Carb change - what performance increase ?

[Hammer RB230]

Hi All I need some advice,
Ive finally run in my rebuilt L150 with a 175 top end, no porting. Breathing through an opened up air box (baffle/elbow removed) and a BGM fast flow filter. Exiting through a AF clubman exhaust. It currently has a Jetex 22mm on it. Performance wise it will do only 55mph flat out.

The questions are

A, am I expecting too much from it (my other Lambretta is a tuned RB230) and this performance is normal.

B, would the fitting of a 25mm Dellorto improve performance at all.


Any positive thoughts greatly received, before I spend some money !

[Timexit17]

A genuine 55mph is perfectly respectable for a 175 IMHO.
Obviously the Jetex is agricultural compared with a PHBH but doubt it's carburettor holding the scooter back tbh.

It depends what load it's carrying too to be fair also.

[Knowledge]

The recent Scootering bang-for-your-buck articles, they tried a 26mm carb in place of the 22mm Dell'orto and they found no difference. It only became a factor when higher levels of tune are employed.

[EddieStone]

Unless you get it to rev faster, your top speed probably won't increase. You'll hopefully find that you'll maintain your speed more on slopes and into headwinds, and that a pillion doesn't affect the performance as badly.

If you want to increase speed, I'd recommend getting it ported a bit - a Stage 4 175 can produce a cheap and cheerful level of performance. I'd only consider a different carb if you are fitting a full on expansion exhaust - the 22mm Jetex should be fine for what you have. You can only go so far before you have to start to consider up rating the crank.

[johnnyXS]

what jets and slide have you fitted hammer?
I have a standard LiS150 with a 22mm Jetex and it really flies . 55mph is easily reached and it will cruise at an indicated 50mph on part throttle.

I have a standard exhaust fitted and a 45 pilot, 5889-2 Atomiser and a 106 main .

I do have my timing set to 19 degrees which seems higher than most and probably accounts for the quick throttle response and acceleration.

One thing to watch out for is the exhaust manifold gasket. If you are using a 42mm Clubman you'll need the appropriate copper gasket for a 42mm . if you use a standard 150 exhaust manifold gasket it will restrict your exhaust .

[johnnyXS]

oops