Sunday 8 October 2023

Dre-XT-Stück - head(er)s or tails

Let's assume you have a bike that is working (moderately) fine and it even has a stainless steel aftermarket header installed. What would you do? Obviously you would leave it the hell alone, especially as there are plenty of other issues that have to be tackled in other areas. But as the TT600 header will not bend the headstuds (as much) and is generally a lot nicer... Also I put the port for the wideband AFR probe at a very vertical angle, which is good for the wideband sensor, but bad for my right leg as the plug will touch my leg ever so slightly. 

With all that in mind I marked a good/better location for the port.

What followed next is probably best described with it being the equivalent of a frontal assault on the castle gate, but with step drills and a die grinder. In short, on large diameter tubing this would quite literally just be a job of poking a relatively round hole and call it a day, but on this comparatively small diameter, it's more of an oval than anything else. Then again, if the hole is somewhat neat, welding is an absolute breeze. 

Admittedly cheating a bit, with pulsed TIG welding here to limit heat input and using the plug as an additional heat sink, but that came out lovely.

With the exhaust back in place, I reinstalled the plug with PLENTY of copper grease, just to be sure it wouldn't seize in the bung. 

... and with the wideband installed just to check fitment. Bit difficult to get it started, but once it is in, it's in. 

With the sensor installed, it would be kind of rude to not put it through its paces and check the AFR-values with the current setup (stock exhaust). Yes, compared to a modern EFI bike the XT is running a tad on the rich side, but this is also in part to help with internal cooling. (One can jet it leaner, but will then have to face the thermal consequences.)

Idle - starts great with it being slightly on the rich side, after rejetting lately, high 11s appears to be the sweet spot for brilliant hot and cold starting.

Approx. 1/4 turn on the throttle "running on the needle" as the old-timers would say - going lean here helps with fuel economy as this is actually where you end up most of the time when riding on the road.

Probably 1/3 to 1/2 throttle - the dip towards lean is a bit of an oddity that is necessary on XT600s, because up to roughly this point you only run on the left (slider) carb. If you jet it richer, you will have one hell of a time once the second carb opens.

Wide open throttle - aiming for 12:1, which is on the rich side, but again the Dre-XT-Stück is based on a 43F and thus has no oil-cooler, so jetting it on the rich side is mandatory to avoid big problems, when I have my moments and want to see how much she can do.

 In the not too distant future a very similar post will come up, as the AFR values shown here were photographed, when the ignition was playing up REALLY bad and thus the last four paragraphs you just read are technically worthless, as I jetted a bike with an ignition that was running without any ignition advance. 😛

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