C40TLRX Prime Start Question, Running Rich

[a387673]

40 HP 2-stroke, symptoms include poor idle, excessive fuel consumption, and substantial carbon build-up. I've ruled out a lot of potential causes, and have become suspicious of the prime start system. I tested the electro-thermal valve for resistance and movement. Resistance was in the middle of the acceptable range, and the plunger moved, although my manual does not say how much it should.

It is my understanding that the "bypass" dial/lever, when set to Open is essentially the same as the cold auto operation of the valve, and the Closed position is similar to the warm operation of the valve: Cold (Auto) or Open = Enrich, Warm (Auto) or Closed = Don't enrich. But for some reason, the engine will not run when it's set to Closed. If I switch it back to Normal (Auto), it will run, although poorly. That would seem to indicate a fault on the part of the prime start, such as the plunger not totally restricting the fuel flow.

I'm preparing to replace the prime start diaphragm and gaskets, although I saw no obvious holes or leaks. Is there anything else I need to look for in that system, or any other reason why it would run different on Normal versus Closed with a warm engine? Thanks.

[panasonic]

This may help
https://youtu.be/x35uqVMu2r0

[99yam40]

I would think that the carbs are not functioning properly if the motor will not run with the red lever set to closed and the motor is warm.

when set to open, the motor is not sucking fuel thru the prime start system it is pumping fuel and will flood the motor.

have you checked the fuel pump to see if it is leaking fuel into #3 crankcase?

[a387673]

99, I came across your diagrams of the system..... Exactly what I have been looking for, and I'm not sure can be found elsewhere. Answers any questions about flow/sequence for sure.

One thing I notice as a difference, apparently, in Normal vs Closed (Off) settings, is that the hose to carb vent (upper left on diagram) is open in "Normal", but closed in "Closed". I haven't yet determined exactly what this might impact, but allow it could explain the difference in running in the two modes. Thoughts?

And thanks again for the diagrams.... Tremendously helpful.

primestart1.jpg,

primestart3.jpg

[a387673]

That also apparently applies in hose to manifold, but I guess I need to consider the impact of warm vs cold operation of Normal mode (I.e. what the plunger does when it moves).

[a387673]

Talking more than I'm thinking here...... Obviously, malfunction of the prime start could have various impacts...... (scratches head again). You mentioned the fuel pump, 99. I loosened the mounting screws, and although I did not catch any fuel coming from the port to the crankcase, fuel did appear to come from the mounting screw holes. Is this normal, and with pump mounted, might this allow fuel into the crankcase as you suggested?

[a387673]

Clarification; I loosened the mounting BOLTS, the screws that hold the fuel pump together were not touched, but fuel leaked from somewhere, apparently the mounting bolt holes...... I think I'm talking myself into it. That has to be abnormal, right?

[a387673]

99, I owe you a beer, for remote diagnostics in addition to the prime start diagrams., It was the fuel pump. In retrospect, there aren't too many things that could increase fuel consumption from 3 GPH to 8 GPH. Thanks for the help.

And thanks, Panasonic, for the link. I looked, but knew I was in the wrong place when he started working on that motor in the water. I like to drop stuff when I work.

[99yam40]

99, I owe you a beer, for remote diagnostics in addition to the prime start diagrams., It was the fuel pump. In retrospect, there aren't too many things that could increase fuel consumption from 3 GPH to 8 GPH. Thanks for the help.

And thanks, Panasonic, for the link. I looked, but knew I was in the wrong place when he started working on that motor in the water. I like to drop stuff when I work.

Good you found a problem that might fix your motor,
I did all that when I got my C40TLRX and could not find any info on how it functioned, glad it helped you some