm.

Thank you!

[ChuckB1954]

Don't know what YOUR particular engine is spec'ed at for WOT but many 4 strokes are 5,000 to 6,000.

My F150, (after being installed) was propped INCORRECTLY with a prop that MAX RPMs was 5,000 .

Performance was HORRIBLE. it would barely get on plane, nor PU a skier.

Once re-propped to get to 6,000 Max, it's a whole different engine... Would now easily jump on plane, darn near as fast as the 150 V6 Evinrude it replaced.


Once someone posts for certain, your recommended RPM range, time to get the correct prop for the max RPM...

Also what I plan to do since my buddies boat that has the original engine that came on this boat that I bought is at my house. I will look and see what prop is on his Yamaha 2 stroke and compare it to the one currently on my Yamaha 4 stroke.

[TownsendsFJR1300]

That 1,000 RPM (and that's with a larger engine), made ALL the difference in the world.

If came with an aluminum prop (obviously NOT sea trialed before delivery). I replaced with SS and with the knowledge of the prop shop, got the correct one the first time out..


*I had a link from Yamaha re the general prop for a specific boat / hp, but that link doesn't work anymore(deleted).

Someone may have a newer link. I believe it was under "Yamaha Performance". A good prop shop, telling them what you have, RPM's etc, should be able to get you real close to where you need to be...

With another 1,000 RPM's, you should pick up a little speed too..