Skorpion 660 Lightweight Build

[jpmsteadi]

jpmsteadi

Thanks for the documentation and keep it coming.

two shock question - your riding weight (in lbs) and did you check static sag? Static sag on my CBR1000RR shock conversion is about 3/4-inch

I weight about 145-150.

The static sag is the 1.5" ish, measured at the axle to the rear subframe. The free sag is basiclly nothing. maybe .25"

[droy]

Well I have you by 60 lbs so that stock R6 spring makes more sense. Glad I'm not racing you!!

[jpmsteadi]

Well I have you by 60 lbs so that stock R6 spring makes more sense. Glad I'm not racing you!!

Interestingly enough the spring that came on my R6 shock from ebay is actually a less stiff racetech spring, only 8.9 KG/mm (stock R6 is 10.5 kg/mm)

[jpmsteadi]

A carb update:

Just to those following along (and if some other crazy fool attempts this in the future), I started with this jetting:

155 Main
EMR needle 4th from bottom (middle) position with shim
40 pilot
35 leak
200 main air
100 pilot air
35 leak jet

Initially I was having a bit of a lean spot right off idle, say 1/16 to just under 1/4 throttle. I have progressively gone up in needle root diameters to as rich as I have and its very ride-able (and is much better when the bike is nice and warm), but the spot still exists slightly. On my most recent ride I am running:

155 Main
EMM needle 3rd from bottom
35 pilot
200 main air
100 pilot air
35 leak jet

In jumping to that much larger of a root diameter, my idle has gotten really rich. I have gone to the smallest pilot jet they make for the FCR and I still can't get the bike to die using the idle mixture screw. My theory is that I have entered into a loop of trying to get more fuel in that very light throttle and perhaps went down the wrong route. Since the bike is very ride-able in its current jetting I think I am going to not fuss with it much more until I get the wideband O2 sensor installed. I am going to try a 50 leak jet. The 35 seems way too small (on the leak jet the smaller number results in a larger longer squirt from the accelerator pump). The 35 can apparently cause some fuel dribble out of the AP on slower roll-on throttles. I can certainly feel a bit of ok, then lean on that initial roll into the lean spot. I want to isolate it better if I can. Man fuel injection is so much more precise!

When I took the carb off though I noticed that the PETG adapter I had made was looking worse for the wear. It seems I over-tightened the clamp on the head side of the carb boot and crunched it slightly. I took the opportunity to redesign the adapter to match the grizzly manifold better. I also had problems with my printer which required some service on that, but that is for a different forum!

Anyway, got the printer up and running and printed up the new adapter. It has two locating notches to ensure it goes on the correct orientation, is a better slight press-fit, and has a shoulder inside that mates to the front of the grizzly manifold and matches the contour pretty good. hopefully will make the intake track a bit smoother.

[jpmsteadi]

A quick update. I put in the 50 leak jet and went for a decently long ride (about 20 miles or so). No negative effects at all. Maybe even a little snappier on the throttle. really pleased with how it runs, except for that lean spot. I know i said in the post above that I wasn't gonna mess with the jetting until I got the wideband, but..... I am probably gonna keep playing. It is fun after all.....

[breakwellmz]

Sounds good despite all the possible permutations of Main, pilot, needle and leak! Does it have two main jets?!
Makes me realise how lucky i got, all i`ve done is shim my needle!

[jpmsteadi]

Sounds good despite all the possible permutations of Main, pilot, needle and leak! Does it have two main jets?!
Makes me realise how lucky i got, all i`ve done is shim my needle!

The FCR has a ton of tuning options. There are air circuits for the pilot jet and main jet that allow you to tune kinda an air bypass that can adjust how much fuel get delivered based on RPM, not load. if you have the mixture right at low rpm, and it's too rich at high rpm, the air jet is too small. Or if you have it just right at high rpm and it's too lean at low rpm, you have an air jet that's too small and you need a bigger one. The converse is true as well. (source: http://www.factorypro.com/tech/tech_tun ... s,Pat.html) This allows you to further fine tune the fuel delivery. A really clever system, but WAY more things to adjust. On the 39mm FCR-MX (at least the specific model I have on my bike) the Main Air jet is built into the casting at 200. No way to change it. But the pilot air jet is adjustable.

If you get all the parameters right, the result is an incredibly smooth throttle with instantaneous response to large changes. Pretty fantastic. In fact the well tuned FCR i have ridden beats most of the FI bikes I have ridden (save for modern Triumphs, they are doing fuel injection right). Obviously I understand that someone putting a nicer pumper carb on their bike doesn't have emissions to deal with and that is what causes the OEM fuel injection to be so jerky at times. But still. Properly set up, its a pretty fantastic solution.

[jpmsteadi]

First off, I am double posting like crazy, but hopefully someone finds this interesting enough for me to keep posting.

I installed the KTM thermostat today. WAY simpler than I though it would be. If you buy one from ebay that includes the hoses and the t-joint it ends up almost being a plug and play solution. One of the KTM hoses is the perfect size to go from the head to the thermostat, but alas it had a tiny hole in it. Thankfully the MZ hose also fit perfectly. The stock MZ hose from the thermostat to the radiator fits. And the KTM bypass hose from the thermostat to the t-junction is the perfect size for the MZ.

I cut the t-junction piece's flange off, leaving just enough of a shoulder to act as a flare (Make sure you deburr and sand this down, don't want to develop small cuts in the hose). I used the extra KTM hose as the piece from the bottom of the radiator to the t-junction and the t-junction to the water pump inlet.

