Need Help! Carburetor jet and adjustment Yamaha 2000, F100TXRY

[arubanjames]

I am hoping someone here is able and willing to give me some assistance.

I have a 1985, 18’ Boston Whaler outrage. I bought 14 years ago it was a little rough but usable. The 2000 Yamaha F100TXRY (good compression and still does) had an idle sneeze and stumbled through the mid range, you had to massage the throttle or it would stall. But it ALWAYS started and ran WOT great! It has NEVER let us down!

When I first got it I had no idea how to clean a carb, so a marine mechanic buddy helped me, it ran a little better, and was usable for years. The I had to have them cleaned by another friend and this time I watched and then later successfully did it myself. Now I have done it a few times.

Then I decide to buy a balancer and try to balance the carbs, I am successful, but it wants to sound the overheat, so I get the meat thermometer from the kitchen and dial them into the safe zone that way. I had 2 great summers after that.

Then I could only get it to idle. It would just stall with any throttle (I just realize it may have been a tiny hole in the fuel pump diaphragm so they are on order now) So I bought an ultrasonic, and I had to replace a striped idle jet for the first time. I made the “mistake” of taking all the jets out and putting them in a jar together to clean. While all 4 carb bodies were cleaning.

Now I have all the jets and floats mixed up. Then I saw somewhere that the jets and floats might be matched to the different carbs depending on placement? And I’m wondering if before I got it they may have been mixed up? And that could have been part of the problem all along.

I can no longer read the writing on the jets, so do I need to order new ones? On the Crowley marine websight they only show one idle jet part number. But when the new one arrived it visibly looks smaller. Do I need to order a gauge? Do I want all four the same? Or small at the top and going bigger toward the bottom? Any help is appreciated!

Oh, and with the plugs out the sneeze looks like an intake valve is not seating, with the carbs off lots of carbon. So if I can get it running I have (illegal) Dealer only Yamaha Ring Free, to run in it.

Thank you!!!!

 

[99yam40]

the parts breakdown for that motor says all 4 main jets are the same (#128) and the needle jets are the same and the #42 jets are the same.
if you stripped a pilot screw, there is a good chance the seat that pilot screw seats into is messed up also.
there is a reason they say to lightly seat that screw and then back out to spec

being 4 stroke motor I would think there should be specs on valve lash. make sure all of them are

did you check spark timing to make sure it is in spec at idle and at WOT
if firing when intake valves are open maybe cam timing is off or spark timing

I have seen where someone drilled out jets to get more fuel into the motor before.
so see if you can find some way to measure the old and new jets

I have no idea what you dialed in for temperature safe zone

 

[arubanjames]

Thank you! To clarify the previous owner/mechanic, striped the flat head slot on the #42 jet (parts diagram just says “jet” I was calling that the idle jet because it is so small) I sharpened the head of the correct size flathead screwdriver and gently tapped it in and luckily got it to back out. That is the part I replaced, the threads are good there.

I believe that jet should be turned down snug. Which is what I do. The air fuel screws that turn down to closed then back out to spec, then hey have brass plugs over them and I do not want to drill those plugs out. (Or so I have been told).

The screws I adjusted to “dial in the overheat” are the 4 adjustment screws, with yellow lock-tight on them. They have a small spring to keep pressure. The screws on the bottom carb moves the linkage to all four, then the top three carbs each have their own adjustment. It is the only screw I know of that is for adjustment?

I am going to order 3 more new “idle jets” and 4 main jets. Just for the sake of continuity.

I will have to do some research on how to check/set valve lash. And I bought a timing gun last time to try and check that, but wasn’t confident I was doing that right. And I got it running as good or better then it had run in my ownership, so I just went with it.

This motor does have about 1800 hours on it now. 500 being in my care. So I can’t really justify taking it to a mechanic for a $1200 carb adjustment. When this gets to where I am forced to give up on it I will likely sell it as a whole motor and look for a slightly newer motor that is fuel injected with lower hours.

Thank you for any input anyone/everyone for me this motor is a journey of learning.