Muffler bypass tube - fix or weld shut?

[jayhawk]

Hi there - new to this forum, but a long time 2t 49cc owner (since 1980). My current scoot is a Lambretta/Adly Due (panther if an Adly) 50.

It has the minarelli 2t motor, and the exhaust has a small tube coming off at the base of the muffler that connects to rubber tubing that curves up to a little plastic box (that then has an L shaped tube hanging down that connects to nothing). The metal part curving off the muffler is fine, but the rubber/foam tube coming off it the metal part (that connects the small box and the muffler exhaust bypass) ripped in half after 4800 km. This made the scoot exceptionally loud (I thought the muffler had a hole or something needed to be tightened) and it ran rougher, too.

I think it's a bypass that is a form of restriction. My scoot does a radar tested 47 mph, so I am not after the extra speed. I wouldn't mind more low end, but I doubt closing off this bypass will help initial acceleration (I think roller weights would take care of that).

I went to advanced auto parts, couldn't find a precurved tube to fit, but bought a longer section of straight tubing of the same diameter. I hoped I could curve it nicely, but it ended up folding over on itself.

The scoot runs fine, sounds right, but I want to make sure I'm not hurting anything. My logic is that folder over, the thick tubing may allow some exhaust to get through so that's OK. Or, if it's pinched closed, it's no different than welding the metal part of the bypass tube closed.

What do you all think? Will I hurt my motor with my current set up?

Thanks,

Eric

[90GTVert]

:welcome2:

I think you are on the right track with your logic. If you really want it to work and stay curved without folding over you could see if you could find a spring that fits snug inside the tube to keep it open.

[jayhawk]

Thanks 90GTVert. Unless it starts running rough or sounds funny, I'll run her like she is right now.

Eric

[jimh]

Hi Jayhawk, my scoot has the tube coming off the stock muffler which connects by a rubber hose to an air pump which then goes to another larger, metal tube that also goes to nowhere. This I think has something to do with the catalytic converter in the muffler...for curiosity sake, yesterday I put the stock muffler back on and hooked it up to the air pump. My speed dropped to 33mph from 45 mph. I then crimped the metal tube coming off the muffler and was able to do 40 mph. I was going to run the stock muffler for the rest of the summer but decided to put my technigas pipe back on today because I like the added power going uphill and against the wind. The pipe coming off your muffler is a restriction about which I'd originally read on an Aprilia forum when I first got this scoot and was beginning to learn about 2 strokes and how to eliminate the many restrictions on my particular scooter. Hope this is helpful. If you're able to do 47 mph with the stock muffler, imagine what you may be able to do if you crimp that restriction or replace with a power pipe, WOW!

[jayhawk]

It's funny, with the rubber tube I put on, I have improved low range response but have not lost top end...obviously, tube on is better than wide open.

I do imagine cut off and welded shut I'd get better performance, but I really don't need to go faster. Top speed on all the roads I ride on is only 35 mph (I live near the middle of the city). If welding shut would improve my low end...I might give it a go.

Right now, it's running really smooth. Beat a massive 1" in 30 minutes downpour by 10 minutes. If not for the thunder at every stop, it would have been a nice 30 minute ride home. I suspect that tube had a pinhole and slowly progressing leak for some time - overall, the bike feel like it did when it was new.

I appreciate all the advice, and it's good to know I have options on this issue if my tube doesn't hold or burns through.

Eric