Problem after engine rebuilt

[KTy]

I have rebuilt my PX 125 Arco (=Lusso), changing almost everything, bearings, oil seals, ...etc

I have very very few power at low rpm, and then, around 3000rpm it is fine. For example, in 1st gear (!!), if I instantly open full throttle then it will take maybe 2-3s to really start pushing !

I have an idea on what is going on... But I hope I do not have to open the engine again...

Because I had to change my crankshaft, I put an original piaggio, in good condition, BUT home-made cut (16mm).

Could it be the problem ? If so, how can I change the jetting so that it works fine at low rpm ?

I have standard jetting: idle 140/45 and main 140/BE5/100 ...

By the way, is there a toric seal on the mixture screw of a standard SI20/20D ? I thought there were one...

If it is not the problem, what could it be ??

Thanks...

Bearbeitet 19. November 2006 von KTy

[bigbene]

Since the crankshaft is the only change you`ve made, I guess that that's the problem: You might have heavy sprayback at low revs which causes your engine to not accelerate properly.

As far as the jetting is concerned I think it should be fine (at least roughly). What's a toric seal? At the back of the "cover" around the carb were the screw comes out there's a little rubber seal, but I think that it's more or less intended to keep the dirt out- it won't affect your carb settings if not fitted.

[KTy]

On my SI20/20D, I have this kind of mixture screw:

I was wondering if there is an O-ring... ?

I'm going to check the ignition... :-D

[freerider13]

Sure? exactly this mixture screw?

As far as i know is this one only for the SI 24/24 G (for the T5)

The original one for the SI 20/20 D looks different (for screwdriver use).

Usually the T5 screw shouldn´t fit on the SI 20/20 D...

This could be a reason for your Problem.

greets,

Jan

[KTy]

There is two versions of SI20/20D...

An "old" one than comes on Sprint for example as a mixture screw that looks like a normal "screw".

Newer SI20/20D (PX Lusso for example) has this kind of screw and this is logical: They have an electric-start !

Anyway, maybe I'm a bit confused with dellorto PHB series that have a little washer and an o-ring. (Parts 19 to 22 here)

Could an old exhaust gives the same results ? (low power at low rpm and normal power over mid-rpm ??)

[bigbene]

Could also be that the petrol-air mix needs to be richer now due to the longer inlet phase- try a bigger idle jet maybe and a BE3 instead of a BE4 (don't know the english word for that jet, its the one you stick your main jet in).

[KTy]

Yup, I'll try another atomizer !

[KTy]

No better luck... I even tried with a new SI24/24 carb, with the good jets, still very weak at low rpm...

[8ball]

arrow on piston crown pointing to exhaust port?

[KTy]

arrow on piston crown pointing to exhaust port?

Unfortunatly no...

low-mid to high rpm the engine is just very good ! Besides that, I drove 200-300km, I doubt the rings would have survived if I had reversed the piston !

[matripper]

! Besides that, I drove 200-300km, I doubt the rings would have survived if I had reversed the piston !

One of my buddies drove over several weeks with a reverse installed piston

until he realized it... by the way, that was a T5 cylinder.

So, don't be too sure

[KTy]

Okay then ;)