Three questions on a Minarelli Horizontal AC

[Cruz_e_Silva]

Hi,
I have a Aprilia Rally 50 with a Polini EVO 70cc cilinder among other things.

In the instruction paper of the cilinder it tells we have to rebore the crankcase to 75,5mm instead of the original 73mm. I'm no tuning expert but one thing I've learned thru the years is that in 2 strokes there should be the least space left replaced with something to get more crank pressure. Can somebody explain me the reason why should I open my crankcase to 75,5mm and get more space inside?

Another thing I wanted to be answered is about CDI Units.
There are some brands in the aftermarket like Top and Malossi. On the Top ones there are the Racing one and the adjustable one. Can someone explain me the diferences between both? Is not the adjustable one better than the racing as I think that adjustable goes for adjustable ignition timing and the racing is a fixed timing unit? Or is there any enhancements on the racing type that the adjustable one doesn't have?

Third and last question. I have a Dellorto PHBG 21mm carb with a Hebo air filter. My settings are 35 min jet, needle in 2nd position and 98 main jet. the mixture is a bit rich on the top revs. My exhaust is a leovincy hand made Z (ond exhaust) but I'm changing it for the Polini Evolution one. Does the change in exhaust going to change my main jet in many numbers? I read in the Dellorto tuning manual that a change in 1mm bore in carbs within the same setup should increase the jet number in 10%. As the manual in the cilinder says the the main jet should be 98 a 2mm increase in the carb bore should up the number by 20 numbers to 118 aprox. Is there any truth in this calculations?

Thanks for readind all this post.
bye for now

 

[$aint]

Most people driving a Polini Evo haven't rebored their crankcase to a bigger size. So it isn't necessary, but I don't think Polini added that comment for nothing (but keep in mind tht in Italy, they race with 19mm carbs).
Malossi use a con-rod which is 5mm longer (on piaggio Team and on Minarelli Cross), which in realtion to the crankcase volume does the same...

The yellow top CDI (racing) is "derestricted", so it can rev endless, but since an original minarelli CDI doesn't have any problems @ 14k RPM It's kinda useless, the only thing I can think of that can be better is a stronger/faster unloading over the bobin, so a stronger spark...
The red top CDI is a variable one, which you'll have to mount with another half-moon which advances your flywheel x(9, 12, dunno?) degrees, the ignition changes this advance interanlly so it gets later the higer the engine revs...

And yes You'll have to change your jetting with the much better exhaust (btw. try to get the newest evo exhaust)...

 

[Browni]

Originally posted by Cruz_e_Silva
Hi,
I have a Aprilia Rally 50 with a Polini EVO 70cc cilinder among other things.

In the instruction paper of the cilinder it tells we have to rebore the crankcase to 75,5mm instead of the original 73mm. I'm no tuning expert but one thing I've learned thru the years is that in 2 strokes there should be the least space left replaced with something to get more crank pressure. Can somebody explain me the reason why should I open my crankcase to 75,5mm and get more space inside?

Another thing I wanted to be answered is about CDI Units.
There are some brands in the aftermarket like Top and Malossi. On the Top ones there are the Racing one and the adjustable one. Can someone explain me the diferences between both? Is not the adjustable one better than the racing as I think that adjustable goes for adjustable ignition timing and the racing is a fixed timing unit? Or is there any enhancements on the racing type that the adjustable one doesn't have?

Third and last question. I have a Dellorto PHBG 21mm carb with a Hebo air filter. My settings are 35 min jet, needle in 2nd position and 98 main jet. the mixture is a bit rich on the top revs. My exhaust is a leovincy hand made Z (ond exhaust) but I'm changing it for the Polini Evolution one. Does the change in exhaust going to change my main jet in many numbers? I read in the Dellorto tuning manual that a change in 1mm bore in carbs within the same setup should increase the jet number in 10%. As the manual in the cilinder says the the main jet should be 98 a 2mm increase in the carb bore should up the number by 20 numbers to 118 aprox. Is there any truth in this calculations?

Thanks for readind all this post.
bye for now

I've EVO 70 AC for a long time. Polini reccomends the reboring if you use the Polini EVO crank (it's full-circle). But your question is right, cause the EVO crank has same outer diameter like Original Crank. In my opinion they design this cylinder with that denominate crank-case volume. We did the reboring with good result!

And it's funny but I use 98 mainjet too) And it's perfect!

 

[Cruz_e_Silva]

Originally posted by $aint
The red top CDI is a variable one, which you'll have to mount with another half-moon which advances your flywheel x(9, 12, dunno?) degrees, the ignition changes this advance interanlly so it gets later the higer the engine revs...

And yes You'll have to change your jetting with the much better exhaust (btw. try to get the newest evo exhaust)...

