Oil/burnt mixture coming out of the engine

[benexTopic starterBerichten: 44]

Hello, recently i did a full engine service (new bearings, seals and piston rings) in two of my mopeds: Bravo and Si. Specs:

Bravo:
– 50cc
– drilled inlet to 13mm
– 13.13 carb
– forgot the jet size, but over 50
– giannelli original power exhaust
– malossi air filter
– i use 3% mixture

Si
– 50cc
– standard 11,5 inlet
– 12.12 carb
– 52 jet
– sito + exhaust
– standard 6 holes air filter
– 3% mixture

I noticed that there is some oil/burnt mixture leak from the engine (pictures below). It seams like it is coming from the decompression valve and from the exhaust port. Does anyone have any idea what may be the reason of this leak? Maybe the decompression valve needle (it was grinded with the decompression valve with 3 step grind paste) doesn’t fit right to the decompression valve? And/or the exhaust also doesn’t fit enough to the exhaust manifold?

[WimBijdragerBerichten: 3364]

Seems like a slightly too rich mixture so that everything does not want to burn

Try 2% mixture with 98 E5 fuel first.
And later, after the engine has run in, maybe try a smaller main jet,
but keep an eye on the spark plug color.(NGK 6 or simular)

A 13 carburettor is often a bit overkill on a std cylinder

Gr. Wim.

Een oude brommer is alleen leuk als sleutelen uw hobby is.

[niek1992BijdragerBerichten: 1882]

To add to @Semmad,

Looks like ‘normal’ oil leakage to me. Your exhaust isn’t fully seated onto the flange of the cylinder, missing about 2mm. And if the surface is rough you can’t get a proper seal. I always use Bosal Exhaust Cement to fully seal the exhaust port in the summer. In winter i remove that, because having a constant supply of oil around engine components is free rust prevention. It also seems to come from your cylinder gasket

Regarding your decompression valve, make sure the rubber O-ring is under the lower valve assembly. This looks like a Malossi head on the picture, which doesn’t have the ‘cup’ below the lower valve assembly which houses the O-ring.

Source: I own a Malossi head with the exact same problem. You’ll need to modify the head if you want the head to be oil free.

[benexTopic starterBerichten: 44]

To Semmad post:

I drive 3% because of a new piston rings (i read some comments that suggest more lubrication during first circa 500 km). Before the full service i drove on a 2% 95 fuel mixture and everything was ok, no leaks.

I also read that to gain some power it is good to drill inlet to 13mm and get 13.13 carb. Maybe it has more sense with a 60cc. Now (with 13.13 carb) the moped drives alright and has a better acceleration. Isn’t 12.12 carb too small for a 13mm inlet?

To niek1992 post:

Before the engine service there was no oil leak at all, so i guess something must be wrong now. The exhaust is a modified Giannelli Original Power from Ciao, so it may have some flaws 😉 I will try this Bosal Exhaust Cement and also check the gasket.

I don’t know for sure if it is Malossi cylinder, but i didn’t see any Malossi signs on it. I guess it is standard Bravo cylinder. I bought it like this and i think that nobody did anything with the engine before me. I also didn’t see any O-rings in decompression valve in any of my mopeds engines and there was no leak before. There is a standard set (https://www.sip-scootershop.com/pl/product/zestaw-dekompresji-glowica-cylindra_11324200). So the O-ring must be below that rounded shim that holds the spring (see the picture below)?

[niek1992BijdragerBerichten: 1882]

benex wrote:

Before the engine service there was no oil leak at all, so i guess something must be wrong now. The exhaust is a modified Giannelli Original Power from Ciao, so it may have some flaws I will try this Bosal Exhaust Cement and also check the gasket.

And in the process of servicing that engine you removed or even replaced the exhaust. The exhaust might be crudded shut or had similar exhaust paste like Bosal to seal in the gaps. The Exhaust Cement is one time use only and needs to be reapplied after you’ve done work any work on the moped which involves removing the exhaust. Regarding the flange, you could clean it with a wire brush. And if it’s clean already, use a rubber mallet to hit the exhaust firmly onto the flange as far as possible. The exhaust itself is one of the better models in my opinion. It uses thicker steel than a cheap alternative and also a removable clamp.

benex wrote:
I don’t know for sure if it is Malossi cylinder, but i didn’t see any Malossi signs on it. I guess it is standard Bravo cylinder. I bought it like this and i think that nobody did anything with the engine before me. I also didn’t see any O-rings in decompression valve in any of my mopeds engines and there was no leak before. There is a standard set (https://www.sip-scootershop.com/pl/product/zestaw-dekompresji-glowica-cylindra_11324200). So the O-ring must be below that rounded shim that holds the spring (see the picture below)?

If it has the original Piaggio logo on it, then it it’s original. If it has no stampings on it whatsoever it’s a remake and will most likely suffer from the same flaws a Malossi head has. I’m not 100% sure if a Si or Bravo has the same head design structurally (not  as a Ciao head, but all my Ciao’s had a rubber O-ring beneath that red circled part. The head has a little recess for this where the rubber O-ring fits in snuggly. I tried looking up images online that shows what i mean but couldn’t find proper images.

If you place a rubber O-ring beneath that part without modifying the head, you’ll simply squish the O-ring which isn’t going to work. I hope my crappy English is clear enough for you to understand. If not, reply and i’ll grab a disassembled Ciao head and picture what i’m trying to describe.

[benexTopic starterBerichten: 44]

niek1992 wrote:

And in the process of servicing that engine you removed or even replaced the exhaust. The exhaust might be crudded shut or had similar exhaust paste like Bosal to seal in the gaps. The Exhaust Cement is one time use only and needs to be reapplied after you’ve done work any work on the moped which involves removing the exhaust. Regarding the flange, you could clean it with a wire brush. And if it’s clean already, use a rubber mallet to hit the exhaust firmly onto the flange as far as possible. The exhaust itself is one of the better models in my opinion. It uses thicker steel than a cheap alternative and also a removable clamp.

Okok, the exhaust manifold can be a little out of its original shape ;P

If it has the original Piaggio logo on it, then it’s original. If it has no stampings on it whatsoever it’s a remake and will most likely suffer from the same flaws a Malossi head has. I’m not 100% sure if a Si or Bravo has the same head design structurally (not as a Ciao head, but all my Ciao’s had a rubber O-ring beneath that red circled part. The head has a little recess for this where the rubber O-ring fits in snuggly. If you place a rubber O-ring beneath that part without modifying the head, you’ll simply squish the O-ring which isn’t going to work . If not, reply and i’ll grab a disassembled Ciao head and picture what i’m trying to describe .

Your explanation is alright and i do understand it 😉 I remember that this cylinder head has a Piaggio logo on it. And i am pretty sure that i didn’t see any O-ring or any recess for this O-ring on any of my cylinder heads. I guess I must make such a recess for the O-ring.

I will try all of your advices and see how it goes. If the problem will still be there, I will write here. thanks guys 😉

[niek1992BijdragerBerichten: 1882]

Hi @benex,

Was doing something else and found a disassembled Ciao head. See picture below:

[benexTopic starterBerichten: 44]

niek1992 wrote:

Hi @benex, Was doing something else and found a disassembled Ciao head. See picture below:

Thanks for the picture. I didn’t see such recess in one of my cylinders. I must check other that leak oil. I can always use a dremel and make it on my own 😉

[Gebruiker]

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