C40TLRY Carb sync

[underdog378]

Hello,
I have a new to me 2000 Yamaha 40hp 2 stroke model C40TLRY that I just picked up. It starts great and runs well but has a bit of an intermittent lean sneeze at idle on the muffs. I pulled the carbs off to clean and they looked spotless, I still gave them a cleaning and reinstalled the carbs. My question is in regards to the sync of the carbs. The service manual is a little too vague for me and doesn't match up with other things I've read online. I have the 3 linkage screws that can be loosened by turning clockwise. I have the idle screw backed off completely and without the linkage rod that connects the 3 (broke mine and waiting for new to arrive), the top 2 carbs are completely closed, but the bottom carb plate is cracked open due to the bushing resting against the cam. I attached a picture showing what I'm talking about. If I am to truly sync the 3 plates I am going to need to also loosen the linkage screw for the bottom carb so that bottom plate can fully close, correct? This is my thought process going forward: If all three linkage screws are loose with the linkage rod attached, make sure all 3 plates are closed, tighten linkage screws with bottom carb bushing resting against the cam. Once I adjust the idle with the idle screw, that bushing will be slightly lifted off the cam, should that be the case, or should that linkage be touching the cam at idle, which is how it was before? I know someone has messed with it before, because the linkage screw is marked up from a mis sized screwdriver, so I don't trust that it was done correctly before. My plan was to also reset the pilot screws at 1 1/2 turns out per the manual, and start from scratch there with the resynched carbs, currently the top 2 are 1 3/4 turns out and the bottom carb is 1 1/4 turn out. Appreciate any help, thanks!

[99yam40]

yes you are correct, all 3 need to be close exactly the same.
cam should not be touching when at idle.
make sure the timing is all correct also.
check with a timing light, not just the linkage marks

[underdog378]

Thanks 99yam40. I found a post of yours just recently on another forum that discussed the same issue I had with the service manual and it was very helpful as well.

[underdog378]

Carb clean, resync, and resetting the pilot screws to factory spec and the lean sneeze is gone.

[99yam40]

good to hear it is running as it should.
thanks for giving a final report on it being fixed

[underdog378]

Well it was too good to be true. Running on the muffs was ok but running in the water it is idling rough and frequently stalling when going into gear even with idle set to 850 RPM. Took apart the fuel filter and found grit/crap in the filter both before and after the screen, so I believe my low speed jets are likely clogged again. Runs fantastic off idle. I do have a 10 micron fuel/water separator installed after the tank, so not sure if I missed this before or its coming from somewhere else in the fuel system. Plan now is to re-clean carbs and replace fuel lines, primer bulb, fuel/water separator filter, and drain/clean tank. There was a little junk I could see in the tank but I would think anything that made it through the pickup tube would have been caught by the fuel/water separator.

IMG_20210323_164704.jpg

[TownsendsFJR1300]

I've seen fuel lines (fuel tank to engine) break down from E fuel.

Might want to inspect or replace them.


.

[99yam40]

stuff can hide in the pump and lines,
but the filters should catch it.
I do not remember doing it before, but pulling a piece of white cloth thru the individual pieces of tubing with a string should wipe them out well and show if they are shedding. Mono fishing line should stiff enough to push thru and then tie to a piece of cloth to pull .
could use some seafoam to soak the cloth also.

final adjustment of the carbs should be with lower unit submerged as deep as it would normally sit with boat in the water (Causes some back pressure on the exhaust)

[underdog378]

I've owned the boat about a year and the Evinrude that was on it previously gave up the ghost early this year. I don't know the history of the fuel lines or related fuel components, so I'm doing a major overhaul on the whole fuel system. The Evinrude had oil injection and the final diagnosis on that motor was some sort of oiling failure with 60+% leakdown and scored cylinder walls.

I had adjusted my idle when I was in the water but was having trouble with stalling either in gear at idle or when the CDI would drop the RPM after it's warmup high idle. Other things noticed with fuel system is the generic quick disconnect that was installed on the fuel line would disconnect itself from the outboard and never felt secure on install. Possibly contributing to the issues also. That's getting replaced with a new oem connector as well. I've had quite the run of bad luck with this boat the past few months hoping I can get it squared away without another visit to the shop or further loss of my sanity. I'll update after the parts are here and installed.

[99yam40]

have you checked timing with a timing light to verify it is in spec?

[underdog378]

I have not yet, I will verify when I get it put back together.