Hi, $aint,
The minarelly flywheel has a 14 degree advance as the polini needs but I think that the original CDI may retard the ignition at high revs. I didn't experiment with a strob gun by now but it's what it looks like when I try it(maibe just a personal impression).

What are you meaning when you write "you'll have to mount with another half-moon which advances your flywheel x(9, 12, dunno?) degrees, the ignition changes this advance interanlly so it gets later the higer the engine revs..."?

What part in the magneto unit is the half-moon?

I thougt that in this CDI we could tune it with a strobo light (by the means of a screw or something like this) to how many degrees BTDC we wanted the ignition to be done, like in a car distribuitor when we turn the distribuitor case around, and after that the ignition timing should be fixed to that degree or get sooner (not later) as it should be as the engine rises revs to compensate for the higher speed of the crankshaft.
As I can understand in what you wrote the Red CDI is not adjustable but it has a ignition map that tends to retard the ignition as the rpm gets higher.
Shouldn't it be the opposite way to get a better setup?

BTW is the newest EVO exhaust that everybody writes about part 200.0220 for the AC Minarelly or is a newer one? If so can you give me the new part number?

 

[Cruz_e_Silva]

Re: Re: Three questions on a Minarelli Horizontal AC

Originally posted by Browni
I've EVO 70 AC for a long time. Polini reccomends the reboring if you use the Polini EVO crank (it's full-circle). But your question is right, cause the EVO crank has same outer diameter like Original Crank. In my opinion they design this cylinder with that denominate crank-case volume. We did the reboring with good result!

And it's funny but I use 98 mainjet too) And it's perfect!

Hi Browni,

I have the polini crank for the 10mm piston pin as I instaled first the cilinder with the original crank and only later the new crank.
I had both with me and apart of the con rod for the 12mm pin and the crank variator axle they are the same size and type-full-circle with nylon inserts(both the 12mm EVO one part n.210.0010 and the 10mm one part n.210.0006).
The only reason that I could remember was the need for more mixture volume for the cilinder, but it would be more dificult to send it thru the ports, as the crank pressure would be lower. If I can get a logical explanation that worths I'll may think in reopening the crank case and do it.

BTW what filter brand are you using, carb diameter and setting(min, main and neddle position), spark plug and exhaust?
Thank you all for your help.

 

[$aint]

Originally posted by Cruz_e_Silva
Hi, $aint,
The minarelly flywheel has a 14 degree advance as the polini needs but I think that the original CDI may retard the ignition at high revs. I didn't experiment with a strob gun by now but it's what it looks like when I try it(maibe just a personal impression).

Do you mean with this that with a completly standard setup the fkywheel is already 14 degrees advanced?
(could very well be true, I heard 15 degrees once, unfortunately I don't have the tools (strobo) to check these kinda things)

What are you meaning when you write "you'll have to mount with another half-moon which advances your flywheel x(9, 12, dunno?) degrees, the ignition changes this advance interanlly so it gets later the higer the engine revs..."?
What part in the magneto unit is the half-moon?

I meant the same as what you wrote above this, that the CDI retards the ignition.
Half-Moon is the part that fits into a small "hole" in your crankshaft, that centers the flywheel into the right position.
With the red (advanced) Top ignition you'll get another halfmoon, which is excentric, so it will advance you ignition a number of degrees (I don't know this number)

I thougt that in this CDI we could tune it with a strobo light (by the means of a screw or something like this) to how many degrees BTDC we wanted the ignition to be done, like in a car distribuitor when we turn the distribuitor case around, and after that the ignition timing should be fixed to that degree or get sooner (not later) as it should be as the engine rises revs to compensate for the higher speed of the crankshaft.
As I can understand in what you wrote the Red CDI is not adjustable but it has a ignition map that tends to retard the ignition as the rpm gets higher.
Shouldn't it be the opposite way to get a better setup?

You can manually change the ignition of yout flywheel, to get the maximum ignition advance you want.
I understand you have some experience with 4 stroke ignitions.
The funny thing with 2-stroke ignitions is that it's exactly the other way around
Because the quality of the mixture @ top poweris near perfect it will burn a lot faster, so you'll need less spark advance.
If you start to retard it even more or the CDI doesn't retard it (with the advanced halfmoon) it will auto-ignite, like a diesel, and that's not what you want

BTW is the newest EVO exhaust that everybody writes about part 200.0220 for the AC Minarelly or is a newer one? If so can you give me the new part number?

Thought the part-number stayed the same.
see http://forum.scooterforum.net/forum/showthread.php?s=&threadid=40981

for pics (you can see the old evo and the new evo70 exhaust next to eachother)

 

[Speed]

I just purchased a Polini motor and none on the instructions says to re-bore the crankcases out to 75,5mm. I asked the Polini Tech Center thought, they said it should have come with one but they said to bore the casings out to 74mm for Piaggio LC motors.

