Metrakit 2, no power whats upt?

[adas]

Aloha, I'm back after a long absence. I just installed my Metrakit sp2 LC 70cc Minarelli and it has no power. Here's my old and new setup

Old setup
Malossi MHR Replica, stock porting LC
c16
24mm Oko
tuned carters
full circle crank
squish .55mm
This setup the power came on strong about at 9000rpm and made very good power until 11000rpm. Quite a strong engine

New setup
The same as above, but only changed to
Metrakit LC 70cc sp2, stock porting
Tried weights to allow revs anywhere from 8000rpm to 12,000 and
NO POWER curve!!
Whats up?

frank

 

[xzburnoutzx]

Let me guess, the best thing you got is something like this:

Hit the throttle, laggs till 20
Then revvs to 11-12k and stays there, not good torque
but collects speed quite well.

This was with a SP2 on a Runner which I was building. The thing above was the maximum which I was able to get out of it. Well you have better setup aswell. He had like a Shot and 21mm Arrache

 

[adas]

Aloha, I am not worried about lagging until 20 mph, as I have not tuned the rollers and trans to this cylinder yet. Also I have not tuned the carb to this cylinder, I just cannot find a power curve.
I get a small power curve starting about 9500 and the curve is flat up to 11,500. Maybe the power is after 11,500 for this cylinder and better to have a C20?

It is like I installed a stock muffler on a tuned Evo setup!
Weird

frank

 

[IkKe00]

This cilinder is verry high revving, its normal you don't get any power with a c16 (or a shot for instance)

 

[InIMoeK]

He's talking about the SP2 not de PR2. C16 is good for this cilinder. Try another sparkplug or the clearance of the spark plug. This might help.

 

[StepVino]

Hi Frank, I found this port map, but for a Piaggio. Is
this close to your cylinder?

Just playing around with numbers, it seems off from the normal.
When I raise the cylinder 1mm (using 0.7mm deck height), all the
numbers seem to fall into place. But maybe it was traced wrong.

 

[adas]

Aloha: a couple of things

1: yes a SP2
2: the port tracing seems right, but does anyone know for sure if Piaggio is the same as Minarelli?
3: On the tracing, we need to take into account that the head inserts INTO the cylinder by 1.5mm. So if you measure 21mm to the top of the cylinder, you are only getting 19.5mm plus squish to the piston top.
4: I did not mention that I had a 3mm stroker crank as I am sure it will not throw off the power by that much, but I added 1.5 base plate for the install.

As I mentioned before I expected good power but not great power as I knew I had to adjust the base, squish, transmission, carb and compensate for the stroker.
But power is soooo far off that I cannot imagine these adjustments will make the big difference I will need.
But I will start these adjustments below and please comment

1: The piston at the bottom of the stroke goes 1.5mm below the ports, so I will machine 1.5mm off the base and take 3mm off the head. (remove the 1.5mm base gasket and 1.5 machine from base).

2: set the squish to .55mm

3: I am running a bit lean, so raise the needle

4: Install much lighter weights to find the power, then if found increase the weights

Ideas?
frank

 

[StepVino]

If I use that information: 1.5mm spacer + 42mm crank I get
a crazy number 13k-13.5k tuning, with exhaust at ~207, transfer
~145, using above port map. Note I could be completely wrong! ,
just enjoy the figuring. Anyway, blow down time comes out to be ~31
degrees, and from Jenning' book should be about 33-34.

Maybe a full race race pipe would be perfect, but too high a price
to gamble for a test.

 

[adas]

Aloha, most like you are correct. There is a total pipe/cylinder mismatch. I will cut the base from the cylinder until the piston goes to the bottom of the ex port. I think it will be 1.5mm
frank

 

[InIMoeK]

Didn't you forgot the cilinder head that sinks into the cilinder? So you don't get a mismatch with your portmap? The deck will be lower then ( higher timings )

 

[IkKe00]

He's talking about the SP2 not de PR2. C16 is good for this cilinder. Try another sparkplug or the clearance of the spark plug. This might help.

Oops my bad i'm sorry I was talking about the PR2

 

[StepVino]

Didn't you forgot the cilinder head that sinks into the cilinder? So you don't get a mismatch with your portmap? The deck will be lower then ( higher timings )

Doesn't matter, if the cylinder is not moved, timing will stay
the same.

