Skorpion 660 Lightweight Build

[breakwellmz]

Nice!
You could have at least had the drawing square to the photo frame it`s making my neck ache!

[jpmsteadi]

haha, sorry! Didn't even think about that

[jpmsteadi]

I took the exhaust off yesterday in order to weld the O2 sensor bung on and, while I am at it, grind the welds down on at the head. They are quite large on this exhaust. It is a common thing to do on the DR650, so I can't imagine it would hurt this engine breathing at all.

I am still pretty new at TIG welding, but I am decently happy with how this weld turned out!

Hopefully I will get the gauge attached and wired in today.

My plan is to polish the exhaust while it is off too.

[breakwellmz]

Too modest!
To a former TIG welder of stainless medical equipment that looks fine to me and a good polish will improve things as well.
Can`t really see the from your photo what you intend to grind down, but i have heard others say the same.

[Puffs]

In my layman judgement your weld looks fine & would not require any rework.

The sleeve that enters into the head is welded onto the header pipe on the inside and can obstruct flow; file it down. Indeed I vaguely remember something like that on my DR600 a while back.

[jpmsteadi]

There is a weld that attaches the header to the mating surface that nests in the head. It is hard to see with the carbon buildup, but it is clearly in the 3/8" tall world. Not an insignificant amount of obstruction.

And thanks for the kind words on the weld. Its been a fun thing to learn how to do! when I get proficient enough at doing it and have some aluminum practice under my belt I am going to try and do a new rear subframe in aluminum.

[breakwellmz]

When i looked again after my eyes had woken up i could see the weld you want to grind down, quite an obstruction isn`t it.
Don`t get too cocky on the TIG welding yet, thin gauge aluminium is another step on!
(I notice you wrote aluminium not aluminum despite being in the USA?)

[Puffs]

While alu has a lower specific gravity than steel (lighter per unit volume), it is also less strong, so you need more of it. Some frame builders (KTM) swear by sticking to tubular steel, but currently the majority indeed prefers alu. For instance the 2020 Kalex Moto2 frame:
Suter:
For comparison the 2018 KTM Moto2 one:
Which was quite competitive too.

I guess what I'm saying is that replacing steel by alu may not reduce the weight by much.
But for the subframe CF could also be considered; that should give a genuine weight saving. But it is very labour intense, and yet another totally different technique...

[jpmsteadi]

for sure well designed steel (especially chromoly) can be very light. I feel like after taking the subframe off, it is quite heavy, even for what is supports. I will design it in cad and do some basic stress analysis before I try and attempt anything. And for sure welding aluminum is way harder. Thats a ways down the line. I don't want to have TOO many projects going at one time!

[jpmsteadi]

I fitted the exhaust back on this morning after grinding down the head welds:

In order to get the O2 sensor into the right position relative to the airflow I had to modify a sparkplug defouler (which is commonly used to trick OBD-II systems into passing emissions, illegally). Thankfully my application was legal. I drilled the center out to 15mm (the diameter of the O2 sensor is 14.88) and took 3.5mm off the top if the hex section. the mill coming in handy once again.

[jpmsteadi]

The O2 gauge is held onto the handlebars by a 3d printed 7/8" clamp. I built a overly long harness for it as this will not be a permanent installation and I would like for it to be easily adapted to another motorcycle (this O2 setup is actually my friends, but he is letting me borrow it)

The connector for the actual sensor is huge. looks a bit funny on a motorcycle.

[jpmsteadi]

Just went for a little ride around the block. I am running SO RICH everywhere but idle. Full throttle is somewhere between 9.9-10.5 and part throttle doesn't get above 10.8 or so. Idle is right around 12.8-13.9, not too bad. I want to start fiddling around with the jetting BUT:

I was riding around the other day and got caught in the rain. on the way home about a mile from home the bike shut off and didn't want to restart. Was backfiring like crazy and not even idling. I though, maybe something got wet so I let it dry out for about four days while I worked on the exhaust.

Today it started up cold perfectly, rode for about 10 mins, then it did the same thing. trying to start it even with giving some throttle just made it angry, seeming like it was missing every other thump or so. I pulled the plug and while it does look like I have been running rich, it doesn't seem to be fouled. My thoughts go to an electrical problem, but I am trying to think what would give that issue only once hot. Any thoughts?

and yes, I am going to put back on the fenders. haha

[jpmsteadi]

So the new plug helped the low speed hesitation, but did not cure the current problem. bike ran great until it got up to temp, about 6 mins this time and the problem happened again. Looking at the AFR gauge when its happening, it seems like its just slowly going lean/not combusting (a misfire also looks like a lean mixture since the oxygen is still present). I felt the coil and it seemed not too hot, but playing with the connections on it seemed to help temporarily. I have replaced those spade connectors once before when they were slipping off, but I will inspect them again.

I have the nicer CDI ignition system coming from bill in germany, but the package tracking says that it is held up in NY right now for some reason. It, along with the new rectifier, will essentially just have a new electronics system.

Also when I installed the new plug I went back to the base level jetting (40, 155, EMR needle at clip 5 from bottom) and the AFR readings were better. I can still go leaner, which is interesting. But I don't really want to keep pushing the bike home, haha

[Puffs]

That's right, focus on your priorities & get those done first.

Thanks for keeping us posted, and I hope you get it adjusted & running well soon. Bike pushing is good exercise, but so is riding it!

[jpmsteadi]

Indeed. I am going to try and get those done first.

I think the coil is going bad. That is what all the symptoms are looking towards. I think it is just going to be put on the back burner until the parts from Bill come in. Hopefully the USPS won't take too much longer!