Which measurement is right. Fabrizi advises 75,5mm for there FHT 44mm stroker crankshafts and this takes the casings right out to the edge of the engine screw holes.

Does anyone have the paper or any further information for modifying the crankcases when using Polini Piaggio Evolution LC motor. What is the Crankcase measurements.

Speed

 

[Browni]

Originally posted by Speed
I just purchased a Polini motor and none on the instructions says to re-bore the crankcases out to 75,5mm. I asked the Polini Tech Center thought, they said it should have come with one but they said to bore the casings out to 74mm for Piaggio LC motors.

Which measurement is right. Fabrizi advises 75,5mm for there FHT 44mm stroker crankshafts and this takes the casings right out to the edge of the engine screw holes.

Does anyone have the paper or any further information for modifying the crankcases when using Polini Piaggio Evolution LC motor. What is the Crankcase measurements.

Speed

Speed this is very strange because I have the original italian user manual for the EVO and they suggest the reboring!

Here it is:

Polini EVO 70 Minarelli

 

[Cruz_e_Silva]

Originally posted by $aint
Do you mean with this that with a completly standard setup the fkywheel is already 14 degrees advanced?
(could very well be true, I heard 15 degrees once, unfortunately I don't have the tools (strobo) to check these kinda things)

Hi, $aint,

If you don't have a strobo you can as well draw a circle in a cardboard and mark the degrees BTDC that you want (in clockwise direction). After that you just need to mark the TDC in your flywheel taking for reference the center of the pickup and use the timing circle like it's done in the camshafts of 4strokes to time them. You will see that the mark in the out of the flywheel in on the 14degrees place. Besides that I have the Aprilia workshop manual and in the engine characteristics it confirms that the ignition is at 14degrees BTDC.

Originally posted by $aint
I meant the same as what you wrote above this, that the CDI retards the ignition.
Half-Moon is the part that fits into a small "hole" in your crankshaft, that centers the flywheel into the right position.
With the red (advanced) Top ignition you'll get another halfmoon, which is excentric, so it will advance you ignition a number of degrees (I don't know this number)

Ok I see. The only thing that I don't find is information on the Top CDI anywhere on the net (operating and mounting instructions).
About the retard of the ignition on 4strokes it's the way arround, I thought that it was the same with 2 strokes as the theory of more rpm/less time to get the spark may be applyed in 2 strokes.

Originally posted by $aint
You can manually change the ignition of yout flywheel, to get the maximum ignition advance you want.
I understand you have some experience with 4 stroke ignitions.
The funny thing with 2-stroke ignitions is that it's exactly the other way around
Because the quality of the mixture @ top poweris near perfect it will burn a lot faster, so you'll need less spark advance.
If you start to retard it even more or the CDI doesn't retard it (with the advanced halfmoon) it will auto-ignite, like a diesel, and that's not what you want

Do you know any internet pages that have some work on the subject in english? Are you saying that all CDI's retard the ignition at higher revs? Does it have a stoping point or the igniting tends to go near 0 degrees TDC?
I see I need to read some more on the subject.
Does anybody experienced some of the CDI's in the market and can give me a hint?

Originally posted by $aint
Thought the part-number stayed the same.
see http://forum.scooterforum.net/forum/showthread.php?s=&threadid=40981

for pics (you can see the old evo and the new evo70 exhaust next to eachother)

I'm not very good in Dutch but the diference that I saw in the pictures was in the the near cilinder part....the rest looked almost untouched. The one I'm buying is the EVOLUTION2 for AC engines, part n.200.0220. The one before was part n. 200.0183 and was for both AC and LC engines.
I think it's the last one from polini and it appears in the polini online catalogue specified for Rally AC.
Thank you for your replies.

 

[Browni]

Yes, I can confirm that the original ignition advance is 14 degrees, I've measured it and the TOP performances manual says the same too:

(this is for the TOP Due Plus cylinder) You can widen the hole more if you want bigger sparking advance!

 

[Browni]

I can't translate it for you, but here in the middle of the page you can find something about the TOP variable CDI!

 

[Velo]

Re: Re: Three questions on a Minarelli Horizontal AC

Originally posted by Browni
I can't translate it for you, but here in the middle of the page you can find something about the TOP variable CDI!

Danish:
Topperformances Racing CDI, med forskudt noet. Forskyder tændingen til 17º som derfor giver bedre omdrejnings vilkår over 10000 omdrejninger

English:
TP Racing CDI, with advanced halfmoon.
Changes the ignition to 17° (BTDC) wich gives better engine characteristic above 10.000 rpm.