Top of the cylinder is just a reference for easy measurement.
The real distance that is used for port duration is from top of
port, to top (side) of piston at TDC. Since it is not convenient
to get this measurement, you get the same value by subtracting
deck clearance from the distance of top of port to top of cylinder.

If you want to measure deck clearance using where the cylinder
head ends in the cylinder as a reference, you can, but then you
have to use port top to cylinder head as the other measurement,
not port top to cylinder top. When you change both measurements
you will get the same answer as before, the distance between
port top, and top of piston at TDC, which did not change.

 

[DRXRACING]

I just finished setting one of these cylinders up on a minarelli. I used the supplied base gasket and orings. 20mm round slide Kehin carb. KOSO style intake,carbon fiber reeds, and stock DRX(miniquad) Exhaust. Probably around 4 to 4.5 gram Dr. Pulley sliders.
Advancing the timing on the stator plate helps some.
I would reshape the dome to allow for the additional stroke and use the thin base gasket supplied. Keeping the transfer duration numbers down to something more resonable will help things tremendously.

 

[adas]

I just finished setting one of these cylinders up on a minarelli. I used the supplied base gasket and orings. 20mm round slide Kehin carb. KOSO style intake,carbon fiber reeds, and stock DRX(miniquad) Exhaust. Probably around 4 to 4.5 gram Dr. Pulley sliders.
Advancing the timing on the stator plate helps some.
I would reshape the dome to allow for the additional stroke and use the thin base gasket supplied. Keeping the transfer duration numbers down to something more resonable will help things tremendously.

Aloha, where is your power start, and end? Although your exhaust is different, it may give me some idea.
ie starts 9,000 to 11500
frank

 

[adas]

Doesn't matter, if the cylinder is not moved, timing will stay
the same.

Top of the cylinder is just a reference for easy measurement.
The real distance that is used for port duration is from top of
port, to top (side) of piston at TDC. Since it is not convenient
to get this measurement, you get the same value by subtracting
deck clearance from the distance of top of port to top of cylinder.

Aloha, can you give me your formulas?
Also my cylinder looks like it is 20mm from top of exhaust to top of piston.
What rpm power range is this?

frank

 

[StepVino]

Hi Frank, I used 0.7 as the deck hight yesterday, but it was
a guess. What is it actually?

Will send you a link to the program. The site hosting it is
down right now.

 

[adas]

Hi Frank, I used 0.7 as the deck hight yesterday, but it was
a guess. What is it actually?

Will send you a link to the program. The site hosting it is
down right now.

Aloha, from the top of the cylinder to the TDC is 1.5mm ie cylinder head has a 1.5mm lip on it that goes into the cylinder

frank

 

[StepVino]

Aloha, from the top of the cylinder to the TDC is 1.5mm ie cylinder head has a 1.5mm lip on it that goes into the cylinder

frank

I don't understand sorry.. without considering the cylinder head,
what is the distance at tdc between edge of piston and top of
barrel, and distance from top of exhaust port to top of barrel?

If I use 1.5mm deck clearance, 20mm exhaust to top of barrel, and
42mm crank, I literally go off the scale because max is 13500rpm, and
your numbers come out right there best case.

Can't you take the 1.5mm spacer away as drxracing suggested? If I use
those numbers... deck height would go to zero (I assume), 42mm crank,
and exh 20mm to top of barrel, I get 200 degrees duration, and according
to Bell book, 11200-11500 peak power rpm.

 

[adas]

Aloha, I will give you my New measurements since I have taken material off the cylinder base on my lathe.

"I don't understand sorry.. without considering the cylinder head,
what is the distance at tdc between edge of piston and top of
barrel"

Now it is 0 mm (with no base gasket now.)

"and distance from top of exhaust port to top of barrel?"

21.5 mm

Now my head is .30mm from the top of the cylinder and with a base gasket the head is a total .55mm above.

what timing/rpm does that give?

thanks Frank




frankl

 

[adas]

Thanks I have downloaded the file

To be sure is the "DeckClearance" the distance from TDC of piston to top of cylinder?

So if the TDC piston comes to the top of the cylinder now and port-top to barrel top is 21.5 I get
192.4 duration and moving the chart I get 10100 to 10300prm?

Also according to scooter attack 11,000 is the best rpm for the C16 so my result rpm is a bit low for the C16.

thanks
Frank