Debaffling the 125cc prima pipe

lovemysan · Post by **lovemysan** » Fri Mar 15, 2013 3:35 pm

When I installed my prima last year I immediately wanted remove the baffle. Its located where the head pipe steps up 4" before entering the muffler. If you shine a light down into the exhaust you can see it, look past the perforated core(pipe inside with holes in it). Its made of corrugated stainless steel foil. I didn't get a picture of it before we drilled it out. Haven't ridden it yet so don't about power yet.

lovemysan · Post by **lovemysan** » Fri Mar 15, 2013 5:50 pm

So far mid range seems stronger. Maximum noise level seems about the same maybe a touch louder but can't really tell. At low revs it has a stronger lower tone. Sounds good to me.

Tocsik · Post by **Tocsik** » Fri Mar 15, 2013 10:53 pm

So, you cut the pipe and re-welded?

lovemysan · Post by **lovemysan** » Sat Mar 16, 2013 2:45 am

Yep had it welded back for $20.

PeteH · Post by **PeteH** » Sat Mar 16, 2013 3:08 am

Did you get lucky getting the rotation/position correct so that the header flange and the support bracket would all bolt up?

I say this because I bought a second-hand Prima that somebody had dorked up. Gambled and lost, couldn't mount it.

lovemysan · Post by **lovemysan** » Sun Mar 17, 2013 2:40 am

I bolted the pipe to the bike and had it tacked together. Then we took it off and sewed it up. You are right you can't guess. Rode in the parade today. It's not as loud as a stock lambretta 150, or any of the piped Stella's or vespas. It's fast too. For 161cc with 260lbs on board. It's definitely stronger. I suspect that the bike runs better because the needle should have been dropped a notch to lean the midrange when the prima was stock.

rick71454 · Post by **rick71454** » Tue Mar 19, 2013 10:35 pm

Hello Buddyland:

To improve performance and or speed.

One of the things one might try for a short while, is to loosen your two exhaust pipe bolts that connect the exhaust pipe to the engine. This is found directly under the middle of the scooter. This way you might get an idea how less restriction on the exhaust might actually improve performance and or top speed.

This is base on the idea that with less restriction on the exhaust allows faster throughput in the engine resulting in higher RPMs.

As a bit of caution, there are some concerns about causing damage and or tolerances to go out of adjustment, and the back pressure is needed. But for a few miles, that should not be problem.

I actually did this and got 5MPH more on top speed. Removing my air filter did not seem to make any difference. I rode it like this for a couple of months with no damage. It was a bit louder.

Rick71454

lovemysan · Post by **lovemysan** » Thu Mar 21, 2013 4:59 pm

No offense Rick but running with an exhaust leak can burn a valve. I've seen then snap off and fall into the cylinder.

jrsjr · Post by **jrsjr** » Thu Mar 21, 2013 6:25 pm

lovemysan wrote:No offense Rick but running with an exhaust leak can burn a valve. I've seen then snap off and fall into the cylinder.

Yes. To add insult to injury, removing all backpressure from the exhaust system actually reduces the power the motor produces. It is fun to gut the %$#@! exhaust cannister, though, isn't it? Take that, you stupid exhaust can!

Yeah, but now you need to put some backpressure back into the system so you don't burn up your exhaust valve. That's no joke. Sorry.

rick71454 · Post by **rick71454** » Thu Mar 21, 2013 6:38 pm

Hello Lovemysan:

Thank you for bringing to attention about the potential of burning a valve.

I noticed you removed some of the corrugated stainless steel foil from inside the exhaust pipe. Did that ever increase top speed?

If yes, do you think that drilling a hole of the appropriate size and location in the exhaust pipe would also reduce restrictive flow? I was thinking somewhere between where the pipe connects under the engine and the large section that is the muffler itself.

Practical or foolish?

Thanks
Rick71454

BuddyRaton · Post by **BuddyRaton** » Thu Mar 21, 2013 8:18 pm

The people that design, build and sell these things (not just prima) but a lot of thought, time, testing and money into getting the best thing they can to market.

No I'm not saying that I have never done something that could potentially harm a motor...but I have gone into it knowing what the risks are.

As far as unpacking the pipe...I don't think it's a good idea unless you are doing a lot of other modifications...carb, airbox, top end, head etc. Even then you are probably going to need to repack it to work top notch with the new setup or go with a totally different pipe.

It's like many Harley guys that go to straight pipes thinking louder means more power (this may only be true in NASCAR!) and then put their bike on a dyno...only to find out that they have lost significant power in exchange for a lot of noise.

Tuning is a blast! It's fun! I love it! I have also blown up a couple of motors! It is not for the faint of heart!

Keep us updated!

lovemysan · Post by **lovemysan** » Mon Mar 25, 2013 3:30 pm

The muffler canister is untouched. There is little to be gained by gutting the canister other than an obnoxious exhaust tone. I started it with only header pipe on, anything short of 200 yards away sounded awful. I only removed the baffle pre canister. There is a slight step down in diameter inside the canister. If it were a serious restriction I would convert to some type of carbon fiber slip on.

After riding 100 miles I would definitely recommend doing this if you want more sound, its throaty but not annoying. I wear a full face helmet though, keep that in mind.