 

[$aint]

Re: Re: Re: Three questions on a Minarelli Horizontal AC

Originally posted by Velo
Danish:
Topperformances Racing CDI, med forskudt noet. Forskyder tændingen til 17º som derfor giver bedre omdrejnings vilkår over 10000 omdrejninger

English:
TP Racing CDI, with advanced halfmoon.
Changes the ignition to 17° (BTDC) wich gives better engine characteristic above 10.000 rpm.

So that would mean the Top half-moon only advances the flywheel with 3 degrees?

I always heard it was more like 9 to 12 degrees...

 

[Velo]

Re: Re: Re: Re: Three questions on a Minarelli Horizontal AC

I always heard it was more like 9 to 12 degrees... [/B]

Please. Don't ask me about facts on that one.
I don't know it and it is wery long time ago since I last tryed a scooter with stock and then TP Red.

All I did was translate it.

 

[$aint]

Re: Re: Re: Re: Re: Three questions on a Minarelli Horizontal AC

Originally posted by Velo
Please. Don't ask me about facts on that one.

euhmm, do you know....?

I'll see if I can get my hands on 1...

 

[Cruz_e_Silva]

Re: Re: Re: Three questions on a Minarelli Horizontal AC

Originally posted by Velo
Danish:
Topperformances Racing CDI, med forskudt noet. Forskyder tændingen til 17º som derfor giver bedre omdrejnings vilkår over 10000 omdrejninger

English:
TP Racing CDI, with advanced halfmoon.
Changes the ignition to 17° (BTDC) wich gives better engine characteristic above 10.000 rpm.

Hi Velo,
Thank you for the translation. The timing advance that I need is 13 degrees at 7000rpm like it says on the Polini manual.

I'll see if I can find more on the red CDI. I'm thinking on buying one but I wanted to be sure if it worths the € or if I should stay with the original one.

If some of you can get in touch with one of these units and it's instruction manual may you post here your opinion and the a scan of the manual?

Thank you all for your great help.

 

[Browni]

Re: Re: Re: Re: Three questions on a Minarelli Horizontal AC

Originally posted by Cruz_e_Silva
Hi Velo,
Thank you for the translation. The timing advance that I need is 13 degrees at 7000rpm like it says on the Polini manual.

I'll see if I can find more on the red CDI. I'm thinking on buying one but I wanted to be sure if it worths the € or if I should stay with the original one.

If some of you can get in touch with one of these units and it's instruction manual may you post here your opinion and the a scan of the manual?

Thank you all for your great help.

You need'nt to buy a TOP red CDI you can adjust your stator by rotating it (by widen the 2 holes) , like the pictures show above. So you will have a fix 13 advance.
Do you use it for street or track? Cause if you use fix 13 degree your engine works only in high RPM. I use my EVO on street and I adjust the advance to a fix 21 degrees, so it is very good till 10000 it pulls very hard from 0-100

You can buy the Polini CDI this has fix advance too but has a good ignition map.

 

[Velo]

If you wan't to use your stock. Flywheel and stator.
Go clone it with the Polini Centraline.
That is what I have best expirience with.
(and if possible. get a better coil. Ea. a Malossi)

 

[Cruz_e_Silva]

Re: Re: Re: Re: Re: Three questions on a Minarelli Horizontal AC

Originally posted by Browni
You need'nt to buy a TOP red CDI you can adjust your stator by rotating it (by widen the 2 holes) , like the pictures show above. So you will have a fix 13 advance.
Do you use it for street or track? Cause if you use fix 13 degree your engine works only in high RPM. I use my EVO on street and I adjust the advance to a fix 21 degrees, so it is very good till 10000 it pulls very hard from 0-100

You can buy the Polini CDI this has fix advance too but has a good ignition map.

Hi Browni nd Velo,

Last night when I was in the net I saw the polini CDI in a shop.
I thought that more or less like you did. I don't want to change my Flywheel to a inside rotor one because I need the lights to drive on the street. My use for the bike is road only but the polini bandwidth starts near the 10000rpm area and with the polini evo variator and the type of roads in my region (lots of ups and downs) I want it to be that that way.

As I can read the polini one is like the Yellow one from top but with another ignition map. (fixed starting advance that varies through the rev range or the Top one doesn't vary?)

The only thing that a need is some info on the polini CDI, as I want to chose with mind and not money or brand names.
Also with the price of the polini CDI and an extra money I can buy a MVT Millenium (I think it has light coils). What I didn't understand is it brings another CDI or we have to buy it apart.

Can anybody give me some help on this subjects?
Thank You

 

[$aint]

MVT Ignitions are supplied with their own CDI (there are different types of CDI's/Ignitions)