Skorpion 660 Lightweight Build

[jpmsteadi]

I rode around a bunch yesterday and noticed two things on the jetting:

1) when riding with very light throttle then stabbing into more than 1/2 throttle, there is a instantaneous power hit, then it fades into less power.

2) when heavy on the throttle, then dropping the throttle back to about 1/2 or just under, there is a little buck where it feels as though the bike is stumbling for a second.

To me this would indicate that the motor wants more fuel in that upper region. Obviously this area is harder to tune than the lower steady state places and will be much easier to deal with once the tig welder comes in and I install the o2 sensor. But in order to keep making small progress in the meantime I will play with the jetting. This morning I changed the main jet from a 155 to a 160. The first observation seems to have gone away, but the second remains. Any thoughts on this would be greatly appreciated.

In tuning the higher end of the throttle and the rev range it is a bit hard as the adapter plate is still acting as a restriction on the air flow. I don't have a tach on it, but the engine really runs out of steam a bit before it hits the rev limiter, whereas before it would run into it while still building. Considering the fact that this intake tract is a temporary one, I am not sure how much good getting the tuning perfect is. Nor if its worth the time. I think one of the first things I will try and make when the lathe gets in is the adapter with proper spacing for the intakes.

[breakwellmz]

Hi.

Sort the inlet tract out and adjust carb to suit is the way i would go, it`s bound to have an effect on your (now) almost perfectly jetted carb.

Talking of which i`ve been tinkering........

I cut and filed the inlet side of my Grizzly manifold parallel to the mounting plate opposite.
I found a section of 16g stainless tube that can be set into the manifold with a bit of machining and `hand work`, pinned and bonded.
This would allow a flexible rubber manifold to join it to carb. --

[jpmsteadi]

That looks great! a good idea grinding it flat. I'm gonna have to figure out how I want to do it, but that makes a lot of sense.

[Puffs]

Glueing an alu alloy & SS may be difficult: different thermal expansion. Keep a close eye on it.

[breakwellmz]

Hi Puffs.
I don`t see the inlet manifold seeing enough variation in temperature to worry about the bond failing personally, its always got a cooling charge running inside, it could get pretty hot after shutdown i suppose.
I offered the Grizzly manifold up to head on the Mastiff earlier. I`ve decided there just isn`t the space to utilise it within the frame with where the carb should be, there is SO much more room on the Skorpion.
I have been tinkering though.....
Now, what to do with that `transfer`port in the head?









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[jpmsteadi]

Hi Puffs.
I don`t see the inlet manifold seeing enough variation in temperature to worry about the bond failing personally, its always got a cooling charge running inside, it could get pretty hot after shutdown i suppose.
I offered the Grizzly manifold up to head on the Mastiff earlier. I`ve decided there just isn`t the space to utilise it within the frame with where the carb should be, there is SO much more room on the Skorpion.
I have been tinkering though.....
Now, what to do with that `transfer`port in the head?

An interesting idea, but I can't imagine that would flow very much air very well. No idea how it will work, but perhaps you can use some sort of bent intake tract around the frame member? I don't know the design of the Mastiff.





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[DAVID THOMPSON]

what is the outside size of that copper tube between the two Yamaha intake boots
Dave


and is the copper plug in the plugged side a soft plug for a car motor ??
by chance
or a solder on cap for plumbing pipe.

which needle in the carb did you put the shims on how many and how thick
and what slot is the clip located

i work both in inches and MM my dad was a machine shop guy and was his go to guy for MM
when he was scratching his head over size conversion

[breakwellmz]

Hi Guys.

Puffs - I recently added a link tube(rubber) between the RH rubber manifold and LH blanking plate, the ID was only about 9.5mm (3/8") and it wasn`t very direct.
With the engine running the rubber tube collapsed from the internal vacuum so i added a stiffening spring to hold it open.
It made me realise that even with the `transfer` port within the head the LH port still has a huge amount of demand and that any extra relief on that has got to be beneficial.
So what you see here is version 2.

David - That`s 15mm copper tube(Domestic plumbing) with a 1/2mm(0.020") wall.
The copper plug i cut from a piece of 1/8" copper plate a had. I have no idea what the brass fitting is, i found it in my plumbing bits box and it was a perfect fit in the Yamaha manifold.
The slide needle had 828 stamped on it (means nothing to me!) and was non adjustable (No grooves or clip) I added M4 (?) washers to raise the needle (one at a time) until i eliminated the `stumble` when opening from idle jet to needle jet.

[DAVID THOMPSON]

Thanks will keep you updated but mine may take a while there is no air conditioner in the shop
so i have to work on projects there at night
thanks Dave

[jpmsteadi]

A bit of an update: the mill came in!! the first project I did the day I got it was the new dogbones for the MZ. Not the prettiest thing in the world, but is dimensionally accurate:

And almost half the weight of the OEM ones, while being longer:

I have a camera related project I am working on right now, but will do the intake afterwards.

[Puffs]

Good going!

That mill sounds like a desirable thing, can you post a pic (or link) of it?

[jpmsteadi]

Totally!

I got one of these: https://www.precisionmatthews.com/shop/ ... sion-mill/

Precision Matthews has been great through the process and seem to have a real handle on helping hobbiests buy good small import machines.

I have a lathe coming too from them, but it is on backorder some.

[Puffs]

Thanks, that looks great indeed!

Starting to envy you...

[jpmsteadi]

started machining the intake manifold today. doing it all out of one piece of aluminum probably will make it not be super pretty at the end of the day, but should work!

the drawings:

[jpmsteadi]

and the first side operations (after squaring the block). starting with a center drill for the hole locations. The two intake tracts are 60 degrees from the surface of the block. The meet about 50mm in and will be intersected by the bore that will be machined from the opposite side to mate with the carb boot. the oval intake is a 28mm diameter slot and the smaller is a 25mm hole. I will have to take a hand dremel to clean everything up when its done.