Tips for setting up my carb

I need some tips to easy setting up my carb!

Here is my setup :

  • PX150
  • Malossi 166cc
  • SIP Performance exhaust
  • Dell’orto PHBH30
  • Reed valves Malossi¨
  • Airfilter Ramair
  • Cylinder and the casings are ported together
  • Dell’Orto Fuel pump but not mounted on my engine yet.

I will receive my jets normally this tuesday from SIP, I ordered 120, 125, 130, 135 and 140.

…so I discover that not only your inlet port is more or less standard, but that your cranckshaft is standard too.

You are just sitting the malossi block reed on the engincase…

…it will remain a rotative induction with reed in the way…

let’s just say that you have a lot of margin of improvement…

and that you will need a main jet even smaller then thought…

Thanks Curare, it’s more clear now.

I think I’m gonna wait some time and buy a crankshaft and then match the inlet port at the same time so that I dismantle the engine only one time, I did not run for about 4 months as I don’t have any vespa left for the moment, my Primavera and my SS180 are on the way to be painted, they need to be sanded so no way to run, that’s a reason why I want to do this later. Which crankshaft would you choose? The inlet as to be matched perfectly?

Have a good end of week-end!

Mikkke ;D

…if you are interested just contact me on my e-mail,

[email protected]

I have the
21 and the 65 that you need too.

hello Mikke,

have you already opened the inlet port?
Anyway if you are going to get this jets start with 130 and see how it feels. Do the plug chop technic and check the plug. So you will see if you are rich go or lean. It will give you a good direction to order the intermediate jets to fine set the carb.

And it is always good to get same basic carbtuning theorie if is one of the first set up that you are doing. It will make clearer few things.
You could reed something at:

No the inlet port is not opened yet, I planned to open it later since I didn’t ride for about 4 months, since I opened the casings port (cylinder). Is that a problem if I wait?

Can you explain a little more when you will have some time?
What is the „Plug chop technic“?

Thanks for all your help.

Do you have some tips on gearing up a px200 with a Leo Vince
exhaust and a polini 208, all other pieces are original.


hello Mikkke,

renforced cosa clutch basket art.: 93242000

cosa 21 teeth art: 87470000

65 primary drive art.: 1127200

worb5 special lip cranckshaft art: 46020000

You should get also a set of clutch reinforced spring.

In case you would be interested in buy second hand perfect condition, I have a worb5 special lip cranckshaft but longstroke so you should use it either with head gasket or base gasket, but I would use it with head gasket to give the malossi a little more torque since already is very good at high rpm. It will give you more torque, boost the mid range at the cost of high rpm.I find this option better for daily and cruising use.

In case you are interested I will sell it for 80euro postage not included.

…and maybe I have also the 65 and the 21 I have to check

For now, it’s the original one (stock) without any modification, I will buy another one normally on june or july, then at this moment I’ll will need your help for advice because there is so much different design, what would you do? which kind of crankshaft do I have to mount? Do the opening of the inlet port need to be open at the maximum, to fit the base of the Malossi valves bottom, I think it’s like that, I am wrong? Is the crank important with the reedvalve, I thought that it has less importance with a reedvalve?

Normally, I’m gonna try my jets tomorrow morning, I’ll tell you then what happen!!



if the width of the inlet port is standard it means that will be sealed from the left side of the cranckshaft in a given time (lenght of the inlet port and of the cut of the cranckshaft)
If it is sealed in this given time means that it is this given time, rotation of the cranckshaft that decides when the carb feels the depression of the cranckcases created by the piston in the cylinder movement.
The benefit of the reed induction is that the carb is directly connected with the created depression but to be connected to the cranckcase created depression as soon as this depression develops you have mill the inlet port larger then the cranckshft half, if not it will be closed at a given time from the cranckshaft shoulder. In this case the reed will feel the cranckcase depression only when the cranckshaft cut allows.
In this last case you see that the induction it is still governed by the timing of the cranckshaft even though there are reed in beetween. The reed will open when the cranckshaft allows them to feel the depression. It is not a genuine reed induction.

