Emulsion Tube/Flat spot

[jasonm.]

Having both an '82 and '83. I have only done a few jetting changes. The '82 has 135 pilot airs + front '83 pipes on it along with a 127.5 main in front. It goes just like my '83 up to 8500rpm. But the '83 having bigger carbs goes past 10k with ease in 4th gear. Where the '82 just takes a little longer to get to 10k. I have been messing(changing jets) with the '83 lately since my pilot gas jets got partially clogged. Prior to this I changed the pilot airs on the '83 to 135's from OEM 140's. Which eliminated all stumbles @4500rpm and below. The '82 has big pilot gas jets. You cannot buy any bigger. If not set up right the stumble on an '82 is caused by being too rich @ 4500rpm. That is why 135 pilot airs help. Hope to have the '83 tested this weekend.

[Lucky]

I have been messing(changing jets) with the '83 lately since my pilot gas jets got partially clogged.

You know, I doubt there is anyone here who doesn't know to install a fuel filter, and we still get grit in the jets. Of course some of this is probably due to the age of the aluminum bowls themselves, but we really need to investigate a better fuel filter too.
--Lucky

[rick_nowak]

been away for most of the summer but am now catching up with the board.  Re emulsion tube modification, my mechanic at Sturgis yamaha, who is also a car mechanic was thinking along the same lines.  it took 3 hits of slight modification of the tubes, drilling holes larger one number drill step at a time to make the stumble go away until on the last set of drilling it went too far and we had to solder shut and re-drill.  it got too lean.  he also says that the float level setting is really important.
remember, these are essentially car carburetors in design and need to be thought of in that way.  we don't have needle shape and position and cutaways to mess with.  as to why this method was not suggested by yamaha engineers i submit that each bike responds differently and no dealer wants to do four or five hits at solving a problem and yamaha does not want to pay for this many hits.
as to the rude comment about weber carbs being pieces of crap (or some variation), the writer knows very well that the dco and ida series of carbs were carefully optomised for each particular application and, all other specs being correct, cars equipped with factory supplied webers work really well.  the problem is that ignorant tinkerers think carbs are crude instruments not well set up from the factory.  When weber dco and ida series carbs were popular the ignition systems of the cars they came on were not particularly reliable or durable (remember points?) and the ignition caused all sorts of issues that were attributed to the carbs, and since these carbs are easy to tinker with, by design, they were tinkered with.  usually getting them further and further away from optimum.  they are essentially racing carbs, used on engines with high specific outputs.  Alfa Romeo, Ferrari, Maserati, and Lotus come to mind, and until the advent of readily available fuel injection, they were the instruments of choice in almost all racing engines except American v-8's.