Idle speculation....

[John Park]

The last few tanks of gas, my mileage has dropped about 10% and getting worse, while the idle seemed to be slow and erratic, and the off idle seemed rough. All other vital signs were good and the power was normal.

It finally got to where it just wouldn't hold an idle , so I pulled the carbs. They haven't been off a for maybe 20,000 miles so it was time anyway. The bowls had some trinkets and the seats had some more on the screens but all was well. When I removed the idle jets, one was maybe a half turn out and the other was coming loose.

I've never had idle jets walk out of carbs before, but it's easy to see how things would get rich if the jet wasn't hard down on its seat. I tightened them up a little harder than I usually do. It's back to running sweet again.

Anyone have the same experience? Fixes?

[Steve]

Fixes?

Get a four-cylinder bike that doesn't vibrate as much?

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[John Park]

Get a four-cylinder bike that doesn't vibrate as much?

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Actually, with the counterbalance shaft, the thing thinks it's a V4 and vibrates maybe less than the big 4s. However, you do spend a lot more time over 6K where the secondary tingles buzz the mirrors. It's pretty similar to a 550 for vibes, which makes sense.

Now that I know the symptoms, I don't mind dong a carb service every 20K or so, especially when there's only two and easy to remove. BTW, mine has rubber tipped float needles, unsprung, which seems atypical. They may be aftermarket or Yamaha items as the thing was a frequent flyer at a Yamaha shop with the PO.