Monday, 5 June 2017

The Dre-XT-Stück - first tweaking of the carbs

As some might have guess, with the upcoming sale of Ms. Braaaap (my XT500) I needed something else as a substitute. Well, my dad wasn't entirely happy with the Dre-XT-Stück and I wanted something cheap 'n' cheerful and a bit more modern than a XT500. So a deal was struck, I'll take the Dre-XT-Stück off my dad's hands for the price he paid, fix his other XT500-4-valve, which is smoking like mad and everybody (in theory) should be happy again.

The Dre-XT-Stück suffers from a few issues, the most pressing one is some rather unpleasant cutting out when cruising at part-throttle to almost full-throttle starting at 4000 rpm.  Unfortunately this one is the 500cc equivalent of the very first XT600-model, a so-called type 43F. This in itself isn't the unpleasant part, but the fact that Yamaha changed the Teikei-carb a bit and not all of the carb-jets are available anymore for this version. Especially the mainjet of the secondary is no longer available.

I tried playing around with the mainjets first, as the one fitted to the carb isn't marked and looks a bit like someone already messed around with it. So I swapped it for a #124 Hitachi mainjet, which remedied the cutting out quite dramatically and limited it to a small rev-range between 4000 and 4500rpm. Unfortunately it also seems to run out of puff at around 110kph or 6000 rpm.

Mainjets (for the main-carb) are also a bit hard(er) to come by, so I was looking for alternatives and whether I may have some other mainjets that would fit.

The original Teikei mainjet on the left, Hitachi in the middle and Keihin on the right. All of them are a DIN M5 thread and are interchangeable. Even though the hex on the Teikei jets makes it considerably easier to change the jet.

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