Put the coolant in, making sure to give all the hoses a healthy squeeze or two and rock the bike back and forth, getting as much air as I could out of it. I have had good luck with this method, especially on bikes like this one where the overflow tank is the highest point in the system.

I fired it up and went for a small ride around the block, then parked it in my driveway. The KTM thermostat should start to open at 185 and be completely open by 205, according to the internet forums about the 390 Duke. I have my fan set to come on at 195. I used a laser temp gauge to see what the relative temps between the radiator inlet (the closest metal piece to the thermostat outlet) and the t-junction (the closest metal piece to the head outlet). As the engine heated up the temp sensor on the fan slowly increased, then jumped quickly up (as it should when the thermostat opens). The temp hit 195, fan kicked on, the temp spiked at 196.5, then very quickly (within 30 sec) dropped to 189, shutting the fan off.

To me this is indicating that A) the system is working as it should, B) the radiator/fan/thermostat system is probably over-sized for the motor (which is not a bad thing), and C) that this experiment was a success!!!


I rode around some more once it was hot and happy and noticed that the lean spot right off idle had gotten MUCH better. This is what I was hoping for: a more consistent, higher temp in the engine allows you to get more efficient combustion and allow you to get the same air/fuel ratio with less fuel. I am still going to play with the jets and get it perfect, but I am very happy with how this turned out. If anyone is keen to follow my lead the parts are off of a 2018-2019 KTM 390 DUKE. Make sure you get the thermostat, hoses, and t-junction pipe. I got mine for 32 bucks after shipping and tax on ebay.

[jpmsteadi]

Here is one more picture closer of where the thermostat ends up.

Initially I was thinking I would need to build or 3d print a bracket for it, but it seems to be very well held in by the hoses, the oil return line from the head, and the clutch cable.

[breakwellmz]

RESULT!!
Now why couldn`t have MZ/Yamaha have made things easier by using the Rhino/Grizzly head with a built-in, car type thermostat? (extreme left of photo below)

[jpmsteadi]

Indeed that would have made things easier!!


A couple of days ago I put some tape on the throttle tube and marked out where 1/4, 1/2, 3/4 and full throttle is. On riding it around more I noticed that what I though was very very light throttle for the lean spot was in fact about 1/4 throttle. Since I got the cooling system dialed in yesterday I decided this morning to go back to basically base jetting and adjust from there. The one thing I did was pull the needle up more in order to richen that 1/4 throttle area (as opposed to increasing the diameter, which is how I had been adjusting).

I went for a ride with the following jetting:

155 Main
40 pilot
EMP needle second clip from the bottom
50 leak
200 main air
100 pilot air

MAN it is so much better. super smooth. just the tiniest of lean spots right off idle. like 1/16 to 1/8 throttle. I came back in and went to an EMN needle I had (going one size smaller on the diameter, just slightly richer in that 1/8 throttle range). Went on another ride. It is near perfect now. So smooth and lovely. easy to cruise around at very light throttle, but plenty of power there if you wanna rev it out.

[breakwellmz]

It just gets better and better performance-wise then, great! It almost justifies the cost of one!
I`m surprised your thermostat mod makes a noticeable difference to how it runs, i had always assumed a thermostat was purely a means of getting an engine up to an efficient running temperature quickly from cold and once it had it was pretty well redundant, obviously not.
It occurred to me that if the Grizzly head that the single carb manifold comes off doesn`t have a cross-link port between the two main inlet ports (and there is no reason why it should) that said port would be better being filled in when using a single carb on an MZ head.

[jpmsteadi]

I think it totally justifies the cost. The thermostat and FCR and manifold I'm only in for about 275. Not too bad really. I'd obviously wait til I get done: let me make the mistakes! But so far I think it's worth it.

I'm curious as to the purpose of the port and what it does. Perhaps closing it off helps intake velocity at higher rpm? A straighter shot? Could be interesting to play with.

[breakwellmz]

Hi.

I meant the cost of a NEW FCR, have you seen how much they are?!!
In the original twin carb setup that port feeds charge to the two right-side valves at small throttle openings when only the small (LH) carb is open.
With the way i have my LH port blanked off that `transfer`port does allow some charge to the LH valve albeit in a limited and tortuous route!
If the single carb Grizzly/Rhino head doesn`t have that port there is a good argument for blanking it off (JB Weld`putty`?) in your setup i would have thought.

[jpmsteadi]

Oh yeah, no way I would buy a new one, they are crazy expensive. But very easy to find on ebay. And if you don't mind a little overrun popping (It has been less that I thought it would), you can pick up a 37mm FCR for even cheaper (that is what the other body I am using while I fix the worn one is; it doesn't have the air cut valve that adds fuel where there is massive vacuum, like in overrun senarios).

The best bet (in my opinion) is the Yamaha WR450F carb from 2003-2006, but the 37mm can be found on the WR250. Basically the same carb minus the air cut valve and a slightly smaller venturi bore size. Check out http://mxrob.com/mxrob_007.htm for more info on the various carbs and converting them. that site is dedicated to the DR650, but the concepts all roll over.

There are also a bunch of cheap Chinese copy carbs on ebay now. No idea how good they are, but could be interesting. They seem cheap.




That makes a ton of sense re: the port. Probably makes sense to jbweld it off, then polish it somewhat smooth. maybe I will do that when I make the final intake adapter.