Modern Vespa

Hi

I've got a lot of response or thought about not rejetting the LEADER engine with a CV carb.

My theory is that if the exhaust is less restrictive, more vacuum.. so the carb got more air so more fuel is needed..
All bike are different but not rejetting with a non CAT exhaust will lead to an power loss somewhere nah? I FEEL the bike bugging out and starving for fuel at WOT but at the same time I don't know if putting a bigger jet along with the aftermarket pipe yield much more power and top speed ect
My spark plug is half minimal tan and half white.

Your thoughts 🤔

Thanks guys

Changing the intake with, say, a different free flowing filter will effect the jetting more that the exhaust ever will. Changing out the exhaust is usually the last step in tweaking the engine on a 4T. For most people (with a stock engine), it's about changing the exhaust sound, losing some weight over the stock pipe and believing the claims of the manufacturer ("You will gain 25% more horse power"!!!) I would not suggest you change the jets unless the spark plug looks to be running lean.

So there's a possibility that the CAT exhaust yield me more peps and torque than the tecnigas exhaust..?
I think the tecnigas exhaust move the powerband..

I'm guess with cat removed, you will notice a difference. Is this on 4T or a 2T engine?

4T fly 125.. I get less torque with the tecnigas vs my old crusty oem cat one.
It's special.. it's like the tecnigas move the powerband or narrows it.

You might well do, especially if the back pressure isn't timed right or the right amount.

No-one here has ever proved they have increased the power output by adding an aftermarket exhaust.

Can you post the dyno charts that illustrate the difference?

Very interesting point on the back pressure. Never though about that..

I found something interesting..

Do you need back pressure in an exhaust?

As the pulses move along, they generate an exhaust flow. If you have a restrictive exhaust system, it can generate back pressure that works against the positive flow of the exhaust gas that's trying to exit your vehicle. However, a little back pressure is a good thing. In fact, it helps.

What happens if not enough back pressure?

Common symptoms include poor power and fuel economy, a slipping automatic transmission or altered transmission shift points, backfiring through the intake manifold, hesitation, stalling and, if bad enough, an engine that won't run at all.
It applies to motorcycle exhaust too.

Sorry don't have a dyno at home.

Definitely stay with the stock exhaust. The back pressure as Jim point out is so true. I've put back the stock exhaust and got my torque back. You must upjet for sure with the tecnigas and I don't think it's worth the trouble to go in the carb. Only for sound and weight for sure.