As far as the cranckshaft concern:
if the inlet port it is big enough and expecially larger then the cranckshaft shoulder, the reed will feel the depresion when this depression develops, and in this case the use of the type of cranckshaft is not that important and you could keep using the standard crank.

I hope it is a little clear even though this is a bref, fairly basic and superficial explication.

Don’t the induction behave to the reeds?
I understand from your answer that it depends from the crankshaft, is this right?
The inlet port is just welded +/-2mm left and right and is longer just like in the Malossi booklet, do you unsderstand?

I can send you some pictures if you want.

Tell me more of the improvements possible; of course ui you have time!


I try to change the main jet, but I found another problem :

The Malossi manifold plate is moving up and down for something like 0.8mm! Even if the screws are blocked!!

Do you think I have to put some kind of Loctite seal paste?
What is your point of vue?

I’ve have taken some pictures of my inlet port, can you send me your email address so that I send my pictures to you to see it.

Here’s mine : [email protected]

hello Mikkke,

for the reed inlet porting for malossi reed I would do it one next week to be used with a special lip cranckshaft. For a special lip crank I use an opening that is like for a standard carb and not with the 1mm recessed area that follow the inlet opening on each side inside the case (as also suggested by malossi). This to compensate the little crankcase compression lost with the use of special lip crank. The better arodinamic flow of the special lip compensates for the recessed area that are instead absolutely necessary if you use a full circle crank for example.
Which cranckshaft you will be using?

…mikkke if you could go to the topic: new pipes
and explain how you posted your photo here I would appreciate and beerace I think too.

ok let’s go!!

hello Mikke,

no, it is not a problem if you didn’t open your inlet port yet. The only thing is that when you will do it you will have to upjet too. Without the inlet port open your malossi reed will not perform at their best, thats it. You will have a performance equivalent at a rotative inlet. The big advantage of the reed is the possibility of having a bigger inlet port than the standard one which dimension are hold down by the dimension of the cranckshaft.
Up to now I have never set up a Malossi with Malossi reed without the inlet port opened, but it will be just a question of a smaller main jet. I could guess a 125 - 128 instead of 130 - 135 with the port job. This is just my guess. let’s have a try and see if we can learn something togheter!

As far as concern the plug chop tecn. have a look at the net address I gave you. It is explained. If not clear ask again.

My problem is that I have to open once again and do not make it as easy as you.
The second problem is that I don’t have any workshop, I usually work in my garden as with this weather now!!!

I think I’m gonna ride like this for two or three month and then I will do it, it is a little open as I made a mistake first time but it still have to be open more.

I’ll tell you about the jetting if I can set it up.

In between, see you soon, Maestro!



as far as for the cranckshaft after the inlet job done I would either stay with the standard or to get a little more the Worb 5 special lip that is even better balanced the same standard one.

Then I would change your gear ratio to something shorter since we will get the speed with the high rpm the malossi is capable of.
I would use a renforced cosa clutch basket with 21 teeth and 65 primary drive from PX 200.

For the problem with the malossi manifold:

I think it is not sitting flat in the crancase base. Most of the time this problem is due to the side closest to the tire where in the cranckcase there is a kind of a curve that form the higher (less then 1mm) plan of the cases. This curve is often an obstacle for the base of malossi manifold. So either you make this curve larger or mill out the part of the malossi manifold base that is on the way. Or both.
If you don’t do this the manifold base will sit not in a plan base since its side close to the tyre will sit on the slightly higher plane of the cranckcase.
I am 90% sure is this problem.
If I can find same picture I will send them on my net.

My e-mail is : [email protected]

Hello Curare,

Need your help, guy

Can you tell me where to buy these products ( and their article number or reference) :

  • renforced cosa clutch basket with 21 teeth
  • 65 primary drive from PX 200
  • Worb 5 special lip cranckshaft

Once again, thanks!!