Bike running way too rich, fouling plugs

[Joe02151]

All of my idle mixture screws are missing the o rings washers and springs. My bike runs extremely rich, 25-30mpg. Would air flowing past the idle mix screws create a lean or rich mixture? (All mixture screw tips are intact and not broken)

[yamtom]

are you talking early or late carbs

Edit, I see now that you have an 80, so it should be the late carbs which are the ones I have springs material for. There is unlikely to be substantial air flowing past screws, the spring is there to hold the mix screw in place. The other items should be obvious, you may be able to find those tiny o rings locally, the springs, I found at a hardware store and cut them down. I have lots of material left if what you have are the later carbs, I can cut four for you for the price of shipping. The tiny washers, I dont know a source other than oem and you may play heck getting them. You may find someone on the list has extra parts for this. I would assume that without orings and springs, that your screws are backing out, and creating the rich mixture .

[BowlingSS]

I bought four sets of the idle mixture screws and they came with the washer/o-ring and spring. MikeXS and a few others have them.

Bill

[MPittma100]

Too Rich

Yamaha designed these bikes to run lean.

Rich condition can be caused by - wrong main and/or pilot jets, float level adjustment too high (in the bowl), needle clip lower than stock setting (1978-1979 carbs only), and using non-Mikuni jets and float valves. The missing parts on the mixture screws can affect the performance. Try replacing the missing parts and sync carbs first. If that does not work, you will need to check/adjust all of the above. Plug color will verify proper carb setup. Mileage should be 35-40.

Check your oil for gasoline contamination. Verify that petcocks are not leaking.

Proper plug color: